,this file was produced from page images at ,google ,books4 ,transcriber's ,note ,this book was transcribed from a scan of the original found at ,google ,books4 ,i have rotated some images4 ,some of the more elaborate tables are treated as images4 ,illustration3 ,curtiss ,type ,,jn#d;,d ,biplane ,used by ,the ,united ,states ,air ,mail ,service 99,,aeroplane99 99,,construction ,,and99 99,,operation99 ,including ,notes ,on ,aeroplane ,design ,and ,aerodynamic ,calculation1 ,materials1 ,etc4 ,a ,comprehensive ,illustrated ,manual of ,instruction for ,aeroplane ,constructors1 ,aviators1 ,aero-,mechanics1 ,flight ,officers and ,students4 ,adapted ,either for ,schools or ,home ,study4 ,,by ,,john ,b4 ,,rathbun ,,aeronautical ,,engineer ,consulting ,aeronautical ,engineer1 ,chicago ,aero ,works2 ,chief ,engineer1 ,automotive ,engineering ,company4 ,formerly ,instructor in ,aviation and ,machine ,design1 ,chicago ,technical ,college4 99,,chicago99 99,,stanton and ,,van ,,vliet ,,co499 99,,publishers99 #aiai ,copyrighted1 #aiah ,by ,,stanton ,,and ,,van ,,vliet ,,co4 ,,aeroplane ,,construction ,,and ,,operation ,,introduction ,many aeronautical books of a purely descriptive nature have been written for the average man1 but as a rule they contain little of interest for the more serious student of the subject4 ,other books of a highly technical and mathematical class have also been published1 but their contents are all but unintelligible to anyone but a trained engineer4 ,it is the purpose of the author to compromise between these two extremes1 and give only that part of the theory and description that will be of practical use for the builder and flyer4 ,the scope of the subjects covered in this volume has been suggested by the questions asked by students and clients1 and is the result of many years' correspondence with beginner aviators and amateur aeroplane builders4 ,i have endeavored to explain the principles of the aeroplane in simple1 concise language1 starting with the most elementary ideas of flight and finishing with the complete calculations for the surfaces1 power1 weight1 etc4 ,when mathematical operations are necessary they are simple in form1 and are accompanied by practical problems worked out numerically1 so that a man with even the most elementary mathematical knowledge will have no difficulty in applying the principle to his own work4 ,in cases where the calculations would necessarily be complicated1 ,i have substituted tables of dimensions for the mathematical operations1 these dimensions being taken from a number of representative machines4 ,while flying cannot be taught by books1 and is only the result of actual experience1 the chapter devoted to the use of controls under different flight conditions will be of great benefit to the prospective aviator4 ,the portion of the book devoted to operation will be of use in flying schools and training camps since both training methods and control manipulation are covered in detail4 ,in addition ,i have presented considerable data on the requirements of the modern aeronautical motor4 ,so many new firms are now entering the aeroplane industry that there is an ever increasing demand for trained mechanics1 designers and flyers1 and many technical men now working along other lines are taking a keen interest in aeronautical engineering4 ,if the contents of this book will serve to inspire the technical reader to deeper interest and practical research in the fascinating subject of aeronautics1 the author will be more than satisfied with the result of his labor4 ,the aeroplane is rapidly assuming a great commercial importance1 and there is no doubt but what it will develop into an industry rivaling that of the automobile4 ,to keep fully abreast of the times in aeronautic development1 one should be a constant reader of the excellent aeronautical magazines4 ,too much praise cannot be given to the aeronautical press in its effort to maintain an interest in this subject1 and as with all pioneering movements1 these magazines have met with many discouragements and financial setbacks in the earlier days of flying4 ,to the ,american magazines1 ,aerial ,age and ,flying 7,new ,york71 the author owes a debt of gratitude for the use of several of the cuts appearing in this book4 ,the ,english magazines1 ,flight1 ,aeronautics and the ,aeroplane1 have been similarly drawn on4 ,aviation and ,aeronautical ,engineering 7,new ,york7 has suggested the arrangement of several of the tables included herein4 ,all of these papers are of the greatest interest and importance to the engineer1 aviator and aero-mechanic4 ,,john ,b4 ,,rathbun4 ,,aeronautical ,,magazines ,the following list of ,american and ,english aeronautic publications will be of interest to those who wish to keep in touch with the latest developments in aeronautics3 - ,,aviation ,,and ,,aeronautical ,,engineering 7two issues per month74 ,a technical magazine published by ,the ,gardner-,moffat ,co41 ,inc41 #abj ,w4 #cb;d ,st41 ,new ,york4 - ,,aerial ,,age 7weekly74 ,popular and technical4 ,the ,aerial ,age ,co41 ,foster ,bldg41 ,madison ,ave4 and #djth ,st41 ,new ,york4 - ,,air ,,service ,,magazine 7weekly74 ,military and popular subjects4 ,gardner-,moffat ,co41 ,inc41 #abj ,w4 #cb;d ,st41 ,new ,york4 - ,,flying 7monthly74 ,popular and military subjects4 ,published by ,flying ,association1 ,inc41 #bhj ,madison ,ave41 ,new ,york4 - ,,air ,,travel 7weekly74 ,popular subjects4 ,published by ,air ,travel1 ,new ,york4 ,,english ,,magazines4 - ,,flight ,,and ,,the ,,aircraft ,,engineer 7weekly74 ,technical and popular4 ,published by ,flight and ,aircraft ,engineer1 #cf ,great ,queen ,st41 ,kingsway1 ,w4,c4#b1 ,london1 ,england4 - ,,aeronautics 7weekly74 ,technical and industrial4 ,published by ,aeronautics1 #f-h ,bouverie ,st41 ,london1 ,e4,c4#d1 or may be had from #agij ,broadway1 ,new ,york4 - ,,the ,,aeroplane 7weekly74 ,technical and popular4 ,published by ,the ,aeroplane1 #aff ,piccadilly1 ,london1 ,w4#a4 ,,aeroplane ,,construction ,,and ,,operation 444444444444444444444444444444 ,,introduction 4444444444444444444444444444444444444444 444444444444 ,,aeronautical ,,magazines 4444444444444444444444444444444444444444 44 ,,english ,,magazines4 4444444444444444444444444444444444444444 444444 ,,chapter ,i4 ,,principles ,,of ,,the ,,aeroplane4 4444444444444444444444444 ,,chapter ,,ii4 ,,types ,,of ,,military ,,aeroplanes4 44444444444444444444444 ,,chapter ,,iii4 ,,elementary ,,aerodynamics 4444444444444444444444444444 ,,chapter ,,iv4 ,,experimental ,,laboratories4 44444444444444444444444444 ,,chapter ,v4 ,,aerodynamics ,,of ,,lifting ,,surfaces 7,,aerofoils74 44444444 ,,chapter ,,vi4 ,,practical ,,wing ,,sections4 4444444444444444444444444444 ,,correction ,,factors ,,for ,,wing ,,form ,,and ,,size4 44444444444444444444 ,,chapter ,,vii4 ,,biplanes ,,and ,,triplanes4 4444444444444444444444444444 ,,chapter ,,viii4 ,,effects ,,of ,,plan ,,form4 7,,tandem ,,aeroplanes47 44444444 ,,chapter ,,ix4 ,,wing ,,construction4 4444444444444444444444444444444444 ,,chapter ,x4 ,,wing ,,construction ,,details4 444444444444444444444444444 ,,chapter ,,xi ,,fuselage 7,,body7 ,,construction4 444444444444444444444444 ,,chapter ,,xii ,,details ,,of ,,fuselage ,,construction 44444444444444444444 ,,fuselage ,,weights4 4444444444444444444444444444444444444444 44444 ,,size ,,of ,,longerons 4444444444444444444444444444444444444444 44444 ,,chapter ,,xiii4 ,,chassis ,,construction4 44444444444444444444444444444 ,,chapter ,,xiv4 ,,estimation ,,of ,,weight4 444444444444444444444444444444 ,,weights ,,of ,,aeronautical ,,motors4 4444444444444444444444444444444 ,,chapter ,,xv4 ,,balance ,,and ,,stability4 444444444444444444444444444444 ,,chapter ,,xvi4 ,,head ,,resistance ,,calculations4 4444444444444444444444 ,,chapter ,,xvii4 ,,power ,,calculations4 4444444444444444444444444444444 ,,chapter ,,xviii4 ,,propellers4 44444444444444444444444444444444444444 ,,chapter ,,xix4 ,,operation ,,and ,,training4 4444444444444444444444444444 ,,chapter ,,xx4 ,,aeronautical ,,motors4 44444444444444444444444444444444 ,,chapter ,,xxi4 ,,glossary ,,of ,,aeronautical ,,words4 44444444444444444444 ,a 4444444444444444444444444444444444444444 444444444444444444444 ,b 4444444444444444444444444444444444444444 444444444444444444444 ,c 4444444444444444444444444444444444444444 444444444444444444444 ,d 4444444444444444444444444444444444444444 444444444444444444444 ,e 4444444444444444444444444444444444444444 444444444444444444444 ,f 4444444444444444444444444444444444444444 444444444444444444444 ,g 4444444444444444444444444444444444444444 444444444444444444444 ,h 4444444444444444444444444444444444444444 444444444444444444444 ,i 4444444444444444444444444444444444444444 444444444444444444444 ,j 4444444444444444444444444444444444444444 444444444444444444444 ,k 4444444444444444444444444444444444444444 444444444444444444444 ,l 4444444444444444444444444444444444444444 444444444444444444444 ,m 4444444444444444444444444444444444444444 444444444444444444444 ,n 4444444444444444444444444444444444444444 444444444444444444444 ,o 4444444444444444444444444444444444444444 444444444444444444444 ,p 4444444444444444444444444444444444444444 444444444444444444444 ,p 4444444444444444444444444444444444444444 444444444444444444444 ,s 4444444444444444444444444444444444444444 444444444444444444444 ,t 4444444444444444444444444444444444444444 444444444444444444444 ,u 4444444444444444444444444444444444444444 444444444444444444444 ,v 4444444444444444444444444444444444444444 444444444444444444444 ,w 4444444444444444444444444444444444444444 444444444444444444444 ,,chapter ,i4 ,,principles ,,of ,,the ,,aeroplane4 99,mechanical ,flight994 ,although the elementary principles of mechanical flight are not of recent origin1 the practical development of the flying machine is confined almost entirely to the present century4 ,gravity propelled gliders and small models have been flown with success from a comparatively early date1 but the first actual sustained flight with a power driven machine was performed by the ,wright ,brothers in #aijc4 ,there was no single element on this first successful machine that had not been proposed many years before by ,langley1 ,chanute1 ,montgomery1 ,henson1 ,mouillard1 and others1 but this first flight must be attributed principally to the fact that the ,wrights started carefully and painstakingly to learn how to operate 7,by practicing with gliders7 before starting on the first power machine4 ,if ,langley had studied the operation of his machine as carefully as he did its theory and design1 he would have been flying long before the ,wrights as his original machine was afterwards successfully flown by ,curtiss4 ,when once actual flight was achieved1 and the success of the ,wright ,brothers became generally known1 the development proceeded with leaps and bounds4 ,all the resources of science and engineering skill were at once applied to the new device until our present scientific knowledge of the aeroplane compares very favorably with the older engineering sciences4 ,in the few years that have elapsed since the first flight1 the aeroplane holds all records for speed1 endurance1 and radius of action4 ,a great deal of the success so rapidly acquired can be credited to the automobile and motorcycle industries1 since it was the development of the light internal combustion motors used on these machines that paved the way for the still lighter aeronautic motor4 ,again1 the automobile industry was responsible for the light and powerful materials of construction1 such as alloy steel1 aluminum alloys1 and also for the highly important constructional details1 such as ball bearings1 pneumatic tires1 carburetors1 magnetos1 steel tubing1 etc4 ,the special methods developed in automobile work have helped to make the aeroplane an immediate commercial proposition4 ,illustration3 ,curtiss ,type ,,jn#d-;,b ,primary ,trainer 99,types of ,flying ,machines994 ,in general1 flight apparatus may be divided into two classes1 7#a7 ,the ,lighter ,than ,air ,type1 such as the balloon and dirigible1 and 7#b7 ,the ,heavier ,than ,air ,machine1 represented by the aeroplane1 helicopter and ornithopter4 ,the lighter than air machine is supported in flight by buoyancy in much the same manner that a piece of wood floats in water4 ,when a balloon or dirigible1 because of its large volume1 displaces a volume of air equal to its own weight1 the device will float4 ,when the weight of air displaced exceeds the weight of the balloon or dirigible1 it will continue to rise until it reaches an altitude where the diminished air density again results in an equality between the weight of the device and the air displaced4 ,at this point it rests1 or is in equilibrium4 ,the flotation of such a device is entirely due to static forces and hence 7#a7 is often called an aerostat4 ,the sustenation of a ,heavier ,than ,air ,machine is due to an entirely different application of forces4 ,forces in motion 7,dynamic ,forces7 are essential to the support of a heavier than air machine1 and it is the resultant of these forces that performs the actual lifting operation1 this resultant corresponding to the buoyant force of the aerostat4 ,dynamic flight is obtained by an apparatus in which an arrangement of surfaces are moved in such a way as to cause an upward component of the forces generated by the impact of the air on the surfaces4 ,the surfaces drive the air down and when the force necessary for the continuous downward deflection of air becomes equal to the weight of the machine it is sustained in flight4 ,dynamic flight therefore depends on the continuous downward deflection of masses of air1 and when this motion ceases1 sustentation also ceases4 ,an aeroplane is provided with a deflecting surface that is fixed rigidly in regard to the body of the machine1 and the motion necessary for its support is provided by driving the machine forward1 the forward motion being produced by the horizontal pull of air screws or propellers4 ,it is at once evident that the forward horizontal motion of the aeroplane must be maintained for its support1 for the surfaces are fixed and there is no other possible way of producing a relative motion between the wings and the air4 ,to overcome the objection of forward motion1 several other machines have been proposed in which the surfaces are moved in relation to the body1 as well as the air1 thus making it possible for the device to stand stationary while the revolving or reciprocating surfaces still continue in motion in regard to the air4 ,one type of the moving surface machine1 the ,helicopter1 is provided with revolving surfaces arranged in the form of vertical air screws or propellers1 the blades of the propellers being inclined so that they drive down a continuous stream of air and produce the continuous upward reaction that supports the machine4 ,while such machines have succeeded in raising themselves off the ground they are not yet practical flying devices4 ,the ornithopter or orthopter is a flapping wing machine that maintains flight after the manner of the bird 7,ornis74 ,like the helicopter1 the ornithopter has not yet proved successful4 ,illustration3 ,fig4 #a4 ,comparison ,between the ,kite and ,aeroplane2 ,fig4 #b1 ,showing the ,lift and ,drag ,forces ,produced by the ,air ,stream4 ,the ,propeller 7,p71 ,acts in a ,manner ,similar to the ,kite ,string 7,s7 in ,producing ,relative ,motion ,between the ,air and the ,lifting ,surfaces4 99,principles of the ,aeroplane994 ,in its elementary principles1 the aeroplane can be compared with the kite1 as both are supported by the impact of a horizontal stream of air4 ,in ,diagram #a1 the kite surface is indicated by ,x-,x with the relative air stream ,w-,w-,w-,w moving from left to the right as indicated by the arrow heads4 ,on striking the surface1 the air stream is deflected vertically1 and in a downward direction1 as shown by the streams lines ,r-,r-,r-,r4 ,the reaction of the air deflection produces the lift shown vertically and upwards by the arrow ,l4 ,the kite surface is held against the impact of the air stream by the string ,s so that there is relative motion between the air and the kite1 and so that the surface will not be carried along with the air current toward the right4 ,if the kite were allowed to drift with the wind there could be no relative motion between the surface and the air stream1 hence the kite would fall as soon as it attained the velocity of the wind4 ,the horizontal force exerted by the wind tending to carry the kite toward the right is indicated by the arrow ,d and is known as the drag or drift force4 ,there are thus three forces1 the lift 7,l71 the drag 7,d71 and the resultant of the two forces indicated by the string 7,s74 ,the forces of lift and drag are nearly at right angles to one another4 ,the kite tail ,t is simply a stabilizing device whose purpose is to maintain a constant angle between the surface and the wind and it performs an almost negligible amount of lift4 ,a few more words in regard to the relative velocity between the surface and wind4 ,in the figure1 the kite is assumed as being stationary1 while the wind moves from left to right4 ,with a thirty mile per hour wind1 the relative air velocity in regard to the surface would be #cj ,m4 ,p4 ,h4 ,if the air particles are now considered stationary1 and if the kite is towed toward the left 7opposite to figure7 at #cj miles per hour1 the relative velocity between the surface and air would still be #cj ,m4 ,p4 ,h4 ,in other words1 the kite may be stationary1 or may move in regard to the earth1 but its lift is unaffected as long as the relative motion between the surface and air remains constant4 ,the motion between an aeroplane and the earth depends upon the difference of the aeroplane and wind velocities4 ,for example1 a aeroplane with a relative speed of #fj miles per hour1 flying against a headwind of #cj miles per hour1 moves #fj-cj #cj miles per hour in regard to the earth4 ,the same aeroplane flying with the above wind would have a velocity of #fjcjij miles per hour past a fixed point on the earth's surface1 yet in both cases1 the relative velocity of the surface in regard to the air would be the same4 ,fig4 #b is a diagram of an aeroplane that shows the connection between the kite and aeroplane principles4 ,in this figure1 the wing surface of the aeroplane1 ,x-,x corresponds to the kite surface ,x-,x4 ,the relative air ,w-,,ww-,w striking the wing from the left is deflected down along the arrows ,r-,r-,r-,r and results in an equivalent lift force ,l1 and a drag force ,d as in the case of the kite4 ,the resultant force required to maintain the relative velocity between the air and wings is indicated by ,d1 opposite and equal to the drag force ,d4 ,the resultant required for overcoming the drag is provided by the screw propeller ,p instead of the string ,s shown in ,fig4 #a4 ,the propeller thrust 7,d7 is parallel to the air stream instead of being inclined as in the case of the string1 but the total effect is the same since both are ,resultants of the lift and drag4 ,to sustain the aeroplane1 the lift 7,l7 must be equal and opposite to the weight shown by ,m4 ,the fact that ,m and ,l are opposite and equal makes it only necessary for the propeller to overcome the horizontal drag1 and hence the thrust can be made parallel to the air flow--or nearly so4 ,the aeroplane is provided with a small tail surface 7,t7 that corresponds to the kite tail 7,t74 ,it maintains the lifting surfaces ,x-,x at a given angle with the air stream4 ,the tail may1 or may not aid in supporting the machine1 but in modern machines it is common to employ a tail surface that is non-lifting under ordinary conditions of normal flight4 ,the body 7,b7 contains the pilot1 motive power1 fuel1 and such useful load as it may be necessary to carry4 ,illustration3 ,fig4 #c4 ,caudron ,monoplane4 ,side ,elevation4 ,fig4 #c shows a ,caudron monoplane in side elevation4 ,this view illustrates the application of the principles shown by ,fig4 #b1 except for the vertical rudder at the rear4 ,the latter is used for steering in a horizontal direction4 ,fig4 #d shows the construction even more clearly since it is a perspective view4 ,the machine is a ,morane ,parasol monoplane with the wing placed over the body4 ,this location of the main lifting surface is for the purpose of improving the view of the pilot and in no way affects the principles just described4 ,the wires shown above the wing are bracing stays4 ,the tail is hinged near the rear so that the angle of the rear portion can be changed 7,elevator flaps71 and permits the angle of the main wings to be altered in regard to the air stream1 thus causing the machine to ascend or descend4 ,the tail also damps out oscillations or vibrations due to irregularities in the air current4 ,the wheels and running gear 7,chassis7 allow the machine to be run over the ground until the relative air speed is sufficient to support the machine in flight4 ,illustration3 ,fig4 #d4 ,morane ,umbrella ,type ,monoplane4 ,courtesy of ,flight4 99,multiplanes994 ,in order to support a heavy load1 and at the same time have a small compact machine1 it is necessary to have more than one layer of wing surface4 ,it is evident that the wing length or span can be made much less than that of the monoplane surface shown1 if the total area could be divided into two or more parts4 ,a machine having its main lifting surface divided into two or more separate sections is known as a multiplane1 this term becoming ,biplane1 ,triplane1 or ,quadraplane1 depending on whether there are two1 three or four independent lifting surfaces4 ,there is almost a limitless variety of arrangements possible1 but the most common arrangement by far is that of the biplane1 in which there are two superposed surfaces as shown by ,fig4 #e4 ,in this type1 the two lifting surfaces are placed over one another with a considerable gap or space between4 ,the body is placed between the wings and the tail surfaces and chassis remain the same as in the monoplane4 ,this is known as a ,tractor biplane since the propeller is in front and pulls the machine along while ,fig4#f shows a ,pusher type biplane in which the propeller is mounted behind the wings and therefore pushes the machine4 ,illustration3 ,fig4 #d-;,a4 ,deperdussin ,monoplane with ,monocoque ,body4 ,gordon-,bennett ,racer4 99,biplanes994 ,besides the advantages of size1 the biplane has a number of other good features4 ,the deep spacing of the upper and lower surfaces permits of a powerful and light system of trussing being placed in the gap1 and therefore the biplane can be made stronger 7weight for weight7 than the monoplane in which no such trussing can be economically applied4 ,the vertical struts of the bracing can be clearly seen in the figure4 ,the efficiency of this interplane trussing greatly increases the possible size and capacity of the aeroplane4 ,with monoplanes it is seldom possible to exceed a wing span of #cf feet without running into almost unsurmountable structural difficulties4 ,the weight of the large monoplane also increases is leaps and bounds when this critical span is once exceeded4 ,to maintain an equal degree of strength the monoplane requires very careful attention in regard to the design and construction1 and is correspondingly more expensive and difficult to build than the biplane1 although the latter has by far the greater number of parts4 ,by suitable arrangements in the location of the biplane surfaces a very fair degree of stability can be obtained1 an advantage which is impossible with the monoplane4 ,illustration3 ,fig4 #e4 ,s4 ,p4 ,a4 ,d4 ,tractor ,biplane ,speed ,scout4 ,a distinct disadvantage of the two superposed surfaces of the biplane is due to the fact that there is interference between the upper and lower wings1 and that the lift for equal areas is less than in the case of the monoplane4 ,with a given form of wing1 #ajj square feet of monoplane surface will lift considerably more than the same area applied in biplane form4 ,the amount of the drag for the support of a given load is increased1 and with it the amount of power required4 ,the greater the separation or gap between the wings1 the greater will be the lift1 but when the gap is unduly increased to obtain a great lift the length of the interplane bracing is increased to such an extent that the resistance of the bracing will more than overcome the advantages due to the large gap4 ,there is a fixed limit to the gap beyond which it is not practical to go4 ,the bracing has a very material effect on the air resistance1 no matter how small the gap4 ,illustration3 ,fig4 #f4 ,pusher ,type ,biplane in ,which the ,propeller ,is ,placed ,behind the ,wings4 99,triplanes994 ,of late the triplane has been rapidly increasing in use1 and in certain respects has many advantages over either the monoplane or biplane4 ,this type has three superposed surfaces which still further diminishes the size for a given area4 ,the interference between the surfaces is even greater than with the biplane1 and hence the lift is less for a given area and aspect ratio4 ,this latter defect is partly1 or wholly overcome by the possibility of using long narrow wings1 and because of the reduced span there is a corresponding reduction in the bracing resistance4 ,it should be noted at this point that the efficiency of a lifting surface is greatly increased when the ratio of the length to the width is increased1 that is1 a long1 narrow wing will be more efficient than a short1 wide shape4 ,the relation of the length to the width is called aspect ratio1 and will be described in more detail in a following chapter4 ,illustration3 ,fig4 #f-;,a4 ,farman ,type ,pusher ,biplane4444 ,note the ,propeller ,at the ,rear of ,body1 and the ,position of the ,pilot and ,passenger4 ,illustration3 ,fig4 #f-;,b4 ,the ,mann ,two-,propeller ,pusher ,biplane4 ,the ,propellers ,are ,mounted on ,either ,side of the ,body1 and ,are ,driven by a ,single ,motor ,through a ,chain ,transmission4 ,this ,drive ,is ,similar to the ,early ,wright ,machines4 ,fig4 #g is a sketch of a ,sopwith ,triplane ,scout and shows clearly the three superposed wings4 ,the small amount of interplane bracing1 and the great aspect ratio1 makes this type very suitable for high speed4 ,the body1 tail and chassis arrangements are practically the same as those of a biplane4 ,the ,curtiss ,triplane ,scout is the pioneer of this type of machine1 although experimental work on the triplane had been performed in ,england by ,a4 ,v4 ,roe many years ago4 ,the ,roe triplane was lightly powered and for its time was successful in a way1 but the ,curtiss is the first to enter into active competition against the biplane scout4 ,owing to the small span required for a given area1 and the possibilities of very light and simple bracing1 the triplane is an ideal type for heavy duty machines of the bombing species4 ,enormous triplanes have been made that are capable of a useful load running up into the tons1 the large ,curtiss and ,caproni's being notable examples4 ,as the triplane is much higher than the biplane of equal area1 the interplane bracing is deeper and more effective without causing proportionately higher resistance4 ,illustration3 ,fig4 #g4 ,sopwith ,triplane ,speed ,scout4 99,quadraplane994 ,the use of four superposed surfaces has not been extended1 there probably being only one or two of these machines that can be said to be successful4 ,the small quad built by ,matthew ,b4 ,sellers is probably the best known4 ,the power required to maintain this machine in flight was surprisingly small1 the machine getting off the ground with a #d horsepower motor1 although an #h horsepower was afterwards installed to maintain continuous flight4 ,the empty weight was #aaj pounds with the #h horsepower motor4 ,the span of the wings was #ah' #j and the width or chord #c' #j1 giving a total area of about #bjj square feet4 ,illustration3 ,fig4 #g-;,a4 ,curtiss ,triplane ,speed ,scout4 ,courtesy ,aerial ,age4 99,tandem ,aeroplanes994 ,a tandem aeroplane may be described as being one in which the surfaces are arranged fore and aft4 ,the ,langley ,aerodrome was of the tandem monoplane type and consisted of two sets of monoplane wings arranged in tandem4 ,this pioneer machine is shown in ,fig4 #h1 and is the first power driven model to achieve a continuous flight of any length4 ,instead of two monoplane surfaces1 two biplane units or triplane units can be arranged fore and aft in the same manner4 ,while there have been a number of tandem machines built1 they have not come into extensive use4 ,successful flight was obtained with a full size ,langley ,aerodrome1 and this machine flew with a fair degree of stability4 ,the failure of other tandem machines to make good was due1 in the writer's opinion1 to poor construction and design rather than to a failure of the tandem principle4 ,the ,montgomery glider1 famed for its stability1 was a tandem type but the machine was never successfully built as a powered machine4 ,the wings must be separated by a sufficient distance so that the rear set will not be greatly influenced by the downward trend of the air caused by the leading wings4 ,as the rear surfaces always work on disturbed air they should be changed in angle1 increased in area1 or be equipped with a different wing curvature if they are to carry an equal proportion of the load4 ,usually1 however1 the areas of the front and rear wings are equal1 and the difference in lift is made by changes in the wing form or angle at which they are set4 ,in some cases the wings are approximately the same1 the difference in lift being compensated for by moving the load further forward1 thus throwing more of the weight on the front wings4 ,illustration3 ,fig4 #h4 ,langley's ,aerodrome1 ,an ,early ,type of ,tandem ,monoplane4 99,the ,aeroplane in ,flight994 ,up to the present we have only considered horizontal flight at a continuous speed4 ,in actual flight the altitude is frequently varied and the speed is changed to meet different conditions4 ,again1 the load is not an absolutely constant quantity owing to variations in the weight of passengers1 and variations in the weight of fuel1 the weight of the latter diminishing directly with the length of the time of flight4 ,to meet these variations1 the lift of the wings must be altered to suit the loading and speed--generally by altering the angle of the wings made with the line of flight4 ,fig4#i shows an aeroplane in horizontal flight and lightly loaded1 the machine traveling along the horizontal flight path ,f-,f4 ,with the light load1 the angle made by the wings with the flight path is shown by 7i71 the tail and body remaining horizontal1 or parallel to the flight path4 ,with an increased load it is necessary to increase the angle of the wings with the flight line1 since within certain limits the lift increases with an increase in the angle of incidence 7i74 ,fig4 #aj shows the adjustment for a heavier load 7,w71 the angle of incidence being increased to 7i'71 and the body is turned down through a corresponding angle4 ,the increased angle is obtained by turning the elevator flaps 7,t7 up1 thus causing a downward force 7t7 on the tail4 ,the force 7t7 acts through the body as a lever arm1 and turns the machine into its new position4 ,it will be noted that when the angle of incidence is great that the rear of the body drags down and causes a heavy resistance4 ,this position of a dragging tail is known to the ,french as flying ,cabr4 ,with high angles cabr flight is dangerous1 for should the propeller thrust cease for an instant the machine would be likely to tail dive before the pilot could regain control4 ,this sort of flight is also wasteful of power4 ,cabr flight is unnecessary in a variable incidence machine1 the wing being turned to the required angle independently of the body1 so that the body follows the flight line in a horizontal position1 no matter what the angle of incidence may be4 ,in this type of machine the wings are pivoted to the body1 and are operated by some form of manual control4 ,illustration3 ,figs4 #i-aj-aa-ab4 ,showing the ,use of ,elevators in ,changing ,angle of ,incidence4 - ,machine ,shown in ,four ,principal ,attitudes of ,flight4 ,as the ,body and ,wings ,are in a ,single ,unit1 the ,body ,must ,be ,turned for ,each ,different ,wing ,angle4 ,in ,fig4 #aa1 the large angle 7i'7 is still maintained1 but the load is reduced to the value given in ,fig4 #i4 ,with an equal load1 an increased angle of incidence causes the machine to climb1 as along the new flight line f-f4 ,with the load 7,w7 equal to that in ,fig4 #i1 the angle of incidence will still be 7i7 but this will be along a new flight line if the large angle 7i'7 is maintained with the horizontal as shown by ,fig4 #aa4 ,with the wings making an angle of 7i'7 with the horizontal1 and angle of incidence 7i7 with the flight line1 it is evident from ,fig4 #aa that the new flight line f-f must make an angle 7c7 with the original horizontal flight line ,f-,f4 ,this shows how an increased angle with a constant load causes climbing1 providing1 of course1 that the speed and power are maintained4 ,with a given wing and load there is a definite angle of incidence if the speed is kept constant4 ,should a load be dropped1 such as a bomb1 with the wing angle kept constant1 the new path of travel will be changed from ,f-,f to f-f4 ,fig4 #ab shows the condition when the rear end of the body is elevated by depressing the elevator flap ,t4 ,this occasions an upward tail force that turns the wings down through the total angle 7i'74 ,with the former loading and speed1 the angle of incidence is still 7i7 degrees with the new flight path f-f1 the new flight path being at an angle 7c7 with the horizontal ,f-,f4 ,the body is turned through angle 7i'71 but the angle 7i7 with the flight path f-f is still constant with equal loads and speeds4 ,to cause an aeroplane to climb1 or to carry a heavier load1 the elevator flap is pointed up4 ,to descend1 or care for a lighter load1 the elevator is turned down4 ,in normal horizontal flight the machine should be balanced so that the tail is horizontal and thus creates no drag4 ,when the elevator 99must99 be used to keep the tail up in horizontal flight1 the machine is said to be tail heavy4 99,longitudinal ,stability994 ,in ,figs4 #i-aj-aa-ab the machine was assumed to be flying in still air1 the attitudes of the machine being simply due to changes in the loading or to a change in altitude4 ,the actual case is more complicated than this1 for the reason that the machine is never operating in still air but encounters sudden gusts1 whorls1 and other erratic variations in the density and velocity of the air4 ,each variation in the surrounding air causes a change in the lift of the wings1 or in the effect of the tail surfaces1 and hence tends to upset the machine4 ,if such wind gusts would always strike the wings1 body1 and tail simultaneously1 there would be no trouble1 but1 unfortunately1 the air gust strikes one portion of the machine and an appreciable length of time elapses before it travels far enough to strike another4 ,though this may seem to be a small fraction of time1 it is in reality of sufficient duration to have a material effect on the poise of the aeroplane4 ,vertical gusts due to the wind passing over buildings1 hills1 cliffs1 etc41 not only tend to upset the machine1 but also tend to change the altitude since the machine rises with an up gust and sinks with a down trend in the ,stream4 ,assume a machine as in ,fig4 #i to be traveling steadily along a horizontal path in still air4 ,a sudden horizontal gust now strikes the machine from the front1 thus causing a sudden lift in the main wings4 ,as this gust strikes the wings before the tail1 the tail will stand at the old altitude while the wings are lifted1 thus giving the position shown by ,fig4 #aj4 ,after passing over the wings it lifts the tail1 this effect probably not being sufficient to restore the wing and the tail to their old relative attitude since the gust generally loses velocity after passing the wings4 ,a head gust of this type often strikes the front wings diagonally so that it never reaches the tail at all4 ,to remedy this upsetting action of the gust1 the pilot must move his rear elevator so that the elevator is in the position shown by ,fig4 #ab1 that is1 the flap must be turned down so as to raise the tail4 ,a gust striking from behind may1 or may not affect the elevator flaps1 this depending on their position at the time that the gust strikes4 ,if the flaps are turned up1 the rear end will be raised by the gust and the machine will head dive3 if turned down1 the gust will depress the tail1 raise the head and tend to stall the machine4 ,if the tail is of the lifting type1 the rear entering gust will reduce the relative velocity1 and the lift1 and cause the tail to drop4 ,on passing over the tail and striking the wings1 the rear gust will reduce the velocity and cause a loss in lift4 ,this will either cause the machine to head dive or drop vertically through a certain distance until it again assumes its normal velocity4 ,all of these variations cause a continually fore and aft upsetting movement that must be continually corrected by raising and lowering the elevator flaps1 and in very gusty weather this is a very tedious and wearing job4 ,it requires the continual attention of the pilot unless the action is performed automatically by some mechanical device1 such as the ,sperry ,gyroscopic1 or else by some arrangement of the surfaces that give inherent stability4 ,control by means of the elevator flaps 7which raise and lower the body in a fore and aft direction1 as shown7 is known as longitudinal control1 and when the machine is so built that correction for the longitudinal attitude is obtained inherently1 the machine is said to be longitudinally stable4 ,modern machines can be made very nearly longitudinally stable1 and are comparatively unaffected by any than the heaviest gusts4 99,lateral ,stability994 ,the gusts also affect the side to side1 or lateral balance by causing a difference in lift on either end of the wings4 ,should the gust strike one tip before the other1 or should it strike one tip harder than the other1 the tendency will be to turn the machine over sidewise4 ,this is a more difficult problem to solve than the longitudinal moment1 although perfect inherent stability has been attained in one or two machines without the use of additional automatic control mechanism4 ,inherent lateral stability has always been attended by a considerable loss in the efficiency of the aeroplane and speed due to the peculiar arrangements in the main lifting surfaces4 ,at present we must make a decision between efficiency and stability1 for one feature must be attained at a sacrifice in the other4 ,contrary to the general opinion1 perfect stability is not desirable1 for almost invariably it affects the control of a machine and makes it difficult to maneuver4 ,should the stability appliances be arranged so that they can be cut out of action at will1 as in the case of the ,sperry ,gyroscopic ,stabilizer1 they will fulfill the needs of the aviator much more fully than those of the fixed inherent type4 ,the first thoroughly stable machine1 both longitudinally and laterally1 was that designed by ,lieutenant ,dunne1 and this obtained its distinctive feature by a very peculiar arrangement of the wing surfaces4 ,it was excessively stable1 and as with all very stable machines1 was difficult to steer in a straight line in windy weather1 and was correspondingly difficult to land4 ,illustration3 ,fig4 #ab4;,a4 ,diagram of the ,tractor ,biplane ,the first machine of the ordinary biplane type that proved inherently stable was the ,r4 ,e4-#a designed in ,england by ,edward ,busk4 ,this machine was flown from ,farnborough to ,salisbury ,plain1 and during this flight the only control touched was the vertical rudder used in steering4 ,since then1 all ,english machines have been made at least partially stable1 the degree depending upon the service for which it was intended4 ,it has been found that in fighting1 a very controllable machine is necessary1 hence stability must be sacrificed1 or the control surfaces must be made sufficiently powerful to overcome the stable tendency of the machine4 ,war machines are made to be just comfortably stable over the range of ordinary flight speeds1 and with controls powerful enough so that the inherent stability can be overcome when maneuvering in battle4 ,the present war machine always contains an element of danger for the unskilled pilot4 99,dihedral ,angle994 ,this was the first lateral stability arrangement to be applied to an aeroplane1 but is only effective in still air4 ,in rough weather its general tendency is to destroy stability by allowing dangerous oscillations to take place4 ,fig4 #ac is a front view of a monoplane in which the wings 7w7 and 7w'7 are set at an angle 7d71 this angle being known as the dihedral angle4 ,the dotted line 7m-m7 shows the line of a pair of perfectly horizontal wings and aids in illustrating the dihedral4 ,assuming the center of lift at ,,cl on the wings1 it will be seen that an increase in the dihedral raises the center of lift above the center of gravity line ,c4 ,g4 by the amount 7h74 ,with the center of gravity below the center of lift it is evident that the weight of the machine would tend to keep it on a level keel1 although the same effect could1 of course1 be attained in another way4 ,the principal righting effect of the dihedral is shown by ,fig4 #ad in which the wings 7w7 and 7w'7 are set as before4 ,the machine is tipped or listed toward the left 7seen from aviator's seat7 so that wing 7w'7 is down4 ,by drawing vertical lines down until they intersect the horizontal line ,x-,x 7the line of equilibrium71 it will be seen that wing 7w'7 presents more horizontal lift surface than 7w7 since the projected or effective wing length 7,c7 is greater than 7b74 ,since 7w'7 presents the greater surface1 the lift 7,l7 tends to restore the machine to its original level position4 ,if the wings were both set on the same straight line1 the projected lengths 7b7 and 7c7 would be the same and there would be no restoring effect4 ,the dihedral would be very effective in still air1 but in turbulent air1 and with the body swinging back and forth1 the dihedral would act in the nature of a circular guiding path1 and thus tend to allow the swinging to persist or increase rather than to damp it down1 as would be the case with level straight wings4 ,again1 with the wing bent up at a considerable angle1 a side gust as at 7,s7 would tend to throw the machine still further over1 and thus increase rather than diminish the difficulty4 ,in practical machines1 the dihedral is usually made very small 7d #agf degrees71 the angle of each wing with the horizontal being about #b degrees1 or even less4 ,i think the advantage of such a small angle is rather more imaginary than actual1 and at present the greater number of war machines have no dihedral at all4 ,in the older monoplanes the angle was very pronounced4 ,fig4 #ae shows the dihedral applied both to the upper wing 7,u7 and the lower wing 7,l71 the usual method of applying dihedral to large biplanes4 ,fig4 #af shows the method of applying the dihedral to small1 fast machines1 such as speed scouts1 the dihedral in this case being used only on the lower wing4 ,the dihedral on the bottom wing is usually for the purpose of clearing the wing tips when turning on the ground rather than for stability4 ,a lower wing with a dihedral is less likely to strike the ground or to become fouled when it encounters a side gust in landing or getting off4 ,the use of straight upper wings makes the construction much simpler1 especially on the small machines where it is possible to make the wing in one continuous length4 99,ailerons and ,wing ,warping994 ,since the dihedral is not effective in producing lateral stability1 some other method must be used that is powerful enough to overcome both the upsetting movements and the lateral oscillations caused by the pendulum effect of a low center of gravity4 ,in the ordinary type of aeroplane this righting effect is performed by movable surfaces that increase the lift on the lower wing tip1 and decrease the lift on the high side4 ,in ,some cases the lateral control surfaces are separate from the wing proper 7,ailerons71 and in some the tip of the wing is twisted or warped so as to produce the same effect4 ,these control surfaces may be operated manually by the pilot or by some type of mechanism1 such as the gyroscope1 although the former is the method most used4 ,the lateral control1 or side to side balancing of an aeroplane1 can be compared to the side to side balancing of a bicycle in which the unbalance is continually1 being corrected by the movement of the handle bars4 ,fig4 #ag shows the control surfaces or ,ailerons 7,a-,a'71 mounted near the tips1 and at the rear edge of the wing ,w4 ,as shown1 they are cut into and hinged to the main wings so that they are free to move up and down through a total angle of about #fj degrees4 ,in a biplane they may be fitted to the upper wing alone or to both top and bottom wings1 according to conditions4 ,for simplicity we will consider only the monoplane in the present instance4 ,in ,fig4 #ah1 a front view of the monoplane1 the machine is shown heeled over so that the wing tip 7w7 is low4 ,to correct this displacement1 the aileron 7,a7 on the low side1 is pulled down and the aileron 7,a'7 on the opposite end is pulled up4 ,this1 of course1 increases the lift on the low end 7w7 and decreases the lift on the high side 7w'74 ,the righting forces exerted are shown by ,l-,l'4 ,the increased angles made by ,a-,a' with the wind stream affects the forces acting on the wings1 although in opposite directions1 causing a left hand rotation of the whole machine4 ,in ,fig4 #ai1 conditions are normal with the machine on an even keel and with both ailerons brought back to a point where they are level with the surface of the wing1 or in neutral4 ,fig4 #bj shows the machine canted in the opposite direction with 7w'7 low and 7w7 high4 ,this is corrected by bringing down aileron 7,a'7 and raising 7,a71 the forces ,l-,l' showing the rotation direction4 ,by alternately raising and lowering the ailerons we can correspondingly raise or lower the wing tips4 ,it should be noted here that in some machines the ailerons are only single acting1 that is1 the aileron on the low side can be pulled down to increase the lift1 but the opposite aileron remains in the plane of the wings1 and does not tend to push down the high side4 ,since all of the aileron resistance in a horizontal direction is now confined to the low side1 it turns the machine from its path1 the high wing swinging about the lower tip with the latter as a pivot4 ,in the double acting control as shown in ,figs4 #ag to #bc1 the resistance is nearly equal at both tips and hence there is no tendency to disturb the flight direction4 ,with single acting ailerons1 the directional disturbance is corrected with the rudder so that when the aileron is pulled down it is necessary to set the rudder to oppose the turn4 ,on early ,wright machines the rudder and lateral controls were interconnected so that the rudder automatically responded to the action of the ailerons4 ,fig4 #ba is a detailed front elevation of the machine and shows the control wheel 7,c7 and cable connections between the wheel and the ailerons ,a-,a'4 ,when the wheel ,c is turned in the direction of the arrow ,k1 the aileron ,a' is pulled down by the flexible cable 7i71 and a corresponding amount of cable 7h7 is paid off the wheel to the rising aileron ,a4 ,aileron ,a is pulled up by the connecting cable 7e7 which is attached to ,a' at one end and to ,a at the other4 ,pulleys 7f7 and 7g7 guide the interconnection cable4 ,on turning the wheel in the opposite direction1 aileron ,a is pulled down and ,a' is elevated4 ,in flight1 especially in rough weather1 there is almost continuous operation of the control wheel4 ,figs4 #bb and #bc are sections taken through the wing ,w and the ailerons1 showing the method of hinging and travel4 ,fig4 #bb shows the aileron depressed for raising the wing in the direction of ,l1 while ,fig4 #bc shows the aileron lifted to lower the wing4 ,in normal flight1 with the machine level1 the aileron forms a part of the wing outline 7in neutral position74 ,in the original ,wright aeroplane1 and in the majority of monoplanes1 no ailerons are used1 the rear of main wing tip being bent down bodily to increase the lift4 ,this is known as wing warping1 and is practically a single acting process since the depressing force on the high tip is seldom as effective as the lift on the low4 ,warping is not generally used on modern biplanes since it is impossible to maintain a strong rigid structure with flexible tips4 ,the control warping and twisting of such wings soon loosens them up and destroys what remaining strength they may have had4 ,illustration3 ,figs4 #ag-bc4 ,showing ,use of ,ailerons in ,maintaining ,lateral ,balance4 99,banking and ,turning994 ,in making a sharp turn the outer wing tip must be elevated to prevent slipping sidewise through the effects of the centrifugal force 7side slip74 ,this is known as banking4 ,the faster and sharper the turn1 the steeper must be the bank1 or the angle of the wings1 until in some cases of stunt flying the wings stand almost straight up and down4 ,should the bank be too steep there will be an equal tendency to slip down1 and inwardly1 since the end resistance against side slip is very slight4 ,some aeroplanes assume the correct angle of bank automatically without attention from the pilot since the extra lift due to the rapid motion of the outer tip causes it to rise4 ,on other machines the natural banking effort of the machine is not sufficient1 and this must be increased by pulling down the aileron on the outer wing tip4 ,machines that have a tendency to over-bank must have the ailerons applied in the reverse direction so as to depress the outer tip4 ,in cases of under1 or overbanking machines it formerly required experience and judgment on the part of the pilot to obtain the correct banking angle4 ,there are now banking indicators on the market that show whether the machine is correctly banked or is side-slipping4 ,illustration3 ,fig4 #bd4 ,a ,deperdussin ,monoplane ,banking ,around a ,sharp ,turn at ,high ,speed4 ,note the ,elevation of the ,outer ,wing ,tip and the ,angle ,made with the ,horizontal by the ,wings4 ,speed1 #aje ,miles ,per ,hour4 ,illustration3 ,standard ,h-#c ,training ,biplane4 ,,chapter ,,ii4 ,,types ,,of ,,military ,,aeroplanes4 99,divisions of ,service994 ,in the army and navy1 aeroplanes are used both for offensive and defensive operations4 ,they must carry out their own work and intentions and prevent hostile craft from carrying out theirs4 ,in offensive operations the machines fly continuously over the enemy's country and attack every hostile craft sighted1 thus creating a danger zone within the enemy's lines where no opposing machine can work without being threatened with an overwhelming attack4 ,the offensive also includes bombing operations and the destruction of supply depots and transportation centers4 ,defensive aerial operation consists in driving out the enemy craft from our own lines1 and in protecting working machines when on photographing or observation trips4 ,with a powerful offensive there is of course little need for defense4 ,the former method is a costly one1 and is productive of severe material and personal losses4 ,at the present time there are eight principle functions performed by military aeroplanes3 #a4 ,offensive operations against enemy machines4 #b4 ,reconnaissance1 observation1 special missions4 #c4 ,bombing supply centers1 railways1 etc4 #d4 ,photography4 #e4 ,spotting for the artillery4 #f4 ,signalling for infantry operations4 #g4 ,submarine hunting4 #h4 ,patrol and barrage4 ,illustration3 ,fig4 #a4 ,curtiss ,baby4 ,biplane ,speed ,scout4 ,equipped with #ajj ,horsepower ,water ,cooled ,motor4 ,probably the most important service of all is performed by machines under heading 7#a74 ,if a successful offensive can be maintained over the enemy's lines he is unable to intelligently direct his artillery fire1 and can obtain no information regarding reinforcements1 or troop concentrations for an impending attack4 ,with fighting aeroplanes clearing the way for our own observation machines and artillery spotters1 the enemy is not only blinded1 but is blocked in any attempt to attack or concentrate his forces4 ,the fact that the ,french aerial offensive at ,verdun was so efficiently and well maintained accounts for the failure of the heavy ,german artillery4 ,driven far back over their own lines1 the ,german aviators were seldom able to observe the placing of the shells1 and as a result their gunners were practically trusting to luck in reaching their target4 ,an immediate and accurate bombardment always followed one of the very infrequent ,german air raids over the ,french lines4 ,whenever the ,french1 partially abandoned their aerial offensive in favor of a defensive campaign1 they soon lost their mastery of the air4 ,as long as enemy machines can be kept back of their own lines1 new trench systems can be constructed1 transportation lines can be extended and ammunition dumps arranged1 undertakings that would be highly precarious with enemy observation machines continually passing overhead4 ,illustration3 ,fig4 #a4 ,italian ,pomilio ,two ,seater ,biplane4 ,courtesy ,flying4 ,to maintain an effective offensive places a tremendous strain on both the men and the machines1 for though the aeroplanes do not penetrate far beyond the lines they usually meet with superior numbers1 and in addition are continually in range of the anti-aircraft guns4 ,in an attack over hostile country a slight mishap may cause the loss of a 'plane1 for usually the distance from its base is so great as to prevent a gliding return4 ,over its own lines an engine failure is usually only a temporary inconvenience4 ,fighting aeroplanes1 for the offensive1 are small high powered machines generally of the single seater type1 and are capable of high horizontal and climbing speeds4 ,the armament consists of a machine gun of the ,lewis type1 and occasionally a few light bombs may be included in the equipment4 ,as they do not carry out operations far to the rear of the enemy's lines they are provided with fuel for only two or three hours1 and this reduced fuel load is necessary for the high speeds that must necessarily be attained4 ,the area is limited to permit of quick maneuvers in attack and escape1 and at the same time to reduce the head resistance and weight4 ,the horizontal speed may run up to #aej miles per hour1 with a climbing velocity that may exceed #a1jjj feet per minute4 ,such machines are variously known as ,speed ,scouts1 ,chasers1 or ,pursuit ,type 7,french ,de,chasse74 ,at the beginning of the war the chasers were largely of the monoplane type1 but at present the biplane is in almost exclusive use4 ,illustration3 ,fig4 #b4 ,machine ,gun ,mounting on ,morane ,monoplane4 ,gun ,fires ,directly ,through the ,propeller ,disc4 ,the ,deflecting ,plate ,attached to the ,root of the ,propeller ,blade ,protects the ,propeller ,when in ,line of ,fire4 ,ammunition in ,this ,gun ,is ,furnished in ,straight ,strips or ,clips4 ,the aeroplane employed for surveys of the enemy country and battle front 7#b7 are of an entirely different type and are much larger and slower4 ,these ,reconnaissance machines are generally of the two-seater type1 the personnel consisting of an observer and the pilot1 although in some cases a third man is carried as an assistant to the observer1 or to handle a machine gun against an attack4 ,since their speed is comparatively low1 they are generally provided with an escort of chasers1 especially when employed on distant missions1 this escort repelling attacks while the observations are being made4 ,illustration3 ,fig4 #b-;a4 ,machine ,gun ,mounting on ,s4 ,p4 ,a4 ,d4 ,biplane4 ,gun ,is ,rigidly ,attached to ,fuselage ,top in ,front of ,pilot4 ,for accurate observation and mapping1 the speed of an observation machine must be necessarily low1 and as they are additionally burdened with a wireless set1 an observer1 a large fuel reserve1 and other impedimenta1 they have a comparatively great area and are therefore lacking in the maneuvering qualities of the chaser4 ,the span will average about #dj feet1 and the weight carried per horsepower is greatly in excess of that of the chaser4 ,from a number of examples1 the reconnaissance type will average from #af to #ah pounds per horsepower1 while the loading of the scout is from #h to #ab4 ,this means that the former has comparatively little reserve power for rapid climbing4 ,the present reconnaissance type is always armed1 and must not be confused with the early machine by that name1 which1 in fact1 was merely an enlarged training machine and had neither offensive nor defensive powers4 ,the ,observer acts as gunner1 and is located at a point where he has the greatest possible range of vision1 and where the angle of fire is as little obstructed as possible4 ,the radius of action1 or the distance traveled per tank of fuel1 is greater with the reconnaissance than with the chaser1 present machines having a capacity of from #aj to #ab hours on a single filling at normal flight speed4 ,in bombing operations 7#c71 the loading is very heavy and consequently a ,bomber must be a weight lifter to the exclusion of all other qualities4 ,not only is the bomb load requirement severe1 but the fuel load is also of great importance1 since bombing is usually carried out at considerable distances from the base4 ,such machines may carry from three to six men4 ,all this calls for a tremendous area and a large power plant4 ,the ,handley-,page ,giant1 and the ,caproni ,triplane are examples of ,allied machines of this type while the ,german ,gotha1 used in the ,london air raids1 is an equivalent enemy machine4 ,as an example of the weight carrying capacity of a typical bomber1 the ,handley-,page has carried a test crew of #ba men1 or a personnel load of #c1egj pounds4 ,the total weight1 fully loaded1 has been given as #aa1ejj pounds with a power plant of #edj horsepower4 ,the maximum speed is #ij miles per hour with a climbing velocity of about #ccj feet per minute4 ,duration is about #e hours at normal speed and full load4 ,illustration3 ,fig4 #c4 ,handley-,page ,giant ,bombing ,type ,biplane4 ,courtesy ,the ,aeroplane4 ,illustration3 ,fig4 #d4 ,curtiss ,twin ,motor ,biplane-,type ,,jn4 ,bombing is of great importance1 not only because of the damage caused to munition factories1 transportation lines1 store houses1 etc41 but also because of the moral effect on both the enemy troops and the civil population4 ,a well-timed bombing raid will do more to disorganize an army than almost any other form of attack1 and this is attended with a much less loss of life1 and with less cost and equipment4 ,points in enemy territory that could be reached in no other way are readily attacked by bombing planes with all the disastrous effects of heavy artillery fire4 ,the aeroplane is better adapted for this service than dirigibles of the ,zeppelin type1 for they require fewer men for their operation1 and in addition cost less to operate and build4 ,illustration3 ,fig4 #d;a4 ,curtiss ,wireless ,speed ,scouts 7,s-#b74 ,by an ,ingenious ,arrangement of the ,interplane ,struts ,there ,is ,no ,exposed ,wire or ,cable4 ,bombing operations against well protected objectives are best made at night since there is less chance of loss through anti-aircraft gun fire1 and also because of the difficulty that the defense machines have in locating the raiders4 ,even when well equipped with searchlights and listening stations1 it is not the easiest thing in the world to pick out and hold the location of an attacking squadron1 for the searchlights immediately betray themselves and can then be put out of action by fire from the invaders4 ,with the searchlights out of commission1 it is almost impossible for the defending chasers to locate and engage the raiders1 even before the bombs have been dropped4 ,after the bomb dropping has been accomplished 7and with comparative accuracy because of the flares dropped by the bombing party71 the raiders are lightened of a considerable portion of their load1 and are correspondingly increased in their ability to climb and to evade the enemy chasers4 ,illustration3 ,fig4 #e4 ,sopwith ,speed ,scout or ,chaser4 ,illustration3 ,fig4 #f4 ,nieuport ,biplane ,scout with ,machine ,gun ,pivoted ,above the ,upper ,wing4 ,this ,gun ,fires ,above the ,propeller4 ,night flying in squadrons always introduces the danger of collision1 and to minimize this danger1 by decreasing the number of machines1 the size and carrying capacity of the bombers has been continually increased4 ,again1 bombing requires the steady platform that only a large machine can give1 and for accuracy the span and area must be greater than that of the reconnaissance type4 ,in night flying a large machine is safer to handle owing to its lower landing speed and ability to come to rest quickly after landing1 and this is of the greatest importance when landing outside of the aerodrome4 ,for daylight work at comparatively short distances the smaller bomb carrier used at the beginning of the war is probably preferable as it has better maneuvering qualities1 and as the bombs are divided among a greater number of machines they are not so likely to be defeated before accomplishing their object4 ,because of their great size1 these bombing aeroplanes are nearly always of the twin motor type with two1 or even three1 independent power plants4 ,the use of a twin power plant is an added insurance against forced landings in hostile country1 or over unsuitable ground1 and even with one dead engine the machine can be flown home at a fair speed4 ,illustration3 ,fig4 #h4 ,fokker ,synchronized ,machine ,gun4 ,the ,gun ,is ,driven by the ,motor in ,such a ,way ,that the ,bullets ,pass ,between the ,propeller ,blades4 ,l',aerophile4 ,spotting for the guidance of the artillery is a duty usually performed by the reconnaissance type1 or small bombing type1 and is usually done under the escort of chasers4 ,their duty is to direct the battery as to the placing of shots4 ,the ideal machine for such a purpose would be the direct lift type similar to a helicopter which could hover over one particular spot until its object had been accomplished in making measurements1 and plotting enemy positions4 ,since no such machine is at present available1 the duty must be performed by a low speed aeroplane1 that is large enough to provide a fairly steady platform and at the same time has sufficient speed for a quick getaway4 ,a dirigible has the necessary hovering qualities but lacks the speed necessary for avoiding attack from even the slowest of aeroplanes1 and in addition is a magnificent target for anti-craft guns if kept at an altitude low enough for accurate observation4 ,a large speed range is a desirable characteristic in such service4 ,photography is of the greatest importance in reconnaissance1 since the camera distinctly records objects on the terrain1 so small and obscure that they may entirely escape the eye of the observer4 ,again1 the photograph is a permanent record that may be studied at leisure in headquarters1 or may be used in comparisons with photographs taken at an earlier date in the same territory4 ,thus changes in the disposition of enemy batteries1 trenches1 and troops can be quickly identified4 ,with modern aeroplane photographic equipment1 a vast territory may be investigated and mapped out by a single machine in a few hours4 ,camouflage has but few terrors for the camera1 and the photographs often clearly reveal that which has been passed over time and time again by the observers4 ,when sent out on a specific mission1 the aeroplane returns the films in an amazingly short length of time1 and within a few minutes they are developed and are ready for the inspection of the officers in charge4 ,the analysis of these photographs has rapidly developed into a science well worthy of a ,sherlock ,holmes4 ,changes in the position of shadows1 suspiciously sudden growths of underbrush1 changes in the direction of paths1 and fresh mounds of earth all have a definite meaning to the photographic expert4 ,illustration3 ,fig4 #i4 ,types of ,aeroplane ,bombs4 ,the ,tail ,surfaces ,guide the ,bomb ,so ,that ,it ,strikes on the ,firing ,pin and at the ,same ,time ,safeties the ,bomb ,so ,that it ,will ,not ,explode ,until it ,has ,fallen for ,some ,distance4 ,in ,falling1 the ,tail ,blades ,rotate and ,release the ,firing ,mechanism ,after the ,bomb ,has ,fallen ,clear of the ,aeroplane4 ,courtesy of ,flying4 ,illustration3 ,fig4 #i-;a4 ,curtiss ,,jn ,twin ,motor ,biplane4 ,observer ,is ,seated in ,front4 ,in the navy the aeroplane has proved of much value in scouting and particularly in defense against the submarine4 ,because of its great speed it has a daily radius of action many times that of a torpedo boat1 and because of its altitude the effective range of vision is still further increased4 ,at a fair height the observer can easily detect a submarine even when submerged to a considerable depth1 a feat impossible when near the sea level4 ,for disclosing the conditions existing in an enemy harbor the aeroplane is fully the equal of the dirigible since it can approach and retreat rapidly1 and without much danger at comparatively low altitudes4 ,while the dirigible can float indefinitely at one point1 it must be done at an altitude that is safely out of range of the enemy guns1 and this is usually at a point where observation is a difficult proposition4 ,it does not take long to get the range of such a target as a hovering dirigible1 yet at a much lower altitude it is difficult to handle naval anti-aircraft guns effectively against a speeding aeroplane4 ,the smaller scouting seaplanes can report the position of a submarine to a torpedo boat or sub-chaser1 while the larger machines are perfectly capable of dealing with the submarine at first hand4 ,on the large bombing type1 a three-pounder gun and a number of large bombs can be carried1 either of which would be sufficient for the purpose4 ,illustration3 ,fig4 #aj4 ,explosion of a ,german ,aeroplane ,bomb ,near ,mesopotamia4 ,courtesy of ,flying4 ,in land defense chasers and fighters are used for patrol1 and to maintain a barrage against the entrance of enemy machines into our lines4 ,the patrol machines work along the front line trenches1 while the machines maintaining the barrage are generally arranged in two parallel lines back of the trenches1 the first being about five miles1 and the second about ten miles from the front4 ,all three lines are generally placed between the enemy and the principal stations and railroad centers to insure protection from enemy bombers and reconnaissance machines4 ,should the first line patrol fail to keep raiders from crossing the first line trenches1 they will have to pass through at least two more zones of organized fighting squadrons before reaching a vulnerable spot in our lines4 ,the machines used for patrol and barrage are of the high speed and fast climbing chaser type4 ,the response to an attack involves rapid climbing1 and a high degree of maneuvering4 ,illustration3 ,fig4 #aa4 ,caproni ,triplane with ,three ,independent ,power ,plants4 ,the ,motor in the ,central ,body ,drives a ,pusher ,propeller1 ,while the ,other ,power ,plants ,are ,mounted in the ,two ,outer ,bodies and ,drive ,tractor ,screws4 ,this is an ,example of the ,larger ,bombing ,aeroplanes4 ,the ,gun ,is ,mounted in the ,front of the ,center ,body4 ,courtesy ,the ,aeroplane4 ,except for the bombers and battle planes1 the machine gun or ,mitraleuse has been the only form of arm in common use on aeroplanes4 ,these use ammunition approximating service rifle caliber and are furnished in bands1 strips or drums according to the type of gun4 ,with larger guns1 the weight of the ammunition has been found excessive with all but the largest bombing machines1 and the recoil of a large caliber gun has also been difficult to overcome4 ,in a modern ,american aeroplane gun of large caliber the recoil has been reduced to almost a negligible degree1 even up to the four-pounder size1 by a system of balanced projectile reactions4 ,this gun has met successful tests1 but whether it has met with general adoption would be difficult to say at the present time4 ,in ,europe1 large caliber aeroplane guns have been used on large battle planes or gun planes for shelling dirigibles1 or in destroying searchlight stations in bombing raids4 ,the battle planes are nearly always of the ,twin type with the gun mounted in the front end of the fuselage4 99,summary of ,types994 ,to sum up the types required in military operations1 we have3 7#a7 ,high speed ,chaser or ,scout 7,single seater71 7#b7 ,high speed ,chaser 7,two-seat type71 7#c7 ,reconnaissance type1 7#d7 ,bombing type1 7#e7 ,gun or ,battle ,planes4 ,this does not include the training machines of the two place and ,penguin types1 but as these are simply unarmed modifications of the two place reconnaissance and single seat machine1 respectively1 we will not go into further details at this point regarding their construction4 99,the ,chaser or ,pursuit ,type994 ,the most important factors in the design of a chaser are speed and maneuvering ability4 ,the speed must be at a maximum in both the horizontal and vertical directions1 for climbing ability is fully of as much importance as horizontal speed4 ,second in importance is the maximum altitude or ,height of ceiling to which the machine can ascend4 ,this maximum ,ceiling generally goes hand in hand with the climbing speed1 since a fast climber generally has a correspondingly high maximum altitude4 ,the combination of weight and head resistance must be such that the climb interferes as little as possible with the forward velocity4 ,illustration3 ,de ,havilland4 ,v4 ,single ,seat ,chaser or ,speed ,scout with a ,single ,rigidly ,mounted ,machine ,gun on ,top of ,hood 7,to ,left74 ,it will ,be ,noted ,that the ,top ,wing is ,staggered ,back ,instead of ,forward as in the ,usual ,type1 ,thus ,allowing the ,pilot to ,look ,directly ,up and in ,front of the ,top ,wing4 ,dimensions ,are in ,millimeters4 ,great climbing ability means a large power reserve1 hence the weight carried per horsepower is reduced to from #h to #ab pounds on the fastest machines1 against the #af to #ah pounds carried on the larger and slower reconnaissance types4 ,strength must be sacrificed to meet these conditions1 so that instead of having a safety factor of from #h to #ab as in the larger machines1 it is cut to about #e4e1 or in other words1 the strength is relatively only half that of the usual type of aeroplane4 ,this great reduction in strength calls for careful handling1 especially in landing1 and also painstaking care in the design and choice of materials4 ,high speeds and maneuvering ability both call for small wing areas and short spans1 the areas being so adjusted that the resistance is at a minimum at the highest speeds4 ,the short spans have a minimum of exposed interplane bracing and thus indirectly reduce both the head resistance and the weight4 ,unfortunately1 the most favorable areas at high speeds are too small for safe landing speeds4 ,with a fixed area1 the minimum landing speed is only a little less than one-half of the maximum flying speed1 hence with a maximum of #aej miles per hour the minimum will probably be little less than #gj miles per hour4 ,the most efficient wing sections1 and the greatest refinement in the body design1 bracing1 and chassis are necessary at speeds of over #ajj miles per hour4 ,all other conditions being equal1 the resistance varies as the square of the velocity1 hence at #aej miles per hour1 the resistance is #b4be times that at #ajj miles per hour4 ,the following table gives approximately the apportionment of the head resistance producing items in a typical speed scout or chaser4 ,body 7,fuselage7 #fh per cent ,chassis1 wheels1 struts1 etc4 #ae per cent ,tail1 rudder1 fin1 elevator #e per cent ,wing structure1 struts1 wire1 fittings4 #ab per cent ,the aerodynamic drag due to the lift of the wings is not included in the above1 the useless or parasitic resistance alone being considered4 ,it will be noted that the body causes by far the greater part of the resistance1 and as a result1 the body of the speed scout requires the most careful attention in regard to streamline form4 ,fortunately this is possible with the short stumpy body of the chaser1 since a true streamline form approximates the average body dimensions of the scout4 ,in the larger machines1 the body resistance is not as great in proportion to the other items since there are more struts and stay wires1 the chassis is larger1 and the tail surfaces are of greater area4 ,the chassis is the next largest item and is one of the most difficult items to reduce4 ,it has been suggested by several people that the chassis could be stored away in the body while in flight1 but this adds additional mechanism and weight1 and any automatic mechanism for folding up the chassis members would likely prove unreliable4 99,chaser ,armament994 ,a single seat chaser is provided with one or two machine guns mounted on top of the fuselage1 and directly in front of the pilot1 the length of the barrel being parallel with the fore and aft center line4 ,they may either be fixed rigidly to the fuselage top1 or so that they can be pointed up1 and over the top of the upper wing4 ,with the machine guns fixed rigidly to the body1 as in the early chaser monoplanes used by ,garros and ,vedrines1 it was necessary at all times to fire directly through the disc area swept out by the propeller4 ,two plans were tried for preventing the propeller from being broken by the bullets4 ,the first consisted of a device operated by the motor that stopped the gun whenever the propeller blade came within the path of the bullets4 ,this early mechanism proved unreliable1 since the frequent stopping1 with the propellers running #abjj revolutions per minute1 soon put the apparatus out of order4 ,soon after the failure of this method1 designers mounted curved protective steel plates on the inner portions of the propeller blades at points where they were likely to be struck with bullets4 ,according to calculations in probability and chance1 only one bullet out of every eighteen will strike the protective plate on the propeller blade1 and hence only one out of eighteen bullets will be wasted4 ,this1 however1 was a makeshift1 and on modern machines the gun is driven1 or ,synchronized with the motor so that the bullets pass between the blades4 ,illustration3 ,curtiss ,biplane in ,flight4 ,taken from ,another ,machine4 ,courtesy ,aerial ,age4 ,many modern single seat chasers have the gun pivoted to the top of the fuselage so that the pilot can fire above the top plane and to either side of the body4 ,this does away with the difficulty of keeping the machine headed directly at the enemy when in action1 a method that is imperative with the fixed type of gun4 ,two seater chasers are generally arranged so that the gunner is seated back of the pilot1 and the gun is so pivoted and supported that it can be swung through a wide radius both toward the front and on either side4 ,this freedom of gun action at least partly compensates for the slower maneuvering qualities of the two seater type1 since the gun may be swung with the target through quite a range of field1 and without changing the flight direction of the machine4 ,a gun of this type is provided with stops which prevent the gunner from shooting into the outlying parts of his own machine4 ,the gun mounting in many cases of two seater construction consists of a light circular track that runs around the edge of the cockpit opening4 ,the gun standard runs on this track1 and the gun is pivoted at the upper end of the standard so that the muzzle can be raised or lowered4 ,the gun turns in a horizontal plane by sliding on the track1 and can be followed around by the gunner who is seated in the center on a pivoted seat4 ,with this mounting it is possible to guard against a rear attack1 to shoot straight up1 or nearly straight down over the sides of the fuselage4 ,in a few machines of the two seater type1 two machine guns are provided1 one pivoted gun in the rear1 and one gun rigidly fastened to the fuselage in front of the pilot4 ,it is very seldom that both guns can be brought into action at once unless engaged with a number of enemy machines1 although the front gun is handy in pursuit1 and at a time when the rear gun is ineffective because of the pilot in front of him4 ,even with the double equipment1 the superior maneuvering qualities of the single seater makes matters more even than would commonly be supposed4 ,an added advantage of the single seater is that it is smaller and therefore more difficult to hit4 ,english speed scouts have largely adopted the ,american ,lewis gun4 ,the cartridges in this gun are arranged radially in a circular drum1 and are fed to the gun as the drum revolves4 ,the drum is mounted on the barrel near the breech and is operated automatically by the successive explosions4 ,this feeds the cartridges and rejects the empty shells without the attention of the pilot4 ,it fires about #fjj shots per minute4 ,when one drum is exhausted1 another drum of new cartridges can be quickly and easily inserted4 ,the ,french use the belt system to a large extent4 ,in this system the cartridges are attached side by side on a cotton web belt as in the older types of army machine guns4 ,as in the ,lewis gun1 the cartridges are fed automatically by the recoil of the explosions1 and the belt moves through the breech with a step by step movement until the ammunition is exhausted4 ,this is not nearly as compact an arrangement as the ,lewis gun1 and is more difficult to pivot on account of the dangling belts4 ,on the right hand side of the ,nieuport body there is a drum on which the belt with the loaded cartridges is wound4 ,the empty end of the belt is wound on a drum at the left1 this drum being provided with a spring to keep the belt taut4 ,the empty cartridges are discharged through a tube that passes through the side of the body4 ,on the #aiaf ,fokker the gun is of the ,maxim type1 and is immovably fastened above the engine cowl and slightly to the right4 ,to fire the gun1 the pilot presses down a small lever fastened to the control column1 and from this lever the connecting ,bowden wire closes the motor clutch and starts the gun4 ,a cam is fixed to the motor shaft in relation to the propeller blades4 ,when firing1 the elevator control is locked fore and aft1 while the lateral control movement is operated by the pilot's knees4 ,steering is by the action of his feet on the rudder bar4 ,thus the pilot can balance laterally1 and steer with his hands free for the manipulation of the gun1 but he cannot change his elevation4 ,illustration3 ,aeromarine ,training ,seaplane 99,power ,plant of the ,chaser994 ,in the smaller speed scouts1 the motor is of the rotary air cooled type1 the output ranging from #hj to #aaj horsepower1 but as the power demands increased the water-cooled motor came into use1 and at the present time has found favor with a large number of builders4 ,when the power exceeds about #abj horsepower it is difficult to thoroughly cool the rotary engine1 and although the ,gnome1 ,clerget and ,le ,rhone are extremely desirable on a chaser because of their light weight1 they cannot be used profitably on the larger scouts4 ,up to the present time1 the ,nieuport and ,sopwith use the ,clerget and ,le ,rhone rotary motors1 but the ,s4 ,p4 ,a4 ,d4 and several others have adopted the water-cooled type4 ,nearly all of the ,german chasers1 such as the ,roland and ,albatros1 are water-cooled4 ,such motors must weigh well below #c pounds per horsepower if there is to be sufficient power reserve for fast climbing4 ,the ,curtiss scouts are also water-cooled1 although the rating is only #ajj horsepower4 ,the ,french and ,german machines are very heavily powered1 motors of #age horsepower being very common1 even on single seaters4 ,the fuel capacity is very limited1 probably not exceeding #b4e to #c hours in any case4 99,general ,dimensions of ,scouts994 ,the following table will give a better idea of the principal characteristics of these machines4 ,it gives the overall dimensions1 power1 speed1 climb1 etc4 ,it will be noted that the ,nieuport biplane scouts have a smaller lower chord 79974 ,the speeds given are the sea level speeds since a great change in altitude affects the performance to a marked degree4 99,reconnaissance ,type ,arrangement994 ,these machines are almost invariably of the two seater type1 and are equipped either with one machine gun for the observer1 or with a rigidly fixed gun for the pilot and a pivoted gun at the rear for the observer4 ,in the majority of cases the observer is seated in the rear cockpit 7,tractor types71 and at a point where he has a greater visual radius and field of fire4 ,with the pusher type1 the observer is1 of course1 seated in the extreme front of the body1 where he has an extremely wide angle of vision4 ,the pilot in the rear seat of the pusher is effectually screened from any gun action1 either from the front1 side or rear1 as the propeller cuts off the field at the back and the observer and interplane bracing blocks the way at the front and sides4 ,the observer's cock-pit is equipped with the signalling apparatus1 photographic equipment1 map boards1 etc41 as well as the ammunition for the gun4 ,the pilot's compartment contains the navigating instruments and controls4 99,armament994 ,at the beginning of the war nearly all of the ,french two seaters were of the pusher type1 this arrangement1 of course1 resulted in almost a completely dead angle of fire in the rear1 and a front horizontal angle that was practically restricted to #afj degrees4 ,owing to the forward position of the gun the vertical angle was quite good1 #bcj degrees or even better4 ,in the tractor two seater1 with a single movable gun mounted ,en barbette at the rear1 the horizontal angle is about #ahj degrees1 but the vertical angle is less than with the pusher type4 ,when the rear gun is supplemented with a front rigidly mounted gun1 there is some protection at the front1 but the rigid gun is far from being as effective as the pivoted rear gun4 ,the front gun of course fires through the propeller4 ,this armament is used by the ,german machines ,aviatic1 ,rumpler1 ,albatros1 and ,l4 ,v4 ,g4 ,the forward rigid gun is usually of the infantry type1 while the movable rear gun is lighter4 ,the latter is fed by drums1 or rolled bands on spools1 so that reloading can be performed in the wind stream4 ,with the two seater type used in reconnaissance1 artillery spotting1 or photography1 the power is generally in the neighborhood of #bbj-bfj horsepower1 and the speed varies from #he to #ajj miles per hour4 ,the area is approximately #djj to #dhj square feet4 ,a single engine is generally used4 99,general ,dimensions and ,speeds994 ,reconnaissance machines of various types and makes are listed in the following table4 ,a pusher is indicated by 7,p7 and a tractor by 7,t74 ,the ,german aeroplanes 7,g71 and the ,allied aeroplanes 7,a71 are both listed for comparison3 ,it will be noted that several types of machines have been made by the same firms1 and that in some cases the same machines have different power plants4 ,the ,albatros ,c-,,iii has been furnished with both the #agj and #bbj ,mercedes motor4 ,the ,ago biplane has a tapering wing1 and the chord width 7997 given is taken at the body4 ,while very recent machines cannot be described1 because of certain restrictions1 the horsepower of the latest two seaters will average about #bdj horsepower4 ,if the dates and power items are noted1 it will be seen that the machines used in #aiag have much larger motors than those built in #aiaf4 ,the weight per square foot of surface will average about #f4e pounds4 ,the loading per horsepower rarely exceeds #ag4j pounds4 99,bombing ,type ,aeroplanes994 ,these large aeroplanes are fitted with either two or three independent power plants4 ,the ,german bombers are represented by the ,gotha1 ,a4 ,e4 ,g41 ,friedrichshafen1 and ,rumpler ,g1 while the ,allied bombers are the ,caproni1 ,handley-,page1 ,farman1 ,voisin1 etc4 ,the speed is about that of the reconnaissance type1 and will seat three or more men4 ,the motors average #ejj #efj horsepower per power plant1 and the wing area is usually well over #a1jjj square feet4 ,the small two seaters are generally equipped with two pivoted machine guns1 while the three seaters have a third machine gun arranged so that it can be lowered and fired through a trap door in the bottom of the body4 ,defense may thus be had from the rear1 or below4 ,in some of the pusher types1 a rapid fire gun of comparatively heavy caliber is mounted at the front of the body in place of the usual machine gun4 ,this is usually the case with the sea planes used for submarine chasing4 ,in addition to bombing operations1 these large machines are also used for the protection of spotting aeroplanes1 or for the direct protection of the lines against land attacks4 ,these heavily armed bombers are very difficult to attack1 even for the smaller and more agile ,chasers1 as they can fire from below as well as from the front1 top1 or sides4 ,in the bombers which have only a single gun in the rear1 the gunner is working at a disadvantage if his adversary forces him to continually raise and lower his gun from the top of the body to the lower trap door4 ,this is very tiring to the rear gunner1 and if the chaser's tactics are carried out for a sufficient length of time1 it can wear out the gunner by continually rising and dropping at the tail of the bombing plane4 ,in regard to the front gun1 the twin motor type offers many of the advantages of the pusher1 and as a whole1 the twin arrangement will nearly double the field of fire of either the tractor or pusher4 ,the bombing planes must have a very large radius of action1 particularly those that are used in night bombing operations4 ,the ,gothas in bombing ,london fly several hundred miles from their base1 and recently a ,handley-,page bombing plane flew from ,london to ,constantinople1 ,turkey1 making only a few stops on the way4 ,starting out from ,hendon1 ,england1 the ,handley-,page machine flew to ,paris1 down the ,rhone valley to ,lyons and ,marseilles1 and then to ,pisa1 and ,rome 7,italy71 where they landed4 ,from ,rome the machine passed over ,naples1 over ,oranto and then over the ,albanian ,alps to the base at ,salonica4 ,making preparations at this base they flew the final stage of the trip to ,constantinople1 a distance of #bej miles over hostile country4 ,the bombing of the ,turkish capital was done at night after a flight of #b #a_/b hours from ,salonica4 ,when over the sea of ,marmora1 the ship ,goeben was bombed1 and in addition a hit was scored on the two submarines lying at her side4 ,four bombs struck the ,goeben directly1 from an altitude of #hjj feet4 ,two more bombs were dropped on the ,german ship1 ,general1 which was the headquarters of the ,german staff4 ,finally1 after #cj minutes over the city of ,constantinople1 the ,turkish ,war ,office was the recipient of two more bombs4 ,in the words of the ,turkish communiqu this ,was not entirely destroyed4 ,on its return to ,salonica it was found that the machine had been struck by #bf shrapnel bullets4 ,this disabled one of the power plants so that the greater part of the return journey was made on a single motor4 ,from ,london to ,salonica five men were carried4 ,in addition was their luggage1 bedding1 two tool boxes1 spare parts equivalent in weight to one engine1 and two #aa'-f spare propellers4 ,complete1 the machine weighed over #f tons1 with a useful load of about #f1jjj pounds4 ,in crossing the ,albanian ,alps the machine frequently was at an altitude of #aj1jjj feet4 ,the power plant consisted of two #bge horsepower ,rolls-,royce motors1 and even at this high altitude1 and with the heavy loading1 no trouble was experienced4 ,during the bombing1 only three men were carried1 the remainder of the useful weight being made up of bombs and other ammunition4 ,while this record will probably be beaten before this book goes to press1 it will at least give an idea as to the requirements and capabilities of the bombing type aeroplane4 99,military ,training ,machines994 ,the military training machines used in the ,united ,states are generally of the two seater tractor type1 similar in external appearance to the reconnaissance type machines already described4 ,they are low powered1 #ij to #abe horsepower1 and will have an average span of #dj'-j4 ,the controls are in duplicate so that the student's controls move in unison with the instructor's4 ,,chapter ,,iii4 ,,elementary ,,aerodynamics 99,definition994 ,aerodynamics treats of the forces produced by air in motion1 and is the basic subject in the study of the aeroplane4 ,it is the purpose of this chapter to describe in detail the action of the wing in flight1 and the aerodynamic behavior of the other bodies that enter into the construction of the aeroplane4 ,at present1 aerodynamic data is almost entirely based on experimental investigations4 ,the motions and reactions produced by disturbed air are so complex and involved that no complete mathematical theory has yet been advanced that permits of direct calculation4 99,properties of ,air994 ,air being a material substance1 possesses the properties of volume1 weight1 viscosity and compressibility4 ,it is a mechanical mixture of the two elementary gases1 oxygen and nitrogen1 in the proportion of #bc per cent of oxygen to #gg per cent of nitrogen4 ,it is the oxygen element that produces combustion1 while the nitrogen is inert and does not readily enter into combination with other elements1 its evident function being to act as a dilutant for the energetic oxygen4 ,in combustion1 the oxygen enters into a chemical combination with the fuel while the nitrogen passes off with the products of combustion unchanged4 ,air is considered as a fluid since it is capable of flowing like water1 but unlike water1 it is highly compressible4 ,owing to the difference between air and water in regard to compressibility1 they do not follow exactly the same laws1 but at ordinary flight speeds and in the open air1 the variations in the pressure are so slight as to cause little difference in the density4 ,hence for 99flight alone991 air may be considered as incompressible4 ,it should be noted that a compressible fluid is changed in density by variations in the pressure1 that is1 by applying pressure the weight of a cubic foot of a compressible fluid is greater than the same fluid under a lighter pressure4 ,this is an important consideration since the density of the air greatly affects the forces that set it in motion1 and for this reason the density 7weight per cubic foot7 is always specified in a test4 ,every existing fluid resists the motion of a body1 the opposition to the motion being commonly known as resistance4 ,this is due to the cohesion between the fluid particles and the resistance is the actual force required to break them apart and make room for the moving body4 ,fluids exhibiting resistance are said to have viscosity4 ,in early aerodynamic researches1 and in the study of hydrodynamics1 the mathematical theory is based on a perfect fluid1 that is1 on a theoretical fluid possessing no viscosity1 and while this conception is an aid in studying the reactions1 the actual laboratory results are far from the computed values4 ,such theory would assume that a body could move in a fluid without encountering resistance1 which in practice is1 of course1 impossible4 ,in regard to viscosity1 it may be noted that air is highly viscuous--relatively much higher than water4 ,density for density1 the viscosity of air is about #ad times that of water1 and consequently the effects of viscosity in air are of the utmost importance in the calculation of resistance of moving parts4 ,atmospheric air at sea level is about #a_/hjj of the density of water4 ,its density varies with the altitude and with various atmospheric conditions1 and for this reason the density is usually specified at sea level as this altitude gives a constant base of measurement for all parts of the world4 ,as the density is also affected by changes in temperature1 a standard temperature is also specified4 ,experimental results1 whatever the pressure and temperature at which they were made1 are reduced to the corresponding values at standard temperature and at the normal sea level pressure1 in order that these results may be readily comparable with other data4 ,the normal 7average7 pressure at sea level is #ad4g pounds per square inch1 or #b1aai pounds per square foot at a temperature of #fj ,fahrenheit4 ,at this temperature #a pound of air occupies a volume of #ac4ada cubic feet1 while at #j ,f4 the volume shrinks to #aa4eh cubic feet1 the corresponding densities being #j4jgfaj and #j4jhfcc pounds per cubic foot1 respectively4 ,this refers to dry air only as the presence of water vapor makes a change in the density4 ,with a reduction in temperature the pressure increases with the density increase so that the effect of heat is twofold in its effect4 ,with a constant temperature1 the pressure and density both decrease as the altitude increases1 a density at sea level of #j4jgfaj pounds per cubic foot is reduced to #j4jceg pounds per cubic foot at an altitude of #bj1jjj feet4 ,during this increase in altitude1 the pressure drops from #ad4g pounds per square inch to #f4hg pounds per square inch4 ,this variation1 of course1 greatly affects the performance of aeroplanes flying at different altitudes1 and still more affects the performance of the motor1 since the latter cannot take in as much fuel per stroke at high altitudes as at low1 and as a result the power is diminished as we gain in altitude4 ,the following table gives the power variations at different heights above sea level4 ,this air table also gives the properties of air through the usual range of flight altitudes4 ,the pressures corresponding to the altitudes are given both in pounds per square inch and in inches of mercury so that barometer and pressure readings can be compared4 ,in the fourth column is the percentage of the horsepower available at different altitudes1 the horsepower at sea level being taken as unity4 ,for example1 if an engine develops #ajj horsepower at sea level1 it will develop #ajj #j4ffff horsepower at an altitude of #aj1jjj feet above sea level4 ,the barometric pressure in pounds per square inch can be obtained by multiplying the pressure in inches of mercury by the factor #j4dije1 this being the weight of a mercury column #a inch high4 ,illustration3 ,,note4-,densities marked 99 are interpolated from a graph1 but are close enough for all ordinary purposes4 ,in aerodynamic laboratory reports1 the standard density of air is #j4jgfjh pounds per cubic foot at sea level1 the temperature being #ae degrees ,centigrade 7#ei degrees ,fahrenheit74 ,this standard density will be assumed throughout the book1 and hence for any other altitude or density the corresponding corrections must be made4 ,owing to the fact that the temperature decreases as we gain altitude1 further corrections must be made in the tabular values1 but as the changes are rather difficult to make and are relatively small we will not take the matter up at this point4 ,illustration3 ,fig4 #a4 ,air ,flow ,about a ,flat ,normal ,plate4 ,pressure ,zone at ,front and 44 ,turbulent ,zone at ,rear 7,h74 ,arrows ,show ,direction ,o ,,ow4 99,air ,pressure on ,normal ,flat ,plates994 ,when a flat plate or plane is held at right angles or normal to an air stream1 it obstructs the flow and a force is produced that tends to move it with the stream4 ,the stream divides1as shown in ,fig4 #a and passes all around the edges of the plate 7,p-,r71 the stream reuniting at a point 7,m7 far in the rear4 ,assuming the air flow from left to right1 as in the figure1 it will be noted that the rear of the plate at 7,h7 is under a slight vacuum1 and that it is filled with a complicated whirling mass of air4 ,the general trend of the eddy paths are indicated by the arrows4 ,at the front where the air current first strikes the plate there is a considerable pressure due to the impact of the air particles4 ,in the figure1 pressure above the atmospheric is indicated by 9999991 while the vacuous space at the rear is indicated by fine dots4 ,as the pressure in front1 and the vacuum in the rear1 both tend to move the surface to the right in the direction of the air stream1 the total force tending to move the plate will be the difference of pressure on the front and rear faces multiplied by the area of the plate4 ,thus if ,f is the force due to the impact pressure at the front1 and ,g is the force due to the vacuum at the rear1 then the total resistance 7,d7 or ,drag is the sum of the two forces4 ,contrary to the common opinion1 the vacuous part of the drag is by far the greater1 say in the neighborhood of from #fj to #ge per cent of the total4 ,when a body experiences pressure due to the breaking up of an air stream1 as in the present case1 the pressure is said to be due to turbulence1 and the body is said to produce turbulent flow4 ,this is to distinguish the forces due to impact and suction1 from the forces due to the frictional drag produced by the air stream rubbing over the surface4 ,forces due to turbulent flow do not vary directly as the velocity of the air past the plate1 but at a much higher rate4 ,if the velocity is doubled1 the plate not only meets with twice the volume of air1 but it also meets it twice as fast4 ,the total effect is four times as great as in the first place4 ,the forces due to turbulent flow therefore vary as the square of the velocity1 and the pressure increases very rapidly with a small increase in the velocity4 ,the force exerted on a plate also increases directly with the area1 and to a lesser extent the drag is also affected by the shape and proportions4 ,expressed as a formula1 the total resistance 7,d7 becomes3 ,d ,,kav1 where ,k co-efficient of resistance determined by experiment1 ,a area of plate in square feet1 and ,v velocity in miles per hour4 ,the value of ,k takes the shape and proportion of the plate into consideration1 and also the air density4 99,example994 ,if the area of a flat plate is #f square feet1 the co-efficient ,k #j4jjc1 and the velocity is #fj miles per hour1 what is the drag of the plate in pounds8 99,solution994 ,d ,,kav #j4jjc #f 7#fj ,x #fj7 #fd4hj pounds drag4 ,for a square flat plate1 the co-efficient ,k can be taken as #j4jjc4 99,aspect ,ratio994 ,the aspect ratio of a plate is the ratio of the length to the width4 ,thus1 with an aspect ratio of #b4j1 we understand that the plate is twice as long as it is wide4 ,the ratio of the length to the width has a very considerable influence of the resistance or drag1 this increasing as the ratio is made greater4 ,if the resistance of a square plate is taken as #a4jj1 the resistance of a plate with an aspect ratio of #bj will be about #a4cd times as great4 ,the following table will give the effects of aspect ratio on the resistance of a flat plane4 ,,effects ,,of ,,aspect ,,ratio ,,on ,,flat ,,plates4 ,aspect ,ratio4 ,resistance ,k as a ,multiple of a ,square ,length_/,width ,plate4 #a4jj 7square7 #a4jj #a4ej #a4jd #b4jj #a4je #c4jj #a4jg #d4jj #a4jh #e4jj #a4ji #f4jj #a4aj #g4jj #a4ab #i4jj #a4ad #aj4jj #a4ae #ae4jj #a4bf #bj4jj #a4cd #cj4jj #a4dj ,to convert the values of a square plate into a flat plate of given aspect ratio1 multiply the resistance of the square plate by the factor under the ,k heading4 ,for example3 ,the resistance of a certain square plate is #bj pounds1 find the resistance of a plate of the same area1 but with an aspect ratio of #ae4 99,solution994 ,the factor for a ratio of #ae will be found to be #a4bf1 hence the resistance of the required plate will be #bj #a4bfbe4b pounds4 ,illustration3 ,fig4 #b4 ,air ,flow ,about a ,streamline ,body ,showing an ,almost ,complete ,absence of ,turbulence ,except at the ,extreme ,rear ,edge4 ,resistance ,is ,principally ,due to ,skin ,friction4 99,streamline ,forms994 ,when a body is of such form that it does not cause turbulence when moved through the air1 the drag is entirely due to skin friction4 ,such a body is known as a streamline form and approximations are used for the exposed structural parts of aeroplanes in order to reduce the resistance4 ,streamline bodies are fishlike or torpedo-shaped1 as shown by ,fig4 #b1 and it will be noted that the air stream hangs closely to the outline through nearly its entire length4 ,the drag is therefore entirely due to the friction of the air on the sides of the body since there is no turbulence or discontinuity4 ,in practical bodies it is impossible to prevent the small turbulence 7,i71 but in well-designed forms its effect is almost negligible4 ,in poor attempts at streamline form1 the flow discontinues its adherence to the body at a point near the tail4 ,the poorer the streamline1 and the higher the resistance1 the sooner the stream starts to break away from the body and cause a turbulent region4 ,the resistance now becomes partly turbulent and partly frictional1 with the resistance increasing rapidly as the percentage of the turbulent region is increased4 ,the fact that the resistance is due to two factors1 makes the resistance of an approximate streamline body very difficult to calculate1 as the frictional drag and the turbulent drag do not increase at the same rate for different speeds4 ,the drag due to turbulence varies as ,v squared while the frictional resistance only varies at the rate of ,v to the #a4hfth power1 hence the drag due to turbulence increases much faster with the velocity than the frictional component4 ,if we could foretell the percentage of friction1 it would be fairly easy to calculate the total effect1 but this percentage is exactly what we do not know4 ,the only sure method is to take the results of a full size test4 ,fig4 #b gives the approximate section through a streamline strut such as used in the interplane bracing of a biplane4 ,the length is 7,l7 and the width is 7d71 the latter being measured at the widest point4 ,the relation of the length to the width is known as the fineness ratio and in interplane struts this may vary from #b4e to #d4e1 that is1 the length of the section ranges from #b4e to #d4e times the width4 ,the ideal streamline form has a ratio of from #e4 to #e4ge4 ,such large ratios are difficult to obtain with economy on practical struts as the small width would result in a weak strut unless the weight were unduly increased4 ,interplane struts reach a maximum fineness ratio at about #c4e to #d4e4 ,fig4 #c shows the result of a small fineness ratio1 the short1 stubby body causing the stream to break away near the front and form a large turbulent region in the rear4 ,an approximate formula showing the relation of fineness ratio and resistance 7curvature equal7 was developed by ,a4 ,e4 ,berriman1 and published in ,flight ,nov4 #ab1 #aiae4 ,let ,d resistance of a flat plate at a given speed1 and ,r resistance of a strut at the same speed and of the same area1 then the relation between the resistance of the flat plate1 and the strut will be expressed by the formula ,r_/,d#d,l_/#cjj;d1 where ,l length of section and d width as in ,fig4 #b4 ,this can be transposed for convenience1 by assuming the drag of a flat plate as ,d #j4jjc;,,av1 where ,a area in square feet1 and ,v velocity in miles per hour4 ,the ratio of the strut resistance to the flat plate resistance1 given by ,berriman's formula1 can now be multiplied by the flat plate resistance1 or strut resistance ,r #j4jjc;,,av ,x #d,l_/#cjj;d4 #j4jab,,lav_/#cjj;d4 ,it should be understood that the area mentioned above is the greatest area presented to the wind in square feet1 and hence is equal to the length of the strut 7not section7 multiplied by the width 7d74 ,illustration3 ,fig4 #c4 ,imperfect ,streamline ,body with a ,considerable ,turbulence ,due to the ,short1 ,stubby ,form4 ,fig4 #d ,shows the ,flow ,about a ,circular ,rod or ,cylinder4 ,assuming the length 7,l7 of the section as #g4e inches1 and the width 7d7 as one inch1 the fineness ratio will be #g4e4 ,using the ,berriman formula in its original form1 the relative resistance of the strut and flat plate of same area will be found as ,r_/,d#d,l_/#cjjj #j4a1 that is1 the resistance of a streamline form strut of above fineness ratio will be about #j4a of a flat plate of the same area4 ,it should be understood that this is only an approximate formula since even struts of the same fineness vary among themselves according to the outline4 ,results published by the ,national ,physical ,laboratory show streamline sections giving #j4jg of the resistance of a flat plate of the same area1 with fineness ratio #f4e4 ,in ,fig4 #d the effects of flow about a circular rod is shown1 a case where the fineness ratio is #a4 ,the stream follows the body through less than one-half of its circumference1 and the turbulent region is very large2 almost as great as with the flat plate4 ,a circular rod is far from being even an approach to a perfect form4 ,in all the cases shown1 ,figs4 #a-b-c-d1 it will be noticed that the air is affected for a considerable distance in front of the plane1 as it rises to pass over the obstruction before it actually reaches it4 ,the front compression may be perceptible for #f diameters of the object4 ,from the examination of several good low-resistance streamline forms it seems that the best results are obtained with the blunt nose forward and the thin end aft4 ,the best position for the point of greatest thickness lies from #j4be to #j4cc per cent of the length from the front end4 ,from the thickest part it tapers out gradually to nothing at the rear end4 ,that portion to the rear of the maximum width is the most important from the standpoint of resistance1 for any irregularity in this region causes the stream to break away into a turbulent space4 ,from experiments it has been found that as much as one-half of the entering nose can be cut away without materially increasing the resistance4 ,the cut-off nose may be left flat1 and still the loss is only in the neighborhood of #e per cent4 99,resistance ,calculations 7,turbulency7994 ,in any plate or body where the resistance is principally due to turbulent action1 as in the flat plate1 sphere1 cone1 etc41 the resistance can be computed from the formula ,r ,,kav1 where ,r is the resistance in pounds and ,k1 ,a1 and ,v are as before4 ,the resistance co-efficient 7,k7 depends upon the shape of the object under standard air conditions1 and differs greatly with flat plates1 cones1 sphere1 etc4 ,the area 7,a7 is the area presented to the wind1 or is the greatest area that faces the wind1 and is taken at right angles to its direction4 ,the following table gives the value of ,k for the more common forms of objects4 ,see ,figs4 #d to #ab1 inclusive3 ,there are almost an infinite number of different forms1 but for the present the above examples will fill our purpose4 ,as an example in showing how greatly the form of an object influences its resistance1 we will work out the resistance of a flat plate and a spherical ended cone1 both having the same presented diameter4 ,the cone is placed so that the spherical end will face the air stream4 ,the area ,a of both objects will be3 #j4ghed #b #b #c4adaf square feet4 ,with an assumed wind velocity of #ajj miles per hour1 the resistance of the circular flat disc will be3 ,r ,,kav#jjjbhb #c4adaf 7#ajjajj7 #hg4if lbs4 ,for the cone1 ,r ,,kav#j4jjjbbb #c4adaf 7#ajj #ajj7 #f4ig lbs4 ,from this calculation it will be seen that it is advisable to surround the object with a spherical cone shaped body rather than to present the flat surface to the wind4 ,in the above table the value of ,k is given for two positions of the spherical based cone1 the first is with the apex toward the wind1 and the second condition gives the value with the base to the wind4 ,with the blunt end forward1 the resistance is about one-half that when the pointed apex enters the air stream4 ,this is due to the taper closing up the stream without causing turbulence4 ,illustration3 ,figs4 #d;a-#e-f-g-h-i-aj-aa-ab4 ,the ,values of the ,resistance ,co-efficient ,k for ,different ,forms and ,positions of ,solid ,objects4 ,arrows ,indicate the ,direction of the ,relative ,wind4 7,eiffel47 ,with the apex forward there is nothing to fill up the vacuous space when the air passes over the large diameter of the base as the curve of the spherical end is too short to accomplish much in this direction4 99,skin ,friction994 ,the air in rubbing over a surface experiences a frictional resistance similar to water4 ,at the present time the accepted experiments are those of ,dr4 ,zahm but these are still in some question as to accuracy4 ,it was found in these experiments that there was practically no difference caused by the material of the surfaces1 as long as they were equally smooth4 ,linen or cotton gave the same results as smooth wood or zinc as long as there was no nap or lint upon the surface4 ,with a fuzzy surface the friction increased rapidly4 ,this is undoubtedly due to a minute turbulence caused by the uneven surface1 and hence the increase was not purely frictional1 but also due to turbulence4 ,in the tests1 the air current was led parallel to the surface in such a way that only the friction could move the surface4 ,the surface was freely suspended1 and as the wind moved it edgewise1 the movement was measured by a sharp pointer4 ,end shields prevented impact of the air on the end of the test piece so that there was no error from this source4 ,the complete formula given by ,dr4 ,zahm is rather complicated for ordinary use1 especially for those not used to mathematical computations4 ,if ,rf resistance due to friction on one side of surface1 ,l length in direction of wind in feet1 b width of surface in feet1 and ,v velocity in feet per second1 then ,rf #j4jjjjjggh,l4,v4b4 ,it will be noted that the resistance increases at a lower rate than the velocity squared1 and at a less rate than the area4 ,that is to say1 that doubling the area will not double the resistance1 but will be less than twice the amount4 ,giving the formula in terms of area and miles per hour units1 we have3 ,rf #j4jjjjafg;,a4,v44 ,where ,a area in square feet and ,v miles per hour4 ,the area is for one side of the surface only4 ,a rough approximation to ,zahm's equation has been proposed by a writer in ,flight1 the intention being to avoid the complicated formula and yet come close enough to the original for practical purposes4 ,the latter formula reads3 ,rf #j4jjjjji,v where ,rf and ,v are as above4 ,up to #dj miles per hour the results are very close to ,zahm's formula1 and are fairly close from #fj to #ij miles per hour4 ,this approximation is only justified when the length in the direction of the wind is nearly equal to the length4 ,if the length is much greater1 there is a serious error introduced4 ,this formula is applied to surfaces parallel to the wind such as the sides of the body1 rudder1 stabilizer1 and elevator surfaces 7when in neutral74 ,a second important feature of the friction formula is that it illustrates the law of similitude or the results of a change in scale and velocity1 hence it outlines what we must expect when we compute a full size aeroplane from the results of a model test4 99,the ,inclined ,plane994 ,when a flat plate is inclined with the wind1 the resistance or drag will be broken up into two components1 one at right angles to the air stream1 and one parallel to it4 ,if the plate is properly inclined1 the right angled component can be utilized in obtaining lift as with an aeroplane wing4 ,this is shown in ,fig4 #ac where ,l is the vertical lift force at right angles to the air stream and ,d is the horizontal drag acting in the direction of the wind4 ,as in the case of the plate placed normal to the wind1 there is pressure at the front of the plate and a partial vacuum behind4 ,the resultant force will be determined by the difference in pressure between the front and the back of the plate4 ,the forces will vary as ,v since the reaction is caused by turbulent flow4 ,both the lift and drag will vary with the angle made with the stream1 and there will be a different value for the co-efficient ,k for each change in the angle4 ,the angle made with the air stream is known as the ,angle of incidence or the ,angle of attack4 ,the change of drag and lift does not vary at a regular rate with the angle4 ,illustration3 ,fig4 #ac4 ,flow ,about1 ,inclined ,plane and ,forces ,produced by ,stream4 ,fig4 #ad4 ,normal ,plane with ,c4,p4 at center of ,plate4 ,fig4 #ae44 ,c4,p4 ,moves ,toward ,entering ,edge ,when ,plate ,is ,inclined to ,wind4 ,a line ,,or is the resultant of the lift and drag forces ,l and ,d1 this resultant being the force necessary to balance the two forces ,l-,d4 ,it is on the point of application ,o that the plate balances1 and this point is sometimes known as the ,center of pressure4 ,the center of pressure is therefore the point at which the resultant intersects the surface of the flat plate4 ,the resultant ,,or is approximately at right angles to the surface at small incident angles1 and the point ,o is nearer the front or leading edge 7,a7 of the plane4 ,the smaller the angle of incidence the nearer will the point ,o approach the leading edge ,a4 ,by drawing ,,ol to scale1 representing the lift1 and ,,od to scale representing the drag1 we can find the resultant ,,or by drawing ,,lr parallel to the drag ,,od and ,,dr parallel to the lift line ,,ol4 ,all lines drawn through the intersection of ,,lr and ,,dr will give the resultant ,,or to scale4 ,all of the lines must be started from the center of pressure at ,o4 ,the least resultant will1 of course1 occur when the plane is parallel to the air stream4 ,the maximum resultant will occur when the angle of incidence is about #dj degrees1 and on a further increase in the angle1 the value of the resultant will gradually decrease4 ,when the plane is parallel with the stream1 the resultant is parallel to the plate1 but rapidly approaches a position at right angles at about an incidence of #f to #aj degrees4 ,beyond #aj degrees incidence the angle of the resultant increases past the normal4 ,the center of pressure 7,o71 or the point where the resultant force intersects the plane1 moves forward as the angle of incidence is decreased from #ij4 ,when at right angles to the air current1 the center of pressure is exactly in the center of the plane as shown by ,fig4 #ad4 ,in this case the drag 7,d7 is the resultant1 and acting in the center1 exactly balances the air forces4 ,in ,fig4 #ae the angle of incidence is reduced1 consequently the center of pressure moves nearer the leading edge 7,a74 ,as the angle continues to decrease1 the ,c4 ,p4 moves still further forward until it lies directly on the front edge when the plate becomes parallel with the air stream4 ,the center of pressure movement is due to the fact that more and more work is done by the front part of the surface as the angle is decreased4 ,consequently the point of support1 or ,c4 ,p41 must move forward to come under the load4 ,it should be understood that the plane will balance about the ,c4 ,p4 if a knife edge bearing were applied as at ,r in ,fig4 #ae4 99,calculation of ,inclined ,planes994 ,we will now consider the inclined plane as a lifting surface for an aeroplane1 and make the elementary calculations for such purpose4 ,the lift will first be calculated for the support of the given load1 at the given velocity1 and then the drag4 ,for several reasons1 that will afterwards be explained1 the flat plate or plane is not used for the main lifting surfaces1 but the experience gained in computing the plate will be of great assistance when we start calculating actual wings4 99,lift and ,drag ,co-efficients994 ,the lift component 7,l7 of the inclined flat plate depends on the velocity1 area1 aspect ratio and angle of incidence4 ,instead of using the co-efficient 7,k7 formerly used for the total drag1 we will use the lift co-efficient ,ky4 ,the formula for lift now becomes3 ,l ,ky,a,v where ,a area in square feet1 and ,v velocity in miles per hour4 ,the lift co-efficient ,ky1 depends upon the angle of incidence4 ,the horizontal drag ,d will be calculated from the drag co-efficient ,kx1 which is used in the same way as the co-efficient ,k in the case of the normal plate4 ,the subscript 7x7 is used to distinguish it from the lift co-efficient4 ,both ,ky and ,kx must be corrected for aspect ratio4 ,the drag can be calculated from the formula3 ,d ,kx,a,v where the letters ,a and ,v are the same as above4 ,for the calculation of the drag1 we will use a new expression--the ,lift-,drag ,ratio--or as more commonly given1 ,l_/,d4 ,this shows the relation between the lift and drag1 so that by knowing the lift and the ratio for any particular case1 we can compute the drag without the necessity of going through the tedious calculation ,d ,kx,a,v4 ,the lift-drag ratio for a flat plate varies with the angle of incidence1 and the aspect ratio1 and hence a separate value must be used for every inclination and change in aspect4 ,to obtain the drag1 divide the lift by the lift-drag ratio4 ,hence if the lift is #abjj pounds1 and the ratio equals #f4jj1 the drag will be3 #abjj_/fbjj pounds1 or in other words1 the lift is #f times the drag force4 ,changing the angle of incidence through angles ranging from #a degree to #g degrees1 the lift-drag ratio of a flat plate will vary from #a4e to #g4e4 ,when the plane is parallel to the wind stream and gives no lift1 the drag is computed from ,zahm's skin friction formula4 ,the following tables give the values of ,ky1 ,kx1 ,l_/,d1 and center of pressure movement for flat plates of various aspect ratios4 ,the center of pressure 7,c4 ,p47 for each angle is given as a decimal fraction of its distance from the leading edge1 in terms of the width or ,chord4 ,illustration3 ,fig4 #af4 ,plan ,view of ,plate with ,long ,edge to ,wind4 ,fig4 #ag4 ,plate with ,narrow ,edge to ,wind1 ,showing ,loss in ,lift4 #ag;a ,shows ,effect of ,raked ,tips4 ,fig4 #af shows the top view or plan of a lifting surface1 with the direction of the wind stream indicated by the arrows w-w-w w4 ,the longer side or span is indicated by ,s1 while the width or chord is ,c4 ,main lifting surfaces1 or wings1 have the long side at right angles to the wind as shown4 ,when in this position1 the surface is said to be in ,pterygoid ,aspect1 and when the narrow edge is presented to the wind1 the wing is in ,apteroid ,aspect4 ,the word ,pterygoid means ,bird like1 and was chosen for the condition in ,fig4 #af1 as this is the method in which a bird's wing meets the air4 ,contrary to the case with true curved aeroplane wings1 flat planes usually give better lift in apteroid than in pterygoid aspect at high angles4 ,the aspect ratio will be the span 7,s7 divided by the chord 7,c71 or ,aspect ratio ,s_/,c4 ,it will be seen from the above that the lift coefficient ,ky increases with the aspect ratio1 and that it generally declines after an angle of #cj degrees4 ,the center of pressure moves steadily back with an increase in angle4 99,example for ,lifts994 ,a certain flat plane has an area of #bjj square feet1 and moves at #ej miles per hour4 ,the angle of incidence is #aj degrees1 and the aspect ratio is #f4 ,find the total lift and the drag in pounds4 ,also the location of the center of pressure in regard to the leading edge1 if the chord is #e4h feet4 99,solution994 ,under the table headed1 ,aspect ,ratio #f we find that ,ky at #aj #j4jjagc1 and that the lift drag ratio is #e4b4 ,the center of pressure is #j4ccc of the chord from the front edge4 ,the total lift then becomes3 ,l ,ky,a,v #j4jjagc x #bjj x 7#ej x #ej7 #hfe pounds4 ,since the lift drag ratio is #e4b1 the drag ,d #hfe_/e4b #aff4c pounds4 ,the center of pressure will be located #e4h x #j4ccc #a4d feet from the leading edge4 ,under the same conditions1 but with an aspect ratio of #c1 the lift will become3 ,l ,ky,a,v #j4jjad x #bjj x7#ej x #ej7 #gjj pounds4 ,in this case the lift drag ratio is #e4a1 so that the drag will be #acg4h pounds4 ,even with the same area1 the aspect ratio makes a difference of #hfe-gjj #afe pounds4 ,if we were compelled to carry the original #hfe pounds with aspect #c wing1 we would also be compelled to increase the area1 angle1 or speed4 ,if the speed were to be kept constant1 we would be limited to a change in area or angle4 ,in the latter case it would be preferable to increase the area1 since a sufficient increase in the angle would greatly increase the drag4 ,it will be noted that the lift-drag ratio decreases rapidly with an increase in the angle4 ,illustration3 ,burgess ,seaplane ,scout4 99,calculation of ,area993 ,let us assume that we are confined to the use of an aspect ratio of #f1 a speed of #ej miles per hour1 weight #bejj pounds1 and wish to obtain the area that will give the most efficient surface 7,least lift-drag ratio47 ,the equation can be now transposed so that the area ,a ,ky,v4 ,on examination of the table it will be seen that the greatest lift-drag ratio is #f4d at #e degrees1 and that the ,ky at this angle is #j4jjajc4 ,substituting these values in the equation for area1 we have ,a ,l_/,ky,v #bejj_/jjjajc x 7#ej x #ej7 #iga square feet4 ,illustration3 ,wind ,tunnel at ,washington ,navy ,yard in ,which the ,air ,circulates ,continuously ,through a ,closed ,circuit ,,chapter ,,iv4 ,,experimental ,,laboratories4 99,test ,methods in ,general994 ,as already explained1 the behavior of a body in an air stream cannot be predicted with any certainty by direct mathematical calculation1 and for this reason1 each and every aerodynamic body must be tested under conditions that are as nearly similar to the actual working conditions as possible4 ,prior to ,professor ,langley's first experiments in #ahhg1 mechanical flight with a heavier than air machine was derided as an impossibility1 even by such scientists as ,navier1 ,von ,helmotz1 ,gay-,lussac1 and others1 who proved by the most intricate calculations that a body larger than a bird could not be supported by its own energy4 ,such calculations were1 of course1 based on a wrong understanding of air flow1 and as no experimental work had been done up to that time1 the flow was assumed according to the individual taste and belief of the demonstrator4 ,the presence of a vacuum on the back of a plate was not understood1 and as this contributes full two-thirds of the lift1 it is an easy matter to see why all of the early predictions fell short of the actual lifting forces4 ,to quote one classic absurdity1 the scientist ,navier proved mathematically that if mechanical flight were possible1 then #ag swallows would be capable of developing one horsepower4 ,in spite of these discouraging computations1 ,langley proceeded with a very carefully conducted series of experiments1 first investigating the laws of surface sustenation on various forms of plates1 and when the data collected was sufficient for his needs1 he started to construct a number of model flyers with various wing arrangements and aerofoil forms4 ,it was ,langley's experiments upon aerofoils that cleared the way for the ,wright ,brothers1 who started a further and more complete investigation in #ahif4 ,experiments were made on the effect of curvature1 aspect ratio and angle of incidence1 and the results obtained in their wind tunnel were afterwards applied to their successful full size machine4 ,during #aija to #aijb the ,wrights investigated the properties of at least #ajj different aerofoil forms4 ,both ,langley's and ,wrights' experiments were with models1 although they were made in a different manner4 ,it was in this way that experimental evidence gained precedence over theory4 ,langley's specimens were mounted at the end of a revolving arm1 so that with the arm revolving1 a relative air stream of known velocity could be had4 ,the aerofoil was mounted in such a way that the lift and drag could be measured4 ,in the early experiments of the ,wrights1 the models were placed in an enclosed channel through which a stream of air was maintained by a fan4 ,the model was attached to a balance system so that the lift and resistance could be measured4 ,this is what is now known as a wind tunnel1 and at present is almost exclusively used in model tests4 ,several investigators immersed their model aerofoils in running water so that the direction of flow could be visibly observed4 ,while this latter method is of great service in determining disturbances1 stream line flow1 and general characteristics1 it is qualitative rather than quantitative1 and cannot be used in obtaining accurate numerical results4 ,a more accurate method of mapping out the direction of flow1 eddies1 etc41 is to introduce smoke into the air stream4 99,full ,size ,experiments994 ,the old rule of the thumb method of building a full size machine without model test data or other experimental evidence to begin with has seen its day4 ,it is not only exceedingly expensive1 but is highly dangerous1 and many a flyer has met his death in the endeavor to work out untried principles on a full size machine4 ,the first cost of the machine1 the continual breakage and operating expense1 to say nothing of the damage suits and loss of time1 make a preliminary full size tryout an absurdity at the present time4 ,again1 the results of full size experiments are not always reliable1 as so much depends upon the pilot and weather conditions4 ,the instruments used on a large machine are far from being as accurate as those used in model tests4 ,these are also likely to be thrown out of adjustment unknowingly by falls or collisions4 ,the great number of variables that enter into such a test make it almost an impossibility to obtain accurate data on the result of minor alterations1 and1 in fact1 it is almost impossible to get the same results twice without further alterations than changing the pilot4 ,full scale tests are necessary after sufficient data has been obtained and applied in a scientific manner to the design of the machine1 but successful performance cannot be expected from a powered machine built by guess work4 ,when performed in connection with a wind tunnel1 or based on dependable data from other sources1 full size wing tests are very instructive and useful if care is taken to have the tests conducted under uniform and known conditions4 ,many full size experiments of this nature have been carried out by ,saint-,cyr ,university in ,france1 and by the ,royal ,aircraft ,factory in ,great ,britain4 ,both of these institutions have a wind tunnel and an almost unlimited fund of performance data1 and last but not least1 have the services of skilled observers4 ,at ,saint-,cyr1 the full size wings1 or the entire machine1 are carried on an electric car or chariot4 ,the speed of the car1 the lift and drag1 can be determined at any moment during the run through suitable recording devices4 ,actual flying tests have also been made1 the measurement of the propeller thrust giving the drag1 while the lift is known as being equal to the weight of the machine4 ,the ,r4,a4,f4 have carried out a very extensive series of flight tests1 the experiments on the old ,b4 ,e4-#b probably being the best known4 ,the greater part of the experiments performed with the car at ,saint-,cyr differed considerably from the results obtained by model tests1 and apparently these differences followed no specific law4 ,according to theory1 and the results obtained by different laboratories1 the performance of a full size wing should be better than with a model1 but the ,saint-,cyr tests showed that such was not always the case4 ,the center of pressure movement differed in almost every case1 and as a direct result1 the pressure distribution of the large wings was materially different than with the model4 ,the lift-drag ratio results varied1 sometimes being better for the model than for the large wing4 ,these differences can probably be explained as being due to variation in air currents1 side winds1 etc4 99,model ,tests994 ,since lift and resistance are due to relative motion between a body and the air stream1 a model can either be towed through the air1 or it can be held stationary while the air is forced past it4 ,there has been some controversy on the relation between the results obtained by the two methods1 but for the present we will accept the common belief that the results obtained by either method are the same4 ,in testing ship models1 they are always towed through the tank1 but in the case of aero-dynamic bodies this is complicated and not desirable4 ,in towing models through the air a very high velocity is needed and this necessitates either a very long track or a short time length for making the observations4 ,again1 it is almost impossible to avoid errors because of vibration1 inequality of movement due to uneven track1 or air eddies caused by differences in temperature and by the movement of the towing device4 ,in fact1 the same difficulties apply to towed model tests as to the full size electric chariot4 ,the whirling arm method of testing as used by ,langley1 ,maxim-,vickers1 and others1 is a form of towed testing1 but is also open to serious objections4 ,unless the arm is very long1 every part of the model surface will not move at the same velocity1 the outer portions moving the faster4 ,as the forces produced by an air stream vary as the square of the velocity1 this may introduce a serious error4 ,the fact that the body passes repeatedly over the same path introduces error1 as the body after the first revolution is always working in disturbed air4 ,the centrifugal force1 and the currents set up by the arm itself all reduce the accuracy of the method4 ,when a model is placed in a uniform current of air in a properly designed channel or tunnel1 the greater part of the errors due to towed tests are eliminated4 ,the measuring instruments can be placed on a firm foundation1 the air stream can be maintained at a nearly uniform speed and with little error due to eddies1 and the test may be continued under uniform conditions for an indefinite period4 ,while there are minor errors due to wall friction and slight variations in the velocity at different points in the cross section of the tunnel1 they are very small when compared to the errors of towing4 ,for this reason the wind tunnel is the accepted means of testing4 99,eiffel's ,wind ,tunnel994 ,the ,eiffel ,laboratory at ,auteuil1 ,france1 is probably one of the best known4 ,the results in ,chapters ,,iii and ,v were obtained in this laboratory and thousands of similar experiments have been carried out at this place4 ,two tunnels1 a large and small1 are placed side by side in the main laboratory room1 the tunnels being supported midway between the floor and ceiling4 ,the air is drawn from this room into an airtight experimental chamber through a bell-mouthed circular opening4 ,a grill or honeycomb baffle is placed in the opening to straighten out the flow1 and from this point the air passes across the chamber and exits through a circular duct to the suction side of a large fan4 ,from the fan the air is discharged into the room4 ,the same air thus circulates through the tunnel continuously4 ,the test chamber is considerably wider than the openings so that the walls do not influence the flow around the model4 ,a cylinder of air passes through the chamber at a remarkably uniform velocity1 and without any appreciable eddies4 ,diameter of the stream approximates #f4f feet in the large tunnel and #c feet in the smaller4 ,in the large tunnel the maximum velocity is #aje feet per second1 and #aca feet per second is attained in the smaller4 ,a #ej-;horsepower electric motor is used with a multiblade fan of the ,sirocco type4 ,the observer and weighing mechanism are supported above the air stream on a sliding floor1 and a standard extends from the model in the wind stream to the balances on the weighing floor4 ,these balances determine the lift and drag of the models1 the center of pressure1 etc4 99,the ,n4 ,p4 ,l4 ,tunnel994 ,the ,national ,physical ,laboratory at ,teddington1 ,england1 has a remarkably complete and accurate aerodynamic equipment4 ,this consists of a large tunnel of #g square feet area1 a small tunnel of #d square feet1 and a whirling table house4 ,the large tunnel is #hj feet in length with an air flow of #fj feet per second1 the air being circulated by a four-bladed propeller driven by an electric motor of #cj horsepower4 ,the velocity is uniform within one-half per cent1 and the most accurate of results have been obtained4 ,the smaller tunnel is about #ef feet long and the wind velocity is about #dj miles per hour maximum4 ,the propeller revolves at #fjj revolutions and is driven by a #aj-;horsepower electric motor4 ,there is no chamber and the models are suspended in the passage half way between the ,diffuser in the entering end1 and the baffles in the exit4 ,the ,massachusetts ,institute of ,technology1 and the ,curtis ,aeroplane ,company both have similar tunnels4 99,united ,states ,navy ,tunnel994 ,in this tunnel the air is confined in a closed circuit1 the return tunnel being much larger than the section in which the tests are performed4 ,the cross-sectional area is #h square feet at the point of test1 and the stream is uniform within #b per cent4 ,the balance and controls are mounted on the roof of the tunnel1 with an arm extending down through the air stream to the model1 as in the ,eiffel tunnel4 ,the balance is similar to ,eiffel's and is sensitive to less than #b_/ajjj pound4 ,a velocity of #ge miles per hour may be attained by the #ejj-;horsepower motor1 but on account of the heating of the air stream through skin friction1 the tests are generally made at #dj miles per hour4 ,models up to #cf-;inch span can be tested1 while the majority of models tested at ,m4 ,i4 ,t4 are about #ah inches4 ,,chapter ,v4 ,,aerodynamics ,,of ,,lifting ,,surfaces 7,,aerofoils74 99,general ,wing ,requirements994 ,the performance of flat plates when used as lifting surfaces is very poor compared with curved sections or wing forms4 ,it will be remembered that the greatest lift-drag ratio for the flat plate was #f4d1 and the best ,ky was #j4jjbid4 ,modern wing sections have a lift-drag ratio of over #bj4j1 and some sections have a lift coefficient of ,ky-#j4jjcfd1 or about #fj per cent higher than the lift obtained with a flat plate4 ,in fact1 this advantage made flight possible4 ,to ,langley1 above all other men1 we owe a debt of gratitude for his investigations into the value of curved wing surfaces4 99,air ,flow ,about an ,aerofoil994 ,to distinguish the curved wing from the flat plane1 we will use the term ,aerofoil4 ,such wings are variously referred to as ,cambered surfaces1 ,arched surfaces1 etc41 but the term ,aerofoil is more applicable to curved sections4 ,the variety of forms and curvatures is almost without limit1 some aerofoils being curved top and bottom1 while others are curved only on the upper surface4 ,the curve on the bottom face may either be concave or convex1 an aerofoil of the latter type being generally known as ,double cambered4 ,the curves may be circular arcs1 as in the ,wright and ,nieuport wings1 or an approximation to a parabolic curve as with many of the modern wings4 ,fig4 #a-;b shows the general trend of flow about an aerofoil at two different angles of incidence1 the flow in the upper view being characteristic for angles up to about #f degrees1 while the lower view represents the flow at angles approximating #af4 ,at greater angles the air stream breaks away entirely from the top surface and produces a turbulence that greatly resembles the disturbance produced by a flat plate4 ,it will be noted in the top figure 7,at small angles7 that the flow is very similar to the flow about a streamline body1 and that the air adheres very closely to the top surface4 ,the flow at small angles is very steady and a minimum of turbulence is produced at the trailing edge4 ,illustration3 ,figs4 #a;a1 #a;b4 ,aerofoil ,types and ,flow at ,different ,angles4 ,when increased beyond #f1 turbulence begins1 as shown in the lower figure1 and a considerable change takes place in the lift-drag ratio4 ,this is known as the ,lower ,critical ,angle4 ,the turbulence1 however1 is confined to the after part of the wing1 and little or no disturbance takes place in the locality of the lower surface4 ,we observe that an increase in angle and lift produces an increased turbulent flow about the upper surface1 and hence the upper surface is largely responsible for the lift4 ,below #aj the trend of the upper portion of the stream is still approximately parallel to the upper surface4 ,illustration3 ,fig4 #b4 ,showing ,how ,lift ,is ,obtained ,when an ,aerofoil ,is ,inclined at a ,negative ,angle1 the ,line of ,flight ,being ,along ,x-,x4 ,from #af to #ah1 the stream suddenly breaks entirely away from the wing surface1 and produces an exceedingly turbulent flow and mass of eddies4 ,the lift falls off suddenly with the start of the discontinuous flow4 ,the angle at which this drop in lift takes place is known variously as the ,second ,critical ,angle1 the ,burble ,point1 or the ,stalling ,angle4 ,any further increase in angle over the stalling angle causes a drop in lift as the discontinuity is increased4 ,with the flat plane1 the burble point occurs in the neighborhood of #cj and movement beyond this angle also decreases the lift4 ,in flight1 the burble point should not be approached1 for a slight increase in the angle when near this point is likely to cause the machine to drop or ,stall4 ,the fact that the maximum lift occurs at the critical angle makes the drop in lift at a slightly greater angle1 doubly dangerous4 ,a peculiar feature of the aerofoil lies in the fact that lift is still obtained with a zero angle of incidence1 and even with a negative angle4 ,with the aerofoil shown in ,fig4 #b there will be a considerable lift when the flat bottom is parallel with the direction of travel1 and some lift will still be obtained with the front edge dipped down 7,negative ,angle74 ,the curved upper surface causes the air stream to rise toward the front edge1 as at ,e1 hence the wing can be dipped down considerably in regard to the line of motion ,x-,x1 without going below the actual air stream4 99,action in ,producing ,lift994 ,at comparatively high angles of incidence1 where there is turbulent flow1 the lift and drag are due principally to the difference in pressure between the upper and lower surfaces as in the case of the flat plate4 ,there is a positive pressure below as in the front of a flat inclined plane1 and a vacuous region above the upper surface4 ,the drag with the plane below the burble point1 and above the ,lower ,critical ,angle1 is due both to skin friction and turbulence--principally to the latter4 ,below the first critical angle 7#f71 the skin friction effect increases1 owing to the closeness with which the air stream hangs to the upper surface4 ,since there is but little turbulence at the small angles below #f1 the theory of the lift at this point is difficult to explain4 ,the best explanation of lift at small angles is given by ,kutta's ,vortex ,hypothesis4 ,this theory is based on the fact that a wing with a practically streamline flow produces a series of whirling vortices 7,whirlpools7 in the wake of the wings1 and that the forward movement of the plane produces the energy that is stored in the vortices4 ,the relation between these vortices is such1 that when their motion is destroyed1 they give up their energy and produce a lifting reaction by their downward momentum4 ,the upward reaction on the wing is thus equal and opposite to the downward momentum of the air vortices4 99,drag ,components994 ,at large angles of incidence where turbulence exists1 the lift and also the drag are nearly proportional to the velocity squared 7,v74 ,where little turbulence exists1 and where the air stream hugs the surface closely1 the drag is due largely to skin friction1 and consequently this part of the drag varies according to ,zahm's law of friction 7,v74 ,for this reason it is difficult to estimate the difference in drag produced by differences in velocity1 since the two drag components vary at different rates1 and there is no fixed proportion between them4 ,since the frictional drag does not increase in proportion to the area1 but as ,a41 difficulty is also experienced in estimating the drag of a full size wing from data furnished by model tests4 99,incidence and ,lift994 ,up to the burble point the lift increases with an increase in the angle2 but not at a uniform rate for any one aerofoil1 nor at the same rate for different aerofoils4 ,the drag also increases with the angle1 but more rapidly than the lift after an incidence of about #d is passed1 hence the lift-drag ratio is less at angles greater than #d4 ,decreasing the angle below #d also decreases the lift-drag1 but not so rapidly as with the larger angles4 ,at the angle of ,no ,lift the drag is principally due to skin friction4 ,fig4 #c shows a typical lift and incidence chart that gives the relation between the angle of incidence and the lift coefficient4 ,this curve varies greatly for different forms of aerofoils both in shape and numerical value1 and it is only given to show the general form of such a graph4 ,the curve lying to the left1 and above the curve for the ,flat plate1 is the curve for the particular aerofoil shown above the chart4 ,the ,lift-,coefficients at the left hand vertical edge correspond to the coefficient ,ky1 although these must be multiplied by a factor to convert them into values of ,ky4 ,as shown1 they are in terms of the ,absolute units used by the ,national ,physical ,laboratory and to convert them into the ,ky unit they must be multiplied by #j4jjea,v where ,v is in miles per hour1 or #j4jjbcfv where v feet per second4 ,the incidence angle is in degrees4 ,illustration3 ,fig4 #c4 ,chart ,showing ,relation ,between ,incidence ,and ,lift4 ,it will be noted that the lift of the aerofoil is greater than that of the plate at every angle as with nearly every practical aerofoil4 ,the aerofoil has a lift coefficient of #j4jjbe at the negative angle of -#c1 while the lift of the flat plate of course becomes zero at #j4 ,as the incidence of the aerofoil increases the lift coefficient also increases1 until it reaches a maximum at the burble point 7,stalling angle7 of about #aa4e4 ,an increase of angle from this point causes the lift coefficient to drop rapidly until it reaches a minimum lift coefficient of #j4df at #ag4 ,the flat plate as shown1 reaches a maximum at the same angle1 but the lift of the plate does not drop off as rapidly4 ,the maximum coefficient of the aerofoil is #j4eh and of the plate #j4da4 ,the rapid drop in pressure1 due to the air stream breaking away at the burble point1 is clearly shown by the sharp peak in the aerofoil curve4 ,the sharpness of the drop varies among different aerofoils1 the peaks in some forms being very flat and uniform for quite a distance in a horizontal direction1 while others are even sharper than that shown4 ,everything else being equal1 an aerofoil with a flat peak is the more desirable as the lift does not drop off so rapidly in cases where the aviator exceeds the critical angle1 and hence the tendency to stall the machine is not as great4 ,this form of chart is probably the simplest form to read4 ,it contains only one quantity1 the lift-coefficient1 and it shows the small variations more clearly than other types of graphs in which the values of ,kx1 lift-drag1 and the resultant force are all given on a single sheet4 99,center of ,pressure ,movement994 ,as in the case of the flat plate the center of pressure on an aerofoil surface varies with the angle of incidence1 but unlike the plate the center of pressure 7,c4 ,p47 moves backward with a decrease in angle4 ,the rapidity of travel depends upon the form of aerofoil1 in some types the movement is very great with a small change in the angle1 while in others the movement is almost negligible through a wide range4 ,in general1 aerofoils are inherently unstable1 since the ,c4 ,p4 moves toward the trailing edge with decreased angles1 and tends to aggravate a deficiency in the angle4 ,if the angle is too small1 the backward movement tends to make it still smaller1 and with an increasing angle the forward movement of the center of pressure tends to make the angle still greater4 ,fig4 #d is a diagram showing the center of pressure movement for a typical aerofoil with the aerofoil at the top of the chart4 ,the left side of the chart represents the leading edge of the aerofoil and the right side is the trailing edge1 while the movement in percentages of the chord length is shown by the figures along the lower line4 ,thus figure 4#c indicates that the center of pressure is located #j4c of the chord from the leading edge4 ,in practice it is usual to measure the distance of the ,c4 ,p4 from the leading edge in this way4 ,illustration3 ,fig4 #d4 ,chart ,giving ,relation ,between ,incidence and ,c4,p4 ,movement4 ,for an example in the use of the chart1 let us find the location of the ,c4 ,p4 at angles of #j1 #c and #g4 ,starting with the column of degrees at the left hand edge of the chart1 find #j1 and follow along the dotted line to the right until the curve is reached4 ,from this point follow down to the lower row of figures4 ,it will be found that at #j the ,c4 ,p4 lies about half way between #j4e and #j4f1 or more exactly at #j4ee of the chord from the leading edge4 ,similarly at #c the ,c4 ,p4 is at #j4cg of the chord1 and at #g is at #j4c of the chord4 ,from #aa to #ai1 the ,c4 ,p4 for this particular aerofoil moves very little1 remaining almost constant at #j4be of the chord4 ,reducing the angle from #c causes the ,c4 ,p4 to retreat very rapidly to the rear1 so that at -#a the ,c4 ,p4 is at #j4h of the chord1 or very near the trailing edge of the wing4 99,other ,forms of ,charts994 ,the arrangement of wing performance charts differs among the various investigators4 ,some charts show the lift1 drag1 lift-drag ratio1 angle of incidence1 center of pressure movement1 and resultant pressure on a single curve4 ,this is very convenient for the experienced engineer1 but is somewhat complicated for the beginner4 ,whatever the form of chart1 there should be an outline drawing of the aerofoil described in the chart4 ,fig4 #e shows a chart of the ,polar variety in which four of the factors are shown by a single curve4 ,this type was originated by ,eiffel and is generally excellent1 except that the changes at small angles are not shown very clearly or sharply4 ,the curve illustrates the properties of the ,kauffman wing1 or better known as the ,eiffel ,no4 #cg4 ,a more complete description of this aerofoil will be found under the chapter ,practical ,wing ,sections4 ,a single curve is marked at different points with the angle of incidence 7#j to #ab74 ,the column at the left gives the lift-coefficient ,ky1 while the row at the bottom of the sheet gives the drag-coefficients ,kx4 ,at the top of the chart are the lift-drag ratios1 each figure being at the end of a diagonal line4 ,in this way the lift1 drag1 liftdrag and angle of incidence are had from a single curve4 ,take the characteristics at an angle of #aj degrees for example4 ,find the angle of #aj on the curve1 and follow horizontally to the left for ,ky4 ,the lift-coefficient will be found to be #j4jjbf in terms of miles per hour and pounds per square foot4 ,following down from #aj1 it will be found that the drag-coefficient ,kx #j4jjjcf4 ,note the diagonal lines1 and that the #aj point lies nearest to the diagonal headed #g at the top of the chart4 7,it is more nearly a lift-drag ratio of #g4cc than #g47 ,in the same way it will be found that an angle of #h degrees lies almost exactly on the lift-drag diagonal marked #i4 ,the best lift-drag is reached at about #b degrees at which point it is shown as #ag4j4 ,the best lift-coefficient ,ky is #j4jjbgf at #ab degrees4 ,illustration3 ,fig4 #e4 ,polar ,type ,chart ,originated ,by ,eiffel4 ,a third class of chart is shown by ,fig4 #f4 ,this single chart shows three of the factors by means of three curves2 one for the lift-coefficient1 one for the drag-coefficient1 and one for the ,c4 ,p4 movement4 ,follow the solid curves only1 for the dotted lines are for comparison with the results obtained by another laboratory in checking the characteristics of the wing4 ,the curves refer to the ,r4,a4,f4-#f section described in the chapter on ,practical ,wing ,sections4 ,the lift-coefficients ,ky will be found at the right of the chart with the drag-coefficients ,kx at the left and in the lower column of figures4 ,the upper column at the left is for the ,c4 ,p4 movement and gives the ,c4 ,p4 location in terms of the chord length4 ,the angles of incidence will be found at the bottom4 ,values are in terms of pounds per square foot1 and miles per hour4 ,illustration3 ,fig4 #f4 ,chart of ,r4,a4,f4-#f ,wing ,section with ,three ,independent ,curves4 ,in using this chart1 start with the angle of incidence at the bottom1 and follow up vertically to the lift or drag curves4 ,if the value of ,ky is desired1 proceed from the required incidence and up to the ,lift curve1 then horizontally to the right4 ,to obtain the drag1 follow up from the angle of incidence to the drift curve1 and then horizontally to the left4 ,for the position of the ,c4 ,p41 trace up from angle until the ,center of ,pressure curve is reached1 and then across horizontally to the left4 ,if the angle of #h degrees is assumed1 the lift-coefficient will be found as ,ky #j4jjbb1 the drag ,kx #j4jjjaf1 and the center of pressure will be located at #j4cb of the chord from the leading edge4 ,this test was made with the air density at #j4jgfjh pounds per cubic foot1 and at a speed of #bi4he miles per hour4 ,the peak at the burble point is fairly flat1 and gives a good range of angle before the lift drops to a serious extent4 ,the aerofoil ,r4,a4,f4-#f is a practical wing form used in many machines1 and this fact should make the chart of special interest4 99,surface ,calculations994 ,the calculation of lift and drag for an aerofoil are the same as those for a flat plate1 that is1 the total lift is expressed by the formula3 ,l ,ky,a,v where ,a is the area in square feet1 and ,v is the velocity in miles per hour4 ,from this primary equation1 the values of the area and velocity may be found by transposition4 ,a ,l_/,ky,v and ,v ,l_/,ky,a4 ,the drag can be found from the old equation1 ,d ,kx,a,v1 or by dividing the lift by the lift-drag ratio as in the case of the flat plate4 99,example993 ,a wing of the ,r4,a4,f4-#f form has an area of #bjj square feet1 and the speed is #fj miles per hour4 ,what is the lift at #f incidence8 99,solution994 ,from ,chart ,no4 #f the lift coefficient ,ky is #jjjahe at #f1 hence the total lift is3 ,l ,ky,a,v #j4jjahe x #bjj x 7#fj x #fj7 #accb pounds4 ,with an angle of #h degrees1 and with the same speed and area1 the lift becomes1 ,l #j4jjbb x #bjj x 7#fj x #fj7 #aehd pounds4 ,the drag coefficient ,kx at an angle of #f is #j4jjjab1 and at #h is #j4jjjaf4 ,the drag at #f becomes ,d ,kx,a,v #j4jjjab x #bjj x 7#fj x #fj7 #hf4d pounds4 ,the lift-drag ratio at this angle is ,l_/,d #accb_/hfd #ae4d4 ,the drag at #h is ,d ,kx,a,v #j4jjjaf x #bjj x 7#fj x #fj7 #aae4b pounds4 ,the lift-drag at #h is ,l_/,d #aehd_/aae4b #ac4h4 99,forces ,acting on ,aerofoil994 ,fig4 #g is a section through an aerofoil of a usual type1 with a concave under-surface ,in an aerofoil of this character all measurements are made from the chordal line ,x-,x which is a straight line drawn across 7and touching7 the entering and trailing edges of the aerofoil4 ,the angle made by ,x-,x with the horizontal is the angle of incidence 7i74 ,the width of the section1 measured from tip to tip of the entering and trailing edges1 is called the ,chord4 ,in this figure the entering edge is at the left4 ,the direction of lift is ,up or as in the case of any aerofoil1 acts away from the convex side4 ,in the position shown1 with horizontal motion toward the left1 the lift force is indicated by ,l1 and the horizontal drag force by ,d1 the direction of their action being indicated by the arrow heads4 ,the force that is the resultant of the lift and drag1 lies between them1 and is shown by ,r4 ,the point at which the line of the resultant force intersects the chordal line ,x-,x is called the ,center of ,pressure 7,c4 ,p47 ,the resultant is not always at right angles to the chordal line as shown1 but may lie to either side of this right angle line according to the angle of incidence 7i74 ,a force equal to and in the same direction as ,r1 will hold the forces ,l and ,d in equilibrium if applied at the center of pressure 7,c4 ,p47 ,owing to the difference in the relative values of ,l and ,d at various angles of incidence1 the angle made by ,r with the chordal line must vary4 ,the lift and drag are always at right angles to one another4 ,the resultant can be found by drawing both the lines ,l and ,d through the ,c4 ,p41 and at right angles to one another1 and then closing up the parallelogram by drawing lines parallel to ,l and ,d from the extreme ends of the latter4 ,the resultant force in direction and extent will be the diagonal ,r drawn across the corners of the parallelogram4 ,illustration3 ,fig4 #g4 ,forces ,acting on an ,aerofoil1 ,lift1 ,drag1 and ,resultant4 ,relative ,wind ,is from ,left to ,right4 ,the forces acting on the upper and lower surfaces are different1 both in direction and magnitude1 owing to the fact that the upper and lower surfaces do not contribute equally to the support of the aerofoil4 ,the upper surface contributes from #fj to #hj per cent of the total lift4 ,a change in the outline of the upper curved surface vitally affects both the lift and lift-drag1 but a change in the lower surface affects the performance to an almost negligible amount4 ,in the case of thin circular arched plates the curvature has a much more pronounced effect4 ,when the curvature of a thin plate is increased1 both the upper and lower surfaces are increased in curvature1 and this undoubtedly is the cause of the great increase in the lift of the sheet metal aerofoils tested by ,eiffel4 ,the drag component of the front upper surface is ,negative1 that is1 acts with the horizontal force instead of against it4 ,the lower surface drag component is of course opposed to the horizontal propelling force by enough to wholly overcome the assisting negative drag force of the front upper surface4 ,the resultants vary from point to point along the section of the aerofoil both in extent and direction4 ,a resultant true for the entering edge would be entirely different at a point near the trailing edge4 99,distribution of ,pressure994 ,to fully understand the relative pressures and forces acting on different parts of the aerofoil we must refer to the experimental results obtained by the ,eiffel and the ,n4 ,p4 ,l4 laboratories4 ,in these tests small holes were drilled over the aerofoil surface at given intervals1 each hole in turn being connected to a manometer or pressure gauge1 and the pressure at that point recorded4 ,while the reading was being taken1 the wind was passed over the surface so that the pressures corresponded to actual working conditions4 ,it was found that the pressure not only varied in moving from the entering to trailing edge1 but that it also varied from the center to the tips in moving along the length of the plane4 ,the rate of variation differed among different aerofoils1 and with the same aerofoil at different angles of incidence4 ,on the upper surface1 the suction or vacuum was generally very high in the immediate vicinity of the entering edge4 ,from this point it decreased until sometimes the pressure was actually reversed near the trailing edge and at the latter point there was actually a downward pressure acting against the lift4 ,the positive pressure on the under surface reached a maximum more nearly at the center1 and in many cases there was a vacuum near the entering edge or at the trailing edge4 ,with nearly all aerofoils1 an increase in the curvature resulted in a decided increase in the vacuum on the upper surface1 particularly with thin aerofoils curved to a circular arc4 ,illustration3 ,fig4 #h4 ,pressure ,distribution for ,thin ,circular ,section4 ,fig4 #i4 ,shows the ,effect of ,increasing the ,camber4 7,eiffel7 ,by taking the sum of the pressures at the various parts of the surface1 it was found that the total corresponded to the lift of the entire aerofoil1 thus proving the correctness of the investigation4 ,the sum of the drag forces measured at the different openings gave a lower total than the total drag measured by the balance1 and this at once suggests that the difference was due to the skin friction effect that of course gave no pressure indication4 ,the truth of this deduction is still further proved by the fact that the drag values were more nearly equal at large angles where the turbulence formed a greater percentage of the total drag4 ,figs4 #h1 #i1 #aj1 #aa1 #ab are pressure distribution curves taken along the section of several aerofoil surfaces4 ,these are due to ,eiffel4 ,in ,fig4 #h is the pressure curve for a thin circular aerofoil section1 the depth of the curve measured from the chordal line being #a_/ac4e of the chord4 ,the vacuum distribution of the upper surface is indicated by the upper dotted curve1 while the pressure on the bottom surface is given by the solid curve under the aerofoil4 ,the pressures are given by the vertical column of figures at the right and are in terms of inches of water1 that is1 the pressure required for the support of a water column of the specified height4 ,figures lying above #j and marked 7-71 refer to a vacuum or negative pressures1 while the figures below zero are positive pressures above the atmospheric4 ,the entering edge is at the right1 and the angle of incidence in all cases is #f4 ,it will be seen that the vacuum jumps up very suddenly to a maximum at the leading edge1 and again drops as suddenly to about one-half the maximum4 ,from this point it again gradually increases near the center1 and then declines toward the trailing edge4 ,it will also be seen that the pressure on the lower surface1 given by the solid curve1 is far less than the pressure due to the upper surface4 ,since the lower pressure curve crosses up1 and over the zero line at a point near the trailing edge1 it is evident that the supper surface near the trailing edge is under a positive pressure1 or a pressure that acts down and against the lift4 ,the pressures in any case are very minute1 the maximum suction being #j4cedf inch of water1 while the maximum pressure on the under surface is only #j4jhe inch4 ,fig4 #i shows the effect of increasing the curvature or camber1 the aerofoil in this case having a depth equal to #a_/g the chord1 or nearly double the camber of the first4 ,the sharp peak at the entering edge of the pressure curve is slightly reduced1 but the remaining suction pressures over the rest of the surface are much increased1 indicating a marked increase in the total pressure4 ,the pressure at the center is now nearly equal to the front peak1 and the pressure is generally more evenly distributed4 ,there is a vacuum over the entire upper surface and a positive pressure over the lower4 ,the general increase in pressure due to the increased camber is the result of the greater downward deviation of the air stream1 and the corresponding greater change in the momentum of the air4 ,the speed at which the tests were made was #aj meters per second1 or #bb4d miles per hour4 ,the curves are only true at the center of the aerofoil length and for an aspect ratio of #f4 ,the average pressure over the entire surface in ,fig4 #h is #a4bjb pounds per square foot1 and that of ,fig4 #i is #a4ddj pounds1 a difference of #j4bch pound per square foot due to the doubling camber 7#af4e per cent74 ,another aerofoil with a camber of only #a_/bg gave an average pressure of #j4hec pound per square foot under the same conditions4 ,a flat plane gave #j4edf4 ,tabulation of these values will show the results more clearly4 ,camber of ,av4 ,pres4 ,per ,inc4 in ,pres4 in ,efficiency ,surface ,sq4 ,ft4 ,lbs4_/,sq4 ,ft4 ,top4 ,bottom4 ,flat ,plane4 #j4edf #j4jjj #j4hi #j4aa #a_/bg #j4hec #j4cjg #j4gb #j4bh #a_/ac4e #a4bjb #j4cdi #j4ga #j4bi #a_/g #a4ddj #j4bch #j4ei #j4da ,in this table1 the ,efficiencies are the relative lift efficiencies of the top and bottom surfaces4 ,for example1 in the case of the #a_/g camber the top surface lifts #ei per cent1 and the bottom #da per cent of the total lift4 ,fig4 #aj is a thin aerofoil of parabolic form1 while ,fig4 #aa is an approximation to the comparatively thick wing of a bird4 ,in both these sections it will be noted that the front peak is not much greater than the secondary peak1 and that the latter is nearer the leading edge than with the circular aerofoils4 ,also that the drop between the peaks is small or entirely lacking4 ,the lower surface of the trailing edge is subjected to a greater down pressure in the case of the thin parabola1 and there is also a considerable down pressure on the upper leading edge4 ,the pressure in ,fig4 #aj is #a4jj pound per square foot1 and that of ,no4 #aa is #a4bje1 while the efficiency of the top surfaces is respectively #gb and #gd per cent4 ,illustration3 ,fig4 #aj4 ,thin ,parabolic ,aerofoil with ,pressure ,distribution4 ,fig4 #aa4 ,pressure ,distribution of ,thick ,bird's ,wing ,type4 7,eiffel7 ,fig4 #ab shows the effect of changing the angle of the bird wing from zero to #h degrees4 ,the lift per square foot in each case is shown at the upper left hand corner of the diagram while the percentages of the upper and lower surface lifts are included above and below the wing4 ,for these curves ,i am indebted to ,e4 ,r4 ,armstrong1 formerly of ,aero and ,hydro4 ,as the angle is increased1 the suction of the upper surface is much increased 7#j4eda to #a4cgj pounds per square foot71 and the pressure at the leading edge increases from depression to a very long thin peak4 ,the maximum under pressure is not much increased by the angle1 but its distribution and average pressure are much altered4 ,at #j and #b the usual pressure is reduced to a vacuum over the front of the section as shown by the lower curve crossing over the upper side of the wing1 and at this point the under surface sucks down and acts against the lift4 ,illustration3 ,fig4 #ab4 ,effect of ,incidence ,changes on the ,pressure ,distribution of a ,thick ,bird's ,wing4 7,after ,eiffel7 99,distribution of ,drag ,forces994 ,the drag as well as the lift changes in both direction and magnitude for different points on the wing4 ,in the front and upper portions the drag is ,negative1 that is1 instead of producing head resistance to motion it really acts with the propelling force4 ,hence on the upper and front portions the lift is obtained with no expenditure of power1 and in fact thrust is given up and added to that of the propeller4 ,the remaining drag elements at the rear1 and on the lower surface1 of course more than overcome this desirable tendency and give a positive drag for the total wing4 ,the distribution is shown by ,fig #ac which gives the lift1 drag and resultant forces at a number of different points on two circular arc aerofoils having cambers of #a_/ac4e and #a_/g respectively4 ,in this figure1 the horizontal drag forces are marked ,d and d1 and the direction of the drag is shown by the arrows4 ,the lift is shown by ,l and the resultant by ,r as in the ,fig4 #g4 ,as shown1 the arrows pointing to the right are the ,negative drag 7d7 forces that assist in moving the plane forward1 while the drag indicated by arrows 7,d7 pointing to the left are the drag forces that oppose or resist the horizontal motion4 ,with the smaller camber 7#a_/ac4e7 the drag forces are very much smaller than those with the heavier camber of #a_/g1 and the negative drifts 7d7 are correspondingly smaller4 ,all of the drag due to the lower surface1 point to the left 7,d71 and hence produce head resistance to flight4 ,the drag to the rear of the center of the upper surface are the same4 ,in front of the upper center we have right hand1 or negative drifts 7d71 that aid the motion4 ,these forward forces obtained by experiment prove the correctness of ,lilienthal's ,forward ,tangential theory advanced many years ago4 ,illustration3 ,fig4 #ac4 ,direction of ,drag ,over ,different ,portions of ,circular ,arc - ,aerofoils4 ,illustration3 ,fig4 #ad;a4 ,distribution for ,wright ,wing4 7b7 ,m4 ,farman ,wing4 7c7 ,breguet ,wing4 7d7 ,bleriot ,wing4 7e7 ,bleriot #aa-;,bis4 ,illustration3 ,fig4 #ae4 ,pressure ,distribution at ,various ,points ,along the ,length of a ,nieuport ,monoplane ,wing4 99,distribution on ,practical ,wings994 ,with the exception of the bird wing1 the distributions have been given for thin plates that are of little value on an aeroplane4 ,they do not permit of strong structural members for carrying the load4 ,the actual wing must have considerable thickness1 as shown by the aerofoils in ,figs4 #a1 #b1 #c1 etc41 and are of approximately stream line form4 ,fig4 #ad shows the distribution for actual aeroplane wings3 7a7 ,wright1 7b7 ,m4 ,farman1 7c7 ,breguet1 7d7 ,bleriot #aa47;d71 7e7 ,bleriot #aa-;bis4 ,the ,wright wing is very blunt and has an exceedingly high lift at the leading edge4 ,the ,m4 ,farman1 which is slightly less blunt1 has a similar but lower front peak4 ,the ,breguet is of a more modern type with the maximum thickness about #be per cent from the leading edge4 ,the latter shows a remarkably even distribution of pressure1 and is therefore a better type as will be seen from the relative lifts of #j4iaf and #j4ihf pounds per square foot4 ,the lift-drag ratio of the ,breguet is also better1 owing to the greater predominance of the negative drag components4 ,decreasing the thickness and the undercamber of ,bleriot #aa1 resulted in an unusual increase of #aj per cent of the under pressure1 and a decrease in the ,suction1 shown by ,bleriot #aa-;bis4 ,the ,bleriot has the sharpest entering edge and the least upper pressure4 ,in the above practical wing sections the aspect ratio is variable1 being the same in the test model as in the full-size machine4 ,the ,bleriot being a monoplane has a lower aspect ratio 7#e71 than the biplanes 7a71 7b7 and 7c74 ,the ,breguet with an aspect of #h has a lift of #j4ihf pounds per square foot as against the #j4gha of the ,bleriot1 and undoubtedly part of this difference is due to the aspect ratio4 ,the pressure falls off around the tips as shown by the successive sections taken through a ,nieuport monoplane wing in ,fig4 #ae4 ,section 7f7 was taken near the body and shows the greater lift4 ,section 7g7 is midway between the tips and body1 and 7h7 and 7i7 are progressively nearer the tips4 ,as we proceed toward the tips from the body the pressure falls off as shown in the sections1 this reducing from #a4jg to #j4ee pounds per square foot4 ,this wing also thins down toward the tips or washes out1 as it is called4 ,illustration3 ,fig4 #af4 ,showing ,pressure ,distribution on the ,plan ,view of a ,typical ,wing1 ,leading ,edge ,along ,a-,a1 ,trailing ,edge ,d-,c4 ,center of ,pressure4 ,marked ,c4,p4 ,the ,proportion ,pressures ,are ,indicated by the ,shading on the ,surface1 the ,pressure ,being ,negative at the ,tips and ,near the ,rear ,edge4 ,,chapter ,,vi4 ,,practical ,,wing ,,sections4 99,development of ,modern ,wings994 ,the first practical results obtained by ,wright ,brothers1 ,montgomery1 ,chanute1 ,henson1 ,curtiss1 ,langley1 and others1 were obtained by the use of cambered wings4 ,the low value of the lift-drag ratio1 due to the flat planes used by the earlier experimenters1 was principally the cause of their failure to fly4 ,the ,wrights chose wings of very heavy camber so that a maximum lift could be obtained with a minimum speed4 ,these early wings had the very fair lift-drag ratio of #ab to #a4 ,modern wing sections have been developed that give a lift-drag ratio of well over #bj to #a1 although this is attended by a considerable loss in the lift4 ,as before explained1 the total lift of a wing surface depends on the form of the wing1 its area1 and the speed upon which it moves in relation to the air4 ,traveling at a low speed requires either a wing with a high lift co-efficient or an increased area4 ,with a constant value for the lift-drag ratio1 an increase in the lift value of the wing section is preferable to an increase in area1 since the larger area necessitates heavier structural members1 more exposed bracing1 and hence1 more head resistance4 ,unfortunately1 it is not always possible to use the sections giving the heaviest lift1 for the reason that such sections usually have a poor lift-drag ratio4 ,in the practical machine1 a compromise must be effected between the drag of the wings and the drag or head resistance of the structural parts so that the combined or total head resistance will be at a minimum4 ,in making such a compromise1 it must be remembered that the head resistance of the structural parts predominates at high speeds1 while the drag of the wings is the most important at low speeds4 ,in the early days of flying1 the fact that an aeroplane left the ground was a sufficient proof of its excellence1 but nowadays the question of efficiency under different conditions of flight 7performance7 is an essential4 ,each new aeroplane is carefully tested for speed1 rate of climb1 and loading4 ,speed range1 or the relation between the lowest and highest possible flight speeds1 is also of increasing importance1 the most careful calculations being made to obtain this desirable quality4 99,performance994 ,to improve the performance of an aeroplane1 the designer must increase the ratio of the horsepower to the weight1 or in other words1 must either use greater horsepower or decrease the weight carried by a given power4 ,this result may be obtained by improvements in the motor1 or by improvements in the machine itself4 ,improvements in the aeroplane may be attained in several ways3 7#a7 by cutting down the structural weight2 7#b7 by increasing the efficiency of the lifting surfaces2 7#c7 by decreasing the head resistance of the body and exposed structural parts1 and 7#d7 by adjustment of the area or camber of the wings so that the angle of incidence can be maintained at the point of greatest plane efficiency4 ,at present we are principally concerned with item 7#b71 although 7#d7 follows as a directly related item4 ,improvement in the wing characteristics is principally a subject for the wind tunnel experimentalist1 since with our present knowledge1 it is impossible to compute the performance of a wing by direct mathematical methods4 ,having obtained the characteristics of a number of wing sections from the aerodynamic laboratory1 the designer is in a position to proceed with the calculation of the areas1 power1 etc4 ,at present this is rather a matter of elimination1 or survival of the fittest1 as each wing is taken separately and computed through a certain range of performance4 99,wing ,loading994 ,the basic unit for wing lift is the load carried per unit of area4 ,in ,english units this is expressed as being the weight in pounds carried by a square foot of the lifting surface4 ,practically1 this value is obtained by dividing the total loaded weight of the machine by the wing area4 ,thus1 if the weight of a machine is #b1ejj pounds 7loaded71 and the area is #ejj square feet1 the unit loading will be3 w #b1ejj_/ejj #e pounds per square foot4 ,in the metric system the unit loading is given in terms of kilogrammes per square meter4 ,conversely1 with the total weight and loading known1 the area can be computed by dividing the weight by the unit loading4 ,the unit loading adopted for a given machine depends upon the type of machine1 its speed1 and the wing section adopted1 this quantity varying from #c4e to #aj pounds per square foot in usual practice4 ,as will be seen1 the loading is higher for small fast machines than for the slower and larger types4 ,a very good series of wings has been developed1 ranging from the low resistance type carrying #e pounds per square foot at #de miles per hour1 to the high lift wing1 which gives a lift of #g4e pounds per square foot at the same speed4 ,the medium lift wing will be assumed to carry #f pounds per square foot at #de miles per hour4 ,the wing carrying #g4e pounds per square foot gives a great saving in area over the low lift type at #e pounds per square foot1 and therefore a great saving in weight4 ,the weight saved is not due to the saving in area alone1 but is also due to the reduction in stress and the corresponding reduction in the size and weight of the structural members4 ,further1 the smaller area requires a smaller tail surface and a shorter body4 ,a rough approximation gives a saving of #a4e pounds per square foot in favor of the #g4e pound wing loading4 ,this materially increases the horsepower weight ratio in favor of the high lift wing1 and with the reduction in area and weight comes an improvement in the vision range of the pilot and an increased ease in handling 7except in dives74 ,the high lift types in a dive have a low limiting speed4 ,as an offset to these advantages1 the drag of the high lift type of wing is so great at small angles that as soon as the weight per horsepower is increased beyond #ah pounds we find that the speed range of the low resistance type increases far beyond that of the high lift wing4 ,according to ,wing ,commander ,seddon1 of the ,english ,navy1 a scout plane of the future equipped with low resistance wings will have a speed range of from #ej to #aej miles per hour4 ,the same machine equipped with high lift wings would have a range of only #ej to #ajj miles per hour4 ,an excess of power is of value with low resistance wings1 but is increasingly wasteful as the lift co-efficient is increased4 ,landing speeds have a great influence on the type of wing and the area1 since the low speeds necessary for the average machines require a high lift wing1 great area1 or both4 ,with the present wing sections1 low flight speeds are obtained with a sacrifice in the high speed values4 ,in the same way1 high speed machines must land at dangerously high speeds4 ,at present1 the best range that we can hope for with fixed areas is about two to one2 that is1 the high speed is not much more than twice the lowest speed4 ,a machine with a low speed of #de miles per hour cannot be depended upon to safely develop a maximum speed of much over #ij miles per hour1 for at higher speeds the angle of incidence will be so diminished as to come dangerously near to the position of no lift4 ,in any case1 the travel of the center of pressure will be so great at extreme wing angles as to cause considerable manipulation of the elevator surface1 resulting in a further increase in the resistance4 99,resistance and ,power994 ,the horizontal drag 7resistance7 of a wing1 determines the power required for its support since this is the force that must be overcome by the thrust of the propeller4 ,the drag is a component of the weight supported and therefore depends upon the loading and upon the efficiency of the wing4 ,the drag of the average modern wing1 structural resistance neglected1 is about #a_/af of the weight supported1 although there are several sections that give a drag as low as #a_/bc of the weight4 ,the denominators of these fractions1 such as #af and #bc1 are the lift-drag ratios of the wing sections4 ,drag in any wing section is a variable quantity1 the drag varying with the angle of incidence4 ,in general1 the drag is at a minimum at an angle of about #d degrees1 the value increasing rapidly on a further increase or decrease in the angle4 ,usually a high lift section has a greater drag than the low lift type at small angles1 and a smaller drag at large angles1 although this latter is not invariably the case4 99,power ,requirements994 ,power is the rate of doing work1 or the rate at which resistance is overcome4 ,with a constant resistance the power will be increased by an increase in the speed4 ,with a constant speed1 the power will be increased by an increase in the resistance4 ,numerically1 the power is the product of the force and the velocity in feet per second1 feet per minute1 miles per hour1 or meters per second4 ,the most common ,english power unit is the horsepower1 which is obtained by multiplying the resisting force in pounds by the velocity in feet per minute1 this product being divided by #cc1jjj4 ,if ,d is the horizontal drag in pounds1 and v velocity of the wing in feet per minute1 the horsepower ,h will be expressed by3 ,h ,dv _/ #cc1jjj ,since the speed of an aeroplane is seldom given in feet per minute1 the formula for horsepower can be given in terms of miles per hour by3 ,h ,,dv _/ #cge ,where ,v velocity in miles per hour1 ,d and ,h remaining as before4 ,the total power for the entire machine would involve the sum of the wing and structural drags1 with ,d equal to the total resistance of the machine4 99,example994 ,the total weight of an aeroplane is found to be #c1jjj pounds4 ,the lift-drag ratio of the wings is #ae4jj1 and the speed is #ij miles per hour4 ,find the power required for the wings alone4 99,solution994 ,the total drag of the wings will be3 ,d #c1jjj_/ae #bjj pounds4 ,the horsepower required3 ,h ,,dv_/#cge #bjj #ij_/cgedh horsepower4 ,it should be remembered that this is the power absorbed by the wings1 the actual motor power being considerably greater owing to losses in the propeller4 ,with a propeller efficiency of #gj per cent1 the actual motor power will become3 ,hm #dh_/j4gjfh4eg for the wings alone4 ,to include the efficiency into our formula1 we have3 ,h ,,dv_/#cge;,e where ,e propeller efficiency expressed as a decimal4 ,the greater the propeller efficiency1 the less will be the actual motor power1 hence the great necessity for an efficient propeller1 especially in the case of pusher type aeroplanes where the wings do not gain by the increased slip stream4 ,the propeller thrust must be equal and opposite to the drag at the various speeds1 and hence the thrust varies with the plane loading1 wing section1 and angle of incidence4 ,portions of the wing surfaces that lie in the propeller slip stream have a greater lift than those lying outside of this zone because of the greater velocity of the slip stream4 ,for accurate results1 the area in the slip stream should be determined and calculated for the increased velocity4 ,oftentimes it is desirable to obtain the ,unit drag2 that is1 the drag per square foot of lifting surface4 ,this can be obtained by dividing the lift per square foot by the lift-drag ratio1 care being taken to note the angle at which the unit drag is required4 99,advantages of ,cambered ,sections ,summarized994 ,modern wing sections are always of the cambered1 double-surface type for the following reasons3 #a4 ,they give a better lift-drag ratio than the flat surface1 and therefore are more economical in the use of power4 #b4 ,in the majority of cases they give a better lift per square foot of surface than the flat plate and require less area4 #c4 ,the cambered wings can be made thicker and will accommodate heavier spars and structural members without excessive head resistance4 99,properties of ,modern ,wings994 ,the curvature of a wing surface can best be seen by cutting out a section along a line perpendicular to the length of the wing1 and then viewing the cut portion from the end4 ,it is from this method of illustration that the different wing curves1 or types of wings1 are known as wing sections4 ,in all modern wings the top surface is well curved1 and in the majority of cases the bottom surface is also given a curvature1 although this is very small in many instances4 ,fig4 #a4 shows a typical wing section with the names of the different parts and the methods of dimensioning the curves4 ,all measurements to the top and bottom surfaces are taken from the straight chordal line or datum line marked ,x-,x4 ,this line is drawn across the concave undersurface in such a way as to touch the surface only at two points1 one at the front and one at the rear of the wing section4 ,the inclination of the wing with the direction of flight is always given as the angle made by the line ,x-,x with the wind4 ,thus1 if a certain wing is said to have an angle of incidence equal to #d degrees1 we know that the chordal line ,x-,x makes an angle of #d degrees with the direction of travel4 ,this angle is generally designated by the letter 7i71 and is also known as the angle of attack4 ,the distance from the extreme front to the extreme rear edge 7width of wing7 is called the chord width or more commonly the chord4 ,in measuring the curve1 the datum line ,x-,x is divided into a number of equal parts1 usually #aj1 and the lines #a-b-c-d-e-f-g-h-i-aj-aa are drawn perpendicular to ,x-,x4 ,each of the vertical numbered lines is called a station1 the line ,no4 #c being called ,station #c1 and so on4 ,the vertical distance measured from ,x-,x to either of the curves along one of the station lines is known as the ordinate of the curve at that point4 ,thus1 if we know the ordinates at each station1 it is a simple matter to draw the straight line ,x-,x1 divide it into #aj parts1 and then lay off the heights of the ordinates at the various stations4 ,the distances from datum to the upper curve are known as the ,upper ordinates1 while the same measurements to the under surface are known as the ,lower ordinates4 ,this method allows us to quickly draw any wing section from a table that gives the upper and lower ordinates at the different stations4 ,a common method of expressing the value of the depth of a wing section in terms of the chord width is to give the ,camber1 which is numerically the result obtained by dividing the depth of the wing curve at any point by the width of the chord4 ,usually the camber given for a wing is taken to be the maximum camber2 that is1 the camber taken at the point of greatest depth4 ,thus1 if we hear that a certain wing has a camber of #j4jhi1 we take it for granted that this is the camber at the deepest portion of the wing4 ,the correct method would be to give #j4jhi as the maximum camber in order to avoid confusion4 ,to obtain the maximum camber1 divide the maximum ordinate by the chord4 ,illustration3 ,fig4 #a4 ,section ,through a ,typical ,aerofoil or ,wing1 the ,parts and ,measurements ,being ,marked on the ,section4 ,the ,horizontal ,width or ,chord ,is ,divided ,into #aj ,equal ,parts or ,stations1 and the ,height of the ,top and ,bottom ,curves ,are ,measured from the ,chordal ,line ,x-,x at ,each ,station4 ,the ,vertical ,distance from the ,chordal ,line ,is the ,ordinate at the ,point of ,measurement4 99,example994 ,the maximum ordinate of a certain wing is #e inches1 and the chord is #dj inches4 ,what is the maximum camber8 ,the maximum camber is #e_/dj #j4abe4 ,in other words1 the maximum depth of this wing is #ab4e per cent of the chord1 and unless otherwise specified1 is taken as being the camber of the top surface4 ,the maximum camber of a modern wing is generally in the neighborhood of #j4jh1 although there are several ,successful sections that are well below this figure4 ,unfortunately1 the camber is not a direct index to the value of a wing1 either in regard to lifting ability or efficiency4 ,by knowing the camber of a wing we cannot directly calculate the lift or drag1 for there are several examples of wings having widely different cambers that give practically the same lift and drift4 ,at the present time1 we can only determine the characteristics of a wing by experiment1 either on a full size wing or on a scale model4 ,in the best wing sections1 the greatest thickness and camber occurs at a point about #j4c of the chord from the front edge1 this edge being much more blunt and abrupt than the portions near the trailing edge4 ,an efficient wing tapers very gradually from the point of maximum camber towards the rear4 ,this is usually a source of difficulty from a structural standpoint since it is difficult to get an efficient depth of wing beam at a point near the trailing edge4 ,a number of experiments performed by the ,national ,physical ,laboratory show that the position of maximum ordinate or camber should be located at #cc4b per cent from the leading edge4 ,this location gives the greatest lift per square foot1 and also the least resistance for the weight lifted4 ,placing the maximum ordinate further forward is worse than placing it to the rear4 ,thickening the entering edge causes a proportionate loss in efficiency4 ,thickening the rear edge also decreases the efficiency but does not affect the weight lifting value to any great extent4 ,the camber of the under surface seems to have but little effect on the efficiency1 but the lift increases slightly with an increase in the camber of the lower surface4 ,increasing the camber of the lower surface decreases the thickness of the wing and hence decreases the strength of the supporting members1 particularly at points near the trailing edge4 ,the increase of lift due to increasing the under camber is so slight as to be hardly worth the sacrifice in strength4 ,variations in the camber of the upper surface are of much greater importance4 ,it is on this surface that the greater part of the lift takes places1 hence a change in the depth of this curve1 or in its outline1 will cause wider variations in the characteristics of the wing than would be the case with the under surface4 ,increasing the upper camber by about #fj per cent may double the lift of the upper surface1 but the relation of the lift to the drag is increased4 ,from this1 it will be seen that direct calculations from the outline would be most difficult1 and in fact a practical impossibility at the present time4 ,illustration3 ,fig4 #b4 7,upper74 ,shows a ,slight ,reflex or ,upward ,turn of the ,trailing ,edge4 ,fig4 #c4 7,lower7 ,shows an ,excessive ,reflex ,which ,greatly ,reduces the ,c4,p4 ,movement4 ,by putting a reverse curve in the trailing edge of a wing1 as shown by ,fig4 #b1 the stability of the wing may be increased to a surprising degree1 but the lift and efficiency are correspondingly reduced with each increase in the amount of reverse curvature4 ,in this way1 stability is attained at the expense of efficiency and lifting power4 ,with the rear edge raised about #j4jcg of the chord1 the ,n4 ,p4 ,l4 found that the center of pressure could be held stationary1 but the loss of lift was about #be per cent and the loss of efficiency amounted practically #ab per cent4 ,with very slight reverse curvatures it has been possible to maintain the lift and efficiency1 and at the same time to keep the center of pressure movement down to a reasonable extent4 ,the ,new ,u4,s4,a4 sections and the ,eiffel ,no4 #cb section are examples of excellent sections in which a slight reverse or reflex curvature is used4 ,the ,eiffel #cb wing is efficient1 and at the same the center of pressure movement between incident angles of #j and #aj is practically negligible4 ,this wing is thin in the neighborhood of the trailing edge1 and it is very difficult to obtain a strong rear spar4 99,wing ,selection994 ,no single wing section is adapted to all purposes4 ,some wings give a great lift but are inefficient at small angles and with light loading4 ,there are others that give a low lift but are very efficient at the small angles used on high speed machines4 ,as before explained1 there are very stable sections that give but poor results when considered from the standpoint of lift and efficiency4 ,the selection of any one wing section depends upon the type of machine upon which it is to be used1 whether it is to be a small speed machine or a heavy flying boat or bombing plane4 ,there are a multitude of wing sections1 each possessing certain admirable features and also certain faults4 ,to list all of the wings that have been tried or proposed would require a book many times the size of this1 and for this reason ,i have kept the list of wings confined to those that have been most commonly employed on prominent machines1 or that have shown evidence of highly desirable and special qualities4 ,this selection has been made with a view of including wings of widely varying characteristics so that the data can be applied to a wide range of aeroplane types4 ,wings suitable for both speed and weight carrying machines have been included4 ,the wings described are the ,u4,s4,a4 ,sections ,no4 #a1 #b1 #c1 #d1 #e and #f2 the ,r4,a4,f4 ,sections ,nos4 #c and #f1 and the well known ,eiffel ,wings ,no4 #cb1 #cf and #cg4 ,the data given for these wings is obtained from wind tunnel tests made at the ,massachusetts ,institute of ,technology1 the ,national ,physical ,laboratory 7,england71 and the ,eiffel ,laboratory in ,paris4 ,for each of these sections the lift co-efficient 7,ky71 the lift-drift ratio 7,l_/,d71 and the drag co-efficient 7,kx7 are given in terms of miles per hour and pounds per square foot4 ,since these are the results for model wings1 there are certain corrections to be made when the full size wing is considered1 these corrections being made necessary by the fact that the drag does not vary at the same rate as the lift4 ,this ,size or ,scale correction is a function of the product of the wing span in feet by the velocity of the wind in feet per second4 ,a large value of the product results in a better wing performance1 or in other words1 the large wing will always give better lift-drag ratios than would be indicated by the model tests4 ,the lift co-efficient ,ky is practically unaffected by variations in the product4 ,if the model tests are taken without correction1 the designer will always be on the safe side in calculating the power4 ,the method of making the scale corrections will be taken up later4 ,of all the sections described1 the ,r4,a4,f4-#f is probably the best known4 ,the data on this wing is most complete1 and in reality it is a sort of standard by which the performance of other wings is compared4 ,data has been published which describes the performance of the ,r4,a4,f4-#f used in monoplane1 biplane and triplane form2 and with almost every conceivable degree of stagger1 sweep back1 and decalage4 ,in addition to the laboratory data1 the wing has also been used with great success on full size machines1 principally of the ,primary trainer class where an ,all around class of wing is particularly desirable4 ,it is excellent from a structural standpoint since the section is comparatively deep in the vicinity of the trailing edge4 ,the ,u4,s4,a4 sections are of comparatively recent development and are decided improvements on the ,r4,a4,f4 and ,eiffel sections4 ,the only objection is the limited amount of data that is available on these wings--limited at least when the ,r4,a4,f4 data is considered--as we have only the figures for the monoplane arrangement4 99,,wing ,,selection499 997#a7 ,lift-,drag ,ratio994 ,the lift-drag ratio 7,l_/,d7 of a wing is the measure of wing efficiency4 ,numerically1 this is equal to the lift divided by the horizontal drag1 both quantities being expressed in pounds4 ,the greater the weight supported by a given horizontal drag1 the less will be the power required for the propulsion of the aeroplane1 hence a high value of ,l_/,d indicates a desirable wing section--at least from a power standpoint4 ,in the expression ,l_/,d1 ,l lift in pounds1 and ,d horizontal drag in pounds4 ,unfortunately1 this is not the only important factor1 since a wing having a great lift-drag is usually deficient in lift or is sometimes structurally weak4 ,the lift-drag ratio varies with the angle of incidence 7i71 reaching a maximum at an angle of about #d in the majority of wings4 ,the angle of incidence at which the lift-drag is a maximum is generally taken as the angle of incidence for normal horizontal flight4 ,at angles either greater or less1 the ,l_/,d falls off1 generally at a very rapid rate1 and the power increases correspondingly4 ,very efficient wings may have a ratio higher than ,l_/,d#bj at an angle of about #d1 while at #af incidence the value may be reduced to ,l_/,d #d1 or even less4 ,the lift is generally greatest at about #af4 ,the amount of variation in the lift1 and lift-drag1 corresponding to changes in the incidence differs among the different types of wings and must be determined by actual test4 ,after finding a wing with a good value of ,l_/,d1 the value of the lift co-efficient ,ky should be determined at the angle of the maximum ,l_/,d4 ,with two wings having the same lift-drag ratio1 the wing having the greatest lift 7,ky7 at this point is the most desirable wing as the greater lift will require less area and will therefore result in less head resistance and less weight4 ,any increase in the area not only increases the weight of the wing surface proper1 but also increases the wiring and weights of the structural members4 ,with heavy machines1 such as seaplanes or bomb droppers1 a high value of ,ky is necessary if the area is to be kept within practical limits4 ,a small fast scouting plane requires the best possible lift-drag ratio at small angles1 but requires only a small lift co-efficient4 ,at speeds of over #ajj miles per hour a small increase in the resistance will cause a great increase in the power4 997#b7 ,maximum ,lift 7,ky7994 ,with a given wing area and weight1 the maximum value of the lift co-efficient 7,ky7 determines the slow speed1 or landing speed1 of the aeroplane4 ,the greater the value of ,ky1 the slower can be the landing speed4 ,for safety1 the landing speed should be as low as possible4 ,in the majority of wings1 the maximum lift occurs at about #af of incidence1 and in several sections this maximum is fairly well sustained over a considerable range of angle4 ,the angle of maximum lift is variously known as the ,stalling angle or the ,burble point1 since a change of angle in either direction reduces the lift and tends to stall the aeroplane4 ,for safety1 the angle range for maximum lift should be as great as possible1 for if the lift falls off very rapidly with an increase in the angle of incidence1 the pilot may easily increase the angle too far and drop the machine4 ,in the ,r4,a4,f4-#c wing1 the lift is little altered through an angle range of from #ad to #af4e1 the maximum occurring at #ae4g1 while with the ,r4,a4,f4-#d1 the lift drops very suddenly on increasing the angle above #ae4 ,the range of the stalling angle in any of the wings can be increased by suitable biplane or triplane arrangements4 ,if large values of lift are accompanied by a fairly good ,l_/,d value at large angles1 the wing section will be suitable for heavy machines4 997#c7 ,center of ,pressure ,movement994 ,the center of pressure movement with varying angles of incidence is of the greatest importance1 since it not only determines the longitudinal stability but also has an important effect upon the loading of the wing spars and ribs4 ,with the majority of wings a decrease in the angle of incidence causes the center of pressure to move back toward the trailing edge and hence tends to cause nose diving4 ,when decreased beyond #j the movement is very sharp and quick1 the ,c4 ,p4 moving nearly half the chord width in the change from #j to -#a4e4 ,the smaller the angle1 the more rapid will be the movement4 ,between #f and #af1 the center of pressure lies near a point #j4c of the chord from the entering edge in the majority of wing sections4 ,reducing the angle from #f to #b moves the ,c4 ,p4 back to approximately #j4d of the chord from the entering edge4 ,there are wing sections1 however1 in which the ,c4 ,p4 movement is exceedingly small1 the ,eiffel #cb being a notable example of this type4 ,this wing is exceedingly stable1 as the ,c4 ,p4 remains at a trifle more than #j4cj of the chord through nearly the total range of flight angles4 ,an aeroplane equipped with the ,eiffel #cb wing could be provided with exceedingly small tail surfaces without a tendency to dive4 ,should the elevator become inoperative through accident1 the machine could probably be landed without danger4 ,this wing has certain objectionable features1 however1 that offset the advantages4 ,it will be noted that with the unstable wings the center of pressure movement always tends to aggravate the wing attitude4 ,if the machine is diving1 the decrease in angle causes the ,c4 ,p4 to move back and still further increase the diving tendency4 ,if the angle is suddenly increased1 the ,c4 ,p4 moves forward and increases the tendency toward stalling4 ,if the center of pressure could be held stationary at one point1 the wing spars could be arranged so that each spar would take its proper proportion of the load4 ,as it is1 either spar may be called upon to carry anywhere from three-fourths of the load to entire load1 since at extreme angles the ,c4 ,p4 is likely to lie directly on either of the spars4 ,since the rear spar is always shallow and inefficient1 this is most undesirable4 ,this condition alone to a certain extent counterbalances the structural disadvantage of the thin ,eiffel #cb section4 ,although the spars in this wing must of necessity be shallow1 they can be arranged so that each spar will take its proper share of the load and with the assurance that the loading will remain constant throughout the range of flight angles4 ,the comparatively deep front spar could be moved back until it carried the greater part of the load1 thus relieving the rear spar4 ,with a good lift-drag ratio1 and a comparatively high value of ,ky1 the center of pressure movement should be an important consideration in the selection of a wing4 ,it should be remembered in this regard that the stability effects of the ,c4 ,p4 movement can be offset to a considerable extent by suitable biplane arrangements4 997#d7 ,structural ,considerations994 ,for large1 heavy machines1 the structural factor often ranks in importance with the lift-drag ratio and the lift co-efficient4 ,it is also of extreme importance in speed scouts where the number of interplane struts are to be at a minimum and where the bending moment on the wing spars is likely to be great in consequence4 ,a deep1 thick wing section permits of deep strong wing spars4 ,the strength of a spar increases with the square of its depth1 but only in direct proportion to its width4 ,thus1 doubling the depth of the spar increases the strength four times1 while doubling the width only doubles the strength4 ,the increase in weight would be the same in both cases4 ,while very deep wings are not usually efficient1 when considered from the wing section tests alone1 the total efficiency of the wing construction when mounted on the machine is greater than would be supposed4 ,this is due to the lightness of the spars and to the reduction in head resistance made possible by a greater spacing of the interplane struts4 ,thus1 the deep wing alone may have a low ,l_/,d in a model test1 but its structural advantages give a high total efficiency for the machine assembled4 99,summary994 ,it will be seen from the foregoing matter that the selection of a wing consists in making a series of compromises and that no single wing section can be expected to fulfill all conditions4 ,with the purpose of the proposed aeroplane thoroughly in mind1 the various sections are taken up one by one1 until a wing is found that most usefully compromises with all of the conditions4 ,reducing this investigation to its simplest elements we must follow the routine as described above3 7#a7 ,lift-drift ratio and value of ,ky at this ratio4 7#b7 ,maximum value of ,ky and ,l_/,d at this lift4 7#c7 ,center of pressure movement4 7#d7 ,depth of wing and structural characteristics4 99,calculations for ,lift and ,area994 ,although the principles of surface calculations were described in the chapter on elementary aerodynamics1 it will probably simplify matters to review these calculations at this point4 ,the lift of a wing varies with the product of the area1 and the velocity squared1 this result being multiplied by the co-efficient of lift 7,ky74 ,the co-efficient varies with the wing section1 and with the angle of incidence4 ,stated as a formula3 ,l ,ky,a,v where ,a area in square feet1 and ,v velocity of the wing in miles per hour4 ,assuming an area of #bjj square feet1 a velocity of #hj miles per hour1 and with ,k #j4jjbe1 the total life 7,l7 becomes3 ,l ,ky,a,v #j4jjbe x #bjj x 7#hj #hj7 #c1bjj pounds4 ,assuming a lift-drag ratio of #af1 the drag of the wing1 or its resistance to horizontal motion1 will be expressed by ,d ,l_/r#c1bjj_/afbjj pounds1 where r lift-drag ratio4 ,it is this resistance of #bjj pounds that the motor must overcome in driving the wings through the air4 ,the total resistance offered by the aeroplane will be equal to the sum of the wing resistance and the head resistance of the body1 struts1 wiring and other structural parts4 ,in the present instance we will consider only the resistance of the wings4 ,when the lift co-efficient1 speed1 and total lift are known1 the area can be found from ,a ,l_/,ky,v1 the lift1 of course1 being taken as the total weight of the machine4 ,the area of the supporting surface for a speed of #fj miles per hour1 total weight of #b1djj pounds1 and a lift co-efficient of #j4jjb is calculated as follows3 ,a ,l_/,ky,v #b1djj_/j4jjb 7#fj #fj7 #ccc sq4 ft4 ,a third variation in the formula is that used in finding the value of the lift co-efficient for a particular wing loading4 ,from the weight1 speed and area1 we can find the co-efficient ,ky1 and with this value we can find a wing that will correspond to the required co-efficient4 ,this method is particularly convenient when searching for the section with the greatest lift-drag ratio4 ,ky ,l_/,,av1 or when the loading per square foot is known1 the co-efficient becomes ,ky ,l'_/,v4 ,for example1 let us find the co-efficient for a wing loading of #e pounds per square foot at a velocity of #hj miles per hour4 ,inserting the numerical values into the equation we have1 ,ky ,l'_/,v #e_/7hj #hj7 #j4jjjgh4 ,any wing1 at any angle that has a lift co-efficient equal to #j4jjjgh will support the load at the given speed1 although many of the wings would not give a satisfactory lift-drag ratio with this co-efficient4 ,it should be noted in the above calculations that no correction has been made for ,scale1 aspect ratio or biplane interference4 ,in other words1 we have assumed the figures as applying to model monoplanes4 ,in the following tables the lift1 lift-drag and drag must be corrected1 since this data was obtained from model tests on monoplane sections4 ,the effects of biplane interference will be described in the chapter on ,biplane and ,triplane ,arrangement1 but it may be stated that superposing the planes reduces both the lift co-efficient and the liftdrag ratio1 the amount of reduction depending upon the relative gap between the surfaces4 ,thus with a gap equal to the chord1 the lift of the biplane surface will only be about #hj per cent of the lift of a monoplane surface of the same area and section4 99,wing ,test ,data994 ,the data given in this chapter is the result of wind tunnel tests made under standard conditions1 the greater part of the results being published by the ,massachusetts ,institute of ,technology4 ,the tests were all made on the same size of model and at the same wind speed so that an accurate comparison can be made between the different sections4 ,all values are for monoplane wings with an aspect ratio of #f1 the laboratory models being #ahx#c inches4 ,the exception to the above test conditions will be found in the tables of the ,eiffel #cg and #cf sections1 these figures being taken from the results of ,eiffel's laboratory4 ,the ,eiffel models were #ce4dx#e4i inches and were tested at wind velocities of #bb4d1 #dd4h1 and #fg4b miles per hour4 ,the tests made at ,m4 ,i4 ,t4 were all made at a wind speed of #cj miles per hour4 ,the lift co-efficient ,ky is practically independent of the wing size and wind velocity1 but the drag co-efficient ,kx varies with both the size and wind velocity1 and the variation is not the same for the different wings4 ,the results of the ,m4 ,i4 ,t4 tests were published in ,aviation and ,aeronautical ,engineering by ,alexander ,klemin and ,g4 ,m4 ,denkinger4 99,the ,r4,a4,f4 ,wing ,sections994 ,these wings are probably the best known of all wings1 although they are inferior to the new ,u4,s4,a4 sections4 ,they are of ,english origin1 being developed by the ,royal ,aircraft ,factory 7,r4,a4,f471 with the tests performed by the ,national ,physical ,laboratory at ,teddington1 ,england4 ,the ,r4,a4,f4-#f is the nearest approach to the all around wing1 this section having a fairly high ,l_/,d ratio and a good value of ,ky for nearly all angles4 ,it is by no means a speed wing nor is it suitable for heavy machines1 but it comprises well between these limits and has been extensively used on medium size machines1 such as the ,curtiss ,,jn#d-;,b1 the ,london and ,provincial1 and others4 ,the ,r4,a4,f-#c has a very high value for ,ky1 and a very good lift-drag ratio for the high-lift values4 ,it is suitable for seaplanes1 bomb droppers and other heavy machines of a like nature that fly at low or moderate speeds4 ,the outlines of these wings are shown by ,figs4 #g and #h1 and the camber ordinates are marked as percentages of the chord4 ,in laying out a wing rib from these diagrams1 the ordinate at any point is obtained by multiplying the chord length in inches by the ordinate factor at that point4 ,referring to the ,r4,a4,f4-#c diagram1 ,fig4 #h1 it will be seen that the ordinate for the upper surface at the third station from the entering edge is #j4jfd4 ,if the chord of the wing is #fj inches1 the height of the upper curve measured above the datum line ,x-,x at the third station will be1 #j4jfd #fj #c4hd inches4 ,at the same station1 the height of the lower curve will be1 #j4jaf #fj #j4if inch4 ,the chord is divided into #aj equal parts1 and at the entering edge one of the ten parts is subdivided so as to obtain a more accurate curve at this point4 ,in some wing sections it is absolutely necessary to subdivide the first chord division as the curve changes very rapidly in a short distance4 ,the upper curve1 especially at the entering edge1 is by far the most active part of the section and for this reason particular care should be exercised in getting the correct outline at this point4 ,illustration3 ,figs4 #g-h4 ,r4,a4,f4 ,wing ,sections4 ,ordinates as ,decimals of the ,chord4 99,aerodynamic ,properties of the ,r4,a4,f4 ,sections994 ,table #a gives the values of ,ky1 ,kx1 ,l_/,d1 and the center of pressure movement 7,c4 ,p47 for the ,r4,a4,f4-#c section through a range of angles varying from -#b to #bj4 ,the first column at the left gives the angles of incidence 7i71 the corresponding values for the lift 7,ky7 and the drag 7,kx7 being given in the second and third columns1 respectively4 ,the fourth column gives the lift-drag ratio 7,l_/,d74 ,the fifth and last column gives the location of the center of pressure for each different angle of incidence1 the figure indicating the distance of the ,c4 ,p4 from the entering edge expressed as a decimal part of the chord4 ,as an example in the use of the table1 let it be required to find the lift and drag of the ,r4,a4,f4-#c section when inclined at an angle of #f and propelled at a speed of #ij miles per hour4 ,the assumed area will be #cjj square feet4 ,at #f it will be found that the lift co-efficient ,ky is #j4jjbcfi4 ,from our formulae1 the lift will be3 ,l ,ky,a,v or numerically1 ,l#j4jjbcfi #cjj 7#ij #ij7 #e1gefg lbs4 ,at the same speed1 but with the angle of incidence reduced to #b1 the lift will be reduced to ,l #j4jjaeed #cjj x 7#ij #ij7 #c1ggf4b pounds1 where #j4jjaeed is the lift co-efficient at #b4 ,it will be noted that the maximum lift co-efficient occurs at #ad and continues at this value to a little past #ae4 ,the lift at the stalling angle is fairly constant from #ab to #af4 ,the value of the drag can be found in either of two ways3 7#a7 by dividing the total lift 7,l7 by the lift-drag ratio1 or 7#b7 by figuring its value by the formula ,d ,kx,a,v4 ,the first method is shorter and preferable4 ,by consulting the table1 it will be seen that the ,l_/,d ratio at #f is #ad4i4 ,the total wing drag will then be equal to #e1gef4g_/adi #chf4d lbs4 ,figured by the second method1 the value of ,ky at #f is #j4jjjaei1 and the drag is therefore3 ,d ,kx,a,v #j4jjjaei #cjj 7#ij #ij7 #chf4d4 ,this checks exactly with the first method4 ,the lift-drag ratio is best at #d1 the figure being #ae4f1 while the lift at this point is #j4jjaifc4 ,with the same area and speed1 the total lift of the surface at the angle of best lift-drift ratio will be #jjjaifc #cjj 7#ij #ij7 #d1ggj lbs4 ,at #d the center of pressure is #j4che of the chord from the entering edge4 ,if the chord is #fj inches wide1 the center of pressure will be located at #j4che #fj #bc4a inches from the entering edge4 ,at #ae1 the center of pressure will be #j4bi #fj #ag4d inches from the entering edge1 or during the change from #d to #ae the center of pressure will have moved forward by #e4g inches4 ,at -#b1 the pressure has moved over three-quarters of the way toward the trailing edge -#j4ghe of the chord1 to be exact ,through the ordinary flight angles of from #b to #ab1 the travel of the center of pressure is not excessive4 ,the maximum lift co-efficient 7,ky7 is very high in the ,r4,a4,f4-#c section1 reaching a maximum of #j4jjcdha at an incidence of #ad4 ,this is second to only one other wing1 the section ,u4,s4,a4-#d4 ,this makes it suitable for heavy seaplanes4 ,table #b gives the aerodynamic properties of the ,r4,a4,f-#f wing1 the table being arranged in a manner similar to that of the ,r4,a4,f4-#c4 ,in glancing down the column of lift co-efficients 7,ky71 and comparing the values with those of the ,r4,a4,f4-#c section1 it will be noted that the lift of ,r4,a4,f4-#f is much lower at every angle of incidence1 but that the lift-drag ratio of the latter section is not always correspondingly higher4 ,at every angle below #b1 at #f1 and at angles above #ad1 the ,l_/,d ratio of the ,r4,a4,f4-#c is superior in spite of its greater lift4 ,the maximum ,l_/,d ratio of the ,r4,a4,f4-#f at #d is #af4eh1 which is considerably higher than the best ,l_/,d ratio of the ,r4,a4,f4-#c4 ,the best lift co-efficient of the ,r4,a4,f4-#f1 #jjjcjde1 is very much lower than the maximum ,ky of the ,r4,a4,f4-#c4 ,the fact that the ,l_/,d ratio of the ,r4,a4,f4-#c wing is much greater at high lift co-efficients1 and large angles of incidence1 makes it very valuable as at this point the greater ,l_/,d does not tend to stall the plane at slow speed4 ,a large ,l_/,d at great angles1 together with a wide stalling angle tends for safety in slow speed flying4 ,both wing sections are structurally excellent1 being very deep in the region of the rear edge1 the ,r4,a4,f4-#f being particularly deep at this point4 ,a good deep spar can be placed at almost any desirable point in the ,r4,a4,f-#f1 and the trailing edge is deep enough to insure against rib weakness even with a comparatively great overhang4 ,scale corrections for the full size ,r4,a4,f4 wings are very difficult to make4 ,according to the ,n4 ,p4 ,l4 reports1 the corrected value for the maximum ,l_/,d of the ,r4,a4,f4-#c wing is #ah4a1 the model test indicating a maximum value of #ae4f4 ,i believe that ,l_/,d #ag4e would be a safe full size value for this section4 ,the same reports give the full size ,l_/,d for the ,r4,a4,f4-#f as #ah4e1 which would be probably safe at #ah4j under the new conditions4 99,properties of the ,eiffel ,sections 7#cb-cf-cg7994 ,three of the ,eiffel sections are shown by ,figs4 #aj1 #aa and #ab1 these ,sections being selected out of an enormous number tested in the ,eiffel laboratories4 ,they differ widely1 both aerodynamically and structurally1 from the ,r4,a4,f4 aerocurves just illustrated4 ,illustration3 ,fig4 #aj-aa-ab ,ordinates for ,three ,eiffel ,wing ,sections ,eiffel #cb is a very stable wing1 as has already been pointed out1 but the value of the maximum ,l_/,d ratio is in doubt as this quantity is very susceptible to changes in the wind velocity--much more than in the average wing4 ,since ,eiffel's tests were carried out at much higher velocity than at the ,m4 ,i4 ,t41 his lift-drift values at the higher speeds were naturally much better than those obtained by the ,american ,laboratory4 ,when tested at #fg4b miles per hour the lift-drift ratio for the ,eiffel #cb was #ahd while at #bb4d miles per hour1 the ratio dropped to #ac4d4 ,this test alone will give an idea as to the variation possible with changes in scale and wind velocity4 ,the following table gives the results of tests carried out at the ,massachusetts laboratory1 reported by ,alexander ,klemin and ,g4 ,m4 ,denkinger in ,aviation and ,aeronautical ,engineering4 ,wind speed1 #cj miles per hour4 ,the ,c4 ,p4 ,travel in the ,eiffel wing is very small1 as will be seen from ,table #c4 ,at -#b the ,c4 ,p4 is #j4cc of the chord from the leading edge and only moves back to #j4cgh at an angle of #bj1 the intermediate changes being very gradual1 reaching a minimum of #j4cjd at #f incidence4 ,the maximum ,ky of ,eiffel #cb is #j4jjbijh1 while for the ,r4,a4,f4-#f wing1 ,ky #j4jjcjde maximum1 both co-efficients being a maximum at #af incidence1 but the lift-drag at maximum ,ky is much better for the ,r4,a4,f4-#f4 ,structurally1 the ,eiffel #cb is at a disadvantage when compared with the ,r4,a4,f4 sections since it is very narrow at points near the trailing edge4 ,this would necessitate moving the rear spar well up toward the center with the front spar located very near the leading edge4 ,this is the type of wing used in a large number of ,german machines4 ,it will also be noted that there is a very pronounced reverse curve or ,reflex in the rear portion1 the trailing edge actually curving up from the chord line4 ,eiffel #cf is a much thicker wing than either of the other ,eiffel curves shown1 and is deficient in most aerodynamical respects4 ,it has a low value for ,ky and a poor lift-drag ratio4 ,it has1 however1 been used on several ,american training machines1 probably for the reason that it permits of sturdy construction4 ,illustration3 ,fig4 #ac ,characteristic ,curves for ,eiffel ,wings ,sections ,eiffel #cg is essentially a high-speed wing having a high ,l_/,d ratio and a small lift co-efficient4 ,the maximum lift-drag ratio of #bj4d is attained at a negative angle -#jh4 ,the value of ,ky at this point is #j4jjjhf1 an extremely low figure4 ,the maximum ,ky is #j4jjbhh at #ad4j1 the ,l_/,d ratio being #d4j at this angle4 ,structurally it is the worst wing that we have yet discussed1 being almost paper thin for a considerable distance near the trailing edge4 ,the under surface is deeply cambered1 with the maximum under camber about one-third from the trailing edge4 ,it is impossible to use this wing without a very long overhang in the rear of the section1 and like the ,eiffel #cb1 the front spar must be very far forward4 ,for those desiring flexible trailing edges1 this is an ideal section4 ,this wing is best adapted for speed scouts and racing machines because of its great ,l_/,d1 but as its lift is small and the center of pressure movement rapid at the point of maximum lift-drag1 it would be necessary to fly at a small range of angles and land at an extremely high speed4 ,any slight change in the angle of incidence causes the lift-drag ratio to drop at a rapid rate1 and hence the wing could only be manipulated at its most efficient angle by an experienced pilot4 ,again1 the angle of maximum ,l_/,d is only a few degrees from the angle of no lift4 99,u4,s4,a4 ,wing ,sections994 ,these wing sections were developed by the ,aviation ,section of the ,signal ,corps1 ,united ,states ,army1 and are decided improvements on any wing sections yet published4 ,the six ,u4,s4,a4 wings cover a wide range of application1 varying as they do1 from the high speed sections to the heavy lift wings used on large machines4 ,the data was first published by ,captains ,edgar ,s4 ,gorrell and ,h4 ,s4 ,martin1 ,u4,s4,a41 by permission of ,professor ,c4 ,h4 ,peabody1 ,massachusetts ,institute of ,technology4 ,an abstract of the paper by ,alexander ,klemin and ,t4 ,h4 ,huff was afterwards printed in ,aviation and ,aeronautical ,engineering4 ,while several of the curves are modifications of the ,r4,a4,f4 sections already described1 they are aerodynamically and structurally superior to the originals1 and especial attention is called to the marked structural advantages4 ,u4,s4,a4-#a and ,u4,s4,a4-#f are essentially high speed sections with a very high lift-drag ratio1 these wings being suitable for speed scouts or pursuit machines4 ,the difference between the wings is very slight1 ,u4,s4,a4-#a with ,k-#jjjcah giving a better landing speed1 while ,u4,s4,a4-#f is slightly more efficient at low angles and high speeds4 ,illustration3 ,fig4 #ad4 ,u4,s4,a4 ,wing ,sections ,nos4 #a-b-c-d-e-f1 ,showing the ,ordinates at the ,various tations ,expressed as ,decimals of the ,chord4 ,u4,s4,a4-#d is a ,heavy ,lift ,section1 ,while ,u4,s4,a4-#a and ,u4,s4,a4-#f4;are ,high ,speed ,wings4 ,for ,any ,particular ,duty1 the ,above ,wings ,are ,very ,deep and ,permit of ,large ,structural ,members4 ,the ,center of ,pressure ,movement ,is ,comparatively ,slight4 ,with #j incidence1 the ratio of ,u4,s4,a-#aaa4j while the lift-drag of ,u4,s4,a4-#f at #j incidence is #ac4j4 ,the maximum lift of ,u4,s4,a4-#a is superior to that of ,eiffel #cb1 and the maximum lift-drag ratio at equal speeds is far superior1 being #ag4h against #ad4ej of the ,eiffel #cb4 ,compared with the ,eiffel #cb it will be seen that the ,u4,s4,a4 sections are far better from a structural point of view1 especially in the case of ,u4,s4,a4-#a4 ,the depth in the region of the rear spar is exceptionally great1 about the same as that of the ,r4,a4,f4-#f4 ,while neither of the ,u4,s4,a4 wings are as stable as the ,eiffel #cb1 the motion of the ,c4 ,p4 is not sudden nor extensive at ordinary flight angles4 ,probably one of the most remarkable of the ,united ,states ,army wings is the ,u4,s4,a4-#d which has a higher maximum lift co-efficient 7,ky7 than even the ,r4,a4,f4-#c4 ,the maximum ,ky of the ,u4,s4,a4-#d is #j4jjcfd compared with the ,r4,a4,f4-#c in which ,ky 7,maximum7#j4jjcdha4 ,above #d incidence1 the lift-drag ratio of the ,u4,s4,a4-#d is generally better than that of the ,r4,a4,f4-#c1 the maximum ,l_/,d at #d being considerably better4 ,this is a most excellent wing for a heavy seaplane or bomber4 ,the ,u4,s4,a4-#b has an upper surface similar to that of the ,r4,a4,f4-#c1 but the wing has been thickened for structural reasons1 thus causing a modification in the lower surface4 ,this results in no particular aerodynamic loss and it is much better at points near the rear edge for the reception of a deep and efficient rear spar4 ,u4,s4,a4-#c is a modification of ,u4,s4,a4-#b1 and like ,u4,s4,a4-#b would fall under the head of ,all around wings1 a type similar1 but superior to ,r4,a4,f4-#f4 ,these wings are a compromise between the high speed and heavy lift types--suitable for training schools or exhibition flyers4 ,both have a fairly good ,l_/,d ratio and a corresponding value for ,ky4 ,u4,s4,a4-#e has a very good maximum lift-drag ratio 7#af4ba7 and a good lift-drag ratio at the maximum ,ky4 ,its maximum ,ky is superior to all sections with the exception of ,u4,s4,a4-#b and #d4 ,structurally it is very good1 being deep both fore and aft4 ,in review of the ,u4,s4,a4 sections1 it may be said that they are all remarkable in having a very heavy camber on both the upper and lower surfaces1 and at the same time are efficient and structurally excellent4 ,this rather contradicts the usual belief that a heavy camber will produce a low lift-drag ratio1 a belief that is also proven false by the excellent performance of the ,eiffel #cg section4 ,the maximum ,ky is also well sustained at and above #j4jjc4 ,there is no sharp drop of lift at the ,stalling angle and the working range of incidence is large4 99,curtiss ,wing and ,double ,cambered ,sections994 ,an old type of ,curtiss wing is shown by ,fig4 #ae4 ,it is very thick and an efficient wing for general use4 ,it will be noticed that there is a slight reflex curve at the trailing edge of the under surface and that there is ample spar room at almost any point along the section4 ,the nose is very round and thick for a wing possessing the ,l_/,d characteristics exhibited in the tests4 ,the conditions of the test were the same as for the preceding wing sections4 ,fig4 #af shows a remarkable ,curtiss section designed for use as a stabilizing surface4 ,it is double cambered1 the top surface being identical with the lower1 and is therefore non-lifting with the chord horizontal4 ,the force exerted by the surface is equal with equal positive or negative angles of incidence1 a valuable feature in a control surface4 ,in spite of its great thickness1 it is of excellent stream line form and therefore has a very good lift-drag ratio4 ,at #j angle of incidence the resistance is at a minimum1 and is much less than that of a thin1 square edged1 flat plate4 ,this double cambered plane reduces the stay bracing and head resistance necessary with the flat type of stabilizer surface4 ,illustration3 ,fig4 #ae4 ,old ,type of ,curtiss ,wing4 #af4 ,curtiss ,double ,camber for ,control ,surfaces4 ,the ,curtiss sections mentioned above were described in ,aviation and ,aeronautical ,engineering by ,dr4 ,jerome ,c4 ,hunsaker1 but the figures in the above table were obtained by the author on a sliding test wire arrangement that has been under development for some time4 ,at the time of writing several of the ,u4,s4,a4 sections are under investigation on the same device4 ,,correction ,,factors ,,for ,,wing ,,form ,,and ,,size4 99,aspect ,ratio994 ,as previously explained1 the aspect ratio is the relation of the span to the chord1 and this ratio has a considerable effect upon the performance of a wing4 ,in the practical full size machine the aspect ratio may range from #e in monoplanes1 and small biplanes1 to #aj or #ab in the larger biplanes4 ,the aspect in the case of triplanes is even greater1 some examples of the latter having aspects of #af to #bj4 ,in general1 the aspect ratio increases with the gross weight of the machine4 ,control surfaces1 such as the rudder and elevator1 usually have a much lower aspect ratio than the main lifting surfaces1 particularly when flat non-lifting control surfaces are used4 ,the aspect of elevator surfaces will range from unity to #c1 while the vertical rudders generally have an aspect of #a4 ,with a given wing area1 the span increases directly with an increase in the aspect ratio4 ,the additional weight of the structural members due to an increased span tend to offset the aerodynamic advantages gained by a large aspect ratio1 and the increased resistance due to the number and size of the exposed bracing still further reduces the advantage4 99,effects of ,aspect ,ratio994 ,variations in the aspect ratio do not give the same results in all wing sections1 and the lift co-efficient and ,l_/,d ratio change in a very irregular manner with the angle of incidence4 ,the following tables give the results obtained by the ,n4 ,p4 ,l4 on a ,bleriot wing section1 the aspect ratio being plotted against the angle of incidence4 ,the figures are comparative1 an aspect factor of unity 7#a1jjj7 being taken for an aspect ratio of #f at each angle of incidence4 ,to obtain an approximation for any other wing section at any other aspect ratio1 multiply the model test 7,aspect#f7 by the factor that corresponds to the given angle and aspect ratio4 ,at the extreme right of the table is a column of rough averages1 taken without regard to the angles4 ,the column of average values is not the average of the tabular values but is the average of the results obtained by a number of investigators on different wing sections4 ,through the small angles of #j and #b the low aspect ratios give a maximum ,ky greater than with the larger aspects4 ,the larger aspects increase the lift through a larger range of angles but have a lower maximum value for ,ky at small angles4 ,beyond #b the larger aspect ratios give a greater ,ky4 99,aspect for ,flat ,plates994 ,for flat plates the results are different than with cambered sections4 ,the lift-drag ratios are not much improved with an increase in aspect1 but the highest maximum lift is obtained with a small aspect ratio4 ,for this reason1 a small aspect ratio should be used when a high lift is to be obtained at low speeds with a flat plate as in the case of control surfaces4 ,an aspect ratio of unity is satisfactory for flat vertical rudders since a maximum effect is desirable when taxi-ing over the ground at low speeds4 ,the flat plate effects are not important except for control surfaces1 and even in this case the plates are being superseded by double cambered sections4 99,reason for ,aspect ,improvement994 ,the air flows laterally toward the wing tips causing a very decided drop in lift at the outer ends of the wings4 ,the lift-drag ratio is also reduced at this point4 ,the center of pressure moves back near the trailing edge as we approach the tips1 the maximum zone of suction on the upper surface being also near the trailing edge4 ,the lift-drag ratio at the center of the plane is between #d or #e times that at a point near the tips4 ,all of the desirable characteristics of the wing are exhibited at a point near the center4 ,when the aspect ratio is increased1 the inefficient tips form a smaller percentage of the total wing areas1 and hence the losses at the tips are of less importance than would be the case with a small aspect4 ,the end losses are not reduced by end shields or plates1 and in attempts to prevent lateral flow by curtains1 the losses are actually often increased4 ,proper design of the form of the wing tip1 such as raking the tips1 or washing out the camber and incidence1 can be relied upon to increase the lift factor4 ,this change in the tips causes the main wind stream to enter the wings in a direction opposite to the lateral leakage flow and therefore reduces the loss4 ,properly raked tips may increase the lift by #bj per cent4 99,effects of ,scale 7,size and ,velocity7994 ,in the chapter ,elementary ,aerodynamics it was pointed out that the lift of a surface was obtained by the motion of the air1 or the turbulence caused by the entering of the plane4 ,it was also explained that the effect of the lift due to turbulence varied as the square of the velocity and directly as the area of the wings4 ,this would indicate that the lift of a small wing 7,model7 would be in a fixed proportion to a large wing of the same type4 ,this holds true in practice since nearly all laboratories have found by experiment that the lift of a large wing could be computed directly from the results obtained with the model without the use of correction factors4 ,that is to say1 that the lift of a large wing with #dj times the area of the model1 would give #dj times the lift of the model at the same air speed4 ,in the same way1 the lift would be proportional to the squares of the velocities4 ,if the span of the model is taken at #a feet1 and the velocity as ,v feet per second1 the product ,,iv would represent both the model and the full size machine4 ,the lift is due to aerodynamic forces strictly1 and hence there should be no reason why the ,v law should be interfered with in a change from the model to the full size machine4 ,in the case of drag the conditions are different1 since the drag is produced by two factors that vary at different rates4 ,part of the drag is caused by turbulence or aerodynamic forces and part by skin friction1 the former varying as ,v while the skin friction varies as ,v44 ,the aerodynamic drag varies directly with the area or span while the skin friction part of the drag varies as #a41 where #a is the span4 ,from considerations of the span and the speed1 it will be seen that the frictional resistance increases much slower than the aerodynamic resistance1 and consequently the large machine at high speed would give less drag and a higher value of ,l_/,d than the small model4 ,in other words1 the results of a model test must be corrected for drag and the lift-drag ratio when applied to a full size machine4 ,such a correction factor is sometimes known as the ,scale factor4 ,eiffel gives the correction factor as #a4jh1 that is the liftdrag ratio of the full size machine will be approximately #a4jh times as great as the model4 ,a series of full size tests were made by the ,university of ,st4 ,cyr in #aiab-aiac with the object of comparing full size aeroplane wings with small scale models of the same wing section4 ,the full size wings were mounted on an electric trolley car and the tests were made in the open air4 ,many differences were noted when the small reproductions of the wings were tested in the wind tunnel1 and no satisfactory conclusions can be arrived at from these tests4 ,according to the theory1 and the tests made by the ,n4 ,p4 ,l41 the lift-drag ratio should increase with the size but the ,st4 ,cyr tests showed that this was not always the case4 ,in at least three of the tests1 the model showed better results than the full size machine4 ,there seemed to be no fixed relation between the results obtained by the model and the large wing4 ,the center of pressure movement was always different in every comparison made4 ,one cause of such pronounced difference would probably be explained by the difference in the materials used on the model and full size wing1 the model wing being absolutely smooth rigid wood while the full size wing was of the usual fabric construction4 ,the fabric would be likely to change in form under different conditions of angle and speed1 causing a great departure from the true values4 ,again1 the model being of small size1 would be a difficult object to machine to the exact outline4 ,a difference of #a_/ajjj inch from the true dimension would make a great difference in the results obtained with a small surface4 99,plan ,form994 ,wings are made nearly rectangular in form1 with the ends more or less rounded1 and very little is now known about the effect of wings varying from this form4 ,raking the ends of the wing tips at a slight angle increases both the lift-drag and lift by about #bj per cent1 the angle of the raked end being about #ae degrees4 ,raking is a widely adopted practice in the ,united ,states1 especially on large machines4 99,summary of ,corrections994 ,we can now work out the total correction to be made on the wind tunnel tests for a full size machine of any aspect ratio4 ,the lift co-efficient should be used as given by the model test data1 but the corrections can be applied to the lift-drag ratio and the drag4 ,the scale factor is taken at #a4jh1 the form factor due to rake is #a4b1 and the aspect correction is taken from the foregoing table4 ,the total correction factor will be the product of all of the individual factors4 99,example994 ,a certain wing section has a lift-drag ratio of #ae4jj1 as determined by a wind tunnel test on a model1 the aspect of the test plane being #f4 ,the full size wing is to have an aspect ratio of #h1 and the wing tips are to be raked4 ,what is the corrected lift-drag ratio of the full size machine at #ad8 99,solution994 ,the total correction factor will be #a4jh #a4aj #ab #a4dci4 ,the lift-drag ratio of the full size modified wing becomes #ae4jj x #a4dci #ba4ehe4 ,as a comparison1 we will assume the same wing section with rectangular tips and an aspect ratio of #c4 ,the total correction factor for the new arrangement is now #a4jh ,x #j4gb #j4gggf where #j4gb is the relative lift-drag due to an aspect of #c4 ,the total lift-drag is now #ae4jj ,x #j4gggf #aa4ffd4 ,having a large aspect ratio and raked tips makes a very considerable difference as will be seen from the above results1 the rake and aspect of #h making the difference between #ba4ehe and #aa4ffd in the lift-drag4 ,area for area1 the drag of the first plane will be approximately one-half of the drag due to an aspect ratio of three4 99,lift in ,slip ,stream994 ,the portions of a monoplane or tractor biplane lying in the propeller slip stream are subjected to a much higher wind velocity than the outlying parts of the wing4 ,since the lift is proportional to the velocity squared1 it will be seen that the lift in the slip stream is far higher than on the surrounding area4 ,assuming for example1 that a certain propeller has a slip of #cj per cent at a translational speed of #hd miles per hour1 the relative velocity of the slip stream will be #hd_/j4gj #abj miles per hour4 ,assuming a lift factor 7,ky7#j4jjbb1 the lift in the slip stream will be ,l #j4jjbb #abj #abj #ca4fh pounds per square foot4 ,in the translational wind stream of #hd miles per hour1 the lift becomes ,l #j4jjbb ,x #hd ,x #hd #ae4eb pounds per square foot4 ,in other words1 the lift of the portion in the slip stream is nearly double that of the rest of the wing with a propeller efficiency of #gj per cent4 ,,chapter ,,vii4 ,,biplanes ,,and ,,triplanes4 99,biplane ,characteristics994 ,from an aerodynamic standpoint1 the monoplane wing is more efficient than the superposed wings of the biplane type1 since the proximity of the two surfaces in the latter causes a decided loss in the total lift4 ,other practical advantages1 however1 offset the losses due to the superposed surfaces1 and hence the total efficiency of the complete biplane may be even greater than that of the monoplane4 ,for the same area the structural parts of the biplane are lighter1 and this advantage increases rapidly with the size of the machine so that when a span of #cf feet is exceeded1 any other arrangement than that of the biplane or triplane becomes almost a practical impossibility4 ,a biplane is easier and cheaper to make than a monoplane1 since the wing bracing of the former can be arranged to better advantage1 the load-bearing members can be simpler1 and the safety factor made higher for an equal weight4 ,by suitable adjustments between the wings of a biplane1 it is possible to obtain a very high degree of inherent longitudinal stability without incurring much loss in efficiency1 an arrangement that is of course impossible with a single monoplane surface4 ,by staggering1 the view of the pilot is increased1 and the generally smaller size of the machine permits of better maneuvering qualities for a given load4 99,interference994 ,due to interference1 or to the choking of the air stream between the upper and lower surfaces1 the lift of both wings is reduced1 with the drag remaining about the same as with a single surface4 ,this1 of course1 reduces the total lift-drag ratio at all except certain angles4 ,the relative lift-drag ratios of the monoplane and biplane depend to some extent upon the form of the wing4 ,interference causes a loss on the opposing faces of the wings1 the lift being reduced on the top surface of the lower wing1 and on the bottom surface of the top wing4 ,since the upper surface of the lower wing is under suction1 and therefore produces the greater proportion of lift1 it is natural that the lower wing lift should be reduced to a greater extent than in the upper wing1 since it is only the lower surface of the latter that is affected4 ,at normal flight angles the upper wing carries about #ee per cent of the total load4 ,at zero degrees incidence1 the upper wing carries as high as #fb per cent of the total load1 while at #ab degrees this may be reduced to #ed per cent4 99,gap-,chord ,ratio994 ,calling the distance between the upper and lower wings the gap1 it may be said that the ratio of the gap to the wing chord greatly influences the lift4 ,this ratio is called the gap-chord ratio1 and may vary from #j4h to #a4j in small machines or #a4j to #a4b in slow1 heavy aeroplanes4 ,with the drag remaining practically constant1 the lift-drag is of course affected by a change in the gap-chord ratio1 this quantity being diminished at small gap ratios4 ,compared with a monoplane1 the lift of a biplane is about #j4gg when the gap is #j4h of the chord1 and about #j4hi of the monoplane value when the gap-chord ratio is increased to #a4f4 ,in this range the lift-drag approximates #j4hb and #j4hi1 respectively4 ,the center of pressure movement is not greatly changed with any gap-chord ratio1 and to all practical purposes remains the same as with the monoplane4 ,it should be understood that these remarks apply only to the ,orthogonal biplane arrangement in which the wings are vertically over one another4 ,while biplane efficiency is increased by having a large gap-chord ratio 7wing efficiency alone71 the total efficiency of the aeroplane is not always increased by a large gap1 principally because of the great head resistance due to the longer struts and interplane bracing4 ,at high speeds the longer bracing members often more than offset the gain due to wing efficiency1 and as a result the gap of high speed scouts will generally be found in the neighborhood of #j4h the chord4 ,with slow1 heavy machines1 where lift is of great importance1 and where slow speed does not affect the structural resistance to so great an extent1 the gap-chord ratio will range from #a4j to #a4b4 ,in making the above comparisons between monoplanes and biplanes1 equal aspect ratios have been assumed for both types1 but in actual practice the aspect ratio of biplanes is always greater than with monoplanes1 and as a result the biplane loss is usually less than indicated above4 ,when correction has been made for the aspect ratio1 the disparity in the monoplane and biplane values of ,ky and ,l_/,d is not as great as commonly supposed4 ,biplane reduction factors1 or the factors used in reducing monoplane values to those of the biplane1 depend to a great extent upon the wing section as well as upon the gap1 and for exact values of the factors we should have the tests report of the wings in biplane form4 ,lacking this information1 we can adopt the values obtained by the ,n4 ,p4 ,l4 for an old type of wing in order to get approximate results4 ,to obtain the biplane values1 multiply the monoplane values obtained by the wind tunnel test by the factors found under the required gap-chord ratio4 ,these factors apply to an aspect ratio of #f4 ,,biplane ,,reduction ,,factors 7,n4 ,p4 ,l47 7,at ,normal ,flight ,angles7 ,gap-,chord ,ratio4 #j4h #a4j #a4b #a4f ,ky ,reduction ,factor #j4gg #j4hb #j4hf #j4hi ,l_/,d ,reduction ,factor #j4hb #j4hd #j4he #j4hi ,dr4 ,hunsaker conducted experiments at the ,massachusetts ,institute of ,technology on biplane and triplane combinations1 and the results were reported in ,aviation and ,aeronautical ,engineering1 ,nov4 #a1 #aiaf4 ,the ,r4,a4,f4-#f section was used with a gap-chord ratio of #a4b4 ,the biplane portions of the experiments are as follows1 the actual ,ky and ,l_/,d values and reduction factors being arranged according to the angle of incidence3 ,it will be noted that there is steady improvement in the lift factor with an increase in the angle from #b up 7except at #h71 and that the same holds true with the ,l_/,d factor4 ,that is1 the biplane values become nearly monoplane values at high angles1 and in the case of the ,l_/,d ratio the biplane actually is #bd per cent greater than the monoplane value at an angle of #af4 ,the lift coefficient ,ky above1 is not far from the corresponding ,ky1 for gap-chord ratio #a4b in the first table4 ,the maximum biplane value of ,l_/,d occurs at the same point as in the monoplane wing1 that is1 at #d4 ,the fact that the lift-drag is so high at #af is very favorable1 since the biplane would be less likely to stall when flying slowly1 and with a big demand on the engine4 ,the range of angles at the stalling angle is much greater than with the monoplane wing1 and the lift does not fall off so rapidly after the maximum is reached4 99,biplane ,arrangements994 ,in the foregoing data we have assumed that the upper wing was placed directly above the lower1 and with the leading edges on the same vertical line as shown by ,fig4 #c4 ,this is known as an ,orthogonal biplane1 and the gap is indicated by ,g and the chord by ,c4 ,in ,fig4 #d the forward edge of the top wing is advanced beyond the lower1 or is ,staggered1 the amount of the stagger being indicated by ,s4 ,this allows of better view1 and slightly increases both the lift and ,l_/,d values4 ,with a comparatively large stagger the range of the stalling angle is increased1 and the lift does not fall off as rapidly after the maximum is reached as with the orthogonal type4 ,in ,fig4 #e the top wing is given a backward stagger1 but the exact effects of this arrangement are not generally known4 ,there are few machines using the reversed stagger1 the only example1 to the writer's knowledge1 being the ,de ,havilland speed scout4 ,by staggering1 the resistance of the interplane bracing struts 7#c7 is somewhat reduced1 because of their inclination with the wind1 although they are longer for the same gap than in ,fig4 #c4 ,fig4 #f shows the chord of the lower wing 7,c'7 shorter than the upper chord1 a type used in the ,nieuport speed scout4 ,in effect1 this is a form of stagger1 and it undoubtedly widens the view of the pilot1 and to some extent increases the efficiency and the range of the stalling angle4 ,neither the stagger in 7#d7 nor the small lower chord alone improves the stability to any extent4 ,to obtain any marked advantage with the short lower chord1 the chord ,c' must be very much shorter than the upper chord1 say from #j4hj;,c to #j4ej;,c4 ,the loss of area is so great that this would not be permissible on any except the fastest machines1 where lift is not a primary consideration4 ,the pilot's view1 however1 is very much improved with the short lower chord1 and in battle this is an important consideration4 ,fig4 #g shows the chord of the upper wing inclined at an angle with the lower chord by the amount 7d74 ,this is known as ,decalage and is productive of a great degree of longitudinal stability when taken in combination with stagger4 ,the stability attained by decalage and stagger is without a great loss in the ,l_/,d ratio1 while the lift and stalling angle range are both increased4 ,this latter stable combination is shown by ,fig4 #h1 in which the wings are given both stagger and decalage4 ,illustration3 ,slow ,speed1 ,two-,seat ,biplane1 with a ,large ,gap-,chord ,ratio4 ,the ,large ,gap ,is ,permissible in a ,slow ,machine1 as the ,strut ,resistance ,is ,less ,than the ,gain in ,lift-,drag ,ratio ,obtained by the ,greater ,gap4 ,it ,will ,be ,noted ,that ,these ,wings ,have a ,considerable ,amount of ,stagger4 ,the ,position of the ,bottom ,wing ,allows the ,observer to ,see ,almost ,directly ,below4 ,illustration3 ,a ,high ,speed1 ,two-,seat ,fighting ,biplane1 with a ,small ,gap-,chord ,ratio4 ,in ,this ,case1 the ,strut ,resistance ,would ,be ,greater ,than the ,aerodynamic ,gain of the ,wings with a ,greater ,gap ,chord ,ratio4 ,the ,gunner ,is ,located in the ,rear ,seat1 and ,behind the ,trailing ,edge of the ,lower ,wings4 ,he ,has a ,clear ,field to the ,rear an ,over the ,top ,wing4 99,forward ,stagger994 ,eiffel performed experiments with ,dorand wings1 and found that when the top surface was staggered forward by #a_/b4e of the chord 7#j4d;,c71 and with a gap-chord ratio of #j4i1 an increase in lift of from #f to #aj per cent was obtained4 ,the ,l_/,d was the same as with no stagger4 ,with thin circular plates1 #a_/ac4e camber1 and a gap-chord ratio #j4ff1 the lift-drag was better 7than with no stagger7 only when the value of ,ky was greater than #j4jff 7metric74 ,then the ,l_/,d improved progressively with the amount of stagger4 ,ky was improved by #e per cent when the stagger was equal to half the chord1 and by #aj per cent when the stagger was equal to the chord4 ,the ,n4 ,p4 ,l4 with a ,bleriot wing1 aspect ratio#d1 found that ,ky was increased by #e to #f per cent with a stagger of #j4d;,c1 and the ,l_/,d was increased by about #d percent4 ,the gap-chord ratio was #a4jj4 ,illustration3 ,a ,single ,seat ,biplane ,speed ,scout with an ,air ,cooled ,motor4 ,in a series of tests made by ,a4 ,tcherschersky1 the backward stagger as in ,fig4 #e gave about #ae per cent greater lift than the orthogonal biplane1 or about #d per cent less lift than a monoplane surface of the same area4 ,the stagger in this experiment was about #j4cc;,c4 ,in default of more accurate information1 it would seem that backward stagger would give better results than forward stagger1 since the air swept down by the upper surface would pass further to the rear of the lower plane and hence would not so greatly affect the vacuum on the upper surface of the lower wing4 ,this would1 however1 destroy the view of the pilot to a greater extent than any of the other arrangements4 ,stagger always introduces structural difficulties1 makes the wings difficult to assemble1 and the wires are of varying lengths4 ,a simple orthogonal cell is more compact and better from a manufacturing standpoint1 as it simplifies the fittings1 and to a slight extent decreases the weight4 ,when combined with sweep back1 the complication is particularly in evidence4 ,it is pleasing to note the prevalence of orthogonal cells on modern battle-planes4 99,influence of ,camber994 ,the amount of air swept down by the upper wing is largely determined by the curvature of the under surface of the upper wing4 ,by decreasing1 or flattening out the curvature of this surface1 the velocity is increased in a horizontal direction and reduced in a vertical direction1 so that the lower wing is less affected4 ,the upper surface of the upper wing is not influenced by interference4 ,it should be noted at this point that air in striking a convex surface is increased in horizontal speed while the reverse is true of the lower concave surface4 ,if the under surface of the upper wing were made convex1 the down trend of the air would be still further reduced1 and the loss on the lower wing reduced in proportion4 ,increasing the camber on the upper surface of the lower wing increases its horizontal velocity and hence affects the upper wing to a less extent1 but as the upper wing loss is comparatively slight1 the camber increase below is not of great consequence4 ,this has only been tried in one machine to the writer's knowledge1 one of the ,standard seaplanes1 in which the upper wing was an ,r4,a4,f4-#f and the lower wing was a deeply cambered ,u4,s4,a4-#b section4 ,the lower surface of the ,r4,a4,f4-#f is comparatively flat4 99,effects of ,decalage994 ,when the upper wing incidence is increased in regard to that of the lower wing1 or is given decalage1 the stability is increased with a slight increase in the power or drag4 ,this angle shown by 7d7 in ,figs4 #g and #h1 must be accompanied by stagger to obtain stability1 the angle 7d7 ranging from #a to #d4 ,with a decalage of #b4e1 and a stagger of half the chord1 a high degree of stability is attained with a loss in the lift-drag of from #d to #f percent4 ,the lift and the range of the stalling angle are both increased1 the former by about #c percent1 while the latter is nearly double4 ,by increasing the decalage to #d1 the lift-drag is still #d percent less than with the orthogonal cell1 but the range of the stalling angle is nearly tripled4 ,the #d decalage is very stable and is suitable for training machines or for amateurs4 ,in either case1 the stagger-decalage system is usually better than sweep back1 reflex curves or negative wing tips4 ,without regard to the stability1 and only with the idea of a greater ,l_/,d in mind1 it has been usual in several ,european machines to adopt a negative decalage2 that is1 to increase the angle of the lower wing in regard to the upper chord4 ,with the top chord horizontal1 a negative decalage of #d would make the incidence of the lower wing equal to #d4 ,this has not been generally found advantageous in model tests1 but in full size machines there is a considerable increase in the ,l_/,d ratio4 ,the greater incidence of the lower wing also improves the lift of this surface and thus requires less surface for obtaining the same total lift1 especially when top wing is staggered forward4 ,incidence of top wing of ,nieuport #a-cj'4 ,lower wing is set at #c4 99,varying ,incidence994 ,with several types of ,european speed scouts1 and in the case of the old ,handley-,page monoplane1 the angle of incidence is reduced from the center of the wing to the tip4 ,thus in one speed scout1 the incidence at the body is #d1 and #b at the tips4 ,a decrease in angle toward the tips has much the same effect as an increase in aspect ratio2 that is1 it decreases the lateral flow and end leakage4 ,it also has an effect in aiding the lateral stability because there is less lift at the tips1 and hence they are less affected by side gusts4 ,washed out incidence is an aid to longitudinal stability1 as the center of pressure at the tips is moved further back than at the center of the wing1 and therefore the ,c4 ,p4 is distributed over a longer distance fore and aft than it would be with a uniform angle of incidence4 ,in driving the propeller1 the motor tends to turn the body in a direction opposite to that of the propeller rotation1 and if no other provision is made this must be overcome by means of the ailerons4 ,the ,motor torque on small span machines is particularly difficult to overcome in this way1 owing to the short lever arm length of the ailerons4 ,to practically overcome the torque1 without excessively loading the ailerons1 it is usually the practice to set the lower left wing tip at a greater angle than the lower right wing4 ,the greater angle at the left gives a lift that opposes the turning moment of the motor4 ,this compensation can never be complete1 for the motor torque varies with the motor output1 hence an average angle is selected so that the incidence will cover the usual horizontal flight speeds4 99,triplane ,arrangement994 ,when a biplane exceeds a certain weight the area required for a given landing speed makes it desirable to increase the number of lifting surfaces to more than two1 if the span and stress are to be kept down within reasonable limits4 ,thus the biplane has its limits as well as the monoplane1 and in the biplane this limit is generally reached when the span approaches #hj feet4 ,in addition to the increased weight due to spans of over #hj feet1 there are other troubles in regard to the space required for housing1 and awkwardness in maneuvering4 ,on the smaller and faster aeroplanes1 the triplane arrangement permits of space condensation1 and also allows of larger aspect ratios than with the biplane4 ,the greater depth of the triplane structure makes the interplane bracing even more effective than in the case of the biplane4 ,for equal spans there is less bracing exposed to the wind1 and the weight of the wing spars and ribs can be considerably reduced4 ,the shorter ribs of the triplane alone contribute in no small degree to the saving in weight4 ,considering the wings alone1 without reference to the head resistance of the bracing1 etc41 there is a greater loss of lift and ,l_/,d when three tiers of wings are superposed than with a biplane4 ,in experiments by ,dr4 ,hunsaker upon ,r4,a4,f4-#f and ,curtiss wing sections1 it was found that at about #d1 that the triplane required about #f percent more power than the corresponding biplane4 ,at this angle1 the ,l_/,d for the triplane was #ab4h1 against the ratio of #ac4h for the biplane4 ,the gap-chord ratio in each case was maintained at #a4b4 ,both the ,r4,a4,f4-#f and the ,curtiss wings gave results of the same general character1 and there was not a great deal of difference in the numerical values4 ,at very high angles1 #ab to #af1 the lift of the biplane and triplane only differed by about #b percent1 but at very small angles such as are used at normal flight speeds1 the reduction of lift in the triplane was very marked4 ,the drag was not greatly different below #ab1 but at #af the drag-coefficient is less than that of either the biplane or monoplane1 and for machines flying at low speeds1 or heavily loaded1 this decrease is of great advantage since it relieves the motor at a time when power is particularly required4 ,at this point it should be noted that at high angles1 the ,l_/,d generally is better for multiplanes in an almost direct proportion to the number of surfaces4 ,in this experiment1 the lift-drag ratios for a monoplane1 biplane1 and triplane were respectively #d4e1 #e4f1 and #f4e4 ,the drop in lift after the point of maximum lift1 or the stalling angle1 is not as rapid as in the case of the biplane or monoplane1 and hence there is less danger of stalling the triplane4 ,with the same area1 and loading1 the landing speed of the biplane and triplane will be about the same4 ,the following tables give the lift1 and lift-drag ratios as determined in these experiments1 the factors being in terms of the monoplane values of an ,r4,a4,f4-#f wing4 ,thus to obtain triplane values1 multiply the given monoplane values by that number opposite the required angle of incidence4 ,aspect ratio #f4 ,illustration3 ,curtiss ,triplane ,speed ,scout4 ,note the ,great ,aspect ,ratio of the ,wings1 and the ,relatively ,great ,gap-,chord4 ,ratio4 ,only ,one ,set of ,struts ,are ,used in a ,single ,row1 ,hence the ,head ,resistance ,is at a ,minimum4 ,the ,span ,is #be'-j and the ,chord #b'-j1 ,giving an ,aspect ,ratio of #ab4e4 ,thus1 if the monoplane lift value for the ,r4,a4,f4-#f wing at #d is ,ky #j4jja4de1 then the triplane value will be #j4jjade #j4geg #j4jjajig as given in the table4 ,the monoplane lift-coefficient of any other wing section can be handled in the same way with fair accuracy4 ,to obtain the corrected lift-drag ratio for any wing section1 multiply the lift-drag of the monoplane wing by the factor in the above table corresponding to the incidence of the monoplane test wing4 ,illustration3 ,the ,italian ,caproni ,triplane of the ,heavy ,lift or ,bombing ,type4 ,motors ,are ,installed in ,each of the ,three ,bodies1 ,tractor ,propellers ,being ,used in the ,two ,long ,outer ,bodies1 ,while a ,pusher ,screw ,is ,used at the ,rear of the ,central ,passenger ,body4 ,the ,enormous ,size of ,this ,triplane ,can ,be ,seen by ,comparing it with the ,caproni ,monoplane ,shown at the ,right4 ,courtesy ,flying4 ,the upper wing gives the greatest percentage of lift1 and the middle wing the least1 since the latter suffers from interference on both sides4 ,it has been found that the sum of the top and bottom wings of a triplane group gives the same lift as the two wings of a biplane under equal conditions4 ,it was also found that the lift-coefficients and lift-drag of the upper plane alone was very nearly equal to the lift of the combined effects of all three wings1 and at all angles4 ,calling the lift of the middle wing #a4jj 7#d71 the lift of the upper wing will be #a4ia and the lower wing #a4fd4 ,calling the ,l_/,d of the middle wing #a4jj 7#d71 the relative life-drag will be ,l_/,d #b4ei for the upper wing and #a4fi for the lower4 ,with the middle wing still assumed at unity1 the lift of the top plane is at #a4di at #af1 and the lower wing #a4bj4 ,the liftdrag at #af degrees will be respectively #a4jj1 #a4bb1 and #a4aag for middle top and bottom4 ,at #j1 the upper wing will carry #b4fh1 the middle #a4jj1 and the bottom #a4hb4 ,at #j1 the lift-drag of the top is #c4fc1 the middle #a4jj1 and bottom #b4cj4 ,these relative figures are only useful in comparing the loading when computing the strength of the structural parts4 ,see ,aviation and ,aeronautical ,engineering ,nov4 #a1 #aiaf4 99,overhanging ,wing ,tips994 ,in many ,american machines1 and in some ,european machines1 such as the ,farman1 the upper wing is given a much greater span than the lower4 ,of late1 the tendency has been to make the wings of equal1 span and fully #ij per cent of the modern machines will be found to be arranged in this way4 ,while the overhanging tips may slightly increase the efficiency of the biplane by reducing interference at the ends1 it makes the span unduly long and difficult to brace at the end4 ,the added end bracing due to the overhang probably offsets any aerodynamic advantage to be obtained1 although ,i have no accurate data on this point4 ,compactness is certainly not a feature4 ,it is said that ailerons are more effective when mounted on the upper overhang1 and this may be so1 but ,i note that the area is about the same in any case4 ,with overhanging tips1 the ailerons are generally placed on upper wings1 only while with equal or nearly equal spans1 they are placed top and bottom4 ,the overhanging section and the ailerons form a single detachable unit as a general rule4 ,with nearly equal spans1 the upper and lower ailerons are generally interconnected with a small strut in such a way that they act together4 ,small speed scouts1 rarely if ever1 have any overhang since the object of these machines is to make them as small and compact as possible4 ,,chapter ,,viii4 ,,effects ,,of ,,plan ,,form4 7,,tandem ,,aeroplanes47 99,general ,notes994 ,up to the present we have considered only two wing outlines1 the rectangular and the wing with raked tips4 ,in addition1 we have considered only the effect taking place on monoplane surfaces4 ,for the purpose of obtaining longitudinal stability1 or for distributing the lift upon two or more following surfaces1 the plan view in some aeroplanes has been somewhat modified as in the ,dunne1 ,langley and ,ago4 ,undoubtedly the simple rectangular wing1 or the wing with raked tips1 have proved the most efficient from an aerodynamic standpoint1 but as the layman is usually interested in distorted wing shapes1 or odd-looking outlines1 ,i will describe the effect of such stabilizing forms upon the lift and drag4 ,figs4 #a-i show the usual range of wing forms1 at least those that have been used on well known machines1 and all of them have flown with varying results4 ,in any case1 the variations in the values of the lift and lift-drag are not excessive1 the extreme cases varying possibly not more than #bj per cent on either side of the values for a plain rectangular wing4 ,while almost perfect longitudinal stability can be obtained in other ways1 by less loss than by changing the plan form1 certain manufacturers still adhere to one or more deviations from the more usual rectangular form4 ,fig4 #a shows a plan view of a machine with a rectangular wing1 and ,no4 #b shows the machine provided with raked tips4 ,fig4 #c is a wing with an inclined entering edge1 as used on the ,english ,mann biplane4 ,fig4 #d is the ,german ,ago with a diamond form surface1 the evident purpose of which is to simplify the wing spar bracing as shown by the dotted lines4 ,by bringing the wing spars 'together at the tips1 the spars themselves form a triangle to resist the drag stresses4 ,fig4 #e is the common form of sweep back or retreated wing as used in the ,standard ,h-#c training biplane1 and several other modern biplanes4 ,while this arrangement undoubtedly assists longitudinal stability1 it causes certain losses that will be described later4 ,the inherently stable ,dunne is shown by ,fig4 #f in which the sweep back is increased to almost #ij degrees4 ,in fact the retreat is so great that no tail or stabilizing surfaces are used at all1 the elevator functions being performed by the ailerons4 ,it should be noted that the swept back tips really act as stabilizers since they trail back far behind the center of gravity and center of pressure4 ,the ailerons 7a7 are not needed for lateral balance1 hence ascent and descent--and also turning in a horizontal plane--are performed by the ailerons in setting them in different relative positions4 ,being far to the rear they are very effective elevators1 although their action and the extreme retreat of the wings1 causes a considerable drag4 ,this is somewhat offset by the absence of tail resistance4 ,an ,austrian or ,german ,taube is shown by ,fig4 #g with the negative trailing wing tips 7a71 that greatly assist longitudinal stability1 but which are decidedly inefficient4 ,this is evidenced by the fact that neither the ,germans nor ,austrians build this machine at present--at least for active service4 ,the tips 7a7 are bent up at the rear and thus form a negative angle of incidence with the main lifting surface4 ,this was the original invention of ,igo ,etrich1 an ,austrian1 and as with everything else1 the idea was promptly grabbed by the ,germans at the beginning of the war and claimed as their own idea4 ,etrich was one of the pioneers in aviation1 a science that did not prosper in ,germany until the impracticability of the ,zeppelin for universal service was an accepted fact4 ,illustration3 ,figs4 #a-i4 ,plan ,views of ,different ,wing ,arrangements and ,wing ,outlines4 ,fig4 #h is the wing outline of the ,bleriot monoplane1 a representative wing used on the earlier monoplanes4 ,this is really reversed rake1 and hence does not stand for efficiency in lift4 ,a tandem aeroplane is shown by ,fig4 #i in which the leading surface is 7m7 and the trailing wing is 7n74 ,the tail 7t7 may1 or may not be included4 ,this is a type that has been neglected in its practical development although it has been repeatedly proposed4 ,the ,langley machine1 the ,montgomery glider1 and the ,richardson are of this type4 ,in all the figures the wing ribs are indicated by the thin full lines passing across the width of the wing1 with the tail at 7t74 ,the arrow represents the line of flight4 ,it will be noted that with any but rectangular wing outlines the rib lengths are different1 throughout the wing4 ,this makes this wing a bad manufacturing proposition1 and a difficult and expensive wing to repair4 ,to provide against emergencies the aviator must keep a complete extra wing in reserve for repair parts1 while the manufacturer is put to the expense of a great number of rib molds1 and must also keep a large number of ribs in stock4 ,there is a constant difficulty due to the fact that mistakes are often made in ordering the ribs for repair1 and altogether1 anything but a rectangular wing is a decided nuisance4 99,sweep ,back or ,retreat994 ,with swept back wings1 as shown in ,fig4 #e1 the center of pressure movement is peculiar4 ,the ,c4 ,p4 moves forward when reducing the incidence at small angles1 and thus tends to reduce head diving1 but at very large angles the ,c4 ,p4 again moves forward1 tending to increase the angles further and thus stall the machine4 ,this reversal of ,c4 ,p4 movement takes place at about #aj to #ab1 and the movement is sharper and further with each increase in the sweep back4 ,at ordinary angles of flight1 say at from #j to #f the forward ,c4 ,p4 movement is satisfactory1 but at low speeds and high angles stability is only partially secured1 and hence for the total performance sweep back is not to be desired4 ,the wing section used in the above investigation was an ,r4,a4,f4-#f with an aspect ratio of #f4 ,in regard to the lift coefficient ,ky1 it was noted that this factor was decreased with every degree in the angle of sweep back4 ,at the incidence angle of #d for the maximum value of ,l_/,d1 the value of ,ky decreased from #j4jjadc with a sweep back of #j 7,straight wings71 to #j4jjabj with a sweep back of #cj4 ,at the same incidence1 but with a sweep back of #aj1 the lift became3 ,ky #j4jjacj4 ,with a retreat of #bj1 ,ky- #j4jjabi4 ,the lift-drag also suffered with an increase in retreat1 this being #ag4jj with straight wings1 at #af4e at #aj1 #af4b at #bj1 and #ab4h at #cj4 ,up to1 and including a retreat of #bj1 the loss in lift-drag is not so bad1 but in the change from #bj to #cj there is a very great loss4 ,illustration3 ,fig4 #aj4 7,upper7 ,various ,angles ,made by ,wings ,during ,experiments4 7,below7 ,the ,center of ,pressure ,movement with ,varying ,angles4 ,the angle of retreat herein specified is such that each wing is moved back through an angle of one-half the total given retreat 7r7 angle in ,fig4 #e4 ,that is1 with a retreat of #cj1 each wing section makes an angle of #ae with the entering edge of a pair of straight wings4 ,it is more usual to specify the included angle between the leading edges as indicated by 7,s7 in ,fig4 #e4 ,in the upper portion of ,fig4 #aj is shown the various angles of the wings during the experiments1 while below is the ,c4 ,p4 movement according to the different angles of retreat4 ,the above is based on experiments made by ,h4 ,e4 ,rossell and ,c4 ,l4 ,brand1 assistant ,naval ,constructors1 ,u4 ,s4 ,navy1 and published in ,aerial ,age4 ,the center of pressure referred to is that at the forward point of the middle longitudinal section of each wing1 and with a given incidence the ,c4 ,p4 is thrown to the rear by about #j4b of the chord by a sweep back of #aj degrees1 and #j4d of the chord for a sweep back of #bj4 ,the center of gravity of the machine will thus have to be moved to the rear if sweep back is employed4 ,in making a turn a machine with sweep back has a natural tendency to bank up in the correct attitude1 and even a retreat of #aj will add nearly #ajj per cent to the banking tendency when compared to a pair of straight wings4 ,it will be seen that with swept back wings1 the leading edge is radial1 consequently meets the air stream at more nearly a right angle4 ,this gives more lift to the outer wing than would be the case with straight entering edges1 while the inner end losses increase correspondingly in lift and hence tends further to depress the inner tip4 ,the greatest value of sweep back is found in its resistance to side slip4 ,if the machine should be over banked1 and tend to slip down toward the inner side of the turn1 the backward angle of the inner wings will cause the entering edge to meet the side stream at more nearly right angles1 and thus tend to reduce the bank and the inner slide slip4 ,in this respect the retreat is an aid to lateral stability4 ,on the other hand1 the sweep back tends to keep the machine rolling in rough weather for side gusts then meet the inclined wing edges at an effective angle4 ,this is particularly noticeable in landing4 99,raked ,tips994 ,this subject was discussed under ,standard ,wing ,section1 but it may be repeated here1 that ,eiffel in an experiment with the ,coanda ,wing 7,eiffel #ch71 found that the ,l_/,d of the raked wing was #bj per cent higher than with the same wing in rectangular form4 ,this value would not be safe to assume with all sections4 ,illustration3 ,fig4 #aa4 ,influence of ,wash ,down on the ,rear ,wings of a ,tandem ,pair4 ,illustration3 ,fig4 #ab4 ,tandem ,arrangements ,used in ,eiffel ,experiments4 7#a7 ,chords in ,straight ,line1 7#b7 ,rear ,wing at #b4e1 7#c7 ,rear ,wing at #e4 99,tandem ,arrangement994 ,in tandem wings as shown by ,fig4 #i1 the downward wash of the front wing 7m7 will affect the rear wing 7n7 by causing a change in the relative direction of the flow4 ,if the front wings are at an incidence of 7i7 degrees 7,fig4 #aa71 the deviation or washdown of the air stream to the rear will be expressed by3 d 7#j4e;i #a74 ,if i incidence of rear wing measured from the chord of the front wing1 then the angle of incidence made by the rear chord to the horizontal will be3 ,i 7i-i'7 - 7#j4e;i #a71 where ,i is the incidence of the rear plane with the horizontal4 ,experiments by ,eiffel on tandem planes with circular cambered aerofoils gave exceedingly good results for certain combinations 7,fig4 #ab74 ,these arrangements were used1 7#a7 ,chords in a straight line 7#b71 ,rear aerofoil tilted down at a negative angle of #b4e1 7#c71 ,rear ,plane tilted down at a negative angle of #e4 ,in all cases the camber was #a_/ac4e of the chord1 and the front and rear wings were spaced two chord widths apart4 ,while the drag did not change much for any of the arrangements1 the lifts varied widely1 and arrangement 7#b7 is by far the more efficient in lifting capacity4 ,no4 #b is #ej per cent greater than 7#a71 and has twice the lifting ability of 7#c74 ,for the same angle of incidence1 the front wing does the same amount of lifting in all cases1 the difference being entirely due to the changes in the rear surface4 ,in 7#b7 the lift of the rear aerofoil is actually #ac per cent greater than the front plane4 ,the following tables give the results3 ,demo ,table ,,table ,,of ,,lifts ,,in ,,grams ,,for ,,three ,,arrangements4 ,,angle ,,of ,,arrangement ,,arrangement ,,arrangement ,,incidence 7#a7 7#b7 7#c7 #c #ffe #ajid #ccd #f #ihg #aefh #gjc #i #acae #bjfh #ife #ab #aedj #bcbf #acdg ,average at all #aabg #agfd #hcg angles ,percentage #j4fd #a4jj #j4dg ,illustration3 ,fig4 #ac4 ,drzewiecki ,tandem ,arrangement for ,longitudinal ,stability4 ,the lifts in the above table are for the two planes working together1 and the angle of incidence is the angle of the front aerofoil1 or rather the angle of the combination4 ,the wings were #ae x #ij centimeters1 aspect ratio #f4 ,fig4 #ab shows the construction clearly4 ,this is only true for circular arched surfaces of the camber given4 ,illustration3 ,fig4 #ad4 ,drzwiecki ,tandem ,wing ,arrangement for ,stability4 ,m4 ,drzewiecki working with ,eiffel's results on the above combinations1 produced an inherently stable tandem monoplane1 in which the front and rear wings were of different cambers and were set at different incidences4 ,the front wing is ,eiffel ,no4 #h set normally at #h incidence1 and the rear wing is ,eiffel ,no4 #ac-;bis 7,bleriot #aa-;bis71 set normally at #e4 ,the center of gravity is approximately half-way between the two wings1 and the front is smaller than the trailing surface4 ,because of the difference in area1 the lift of the front wing varies less rapidly than the rear when the angle of the machine changes because of disturbed air4 ,should the machine head up1 the rear wing increases faster in lift than the front1 and hence restores the machine to a horizontal position4 ,should the front surface drop1 the incidence is reduced1 but as incidence of the rear wing is less than the front 7#h71 the rear wing is reduced to nearly a zero angle of incidence--7,with little lift74 ,the front wing is still inclined at a considerable incidence3 7#c7 when the rear is at zero4 ,this drops the rear1 and raises the front wing so that the normal attitude is restored4 ,lateral stability is obtained by moving the two halves of the front wing in relation to one another1 the relative movement being similar to that of ailerons4 ,illustration3 ,typical ,wing ,assembling ,shop ,,chapter ,,ix4 ,,wing ,,construction4 99,general ,wing ,frame ,layout994 ,in many ways1 the frame of the wing is one of the most important structural parts of the aeroplane4 ,it not only maintains the proper aerodynamic form of the aerofoil1 but also transmits the air pressure and lift to the body of the machine1 and therefore carries the entire weight of the aeroplane when in flight4 ,in spite of the heavy loading on this frame it has been brought to a remarkable degree of strength and lightness4 ,not only is ,brute strength necessary1 but it must also be rigid enough to properly retain the outlines of the aerofoil with the heaviest loadings1 hence the efficiency of the aeroplane greatly depends upon the stiffness as well as strength4 ,the contour of the entering edge must be particularly accurate and well supported since it is at this point that the greater part of the lift is obtained1 and where a slight deviation in form will materially affect the lift and drag4 ,the fabric surface1 on which the air pressure is exerted1 must transmit the pressure and lift to the main structural members through the parts that give form to the surface4 ,the fabric surfacing1 being flexible and pliant1 must be supported at frequent intervals by the forming members which in effect are similar to the joists of a floor system4 ,the forming members are then supported in turn by longitudinal beams1 or girders1 that transmit the pressure to the point where the load is applied4 ,the girders not only carry the lifting force1 but must also take care of the drag which acts at right angles to the lift4 ,to pass girders that are sufficiently strong1 and yet within the limits of weight1 through the narrow space between the top and bottom surfaces of the wing is not always the simplest of problems4 ,figs4 #a and #b show typical wing frames in diagrammatic form1 the upper views are the plans1 while at the bottom are sections taken through the wing4 ,the outlines of the sections are curved to the outlines of the aerofoil adopted for the wings1 and after this outline is drawn out to scale1 we must maneuver our structural members so that they will lie entirely between the surfaces4 ,in ,fig4 #a1 the forming ribs are indicated by ,r1 these being the members curved to the aerofoil form4 ,they are spaced along the length of the wing at intervals of about one foot and the fabric is applied to the top and bottom edges of the rib4 ,the ribs are fastened to the front spar ,f1 and the rear spar ,s4 ,the spars are equivalent to beams1 and are for the purpose of transmitting the lift of the ribs to the body4 ,a thin strip ,e 7nosing7 running along the entering edge of the wing1 serves to hold the fabric taut at this point and also forms it to the shape of the aerofoil entering edge4 ,the thin trailing edge strip 7,t7 performs the same purpose1 and the wing outline is completed by the ,end bow 7,a7 which retains the fabric at the wing tips4 ,between the front spar ,f and the rear spar ,s is the trussed ,drag bracing1 which binds the two spars into a truss in a horizontal direction1 and against the drag of the surfaces4 ,this consists of the ,drag wires or cables 7d7 and the short wood struts 7e71 although in many cases the ribs are strengthened at the point of attachment of the drag wires and serve as struts4 ,the aileron ,g is located at the outer tip and is hinged to the rear spar or to an extension of the rear spar4 ,between the spars are thin strips known as battens which stiffen the ribs sideways1 these are shown by 7,f74 ,illustration3 ,fig4 #a4 7,left7 ,wing ,assembly with ,spar to the ,rear of the ,entering ,edge4 ,fig4 #b4 7,right7 ,assembly with the ,front ,spar at the ,entering ,edge4 ,metal connection clips ,c1 at the end of the wing spars1 are for attaching the wings to the body1 or for connection of the two halves of the upper wing of a biplane4 ,looking at the lower sectional view we see the interplane struts of a biplane attached to the front and rear spars as at 7m7 and 7n74 ,referring to the plan view1 the location of the struts is indicated by 99 99 99 at the points where the drag-bracing is attached to the spars4 ,fig4 #b is a form of wing in which the spar ,f' also forms the entering edge1 thus eliminating one part of the wing4 ,one objection to this construction is that the front spar must necessarily be shallower than the spar shown in ,fig4 #a4 ,the rear spar is in the usual location at ,s'1 the two spars being connected through the usual end bow ,a'4 ,the trailing edge ,t' may be either a thin strip1 or it may be a thin cable as indicated4 ,this wing is similar to the wing used on the early ,wright machines1 and is still used by ,farman1 ,voisin and other ,european manufacturers of biplanes4 ,usually the trailing ends of the ribs overhang the rear spar for quite a distance1 in this type of wing1 giving a flexible trailing edge4 ,the front and rear interplane struts 7m7 and 7n7 are shown1 the former connecting with the front spar at a point near the entering edge4 ,illustration3 ,fig4 #c4 ,sub-,rib ,construction1 the ,sub-,ribs 7r7 ,are ,placed at the ,entering ,edge4 ,fig4 #c shows the usual construction except that short ,sub-ribs marked 7r7 are placed between the main ribs ,r at the entering edge4 ,these short ribs increase the support and accuracy of the curve at the entering edge1 or else allow wider spacing of the main ribs ,r4 ,the fabric must be well supported at this point1 not only to maintain the best efficiency of the aerofoil1 but to relieve the stress on the fabric1 as it is here 7,top surface7 that the greatest suction pressure comes4 ,should there be a rip or tear near the entering edge1 in the lower surface1 the upper fabric will be subjected to both the pressure underneath and the vacuum above4 ,this adds fully #be per cent to the load on the upper facing4 ,the main spars may be of wood or steel tubing1 although the former material is generally used4 ,they are of a variety of forms1 the ,i beam section1 solid rectangular1 hollow box1 or a combination of plate and ,i sections1 the total object being to obtain the greatest strength with the least possible weight4 ,when made up of several pieces of wood they are known as ,built up spars4 ,illustration3 ,fig4 #d4 ,effects of ,c4,p4 ,movement on ,spar ,loading ,the load on the spars varies with the total weight carried1 and also with the movement of the center of pressure due to changes in the angle of incidence4 ,when the center of pressure moves to any extent1 the loads on the two spars may vary between wide limits1 and in extreme cases1 either spar may carry the full load4 ,this is shown clearly by ,fig4 #d1 a section taken through the wing4 ,the front spar ,f and the rear spar ,s are spaced by the distance ,l1 the respective spar loads being indicated by ,y and ,z4 ,as before explained1 the center of pressure moves forward at large angles 7,,cp71 while at small angles it moves back say to position 7,,cp'74 ,should it move back as far as ,,cp-#b1 the load will come directly under the rear spar and this member will therefore carry the entire load4 ,when at the forward position ,,cp1 the greater part of the load will come on the front spar1 and only a small portion will now come on ,s4 ,in the same way1 when at a small angle of incidence1 the center of pressure will be at ,,cp'1 a distance 7,k7 from the rear spar4 ,the greater part of the load will now be on ,s4 ,the action is the same as if the entire weight ,w or lift1 were concentrated at the center of pressure4 ,when intermediate between the two spars1 the center of pressure causes a bending moment in the rib ,r1 and is at a maximum when the ,,cp is midway between the two spars4 ,it will be seen that the ,c4 ,p4 movement has an important effect outside of the question of stability1 and this travel must be taken into careful consideration when the strength of the spars is calculated4 ,to find the load on the rear spar1 for example1 with the center of pressure at ,,cp1 multiply the lift ,w by the distance ,p1 and divide by the spar spacing ,l4 ,this will give the load ,z4 ,with the ,c4 ,p4 in the same position1 the load on the front spar will be the difference between the total lift ,w and the load on the rear spar1 or ,y ,w-,z4 ,with the load at ,,cp'1 the load on the front spar will be3 ,y ,wx,k_/,l1 and the load on ,s will be ,z ,w - ,y4 ,for example1 we will assume that the lift ,w #ajjj pounds1 and the distance ,p #ab inches4 ,the spar spacing ,l #cj inches and the center pressure is at ,,cp4 ,the load ,z on the rear spar1 will be3 ,z ,wx,p_/,l #ajjj x #ab_/cj #djj pounds4 ,the load on the front spar can be found from the formula1 ,y ,w - ,z #ajjj-djj #fjj pounds4 ,illustration3 ,fig4 #e4 ,perspective ,view of ,wing ,construction 7,rear ,spar ,omitted71 ,showing ,hollowed ,entering ,edge and ,built-,up ,spar4 ,rib ,is of the ,i ,beam ,type4 ,courtesy ,flight4 ,fig4 #e4 shows a typical form of wing construction 7rear spar omitted74 ,the front spar is of the ,built up type1 and the trailing edge is a flattened steel tube4 ,the rear spar is simply a solid rectangular beam4 ,a central ash ,i beam is used as the front spar1 with vertical spruce plates on either side4 ,the spruce entering edge1 or nosing1 is formed to the shape of the entering edge and is hollowed out for lightness4 ,the rib is also of the built up type1 the upper and lower flanges are of spruce and the middle portion 7,web7 is cotton-wood4 ,at the point where the spar passes through the rib1 the rib flanges pass over1 and are tacked to the spar4 ,the spruce nosing fits closely over the front web of the rib4 ,the rib flanges are cut away so that the outside of the nosing will come flush with the flange line of the rib4 ,illustration3 ,fig4 #f4 ,caudron ,monoplane ,wing with ,steel ,tube ,spars and ,flexible ,trailing ,edge4 ,a ,slot in the ,rear of the ,rib ,web ,permits the ,deflection of the ,trailing ,edge4 ,drag ,wire ,bracing ,is ,used ,between the ,front and ,rear ,spars4 ,courtesy ,flight4 ,a wing of decidedly different construction is the ,caudron monoplane wing shown by ,fig4 #f1 the front and rear spars of this wing being steel tubes with an entering edge of thin wood4 ,the drag bracing wires may be seen connected at alternate ribs by small steel plates and the latter also serve to attach the ribs to the spars4 ,instead of being cut out entirely1 the webs of the ribs are hollowed out between the spars4 ,probably the most unique feature is the construction of the long flexible trailing ends of the rib at the right4 ,the trailing rib edge is divided into an upper and lower section by a long slot1 the upper sections being rigid1 while the lower edge is thin and flexible4 ,the flexible edges allow the lower ends of the ribs to give locally1 and reduce the camber when struck by a heavy gust4 ,this aids in the lateral stability1 since the lift is thus considerably reduced at the point of impact1 and it also relieves the wing of unnecessary stresses4 ,the rigid upper section of the rib acts as a limit stop to the lower half1 and prevents the flexure from exceeding a certain amount4 ,owing to the flexibility of the trailing edges a steel wire or cable must be used for the trailing edge4 ,illustration3 ,fig4 #g4 ,standard ,h-#c ,wing ,construction4 ,spar1 ,rib and ,drag ,strut ,connections at ,left4 ,body ,connection ,fitting or ,hinge at ,right4 ,note ,drag ,wire ,fittings4 ,courtesy ,aerial ,age4 ,details of the framing of the ,standard ,h-#c are shown by ,fig4 #g4 ,the figure at the left gives a clear idea of the connections between the drag struts and spar1 while the view at the right shows the body connection at the end of the spar4 ,i am indebted to ,aerial ,age for these sketches4 ,the main spar is in a solid piece1 channeled out to ,i beam form1 except at the point where the spruce drag strut is attached4 ,at the end of this strut is attached a sheet steel fitting that affords a means of connecting the drag wires1 and for fastening the strut to the main wing spar4 ,at the point of attachment1 wooden plates are fastened to either side of the spar4 ,these prevent the fitting bolts and the fitting from sliding along the spar when subjected to an uneven pull in the wires4 ,a veneer top and bottom plate still further strengthen this joint and hold the sub-rib in place4 ,the main ribs are strengthened1 at the point where the spar passes through the rib web1 by small vertical blocks4 ,in the right hand figure the steel clevis is shown bolted to the spar4 ,a lug for the wing drag wire is brought out from the fitting4 ,the clevis on the wing engages with a similar clevis on the body of the machine1 and the two are fastened together with a bolt or pin4 ,illustration3 ,fig4 #h4 ,typical ,biplane ,wing4 ,gap for ,aileron ,shown at ,right ,end of ,wing4 ,left ,end ,rests ,against ,fuselage1 the ,observation ,port ,being ,cut ,out at the ,upper ,left ,hand ,corner4 ,drag ,wire ,bracing ,clearly ,shown4 ,courtesy ,aerial ,age4 ,fig4 #h is a photograph of a biplane wing with the framing members completed and ready for the application of the fabric4 ,at the right is the opening left for the aileron1 and at the left is the observation port1 the latter coming next to the body4 ,as this is a lower wing1 the sockets for the attachment of the interplane struts can be seen on the upper and near edges of the main spar4 ,between the spars are very thin wood strips running with the length of the wing4 ,these are the ,battens used for stiffening the ribs between the points of support at the spars4 ,as the distance between the spars is comparatively great1 in respect to the thickness of the rib flanges1 some sidewise support of this kind is necessary4 ,the drag-bracing cables cross three rib spaces1 or are fastened to every fourth rib4 ,between the front spar 7at the bottom71 and the entering edge1 are the small strips that serve as sub-ribs4 ,double cross bracing is used at the inner end of the wing 7left71 while additional knee braces are placed at the aileron opening1 and at the outer tips4 ,this is necessary to withstand the stresses due to assembling and handling1 rather than for the flight stresses4 ,fig4 #i is a ,standard ,wing ready for covering4 ,before the fabric is applied1 a narrow cloth strip is wrapped over the trailing edge1 as shown1 and is stitched to the frame4 ,this forms a means of stitching the main covering at the rear edge1 where the ends of the upper and lower surfaces meet4 99,wing ,fabric or ,covering994 ,at the present time unbleached ,irish linen is used almost exclusively for covering the wing structure1 although in the early days of flying rubberized fabrics were used to a great extent4 ,illustration3 ,fig4 #i4 ,standard ,h-#c ,wing ,ready for ,covering4 ,opening for ,aileron ,flap ,shown at ,upper ,left ,hand ,edge 7,trailing ,edge74 ,after the linen is stretched on the wing frame1 it is given several coats of a special preparation commonly known as ,dope to proof the fabric against moisture4 ,in addition to waterproofing1 the dope adds considerably to the strength of the fabric and shrinks it tightly on the ribs--much more evenly than could be done by hand4 ,when completely ,doped1 the linen should be proof against the effects of salt water1 moisture1 or extreme dryness1 and the fabric must be ,drum tight at every point on the surface of the wing4 ,the linen should have a tensile strength of at least #ge pounds per inch of width in any direction1 and weigh from #c4ge to #d4d ounces per square yard4 ,it must be wet spun1 free from filling matter and uncalendered4 ,as a usual thing1 the width should not be less than #cf inches1 although the width can be altered to meet conditions of rib spacing1 etc4 ,the ,u4,s4,a4 seaplane specifications 7#aiaf7 require a minimum strength along the warp of #ge pounds per inch width1 and #he pounds per inch of width along the weft4 ,the following table gives the properties of well known wing fabrics3 99,wing ,dope994 ,wing dopes are in nearly every case based on cellulose--either cellulose acetate or nitrate being the most common base4 ,this has proven far superior to the resin1 copal1 gum or oil bases contained in ordinary varnish1 since the cellulose of the dope seems to amalgamate with the cellulose of the flax fiber and bond the whole into an integral structure4 ,the fact that the dope must be elastic bars the use of shellac or other hard resin solutions4 ,the solvents used for the cellulose dopes vary with the makers1 some using amyl-acetate1 tetrachlorethane1 etc41 while others use special secret compounds that are best adapted for their bases4 ,many of the solvents give off poisonous gases in drying1 and this must be guarded against by good ventilation4 ,the vapor of tetrachlorethane is particularly dangerous1 and has resulted in many deaths4 ,illustration3 ,fig4 #aj4 ,complete ,framing ,plan of ,typical ,monoplane ,structure4 7,a7 ,pilot4 7,b7 ,passenger4 7,m7 ,motor4 7,s7 ,stabilizer4 7,e7 ,elevator4 7,r7 ,vertical ,rudder4 ,doped surfaces have from #aj to #be per cent greater tensile strength and resistance to tearing than the undoped linen1 and increases the weight of the fabric by about #j4g ounce per square yard for each coat applied4 ,under ordinary weather conditions1 dope will require from #bj to #dj minutes per coat for drying1 and at least one-half hour should be allowed between each coat4 ,weather conditions have a great effect on the action of dope1 and with cellulose compounds the best results are obtained in a clean dry room1 well warmed1 and without drafts4 ,on rainy days the linen is damp and the dope does not set well1 and this trouble is not greatly helped by artificial heat4 ,drafts cause white spots and streaks1 especially if cold air is allowed to enter directly upon the warm wing surface4 ,to prevent drafts the ventilating ducts should be near the floor1 and as the vapor is heavier than the air1 and flows downwards1 this means of ventilation is entirely practicable4 99,applying the ,dope994 ,the number of coats depend upon the character of the job1 but at least five coats should be applied1 and preferably seven4 ,on the best grade of work1 the dope is generally covered with three or more final coats of spar varnish1 although this is not absolutely necessary4 ,for ordinary work1 dope alone on ,irish linen has proved very satisfactory for land machines1 five coats being the usual amount applied on exhibition aeroplanes and planes for amateur use4 ,seven coats of dope with three coats of spar varnish are specified for military machines that are to be used on salt water4 ,seaplanes are subjected to conditions that are particularly hard on fabric and must be protected accordingly4 ,in applying the dope1 at least one-half hour should be allowed for drying between each coat1 and more if possible4 ,the first two coats should be painted on lightly1 the purpose being simply to fill the pores of the fabric and to prevent the succeeding coats from sinking through4 ,if the first two coats are too heavy1 the dope filters through the mesh of the linen and drops on the lower surface1 causing spots and a waste of a very expensive material4 ,dope is expensive even with the greatest care exercised in its application1 and the writer has seen cases where the first two coats were so heavily applied that fully #ej per cent of the fluid ran through and caked in among the structural parts of the machine4 ,this ran the doping expense up to a terrific figure4 ,the cloth should be dry1 and the work performed1 if possible1 on a dry day4 ,to save dope1 never take out of the supply drum more than can be used for one coat1 for the dope soon becomes tacky on exposure to the air1 and a satisfactory job is hard to obtain if it gets in this condition4 ,illustration3 ,fig4 #aj;a4 ,testing the ,wing ,structure of a ,curtiss ,biplane by ,means of ,sand ,bag ,loading4 ,the ,wings ,are ,turned ,upside ,down and a ,sand ,load ,is ,laid ,uniformly ,over the ,wings4 ,so ,that ,they ,produce a ,load ,equal to1 or ,greater ,than1 the ,flight ,load4 ,in placing the fabric on the wings1 particular care must be taken in stretching so as not to have it too tight when cellulose dope is used4 ,the dope shrinks the linen to a very considerable extent1 and if it is too tight to begin with1 the stress due to shrinkage will place an excessive stress on both the fabric and the structure4 ,when of the proper tautness1 the fabric should sound like a drum when snapped with the finger4 ,any less tension than this will permit the fabric to sag badly when under the air pressure and reduce the efficiency of the wings4 ,in fastening the cloth it should be just stretched taut and no more4 ,in damp weather the cloth can be stretched a little tighter than in dry weather4 99,transparent ,coverings994 ,in some types of battle-planes and scouts1 a part of the wing section directly above the pilot is covered with a transparent fireproof cellulose sheet1 much resembling celluloid4 ,this permits the pilot to see above him through the overhanging wing1 and is of great value in action4 ,in some cases1 a strip is placed on the lower wings along the sides of the body so that the ground is also easily visible4 ,these cellulose sheets will not crack nor splinter1 and are nearly as flexible as rubber4 ,celluloid of the ordinary variety must not be used1 for this is easily ignited and is likely to start a disastrous fire4 99,placing the ,fabric on the ,wings994 ,in some aeroplanes the seams of the fabric are run parallel to the ribs1 and are tacked or sewed directly to them1 while in other cases the seams are run diagonally across the plane or on the bias4 ,diagonal seams are most satisfactory1 and if care is taken there is no more waste of linen than with the straight seam4 ,the seams should be of the double-lapped or ,english welt type1 and this of course necessitates sewing before the fabric is placed on the wings4 ,the seams used on overcoats are satisfactory for this purpose1 and give a covering that will not stretch nor bag4 ,some use linen thread and others use silk1 but the linen is preferable1 since dope often causes silk to rot4 ,the seams should be covered with linen to protect them from the weather and to prevent the entrance of water to the interior woodwork4 ,ordinarily1 the wing is turned upside down for covering1 with the concave side uppermost4 ,the seams are sewed together so that the completed fabric is wider than the length of the wing and is a little longer than is necessary to wrap entirely around the width of the wing4 ,the fabric is then temporarily fastened along the trailing edge1 is passed under the wing to the front edge1 and over the concave upper side back to the trailing edge4 ,at this point the excess material will hang down over the rear edge4 ,with the wing in its upside down position1 the convex side will be at the bottom1 and if a weight is hung on the overhanging material at the rear edge1 the cloth will be pulled tight against the lower convex side and straight across and above the concave side4 ,the fabric at the top is then stretched along the cordal line of the ribs4 ,by laying a narrow board on top of the fabric1 and near the entering edge1 the fabric can be brought down uniformly along the concave edge of the ribs1 and by tacking or sewing as the board is moved back the concave face can be covered without further trouble4 ,after the concave face is disposed of1 the wing can be turned over and the fabric is then fastened to the convex side of the ribs4 ,illustration3 ,fig4 #aa4 ,method of ,stretching ,fabric on ,wings4 ,fabric ,passes ,under and ,then ,over ,concave ,side and ,is ,pressed ,down into ,hollow by a ,board as ,shown4 ,one method of fastening the linen is to lay tape over the ribs1 and then drive tacks through the tape and fabric into the rib4 ,the tape keeps the tacks from tearing through the linen4 ,the tape should be heavy linen of from #c_/d to #a #a_/d inches wide1 and laid in cellulose before tacking1 so that the tape will be cemented to the fabric and the solution will be driven into the tack holes4 ,after the tape is in place1 it should be covered with not less than three coats of cellulose dope before the main surface is treated4 ,this gives an additional three coats over the tape where it is most needed for protection against moisture4 ,in any case1 the seam or tacking strip should be pressed down so that it projects as little as possible above the general surface of the wing4 ,tacking is not desirable1 for tacks and nails always tend to split the thin members of the rib1 and very often corrode the cloth and weaken the fabric4 ,this has resulted in the whole fabric being ripped off while in flight4 ,iron or steel tacks should never be used1 as they destroy the strength of the fabric very rapidly by the formation of rust1 and particularly with sea-planes used on salt water4 ,sewing the fabric to the ribs with linen thread is the most satisfactory method and is in general use among high-grade builders4 ,the fabric can be stitched to bands of thread or tape1 the latter being wrapped about the rib4 ,stitches can also be taken from one surface straight through to the other4 ,the thread or tape bands on the ribs are merely wrappings taken around the rib flange1 and through the lightening holes1 these bands usually being about #d inches apart4 ,they at once tie the flange to the web and form a soft surface into which to take the stitches4 ,fig4 #d in ,chapter ,x shows the thread bands 7d7 wrapped around the rib flange 7,g71 and through the lightening hole1 the fabric lying above and below the rib flanges as shown4 ,a section view through the rib and fabric is shown at the right4 99,varnishing994 ,when varnish is to be used over the dope1 only the best grade of spar varnish should be used1 since any other kind is soon destroyed by moisture4 ,from two to three varnish coats will be sufficient1 and each coat should be thoroughly dried and sandpapered before the next is applied1 care being taken not to injure the fabric with the sandpaper4 ,sandpapering between the dope layers is not necessary1 since each successive coat partially dissolves the preceding coat1 and thus welds the layers together4 ,varnish1 however1 does not act in this way1 and the coats must be roughened4 ,shellac rots the linen and should not be used4 ,the ,government specifies one coat of flexible white enamel in which a small quantity of lead chromate is mixed4 ,this is applied over the last coat of varnish4 ,the lead chromate filters out the actinic rays of the sun1 thus reducing the injurious effect of the sunlight on the covering4 ,if coloring matter is added to the dope1 it should be in liquid form1 as powders destroy the strength and texture of the dope deposit4 ,illustration3 ,fig4 #ab4 ,wing ,structure of ,handley-,page ,giant ,biplane4 ,courtesy ,aerial ,age4 99,patching ,fabric994 ,the majority of dopes can be used as cement for patching1 but as dope will not stick to varnish1 all of the varnish around the patch must be thoroughly removed with some good varnish remover4 ,the varnish must be thoroughly cleaned off or there will be no results4 ,before applying the dope1 the patch must be well stitched all around the edges1 then cemented with the dope4 ,the patch must now be covered with at least five coats of thin dope as in finishing the surface4 ,particular attention must be paid to filling the dope in the stitching4 ,,chapter ,x4 ,,wing ,,construction ,,details4 99,types of ,ribs994 ,the rib first used by the ,wright ,brothers consisted of two spruce strips separated by a series of small pine blocks4 ,practically the same construction was used by ,etrich in ,austria4 ,with the coming of the monoplane1 and its deep heavy spars1 the old ,wright rib was no longer suitable for the blocks were not efficient in thick wing sections4 ,the changes in the wing form then led to the almost universal adoption of the ,i type rib in which an upper and lower flange strip are separated by a thin vertical web of wood4 ,at present the ,i rib is used on nearly every well known machine4 ,it is very strong and light1 and is capable of taking up the end thrust of the drag wires1 as well as taking care of the bending stresses due to the vertical loading or lift4 ,fig4 #a shows the original ,wright rib with the ,battens or flanges 7g7 and the spacing blocks ,b4 ,the front spar is at the leading edge 7,f71 and the rear spar at ,s4 ,an ,i beam1 or ,monoplane type is shown by ,fig4 #b1 and as will be seen is more suitable for deep spars such as 7,f'7 and ,s'4 ,the upper and lower flanges 7g7 are separated by the thin perforated web 7w71 the sectional view at the right showing the connection between the flanges and the web4 ,lightening holes 7h7 reduce the weight of the web1 with enough material left along the center of the web to resist the horizontal forces4 ,the web is glued into a slot cut in the flanges1 and the flanges are then either tacked to the web with fine nails1 or bound to it by turns of thread around the flange4 ,on the average machine1 the web is about #c_/af thick1 while the flanges are from #c_/d to #a inch wide1 and from #c_/af to #a_/d inch thick4 ,on the very large machines1 the dimensions of course are materially increased4 ,at the strut locations in biplanes1 and the point of cable bracing attachment in monoplanes1 the ribs are increased in strength unless the end thrust of the stay wires is taken up by a separate strut4 ,at the point of stay connection in the old ,nieuport monoplane the rib was provided with a double web thus making a hollow box form of section great enough to account for the diagonal pull of the stays4 ,illustration3 ,fig4 #a4 ,wright ,type ,rib with ,battens and ,block ,separators4 ,fig4 #b4 ,monoplane or ,i ,type of ,rib with ,solid ,web4 ,fig4 #c shows the ,nieuport monoplane ribs1 which are good examples of box ribs4 ,the sections at the left are taken through the center of the ribs4 ,the wing chord tapers from the body to the wing tip1 while the thickness of the wing section is greatest at the middle1 and tapers down both toward the tips and toward the body4 ,the upper section is located at the body1 the second is located midway between the body and the tip1 and the other two are near the tips1 the bottom being the last rib at the outer end4 ,the ribs shown are of box form as they are at points of connection1 but the intermediate ribs are of the ,i type shown by ,fig4 #b4 ,illustration3 ,fig4 #c4 ,nieuport ,monoplane ,ribs4 ,this ,wing ,is ,thickest in the ,center and ,washes ,qut ,toward ,either ,end1 ,thus ,making ,all of the ,ribs ,different in ,curvature and ,thickness4 ,at the ,point of ,stay ,wire ,attachment ,double ,webbed ,box ,ribs ,are ,used4 99,rib ,material994 ,in ,american aeroplanes1 the flanges of the ribs are generally made of spruce4 ,the webs are of poplar1 whitewood1 cottonwood or similar light material4 ,there is not a great deal of stress on a rib1 and the strongest material is not necessary1 but as there are a great many ribs in a wing assembly lightness is a primary consideration4 ,a few ounces difference on each rib makes a great deal of difference in the total weight1 especially when there are #hj or more ribs in a complete machine4 ,exception to the above materials will be found in the ,curtiss ,super-,american ,flying ,cruiser which has ribs with pine webs and birch flanges4 ,european aeroplane practice makes use of hardwood in the ribs4 99,web ,stiffeners994 ,the webs being thin and deep1 and cut for lightening as well1 need bracing at the points where concentrated loads are placed1 such as at the front and rear spars1 and at points between the lightening holes4 ,by gluing thin strips to the webs 7in a vertical direction71 and so that the tops and bottoms of the strips come tight against the upper and lower flanges1 a great deal of the strain on the web can be avoided4 ,the stiffening blocks are shown by 7x7 in ,fig4 #d1 and are placed on both sides of the front and rear spars ,f and ,s1 and also between the lightening holes ,h4 ,illustration3 ,fig4 #d4 ,details of ,i ,type ,rib1 ,showing ,lightening ,holes and ,stiffeners4 99,flange ,fastenings994 ,in the section at the right of ,fig4 #d it will be seen that the web is inserted into a groove cut in the flanges and is then glued into place4 ,it would be unsafe to trust entirely to the glue1 owing to the effects of aging1 moisture and heat1 and consequently some additional means of fastening must be had4 ,it has been customary to nail through the flange into the web1 but as the web is only about #c_/af inch thick it is likely to split4 ,an approved method is shown in ,fig4 #d in which ,irish linen thread wraps 7d7 are passed through the lightening holes 7,h71 and over the flanges 7,g74 ,the thread is coated with glue before wrapping and after1 and when dry it is thoroughly varnished for protection against moisture4 ,the bands are spaced from #c to #d inches apart4 ,if nails are used they should be brass nails--never steel or iron4 ,at the points 7,f7 and 7,s7 where the spars pass through the web1 the web is entirely cut out so that the flanges ordinarily lie directly on the spars4 ,in this case it is necessary to bevel the spar so that it at least approximately fits the curve of the flange4 ,sometimes when a full size spar is impossible1 as in cases where the spar tapers toward the tips1 wood packing pieces may be placed between the flange and the spar2 tapered to make up for the curve4 ,the flanges in any case must be securely fastened to the spar by brass wood screws as at 7e71 and the edges of the web should fit tightly against the sides of the spars4 99,wing ,battens994 ,the wing battens run along the length of the wings1 from end to end1 and between the spars1 and serve to brace the ribs sideways as shown in some of the general views of the wing assembly4 ,to accommodate the battens1 the openings 7f7 are cut directly under the flange4 ,usually the battens are thin spruce strips from #c_/af to #a_/d inch thick and #a_/b inch wide1 and should be run through the web at a point near the stiffeners4 ,the thickness from the top of the flange to the under side of the lightening hole is from #a_/b to #c_/d inch as indicated by 7,c74 99,strength of ,wood ,ribs994 ,the strength of a rib for any individual case can be found by the method used in computing beams1 the rib usually being assumed to have a uniformly distributed load1 although this is not actually the case1 as before explained4 ,the greater part of the load in normal flight is near the front spar1 but this shifts back and forth with the angle of incidence so that there is no real stationary point of application1 and the rib must be figured for the maximum condition4 ,the total load carried by one of the intermediate ribs is due to the area between the ribs1 or to the unit loading multiplied by the rib spacing and chord4 ,the portion of the rib between the spars can be calculated as a uniformly loaded beam1 supported at both ends4 ,the entering edge in front of the spar1 and the trailing edge to the rear may be taken as uniformly loaded beams supported at one end4 ,the proportion of the loads coming on the ends and center position can be taken from the pressure distribution diagrams as shown under ,aerofoils4 ,a number of tests were made on ribs by ,mr4 ,heinrich of the ,heinrich ,aeroplane ,company1 the ribs being built up on short pieces of spar so that actual conditions were approached4 ,instead of using a distributed load1 such as usually comes on the rib1 a concentrated load was placed at the center4 ,if the rib were uniform in section the equivalent uniformly distributed load could be taken as one-half the concentrated load1 but because of the lightening holes this would not be very exact4 ,it would be on the safe side1 however1 as such a test would be more severe than with a uniform load4 ,the ribs were of the same type as shown in ,fig4 #e1 and were placed #cb4e inches apart4 ,the front spar was #b #g_/af inches deep1 the rear spar #b #a_/af inches deep1 and the overall depth of the rib at the center was #c #a_/h inches4 ,the rib flanges were of white wood #c_/d inch wide1 and #c_/af inch thick4 ,in rib ,no4 #a the web was solid whitewood1 #c_/af inch thick1 and in ribs ,nos4 #b and #c1 the webs were mahogany three-ply veneer 7#e_/cb inch thick74 99,test of ,rib ,no4 #a994 ,there are #e lightening holes between spars1 with #b inches of material left between the holes1 and #a_/b inch between first hole and front spar opening4 ,with #ie pounds concentrated load at the center1 the first rupture appeared as a split between the first hole and spar opening4 ,at #aai pounds1 the flanges had pulled away from one side of the spar1 and #a_/h inch away from the web4 ,full failure at #abg4e pounds4 ,web was split between each lightening hole with a complete cross break at center of web1 the latter being caused by a brad hole in the web4 99,test of ,rib ,no4 #b994 ,laminated web1 with no brads driven opposite lightening holes4 ,at #adj pounds rib deflected #e_/af inch1 and when relieved sprang back only #c_/af inch4 ,with #age pounds1 the deflection again was #e_/af inch1 but the rib continued to bend slowly1 the flanges pulling away from the web and spars4 ,the wood was not broken anywhere1 the failure being in the brads and glue4 99,test of ,rib ,no4 #c994 ,same materials as ,no4 #b1 but web was fitted inside of the ,i beam spar and the rib flanges were screwed to the spar4 ,at #age pounds there was no sign of rupture anywhere1 and the deflection was #e_/af inch4 ,at #ahe pounds the rib broke very suddenly and cleanly1 and in such a way as to indicate that this was the true strength of the rib4 ,the normal loading on the rib in flight was #ag4e pounds1 uniformly distributed1 so that with a concentrated load of #cgj pounds equivalent1 the safety factor was #ba4a4 ,the conclusions to be arrived at from this test are as follows3 7#a7 ,when a solid soft wood web is used1 there should be at least #b #a_/b to #c inches between lightening holes4 7#b7 ,a laminated or three-ply web is the best4 7#c7 ,no brads should be driven opposite lightening holes4 7#d7 ,the web should fit closely to the spar sides and the flange of the rib should be tightly screwed to the top and bottom of spar4 ,the above gives an idea as to the strength of the usual form of wood rib1 and can be used comparatively for other cases if the reader is not familiar with strength calculations4 ,illustration3 ,fig4 #g4 ,rib ,bending ,press for ,curving the ,rib ,flanges4 99,making the ,rib994 ,wooden webs are cut out on the band saw1 and the webs are so simple that there is not much more to be said on the subject4 ,the flanges1 however1 must be steamed and bent to the nearly correct form before assembly4 ,after planing to size and cutting the groove for the reception of the web1 the ribs are placed in the steamer and thoroughly steamed for at least an hour4 ,a rib flange press shown by ,fig4 #g consists of two heavy blocks with the inner faces cut approximately to the rib outline4 ,the steamed ribs are then placed between the blocks1 the bolts are screwed down tight1 and is left for #bd hours so that the strips have ample time to cool and dry4 ,for the amateur or small builder1 the steamer can be made of a galvanized down-spout connected with an opening cut in the top of an ordinary wash boiler4 ,one end of the spout is permanently sealed1 while the other is provided with a removable cover so that the strips can be inserted4 ,a hole cut near the center of the spout is connected to the opening in the boiler cover by a short length of spouting or pipe4 ,the spout should be made large enough in diameter to contain all of the ribs that can be pressed at one time1 and should be long enough to accommodate longer pieces such as the fuselage longerons1 etc4 ,when removed from the press1 the rib flanges can be glued to the webs taking care that the glue is hot1 and that it thoroughly covers the groove surface4 ,the rib must now be held accurately in place in a second form1 so that the true rib outline will be retained until the glue drys4 ,a great deal depends upon the accuracy of the second form1 and the accuracy with which the web outline is cut4 ,the larger manufacturers use metal rib forms or jigs1 but the small builder must be content with a wooden form consisting of a board fitted with suitable retaining cleats1 or lugs4 ,the outline of the aerofoil is drawn on the board1 the tips of the cleats are brought to the line1 and are screwed to the board so that they can be turned back and forth for the admission and release of the ribs4 ,the strip bending press in ,fig4 #g is only intended to bend the flanges approximately to form1 and hence two layers may be put in the press at one time without much error4 99,wing ,spars994 ,in ,american aeroplanes these members are usually of the solid ,i form for medium size exhibition and training machines1 but for small fast aeroplanes1 where every ounce must be saved1 they are generally of the built up type1 that is1 made up of two or more members4 ,in ,europe1 built up construction is more common than in this country1 and is far preferable for any machine that justifies the additional time and expense4 ,the wing spars are the heaviest and most important members in the wing and no trouble should be spared to have them as light as the strength and expense will permit4 ,they are subjected to a rather severe and complex series of stresses2 bending due to the load carried between supports1 compression due to the pull of the stay wires1 bending due to the twist of non-central wire fittings1 stresses due to drag and those caused by sudden deviations in the flight path and by the torque of the motors4 ,these should be accurately worked out by means of stress diagrams if the best weight efficiency is to be obtained4 ,illustration3 ,fig4 #i4 ,types of ,wing ,spars4 7,a7 ,is the ,i ,beam ,type4 7,b7 ,box ,spar4 7,c7 ,is ,composite ,wood and ,steel1 ,wrapped with ,tape4 ,a number of different wing spar sections are shown by ,figs4 #i1 #aj1 #aa4 ,spar 7,a7 in ,fig4 #i is the solid one piece ,i type 7generally spruce71 channeled out along the sides to remove the inefficient material at the center4 ,the load in this case is assumed to be in a vertical direction4 ,in resisting bending stresses1 it should be noted that the central portion of the material is not nearly as effective as that at the top and bottom1 and that the same weight of material located top and bottom will produce many times the results obtained with material located along the center line4 ,at points of connection1 or where bolts pass through the spar1 the channeling is discontinued to compensate for the material cut away by the bolt and fittings4 ,spar 7,b7 is of the hollow type1 made in two halves and glued together with hardwood dowel strips4 ,the doweling strips may be at the top and bottom as shown1 or on the horizontal center line as shown by ,spar 7,j74 ,the material of the box portion is generally of spruce4 ,this is a very efficient section as the material lies near the outer edge in every direction1 and offers a high resistance to bending1 both horizontally and vertically4 ,unfortunately a great deal depends upon the glued joints1 and these require careful protection against moisture4 ,there is absolutely no means of nailing or keying against a slipping tendency or horizontal shear4 ,the best arrangement to insure against slipping of the two halves is to tape around the outside as shown by spar 7,e74 ,this is strong linen tape and is glued carefully to the spar1 and the whole construction is proofed against moisture by several coats of spar varnish and shellac4 ,in addition to the strengthening effect of the tape1 it also prevents the wood from splintering in accidents4 ,illustration3 ,fig4 #aj4 ,four ,types of ,wing ,spars1 the ,spar ,d ,being a ,simple ,steel ,tube as ,used in the ,caudron and ,breguet ,machines4 ,spar 7,c7 consists of a central ash ,i section1 with steel strips in the grooves4 ,two spruce side strips are placed at either side as stiffeners against lateral flexure1 and the entire construction is taped and glued4 ,this is very effective against downward stresses1 and for its strength is very compact4 ,since spruce is much stiffer than either the thin steel strip1 or the ash1 it is placed on the outside4 ,spar 7,d7 in ,fig4 #aj has been described before4 ,fig4 7,f7 consists of two spruce channels placed back to back1 with a vertical steel strip between them4 ,again the spruce is used as a side stiffener1 and in this case probably also takes a considerable portion of the compression load4 ,spar 7,g7 is a special form of box spar used when the spar is at the entering edge of the wing1 the curved nose being curved to the shape of the aerofoil nose4 ,in ,fig4 #aa 7,h71 a center ash ,i is stiffened by two spruce side plates1 the ash member taking the bending moment1 and the spruce the compression4 ,spar 7,i7 has a compound central ,i1 the upper and lower flanges being of ash and the center web of three ply veneer4 ,the two outer plates are of spruce4 ,this should be a very efficient section1 but one that would be difficult and costly to build4 ,fig4 7,j7 is the same as 7,b71 except that the parting lies in a horizontal plane4 ,spar 7,k7 has ash top and bottom members1 and spruce or veneer side plate4 ,the resistance of this shape to side thrust or twist would be very slight4 ,the sides are both screwed and glued to the top and bottom members4 ,illustration3 ,fig4 #aa4 ,built-,up ,wooden ,wing ,spars1 ,commonly ,used with ,european ,aeroplanes4 ,the front end of a ,hansa-,brandenburg wing is shown by ,fig4 #ab1 the box spar and its installation being drawn to scale and with dimensions in millimeters4 ,the top and bottom are sloped in agreement with the rib flange curve1 and the rib web is strengthened by stiffeners at either side of the spar4 ,the hardwood dowel strips are at top and bottom as in ,fig4 ,b1 and when placed in this position the glued joint is not subjected to the horizontal shear forces4 ,the walls are thicker at top and bottom than at the sides1 in order to resist the greater vertical forces4 ,for the same reason is deeper than it is wide4 ,as will be remembered1 the drag is very much less than the lift1 and again1 the drag stress is greatly reduced by the internal drag wire bracing4 99,leading ,edge ,construction994 ,in the early ,bleriot monoplanes the leading edge was of sheet aluminum1 bent into ,u form over the nose of the rib4 ,in modern biplanes1 this edge is generally of ,u form hollow spruce1 about #c_/af inch thick4 ,another favorite material is flattened steel tubing1 about #a_/b x #a_/d1 and of very light gauge1 the long side being horizontal4 ,the tube has the advantage of being much thinner and much stiffer than the other forms1 and the thin edge makes it very suitable for certain types of aerofoils4 ,the wing tip bows are generally of hollowed ash and are fastened to the spar ends1 leading edges1 and trailing edges with maple dowels1 the joint being of a long scarfed form4 ,when the scarfed joint is doweled together1 it is wrapped with one or two layers of glued linen tape4 ,in some types of machines the top surface of leading edge is covered with thin two ply wood from the extreme front edge to the front spar4 ,this maintains the aerofoil curve exactly at the most critical point of lifting1 and also stiffens the wing against the drag forces4 ,illustration3 ,fig4 #ab;b4 ,an ,old ,type of ,curtiss ,biplane ,strut ,socket1 at ,left4 ,at the ,right ,is a ,more ,modern ,type in ,which the ,bolts ,do ,not ,pierce the ,spar4 99,trailing ,edges994 ,these are either of thin beveled ash or ,steel tube4 ,on army machines1 the rear part of the trailing edge fabric is pierced with holes about #c_/af inch diameter1 the holes being provided with rust proof eyelets4 ,this relieves an excess of pressure due to rips or tears2 one opening being located between each rib and next to the body4 ,illustration3 ,fig4 #ab;c4 ,a ,standard ,h-#c ,interplane ,strut ,socket ,is ,shown at the ,left1 the ,bolts in ,this ,case ,passing on ,either ,side of the ,spar4 ,note the ,stay ,wire ,attachment ,clips and ,pinned ,strut ,connection4 ,a ,german ,strut ,socket at ,right4 ,courtesy ,aerial ,age4 99,protection of ,wing ,wood ,work994 ,in protecting the wood framework of the wings from the effects of moisture1 at least three coats of good spar varnish should be carefully applied1 with an extra coat over the glued surfaces and taping4 ,shellac is not suitable for this purpose4 ,it cracks with the deflection of the wings and finally admits water4 ,the steel parts of the wing should be given two coats of fine lead paint1 and then two coats of spar varnish over the paint4 ,wires are treated with some flexible compound1 as the vibration of the thin wires1 or cables1 soon cracks off any ordinary varnish4 ,the use of shellac cannot be too strongly condemned2 it is not only an indifferent protection1 but it causes the fabric to rot when in contact with the doped surface4 99,monoplane ,wing ,spars994 ,a few representative monoplane wing spars are shown by ,fig4 #ac1 the ,r4 ,e4 ,p41 ,bleriot ,,xi1 and the ,nieuport4 ,except at points where the stay wires are connected1 the ,bleriot spar is channeled out into ,i beam form as indicated in the figure4 ,it will be noted that the top and bottom faces of the spar are slanted to agree with the curvature of the ribs4 ,a4 steel connection plate is bolted to the sides of the spar by through bolts1 and with a lug left top and bottom for the top and bottom guy wires4 ,the ,r4 ,e4 ,p4 is also an ,i type1 the section4 ,a being taken through the channeled portions1 while ,b is taken through one of the connection points where the beam is a solid rectangle4 ,the channeling should always stop at connection points2 first1 so that the plates have a good bearing surface1 and second1 to allow for the material removed by the bolt holes4 ,illustration3 ,fig4 #ac4 ,typical ,monoplane ,wing ,spar ,construction4 ,probably the most interesting of all the spars is the ,nieuport1 which is a combined truss and girder type4 ,this spar tapers down from the center to both ends1 being thickest at the points where the guys are attached4 ,the top flange 7,j71 and the bottom flange 7,l71 are ash1 while the side plates and diagonals 7,h7 are spruce4 ,the diagonals resist the shear1 and are held in place by the tie bolts 7,i74 ,at the left1 the spruce cover plate is removed1 while at the right it is in place with the interior construction shown in dotted lines4 ,the dimensions are in millimeters4 ,illustration3 ,fig4 #ad4 ,plate ,connection for ,monoplane ,stay ,wire ,connection to ,spar4 ,a ,compression ,member or ,drag ,strut ,is ,shown in the ,center of the ,spar ,which ,takes ,up the ,thrust ,due to the ,angularity of the ,stays and ,also the ,drag ,stress4 99,location of ,spars994 ,there are a number of items that affect the location of the spars in regard to the leading edge4 ,the most important factors in the choice of location are3 7#a7 ,shape and depth of wing section1 7#b7 ,center of pressure movement1 7#c7 ,drag bracing requirements1 7#d7 ,width of ailerons1 7#e7 ,method of attaching the interplane struts4 ,,chapter ,,xi ,,fuselage 7,,body7 ,,construction4 99,purpose of ,fuselage994 ,the fuselage of a monoplane or tractor biplane is the backbone of the machine4 ,it forms a means of connecting the tail surfaces to the main wing surfaces1 carries the motor1 fuel and pilot1 and transmits the weight of these items to the wings and chassis4 ,with the exception of the wing structure1 the fuselage is the most important single item in the construction of the aeroplane4 ,fig4 #a shows a typical arrangement of a two-place biplane fuselage equipped with a water-cooled motor4 ,the motor ,e1 propeller ,y1 and radiator ,r are placed in the front of the fuselage1 and considerably in advance of the wings ,w and ,d4 ,immediately behind the motor is the passenger's seat ,a and the fuel tank ,f4 ,the pilot's seat ,b is placed behind the trailing edge of the wings and is behind the passenger's seat4 ,the cockpit openings ,g and ,h are cut in the fuselage top for the passenger and pilot respectively4 ,the rear extension of the fuselage carries the control surfaces1 ,l being the vertical fin1 ,m the rudder1 ,o the fixed tail or stabilizer1 and ,p the elevator4 99,resistance994 ,to reduce the resistance in flight1 the fuselage is of as perfect streamline form as possible1 the fuselage being deepest at a point about one-third from the front4 ,from this point it tapers out gradually to the rear4 ,with the motors now in use it is only possible to approximate the ideal streamline form owing to the front area of the radiator and to the size of the motor4 ,again1 the projection of the pilot's head above the fuselage adds considerably to the resistance4 ,the wind shields ,i disturb the flow of air4 ,the connections to the tail surfaces and to the chassis members ,k also add to the total resistance4 ,an arched turtle deck ,j is generally provided1 of such a shape that the pilot's head is effectively streamlined1 the taper of this deck allowing the disturbed air to close in gradually at the rear4 ,the flat area presented by the radiator ,r is probably the greatest single source of resistance1 and for this reason the radiator is sometimes placed at the side of the fuselage1 or in some other position that will allow of a better front end outline4 ,an example of this construction is shown by ,fig4 #b in which the radiator ,r is placed behind and above the motor ,e4 ,the front fuselage end ,z can now be made of a more suitable streamline form4 ,illustration3 ,figs4 #a-b-c4 ,fuselage and ,motor ,arrangement of ,tractor ,biplanes4 ,fig4 #c is a view of the front end of a typical fuselage in which an air-cooled rotary type of motor is installed4 ,since the diameter of this type of motor is seldom much less than three feet1 it is necessary to have a very great diameter in the extreme front4 ,the motor housing or cowl marked ,e has a diameter d which should smoothly blend into the outline of the fuselage at b4 ,in the older types of construction there was often a very considerable break in the outline at this point1 especially in cases where the circular cowl was abruptly connected to a square fuselage4 ,a break of this sort greatly increases the head resistance4 ,a spinner or propeller cap marked ,z in ,fig4 #c is an aid in reducing the resistance offered by the motor cowl and also reduces the resistance of the inner1 and ineffective1 portion of the propeller blades4 ,the cap in any case is smaller than the cowl opening in order that cooling air be admitted to the enclosed cylinders4 99,distribution of ,loads994 ,returning to ,fig4 #a1 we note that the weight of the fuselage1 pilot1 passenger1 fuel1 control surfaces and motor are carried to the upper wing ,w by the cabane strut members ,c-,c and stays1 the lower wing being connected directly into the sides of the fuselage4 ,continuations of the cabane members on the interior of the fuselage inter-connect the upper and lower wings 7shown in dotted lines74 ,the interplane stays in connection with the cabane members bind the wings and fuselage into a unit4 ,a vertical line ,,cp passes through the center of pressure of both wings1 and approximately through the center of gravity of the machine4 ,in other ,words1 the machine is nearly balanced on the center of pressure line4 ,the turning moments of weights behind the ,,cp must approximately balance the opposite turning moments of the masses located in front of the ,,cp4 ,the exact relation between the center of pressure and the center of gravity will be taken up later4 ,variable loads such as the passenger1 gasoline and oil1 are placed as nearly as possible on the center of pressure line1 so that variation in the weight will not affect the balance4 ,in the figure1 the passenger's seat ,a1 and the fuel tank ,f are on the ,,cp line1 or nearly so4 ,thus1 a reduction in the weight of the fuel will not affect the trim of the machine1 nor will a wide variation in the weight of the passenger produce any such effect4 ,as shown1 the passenger's seat is placed directly on the top of the fuel tank1 an arrangement widely used by ,european constructors4 ,in the majority of ,american machines the fuel tank is placed at the top of the fuselage instead of in the position illustrated4 ,as the pilot is considered as a constant weight1 his location does not affect the balance4 ,when at rest on the ground1 the weight of the rear end of the fuselage is supported by the tail skid ,n4 ,the length of this skid must be such that the tail surfaces are kept well clear of the ground4 ,the center of the chassis wheel ,q is placed in front of the center of gravity so that the weight of the machine will cause the tail skid to bear on the ground when the machine is at rest4 ,if the wheel were behind the center of gravity1 the machine would stand on its nose when making a landing4 ,the wheels must be located so that the tendency to nose over is as small as possible1 and yet must not be set so far forward that they will cause an excessive load on the tail skid4 ,with too much load on the skid1 the tail will not come up1 except after fast and prolonged running1 and heavy stresses will be set up in the framework due to the tail bumping over the ground at high speed4 ,the skids should not be dragged further than absolutely necessary1 especially on rough ground4 ,with proper weight and wheel adjustment1 the tail should come up in a short run4 ,the wheel adjustment will be taken up under the head of ,chassis4 99,position in ,flight994 ,in normal horizontal flight1 the center line of thrust ,,ct is horizontal or nearly so4 ,this line of thrust passes through the center of the motor crankshaft and propeller4 ,in an upward climb1 the ,,ct is inclined at the angle of climb1 and since the ,,ct indicates the line of flight1 the streamline curves of the body should be laid out so that the axis of least body resistance will coincide with the line of thrust4 ,when flying horizontally at the normal speed1 the body must present the minimum of resistance and the wings must be at the most efficient angle of incidence4 ,in climbing1 or flying at a very low speed1 the tail must necessarily be depressed to gain a large angle of wing incidence1 and hence the body resistance will be comparatively high owing to the angle of the body with the flight line4 ,it is best to have the least resistance of the fuselage coincide with the normal horizontal flight speed4 ,this condition at once establishes the angle of the wings in regard to the fuselage center line4 99,center ,line of ,resistance994 ,the center line of thrust should pass through the center of total head resistance as nearly as possible4 ,the total resistance referred to is composed of the wing drag1 body and chassis resistances4 ,in an ordinary military type of aeroplane this line is located approximately at one-third of the gap from the bottom wing4 ,owing to variations in the drag of the ,wings at different angles1 this point varies under different flying conditions1 and again1 it is affected by the form and size of the fuselage and chassis4 ,the exact location of the center of resistance involves the computation of all of the resistance producing items4 ,in addition to passing through the center of resistance1 the center line of thrust should pass slightly below the center of gravity of the machine4 ,in this position the pull of the motor tends to hold the head up1 but in-case of motor failure the machine immediately tends to head-dive and thus to increase its speed4 ,the tendency to dive with a dead motor automatically overcomes the tendency to stall or to lose headway4 ,with the centerline of thrust determined1 and with given motor dimensions1 the fuselage position can be located at once in regard to the wings4 ,this is good enough for a preliminary layout1 but must be modified in the final design4 ,as before explained1 the centerline of thrust is located at a point between the two wings1 approximately one-third of the gap from the lower wing4 ,in machines having a span of #ce feet and over1 it is a trifle less than one-third the gap1 while in small speed scouts it is generally a trifle over one-third4 ,this rule checks very closely with the data obtained from #bb standard machines4 ,thus1 in a machine having a #f-;foot gap1 the propeller centerline will be located about #b feet above the lower wing4 ,the top of the fuselage 7measured under the stabilizer surface7 is from #e to #h inches above the center line of thrust4 ,at the motor end1 the height of the fuselage above the ,,ct is controlled by a number of factors1 either by the type of motor1 or by the arrangements made for access to the motor parts4 ,in a number of ,european machines1 the motor sits well above the top of the fuselage1 this always being the case when a six-cylinder1 vertical water-cooled motor is used4 ,with an air-cooled type1 the top is governed by the cowl diameter4 99,motor ,compartment994 ,the space occupied by the motor and its accessories is known as the motor compartment1 and in monoplane and tractor biplane fuselage it is located in the extreme front of the body4 ,the interior arrangement varies with different types of motors and makes of machines4 ,with rotary cylinder motors1 the compartment is often nothing but a metal cowl1 while with large water-cooled motors it occupies a considerable portion of the body4 ,water-cooled motors are generally covered with automobile type hoods1 these usually being provided with gilled openings for ventilation4 ,owing to the heat generated in the motor1 some sort of ventilation is imperative at this point4 ,whatever the type1 the compartment is always cut off from the rest of the fuselage by a fireproof metal partition to guard against fire reaching the passenger or fuel tanks4 ,the fuel and oil should always be separated from the motor by substantial partitions since a single carbureter pop may cause serious trouble4 ,illustration3 ,fig4 #d4 ,mounting and ,cowls for ,rotary ,cylinder ,motors4 ,courtesy ,flight4 ,accessibility is a most important feature in the design of the motor end1 and hence the hood should be of the hinged automobile type so that it can be easily raised for inspection or repairs4 ,in the ,curtis ,,jn#d-;,b ,military ,training ,tractor1 the cylinder heads and valve mechanism project slightly above the top of the hood so that these parts are amply cooled and are entirely accessible4 ,access to the carbureter can be had through a small hand-hole in the side of the hood4 ,the radiator in this ,curtiss model is located in the extreme front end of the fuselage--automobile fashion4 ,the propeller shaft passes through a central opening in the radiator4 ,in ,fig4 #f the vertical motor ,e is set down low in the frame1 the upper part of the fuselage ,f ending at ,h4 ,the engine bearer ,b1 which carries the motor1 forms the top part of the fuselage at this point4 ,the engine is thus in the clear and access can easily be had to every part of the motor4 ,the radiator is in front of the motor at ,r4 ,when in flight the motor is covered by a sheet metal hood similar to the folding hood used on automobiles4 ,this type is used in the ,martin1 ,sturtevant1 and several ,european machines4 ,illustration3 ,fig4 #e4 ,motor ,compartment of a ,curtiss ,tractor ,biplane ,using a ,front ,type ,radiator4 ,note the ,two ,exhaust ,pipes ,which ,carry the ,gases ,over the ,top of the ,wings4 ,fig4 #g is a very common front end arrangement used with side radiators4 ,the top fuselage member ,f is brought down in a very low curve1 leaving the greater part of the motor projecting above the fuselage4 ,at the extreme front1 the upper fuselage member ,f joins the engine bearer ,b1 the connection being made with a pressed steel plate4 ,the radiator ,r is shown at the side of the fuselage4 ,the cylinders are not usually covered when in flight4 ,in the front view it will be noted that the radiators are arranged on either side of the fuselage4 ,a side view of the ,h4 and ,m4 ,farman ,fighter is shown by ,fig4 #aj4 ,this is a very efficient ,french machine which has seen much active service in the war4 ,the front end is much like that shown in ,fig4 #g except that a spinner cap is fitted to the propeller boss4 ,a ,v type motor allows of the radiator being mounted between the two rows of cylinders1 and in a position where it will cause the least possible head resistance4 ,illustration3 ,figs4 #f-g4 ,various ,motor ,arrangements1 and ,radiator ,locations4 ,illustration3 ,fig4 #aj4 ,a ,type of ,h4 and ,m4 ,farman ,tractor ,fighting ,biplane4 ,this ,machine ,uses a ,v4 ,type ,motor1 with the ,radiator in the ,valve ,alley4 ,the ,gunner and the ,machine ,gun ,are ,mounted in the ,rear ,cock-pit4 ,it ,will ,be ,noted ,that the ,body ,is ,raised ,well ,above the ,lower ,wing ,so that the ,gun ,field ,is ,increased4 ,the ,pilot ,is ,well ,ahead of the ,entering ,edge of the ,lower ,wing4 ,courtesy of ,aerial ,age4 ,the fuselage is of excellent streamline form and shows careful study in regard to the arrangement of the power plant4 ,unlike the majority of machines1 the fuselage is raised well above the bottom wing1 this being done evidently to increase the range of the gun in the rear cockpit4 ,the increased height allows the gun to shoot over the top plane at a fairly small angle1 and the height above the ground permits the use of a very large and efficient propeller without having an excessively high chassis4 ,at the rear the fuselage tapers down to a very thin knife edge and therefore produces little disturbance4 ,illustration3 ,fig4 #aa4 ,radiator ,mounted at ,leading ,edge of ,upper ,wing4 ,this ,type ,is ,used with the ,sturtevant and ,lawson ,aeroplanes and ,is ,very ,effective ,because of the ,improved ,circulation4 ,fig4 #aa shows a ,sturtevant ,training ,biplane in which the radiator is mounted at the front edge of the upper plane4 ,this arrangement was originally introduced by the ,sturtevant ,company in their steel biplanes and has proved a very efficient type for cooling1 although the radiator must affect the lift of the top plane to a very considerable extent4 99,pilot and ,passenger ,compartments994 ,these compartments contain the seats1 controls1 and instruments1 and in the military types contain the gun mounts and ammunition4 ,in some battle-planes1 the passenger or observer occupies the rear seat1 as this position gives a wider range of fire against rear or side attacks4 ,this arrangement is true of the ,h4 and ,m4 ,farman machine just illustrated and described4 ,in the large ,german ,gotha the gunner occupies the rear position and fires through1 or above1 a tunnel built through the rear end of the fuselage4 ,in some forms of training machines1 the pilot and passenger sit side by side instead of in tandem1 as this arrangement allows better communication between the pilot and student1 and permits the former to keep better watch over the movements of the student4 ,a notable example of this type is the ,burgess ,primary ,trainer4 ,a side-by-side machine must have a very wide fuselage and therefore presents more head resistance than one with the seats arranged in tandem1 but with proper attention to the streamline form this can be reduced so that the loss is not as serious as would be imagined from a view of the layout4 ,the seats may be of several types1 7a7 the aluminum bucket type similar to1 but lighter than1 the bucket seats used in racing automobiles2 7b7 the woven wicker seat used in many types of ,german machines1 or 7c7 the modified chair form with wooden side rails and tightly stretched leather back and bottom4 ,whatever the type1 they should be made as comfortable as possible1 since the operation of a heavy machine is trying enough without adding additional discomfort in the form of flimsy hard seats4 ,in the older machines the seats were nothing more than perches on which the pilot balanced himself precariously and in intense discomfort4 ,a few pounds added in the form of a comfortable seat is material well spent since it is a great factor in the efficient operation of the machine4 ,wicker seats are light1 yielding and comfortable1 and can be made as strong or stronger than the other types4 ,it seems strange that they have not been more widely adopted in this country4 ,all seats should be slightly tilted back so that the pilot can lean back in a comfortable position1 with a certain portion of his weight against the back of the seat4 ,sitting in a rigid vertical position is very tiring1 and is especially so when flying in rough weather1 or on long reconnaissance trips4 ,the backs of the seats should be high and head rests should be provided so that the pilot's head can be comfortably supported against the pressure of the wind4 ,if these head rests are streamlined by a long1 tapering1 projecting cone running back along the top of the fuselage1 the resistance can be considerably reduced4 ,this arrangement was first introduced in the ,gordon-,bennett ,deperdussin and has been followed in many modern machines4 ,in the ,deperdussin1 the pilot's head was exposed directly to the full blast of the propeller slipstream and a head support was certainly needed4 ,small1 transparent wind shields are now fastened to the front edge of the cockpit openings which to a certain extent shield the pilot from the terrific wind pressure4 ,these are quite low and present little resistance at high speeds4 ,illustration3 ,fig4 #ab4 ,hall-,scott ,motor and ,side ,type ,radiator ,mounting on a ,typical ,tractor4 ,a heavy leather covered pad1 or roll1 should be run entirely around the edge of the cockpit opening as a protection to the pilot in case of an accident or hard landing4 ,the roll should be at least #c #a_/b in diameter and should be filled with horse hair4 ,all sharp edges in the cockpit should be similarly guarded so that in the event of the pilot being thrown out of his seat1 he will not be cut or bruised4 ,each seat should be provided with an improved safety strap that will securely hold the pilot in his seat1 and yet must be arranged so that it can be quickly and easily released in an emergency4 ,in flight the occupants must be securely strapped in place to prevent being thrown out during rapid maneuvers or in rough weather4 ,buckles should be substantial and well sewed and riveted to the fabric so that there will be no danger of their being torn out4 ,the straps must be arranged so that they will not interfere with the free movement of the pilot1 and so that they will not become entangled with the controls4 ,it is best to copy the sets approved by the government as these are the result of long continued experiment and use4 ,illustration3 ,fig4 #ac4 ,deperdussin ,monoplane with ,monocoque ,body4 ,note the ,streamline ,form of the ,body and the ,spinner ,cap at the ,root of the ,propeller4 ,care must be taken to have the seats located at the correct height from the floor so that the legs will not become cramped4 ,in the majority of machines1 the vertical rudder is operated by the feet4 ,unless the seat is at the proper height1 the pilot will be in a strained position as he cannot shift around nor take his feet from the rudder bar4 ,either the rudder bar or the seat should be adjustable for different lengths of legs4 ,usually the adjustment is made in the rudder bar since it is not usually advisable to shift the seats owing to the necessity of having the pilot's weight in a fixed position4 ,in some old types of monoplanes1 the pilot sat on a small pad placed on the floor of the fuselage4 ,needless to say1 this was a horribly uncomfortable position to be in1 but as the flights of that time were of short duration it did not matter much4 ,if the feet could be removed occasionally from the rudder bar the matter of seat position would not be of so much importance1 but to sit flat on the floor1 with the legs straight out1 for a couple of hours is a terrible strain and has undoubtedly caused many accidents through cramps4 ,as both the passenger and the fuel are varying weights1 the fuel tank seat idea is good4 ,this allows both of these items to be placed at the center of gravity of the machine where weight variation will have no effect on the balance of the plane4 ,in this position1 however1 the fuel must be pumped up to a higher auxiliary tank since the main tank would be too far below the carbureter for gravity feed4 ,the flooring of the cockpits can be either of veneer1 or can be built up of small spruce slats about #a_/b x #a_/b1 the slats being spaced about #a_/b apart4 ,the latter floor is specified by the government for seaplane use1 and is very light and desirable4 ,the floor is placed only at points where it will be stepped on4 ,observation holes are cut in the floor on a line with the edge of the seats so that the occupants can view the ground without looking over the edge of the fuselage4 ,the observation port holes are about #i inches in diameter4 ,glass should never be used in the cockpits except for the instrument covers1 unless it is of the non-splintering triplex laminated type of glass4 ,the use of inflammable celluloid should also be avoided as being even more dangerous than the glass4 ,the triplex glass is built up of two or more layers of glass1 which are cemented together with a celluloid film applied under heavy pressure4 ,this form of construction is very strong1 and while it can be broken1 it will not fly apart in the form of splinters4 ,all instruments should be placed directly in front of the pilot so that he can take observations without turning his head4 ,usually all of the instruments1 with the exception of the compass1 are mounted on a single instrument board placed in front of the pilot and directly under the forward edge of the cockpit opening4 ,the compass can be placed on the floor as in ,american machines1 or inserted in the upper wing as in some ,european machines4 ,the motor control apparatus is placed where it can be reached conveniently from the seat4 ,oil gages1 gasoline gages1 and revolution counters are generally placed on the instrument board where they can be easily observed4 ,if a wireless set is carried1 the switches are placed on1 or near1 the instrument board4 ,owing to the uses to which the different machines are put it is impossible to give a list of instruments that would be suitable for every machine4 ,the simplest machine should have the following instruments3 99,altimeter99 for measuring altitude4 99,clock99 of special aeroplane type4 99,incidence indicator499 99,air speed indicators99 for measuring the speed of the machine relative to the air4 99,gasoline1 oil and pressure gages99 for determining amount of fuel4 ,instruments for ,navy and ,army machines are of course more complete4 ,in the specifications for ,army ,hydroaeroplanes 7twin motor type #aiaf7 the following instruments are specified3 99,aneroid ,barometer994 ,graduated in feet1 and reading from sea-level to #ab1jjj feet4 99,compasses994 ,one in each cockpit4 ,to be of the ,sperry ,gyroscopic type with an elastic suspension and properly damped4 ,shall be attached to1 and synchronized with1 the ground drift indicator4 99,ground ,drift ,indicator994 ,located in observer's cockpit4 ,for noting drift due to side winds4 ,see illustration on page #bdd4 99,clock994 ,special aeroplane type1 built to resist vibration4 ,located in pilot's cockpit4 ,illustration3 ,fig4 #ad4 ,aeroplane ,compass of the ,mc,creagh-,osborn ,type4 7,sperry7 99,gasoline ,supply ,gage994 ,to indicate the amount of fuel in gravity service tank at all attitudes of flight1 and shall be visible from pilot's seat4 ,a gage in the main tank will also be desirable that will register the approaching exhaustion of fuel4 ,this indicator should register when #ge of the fuel in the main tank is exhausted1 and then record the remainder continuously4 99,air ,speed ,indicator994 ,one in pilot's cockpit4 99,angle of ,incidence ,indicator994 ,sperry type4 ,to be located in pilot's cockpit4 99,inclinometer994 ,for measuring angle of inclination of longitudinal axis of machine4 ,in pilot's cockpit1 and placed on instrument board in the vicinity of tachometers4 99,bank ,indicator994 ,for indicating the proper amount of bank on turns4 ,in pilot's cockpit4 99,map ,board994 ,one revolving map board placed in pilot's cockpit4 99,map ,desk994 ,one folding map desk in observer's cockpit4 ,illustration3 ,fig4 #ae4 ,sperry ,ground ,drift ,indicator4 99,tachometers994 ,for measuring speed of motors in revolutions per minute4 ,pilot's cockpit4 99,self-,starter ,switch994 ,for operating self-starter4 ,on instrument board in pilot's cockpit4 ,among the other accessories specified in the cockpit for the above machines are a ,pyrene fire extinguisher2 a #b-;gallon water breaker2 a speaking tube for communication between the pilot and observer 7#a to #a #a_/h72 a flashlight signal for speaking tube2 and a tool kit4 ,the weight of the tool kit shall not exceed #aa lbs4 ,illustration3 ,fig4 #af4 ,cock-pit of a ,london and ,provincial ,biplane4 ,control ,lever in ,foreground and ,instrument ,board ,under ,cowl4 ,courtesy of ,flight4 99,general ,proportions of the ,fuselage994 ,the total length of the fuselage depends upon the type of power plant1 upon the span or chord of the wings1 and upon the arrangement of the tail surfaces4 ,the rear end of the fuselage should be far enough away from the wings to insure that the rear surfaces are not unduly affected by the down-wash or the wake-stream of the wings4 ,a very short fuselage gives a short lever arm to the control surfaces1 hence these surfaces must be very large with a short body4 ,with the stabilizer surface close to the wings1 the damping effect is slight1 that is1 the surface does not effectively kill or damp down oscillations4 ,large tail surfaces are heavy1 difficult to brace1 and cause a very considerable amount of head resistance4 ,the extra weight of a long fuselage is generally offset by the increased weight caused by the large tail area of the short body type4 ,when machines are crated and shipped at frequent intervals1 a very long fuselage is objectionable unless it is built in two sections4 ,it also requires much storage space and a very long hangar4 ,machines for private use must often be sacrificed from the efficiency standpoint in order to keep the dimensions within reasonable limits4 ,an aeroplane requiring an enormous hangar has certainly no attraction for the average man4 ,every effort must be made to condense the overall dimensions or to arrange the extremities so that they can be easily dismounted4 ,exhibition flyers require specially portable machines since they ship them nearly every day1 and the expense of handling a long awkward fuselage may alone determine the choice of a plane4 ,it is usually best to divide the body at a point just to the rear of the pilot's seat1 although many flyers look upon a two-part body with disfavor unless they can be shown that the joint connections are as strong as the rest of the fuselage4 ,illustration3 ,fig4 #ai4 ,fuselage ,dimension ,chart for ,two ,place ,aeroplane ,fuselage4 ,upper ,diagram ,is the ,water ,cooled ,type and the ,lower ,figure ,applies to a ,machine with a ,rotating ,air ,cooled ,motor4 ,see ,table of ,dimensions on ,page #bdh4 ,as a guide in the choice of fuselage proportions1 a set of diagrams and a table are attached which gives the general overall dimensions of several prominent makes of machines4 ,the letters in the diagram refer to the letters heading the columns in the tables so that the general dimensions of any part can be readily determined4 ,i do not claim that these dimensions should be followed religiously in every case1 but they show what has been done in the past and will at least suggest the limits within which a new machine can be built4 ,illustration3 ,fig4 #bj4 ,fuselage ,dimension ,diagrams ,giving the ,principal ,dimensions of ,speed ,scout ,machines4 ,upper ,figure ,shows ,typical ,scout with ,water ,cooled ,motor 7,curtiss71 ,while ,lower ,diagram ,shows an ,arrangement ,common with ,rotary ,air ,cooled ,motors 7,nieuport7 ,fig4 #ai gives the outline and dimension letters for two-place machines of what is known as the ,reconnaissance ,type4 ,both water-cooled and air-cooled motor equipments are shown1 the top machine being of the water-cooled type while the lower figure shows a typical two-place machine with a rotary air-cooled motor4 ,underneath this side elevation is a front view of the fuselage1 and a section taken through the point of greatest depth4 ,as shown1 the fuselage is of square cross-section1 but the dimension ,b applies equally to the diameter of a circular cross-section4 ,dimension ,c gives the height of the curved upper deck1 or turtle deck of the fuselage4 ,dimension ,d shows the extreme length extending in front of the leading edge of the lower wing1 and ,t shows the length of the rear portion back of the leading edge of the lower wing1 the leading edge being taken as a base of measurement4 ,the location of the deepest section1 measured from the extreme front of the fuselage1 is given by ,e1 the depth at this point being indicated by ,b4 ,the extreme width is shown by ,i4 ,in the machine shown1 side radiators are used1 the blunt front end dimensioned by ,g and ,k being the dimension of the front engine plate4 ,when front radiators are used1 the dimensions ,g and ,k also apply to the size of the radiator4 ,the amount of advance1 or the distance of the chassis wheel center from the leading edge is given by ,s1 and the distance of the wheel center below the leading edge is given by ,r4 ,v is the length of the engine projecting above the fuselage top4 ,the passenger or observer is indicated by #a and the pilot by #b4 ,the top plane is #c and the bottom plane #d4 ,the engine is located by #e1 and the top fuselage-rail1 or longeron1 by #g4 ,turtle deck is #f4 ,illustration3 99 ,round monocoque body1 dimensions 7,b7 and 7,f7 measured from outer diameter or top of circle ,fig4 #bj gives the diagrams of speed scout machines1 both of the air-cooled and water-cooled types4 ,these are the small1 fast1 single seat machines so much used in the ,european war for repelling air attacks and for guarding the larger and slower bombing and observation machines4 ,the upper drawing shows a ,curtiss ,speed ,scout equipped with a ,v type water-cooled motor and a circular front radiator4 ,while the front of the body is circular1 it gradually fades out into a square cross-section at the rear4 ,the lower machine is a ,nieuport speed scout equipped with a rotating cylinder air-cooled motor4 ,in this scout1 the diameter of the motor cowl is given by dimension ,k4 ,body is of square cross-section4 ,it will also be noted that the chord of the lower plane is less than that of the upper plane and that the deep body almost entirely fills the gap between the two wings4 ,illustration3 ,fig4 #ba4 ,curtiss ,j ,n #d-;,b ,fuselage ,boxed for ,shipment4 ,with some of the later speed scouts1 the body entirely fills the gap between the wings and the top plane is fastened directly to the top members of the fuselage4 ,this makes windows necessary in the sides of the fuselage4 ,when vertical water-cooled motors are used on speed scouts1 the front view is entirely cut off1 for these are very large motors and project above the fuselage for a considerable distance4 ,this obstruction is avoided in the ,curtiss speed scout shown1 by the use of a ,v type motor4 ,it will be noted that these two scouts1 especially the ,nieuport1 are of excellent stream line form1 a very important item with such high speed machines4 ,the propeller of later ,nieuports is provided with a conical spinner cap which evidently reduces the head resistance to a considerable extent4 ,the different portions of the machine are indicated by the same figures as in the case of the reconnaissance machine4 ,,chapter ,,xii ,,details ,,of ,,fuselage ,,construction ,classification of types4 ,while there are a number of methods adopted in building up the fuselage structure1 the common type is the wire truss in which wood compression members are used in connection with steel wire or cable tension members4 ,four wooden longerons or longitudinals run the entire length of the body and are bent to its general outline4 ,the longitudinals are spaced at the correct distance by wood compression members1 which in turn are held in place by wire cross bracing4 ,this method of trussing forms a very strong and light structure1 although rather complicated1 and difficult to build4 ,the cross-section is rectangular1 although in many cases the body is converted into a circular or elliptical section by the use of light wood formers fastened to the main frame4 ,another well known type is the ,monocoque body1 first used on the ,gordon-,bennett ,deperdussin monoplane4 ,this fuselage is a circular shell built up of three-ply tulip wood1 thus forming a single piece body of great strength4 ,the three-ply shell is really a veneer1 the layers proceeding spirally around the body1 each layer being securely glued to its neighbor4 ,between each layer is a scrim layer of treated silk1 and another fabric layer is generally glued to the outside of the shell4 ,the shell is very thin1 the total thickness of the three layers of wood and fabric in modern machines being rather less than #a4e millimeters 7about #a_/af inch74 ,in the original ,deps this was somewhat greater1 #j4ae inch4 ,monocoque construction as a rule is heavy and expensive1 but offers the great advantage of strength1 perfect alignment at all times1 and of offering resistance to rifle and shell fire4 ,if the longitudinals of a truss type are struck with a bullet1 or shell fragment1 the entire fuselage is likely to fail1 but a monocoque body may be well perforated before failure is likely to take place4 ,the ,american ,l4 ,w4 ,f4 ,tractor ,biplane has a monocoque body in which spruce laminations are used instead of hardwood4 ,one ply runs longitudinally while the other two layers are spiralled to the right and left respectively4 ,between each layer is a scrim layer of treated silk1 the whole construction being covered with a final layer of fabric1 several coats of waterproof compound1 and four final coats of spar varnish4 ,when used for seaplanes the wood plies are stitched together with strong wires to prevent separation due to dampness4 ,since spruce is used in place of hardwood1 the construction is lighter than in ,european models1 and the ,l4 ,w4 ,f4 ,company claim that it is lighter than the usual truss construction4 ,an additional advantage of the monocoque construction is that the pilot is protected against splinters or penetration by the limbs of trees when making a forced landing in the brush4 ,another form of monocoque construction was adopted by the ,french builder1 ,bleriot1 at the beginning of the war4 ,the fuselage of this machine was covered with papier-mache1 the ash longitudinals being buried in this mixture4 ,the papier-mache is built up with glue and silk threads4 ,this construction is very light and strong1 but is expensive and difficult to protect against moisture4 ,the front of the fuselage is protected with a #c millimeter steel armor plate to protect the pilot against bullets and shrapnel4 ,the papier-mache portion of the body is not easily splintered by bullets4 ,a third form of monocoque1 experimented upon by the author1 is the steel shell type in which the three-ply wood veneer is supplanted by a thin steel shell4 ,this outer shell is strengthened by suitable stiffener angles4 ,with a shell thickness of #j4jac inch1 the strength is equal to the strength of a wood shell and is slightly less in weight4 ,it has the advantage of being easily and cheaply formed into shape and is absolutely proof against the influences of heat and moisture4 ,it cannot splinter1 will not catch fire and offers a maximum resistance against penetration4 ,there is yet much experimental work to be done before the construction is perfected4 ,about midway between the truss fuselage and the monocoque is the veneer construction used on many of the modern ,german aeroplanes4 ,in general1 this may be described as being a veneer shell fastened to the conventional wood longitudinals4 ,stay wires are not in general use1 the veneer taking the shear due to the bending movement4 ,six longerons are used instead of four1 the two additional members being located midway on the vertical sides4 ,transverse wood frames take the place of the transverse stay wires used in the truss type4 ,examples of this type are met with in the ,albatros de ,chasse and in the ,gotha bomb dropper4 ,the single seater1 ,roland1 has a fuselage of circular section1 with a true monocoque veneer construction1 but ,german-like1 reinforces the construction with a number of very small longitudinals4 ,in this machine there are #f layers1 or plies1 of wood reinforced by fabrics4 ,the entire thickness of the wood and fabric is only #a4e millimeters 7#a_/af inch74 ,steel tube fuselage dates back to the beginning of the aeroplane industry4 ,in this type the wood longitudinals of the wood truss type are replaced with thin gage steel tubes1 the cross struts being also of this material4 ,the diagonal bracing may be either of steel wire1 as in the wood frames1 or may be made up of inclined steel tube members that perform both the duty of the stay wires and struts4 ,for the greatest weight-efficiency1 a steel tube body should be triangular in section rather than square4 ,a triangular section saves one longitudinal and a multitude of wire struts and connections since no transverse bracing is necessary4 ,connections on a steel tube fuselage are difficult to make and are heavy4 ,they require much brazing and welding with the result that the strength is uncertain and the joint is heavy4 ,a very modern type of steel construction is that developed by the ,sturtevant ,company4 ,the members of the ,sturtevant fuselage are in the form of steel angles and channels1 similar in many respects to the sections used in steel buildings and bridges4 ,the joints are riveted and pinned as in steel structural work4 ,the longitudinals are angles and the struts are channels4 ,crystallization of the steel members is prevented by the use of special pin-connected joints provided with shock absorbing washers4 ,owing to the simplicity of the riveted joints1 there is practically no weight due to connections1 and since the weight of connections is a large item in the total weight of a fuselage1 the ,sturtevant is a very light structure4 ,according to ,g4 ,c4 ,loening1 engineer of the company1 the fittings of a large wood fuselage weigh at least #fj pounds4 ,this is almost entirely saved with the riveted connections4 ,illustration3 ,truss ,type ,fuselage of ,curtiss ,r-#d ,biplane1 ,showing ,motor and ,front ,radiator ,mounted in ,place4 ,it ,will ,be ,noted ,that the ,upper and ,lower ,longerons ,are ,channeled ,out for ,lightness and ,hence ,these ,members ,are of the ,i ,beam or ,channel ,form4 ,propeller ,flange ,is ,shown ,projecting ,through the ,radiator ,opening4 ,a novel type of wood fuselage has been described by ,poulsen in ,flight4 ,eight small longitudinals are used which are held in place by three-ply wooden formers or diaphragms4 ,wire bracing is used in a longitudinal direction1 but not transversely in the plane of the diaphragms4 ,the cross-section is octagonal1 and the completed structure is covered with fabric4 ,for the amateur this offers many advantages since the wiring is reduced to a minimum and all of the members are small and easily bent to shape4 ,it is fully as light as any type of body1 for the connections are only thin strips of steel bolted to the diaphragms with small machine screws4 ,no formers are needed for the deck1 and the machine can be given a close approximation to the ideal stream-line form with little trouble4 99,truss ,type ,fuselage994 ,we will now take up the construction of the truss type of fuselage in more detail1 and investigate the merits of the different types of connections used in fastening the frame together4 ,like every part of the aeroplane1 the fuselage must either be right or wrong1 there is no middle course4 ,fig4 #bc shows a side elevation of a typical truss type fuselage built up with wood longitudinals and struts1 the tension members being high tensile strength steel wire and cable4 ,l and ,l' are the upper and lower longitudinals1 ,s-,s-,s are the vertical struts1 and ,t-,t-,t are the horizontal cross struts which run across the frame4 ,the engine bed is the timber marked ,b at the front of the body4 ,the upper wing is attached to the body through the cabane struts ,c1 and the chassis connections are shown at ,d4 ,the stern post ,e closes the rear end of the body in a knife edge and acts as a support for the rudder and the rear end of the stabilizer4 ,f is the seat rail which carries the seats and supports the control yokes4 ,all cross bracing is of high tensile strength steel wire1 or of high strength aviation cable1 these strands taking the tensile stresses while the wood struts are in compression4 ,in the forward portion1 double stranded cables are generally used1 with solid wire applied to the after portions4 ,the longitudinals are of ash from the motor to the rear of the pilot's seat1 while the rear longitudinals are generally of spruce4 ,in some machines1 however1 the entire length of the longitudinals is ash4 ,the latter arrangement makes a heavier1 but stronger body4 ,the struts are usually of spruce as this material is stiffer than ash and much lighter4 ,illustration3 ,diagram of ,typical ,truss ,type ,fuselage1 ,showing ,principal ,members in ,place4 ,illustration3 ,fuselage of ,hansa-,brandenburg ,fighting ,biplane4 ,see ,page #bfh4 ,figs4 #bg-bh-bi-cj4 ,fuselage ,details4 7,truss ,type7 ,both the struts and longitudinals are frequently channelled out for lightness1 as shown by ,fig4 #bg1 the wooden member being left rectangular in section only at the points where the connections are made with the struts and cables4 ,the channelling-out process1 if correctly followed1 gives very strong stiff members with a minimum of cross-sectional area and weight4 ,many captured ,german machines1 on the contrary1 have solid longitudinals of rectangular section1 wrapped with linen fabric4 ,this fabric strengthens the construction and at the same time reduces the chances of splintering the wooden members in a hard landing4 ,the fabric is glued to the wood and the entire wrapping is then given several coats of a moisture repelling varnish4 ,in the older types of fuselage1 the longitudinals were often of the laminated class1 that is1 were built up of several layers of wood glued together in a single rectangular mass4 ,this reduced the tendency toward splitting1 but was very unreliable because of the uncertainty of the glued joints when exposed to the effects of heat and moisture4 ,laminated longitudinals are now seldom used1 particularly in the region of the motor where water and oil are certain to wreck havoc with the glued up members4 ,as the stresses rapidly diminish toward the tail1 it is the general practice to taper down the section of the longitudinal toward the rear and to reduce the section of the struts4 ,the longitudinals are generally kept constant in section from the motor to the rear of the pilot's seat1 the taper starting at the latter point and continuing to the rear end4 ,for example1 if the longitudinal section at the motor is #a #a_/d x #a #a_/b1 the section at the rear will be #a x #a1 the width of the struts corresponding to this taper4 ,while tapering is very desirable from the weight standpoint1 it makes the fitting problem very difficult since each fitting must be of a different dimension unless the connections can be designed so that they are adjustable to changes in the section of the longitudinals4 ,in one machine1 the width and depth of the longitudinals are kept constant1 the variation in weight and section being accomplished by increasing the depth of the channelling as the rear is approached4 ,with this design1 the same fittings can be applied from one end to the other4 ,illustration3 ,figs4 #bg-bh-bi-cj4 ,fuselage ,framing ,members and ,details4 ,since the loading of the struts is comparatively light1 they can be much reduced in section by channelling or by chamfering1 as shown by ,fig4 #bh4 ,if the width and thickness is maintained1 much of the interior material can be removed without danger of reducing the strength4 ,sketch 7,a7 in ,fig4 #bh shows a very common method of strut reduction1 the strut being of rectangular section throughout its length1 but tapered in such a way that it is thickest at the center 7d7 and thinnest at the two ends 7e74 ,to obtain the correct relation between the center end thickness requires very careful calculation4 ,as shown1 the strut is attached to the upper and lower longitudinals by sheet steel fittings or sockets4 ,sketch 7,b7 shows a simple method1 the rectangular strut being chamfered off at each of the four corners1 and left full size at either end where the fittings connect it with the longitudinals4 ,this form is not correct from a technical standpoint1 but is generally good enough for lightly loaded struts1 and has the advantage of being cheaply and easily constructed4 ,in sketch 7,c7 a channelled strut is shown1 the center portion being channelled out in a manner similar to the channelling of the longitudinals4 ,this lightening process is most commonly adopted with the large heavily loaded struts in the front portion of the fuselage1 and at the points where the motor bed is suspended or where the wings and chassis are attached to the body4 ,the black dots at the ends of the struts indicate the bolt holes for the fittings1 it being permissible to drill holes in the ends of the struts but not in the longitudinal members4 ,if the strut is large enough to resist the bending stresses at the center it will generally allow of holes being drilled near the ends without danger of strength reduction4 ,again1 the struts are always in compression and hence the bolts may be depended upon to partly take the place of the removed material in carrying the compressive stresses4 ,holes should never be drilled in the longitudinals since these members may be either in tension or compression1 depending upon the angle at which the elevator flaps are set4 ,the hole not only destroys the strength at the point at which it is drilled1 but this reduction also extends to a considerable distance on either side of the hole1 owing to the fibrous nature of the wood4 ,in steel members the effect of the hole is purely local and does not usually extend much beyond the edge of the hole4 ,considering the wood beam as consisting of a series of parallel fibers1 it will be seen that severing any one of the fibers will decrease the strength of the wood through a distance equal to the length of the cut fiber1 or at least through a distance equal to the natural shear value of the resins that bind the fibers together4 ,fuselage fittings are almost numberless in the variety of design4 ,they must be very light and strong1 must be applied without drilling the longerons1 and should be simple and cheap to construct4 ,they are usually made of sheet steel of from #j4bj to #j4cj point carbon1 and may be either bent or pressed into shape4 ,at the points where the struts are joined to the longitudinals1 the fittings connect struts and wires in three planes1 the vertical struts and fore and aft wires2 the transverse wires and horizontal struts1 and the top and bottom wires that lie in a horizontal plane4 ,there are at least #f connections at every strut1 four of the connections being made to the stay wires or cables4 ,a simple connection is therefore very hard to design4 ,fig4 #bi shows a typical fuselage panel and the interconnected members in their usual relation4 ,,lu and ,,ll are the top and bottom longitudinals at the right1 while ,,lu' and ,,ll' are the longitudinals at the right hand side4 ,the vertical struts ,,sv and ,,sv' separate the top and bottom longitudinals1 while the horizontal struts ,,sh and ,,sh' separate the right and left hand sides of the fuselage body4 ,the wires w-w-w-w brace the body fore and aft in a vertical plane4 ,the wires t-t lie in a horizontal plane1 produce compression in the horizontal struts ,,sh-,,sh'1 and stiffen the frame against side thrust4 ,the transverse rectangle ,,sv-,,sh-,,sv'-,,sh' is held in shape by the transverse stay wires ,w-,w1 this rectangle1 and the stays resisting torsional stress 7twisting71 act against the struts composing the sides of the rectangle4 ,in some ,european machines1 the wires ,,ww are eliminated1 and are replaced by thin veneer panels1 or short wood knee braces as shown by ,fig4 #cj4 ,the section shows the longitudinals ,l-,l-,l-,l and the struts ,,sv-,,sv'-,,sh-,,sh' braced by the veneer sheet or diaphragm ,d4 ,this diaphragm is well perforated by lightening holes and effectually resists any torsional stress that may be due to motor torque1 etc4 ,since the transverse wires ,w-,w in ,fig4 #bi are rather inaccessible and difficult to adjust1 the veneer diaphragm in ,fig4 #bg has a great advantage4 ,in this regard it may be stated that wire bracing is not a desirable construction1 and the substitution of solid veneer is a step in advance4 ,wire bracing has always seemed like a makeshift to the author4 ,the compression and tension members being of materials of widely different characteristics are not suitable in positions where a strict alignment must be maintained under different conditions of temperature and moisture4 ,the difference in expansion between wire and the wood compression members produces alternate tightness and slackness at the joints1 and as this is not a uniform variation at the different joints1 the frame is always weaving in and out of line4 ,under the influence of moisture the wood either swells or contracts1 while the wire and cable maintain their original lengths and adjustments4 ,the result is that a frame of this kind must be given constant attention if correct alignment is desired4 ,the adjustment of a wire braced wood fuselage should be performed only by a skilled mechanic1 as it is easily possible to strain the members beyond the elastic limit by careless or ignorant handling of the wire straining turnbuckles4 ,in the endeavor to bring an old warped fuselage back into line it is certain that the initial tension in the wires can be made greater than the maximum working stress for which the wires were originally intended4 ,shrinkage of the wood also loosens the bond between the wooden members and the steel fittings unless this is continually being taken up4 ,some form of unit construction1 such as the monocoque body1 is far more desirable than the common form of wire trussed wood body4 ,illustration3 ,fuselage ,details of ,de ,havilland ,v4 ,single ,seat ,chaser4 ,a ,rotary ,le ,rhone ,motor ,is ,used in a ,circular ,cowl4 ,the ,diagonal ,bracing in the ,front ,section is ,reinforced by ,laminated ,wood ,plates ,instead of by ,wires4 ,dimensions in ,millimeters4 99,fuselage ,fittings994 ,in the early days of aviation the fuselage fittings on many machines were made of aluminum alloy4 ,this metal1 while light1 was uncertain in regard to strength1 hence the use of the alloy was gradually abandoned4 ,at present the greater part of the fittings are stamped steel1 formed out of the sheet1 and are of a uniform strength for similar designs and classes of material4 ,the steel best adapted for the fittings has a carbon content of from #j4bj to #j4cj1 with an ultimate strength of #fj1jjj pounds per square inch1 and a #ae per cent elongation4 ,the steel as received from the mill should be annealed before stamping or forming to avoid fracture4 ,after the forming it can be given a strengthening heat treatment4 ,a lower steel lying between #j4aj and #j4ae carbon is softer and can be formed without annealing before the forming process4 ,this material is very weak1 however1 the tensile strength being about #dj1jjj pounds per square inch4 ,fittings made of the #j4ae carbon steel will therefore be heavier than with the #j4cj carbon steel for the same strength4 ,the thickness of the metal will vary from #a_/cb to #a_/af1 depending upon the load coming on the fitting4 ,a typical fuselage strut fitting is shown by ,fig4 #ca-;,a in which ,l-,l-,l are the longerons1 d is the fitting strap passing over the longerons1 ,s and ,so are the vertical and horizontal struts respectively4 ,the stay wires are fastened to ears 7b7 bent out of the fitting1 the wires being attached through the adjustable turnbuckles 7t74 ,the struts are provided with the sheet steel ferrules marked 7,f74 ,there are no bolts passing through the longitudinals ,l-,l'1 the fitting being clamped to the wooden member4 ,this is very simple and light fitting4 ,fig4 #ca-;,b is a similar type1 so simple that further discussion is unnecessary4 ,fig4 #cb shows a fuselage strut fitting as used on the ,standard ,type ,h-#c ,biplane4 ,we are indebted to ,aerial ,age for this illustration4 ,this consists of a sheet metal strap of ,u form which is bent over the longitudinal and is bolted to the vertical strut4 ,at either side of the strut are through bolts to which bent straps attach the turnbuckles4 ,these straps are looped around the bolts and form a clevis for the male ends of the turnbuckles4 ,illustration3 ,fig4 #ca4 ,typical ,fuselage ,strut ,fittings4 ,an old form of fuselage connection used on the ,nieuport monoplane is shown by ,fig4 #cc1 an example of a type in which the bolts are passed through the longeron member4 ,this fitting is very light but objectionable because of the piercing of the longeron4 ,an ,austrian aeroplane1 the ,hansa-,brandenberg1 has a wood fuselage in which no stay wires are used4 ,this fuselage is shown by ,fig4 #bc;a4 ,both the vertical and inclined members are wood struts4 ,the outer covering of wood veneer makes the use of stay wires unnecessary since the sheath takes up all horizontal stresses1 and hence forms a sort of plate girder construction4 ,the ,german ,albatros also employs a wireless veneer fuselage1 the construction being shown in detail by ,figs4 #cf and #cf;a4 ,three longerons are located on either side of the body1 the third member being placed at about the center of the vertical side4 ,as will be seen1 the veneer makes the use of wire bracing and metal connections unnecessary4 ,the veneer also insures perfect alignment4 ,illustration3 ,fig4 #cb4 ,fuselage ,strut ,fittings of the ,standard ,h-#c ,training ,biplane4 99,wing ,connections994 ,the lower wings are attached to the lower longitudinals by a special sheet steel fitting which also generally connects to a vertical strut at this point1 and to an extra heavy horizontal strut4 ,a sheet metal clevis1 or socket1 on the wing spar is pinned to the fuselage half of the fitting so that the wing can be easily detached when the machine is to be dissembled4 ,at this point a connection is also provided for the end of the inner interplane stay wires4 ,the horizontal strut at the point of wing attachment is really a continuation of the wing spar and takes up the thrust due to the inclination of the interplane stays4 ,in the majority of cases the horizontal thrust strut is a steel tube1 with the hinged connection brazed to its outer ends4 ,this is one of the most important and heavily loaded connections on the machine and should be designed accordingly4 ,illustration3 ,fig4 #cc4 ,fuselage ,fittings of the ,nieuport ,monoplane4 ,fig4 #cg shows a typical wing to fuselage connection of the hinge type4 ,the wing spar 7,g7 is covered with a sheet steel ferrule 7,a7 at its inner end4 ,two eye bars 7,b7 are bolted to the wing spar1 and over the ferrule1 the eyes of the bar projecting beyond the end of the spar4 ,this forms the wing half of the connecting hinge4 ,the eyes are fastened to the fuselage hinge member 7,h7 by means of the pin 7,e74 ,this pin has a tapered end for easy entry into the joint1 and is pierced with holes at the outer end for cotter pins or a similar retaining device4 ,the fuselage hinge member 7,h7 is brazed to the end of the steel tube strut 7,t74 ,this tube runs across the fuselage from wing spar end to wing spar end4 ,strut tube 7,t7 lies on1 and is fastened to1 the fuselage longeron 7,l71 and also lies between the two halves of the vertical strut 7,s74 ,the vertical strut is cut out at its lower end for the receipt of the steel tube 7,t74 ,a steel plate is brazed to the tube1 is wrapped about the longeron 7,l7 and is bolted to the vertical strut 7,s74 ,the interplane stay 7,f7 is attached to the pin 7,e7 at the point of juncture of the wing spar eye and the fuselage member of the hinge4 ,a collar 7,i7 is brazed to the tube1 and forms a means of attaching the fuselage stays 7,d74 ,the drift wires 7,c7 of the wings are attached to an eye at the end of one of the wing spar bolts4 ,as shown1 the fitting 7,h7 is a steel forging1 very carefully machined and reduced in weight4 ,the inside wing ribs are indicated by 7,k71 from which it will be seen that there is a gap between the end of the wings and the outside face of the fuselage4 ,illustration3 ,fig4 #cf4 ,veneer ,fuselage ,construction of the ,german ,albatros ,speed ,scout4 ,body ,outline ,is ,obtained by ,veneer ,diaphragms and no ,stay ,wires ,are ,used4 ,fig4 #cf-;a shows the construction of the wing joint of the ,german ,albatros machine4 ,the fuselage is of monocoque construction which allows of a simple attachment to the outer shell4 ,this is a very sturdy and simple connection4 ,fig4 #ch-,z is the wing attachment detail of the ,english ,london and ,provincial ,biplane 7#aiaf71 the fuselage in this case being of the wire trussed wood type4 ,we are indebted to ,flight for this illustration4 ,illustration3 ,fig4 #cf-;a4 ,details of ,albatros ,veneer ,fuselage ,construction4 ,in some machines the interplane stay wires are attached to a lug formed from the attachment plate1 but we do not consider that this construction is as good as the type in which the wire is attached directly to the wing spar pin4 ,while the former may be easier to assemble1 the attachment of the wire to the pin eliminates any eccentricity1 or bending moment1 due to the pull of the interplane stay4 ,the attachment in the ,l4 ,w4 ,f4 insures against any eccentricity in the stay attachment1 and at the same time makes the assembly and dismounting a very simple matter4 ,illustration3 ,fig4 #cg4 ,wing ,connection to ,fuselage4 99,chassis ,member ,attachment994 ,the attachment of the chassis struts generally involves some difficulty as these members usually intersect the line of the longerons at a very awkward angle4 ,if the wing attachment is near the same point1 as it generally is1 the detail is made doubly difficult4 ,the chassis must be pin connected as in the case of the wing joint so that the chassis members can be easily and quickly removed4 ,a detail of a chassis to body connection is shown by ,fig4 #ci4 ,in this figure 7,l7 is the lower longeron1 7,s7 is the vertical fuselage strut1 and 7,c7 is one of the chassis members4 ,the upper end of the chassis member is enveloped in a sheet steel ferrule 7,d7 which is bolted in place1 and which is provided with a clevis at its upper end for the attachment pin 7,p74 ,a plate 7,e7 is bolted to the fuselage strut 7,s7 and is passed around the lower longeron 7,l71 a hinge joint 7,h7 being provided for attachment to the chassis ferrule through the pin 7,p74 ,ears or lugs are left at 7,g-,g7 for the attachment of the fuselage stays 7,b-,b74 ,on the inner side of the plate 7,e7 are attachment lugs for the horizontal strut 7,h74 ,it will be noted that the plate 7,e7 is well provided with lightening holes so that the weight can be kept down to a minimum4 ,the pin is tapered at the end1 and is provided with cotter pin holes4 ,the fitting in general is small1 and does not produce any great degree of head resistance1 the small part exposed being of good streamline form4 ,illustration3 ,fig4 #chx4 ,wing ,connection of the ,albatros ,reconnaissance ,biplane4 ,fig4 #chy4 ,wing ,attachment of ,albatros ,fighter with ,pin ,joint4 ,fig4 #chz4 ,wing ,connection of ,london and ,provincial ,biplane4 ,great care should be taken in brazing or welding these fittings1 since the heat changes the structure of the metal and greatly reduces its strength4 ,the brazing temperature varies from #a1ejj to #a1gjj degrees1 a point well above the tempering heat of steel4 ,attempts have been made to heat treat the metal after the brazing operation1 but with very little success1 owing to the fact that the heat treating temperature is generally at or above the melting point of the brazing spelter1 hence is likely to cause holes and openings in the brazed joints4 ,with acetylene welded joints the parts can1 and should be1 heat treated after the welding4 ,while this is an apparent advantage of acetylene welding1 all parts cannot be successfully handled in this manner4 ,the welding torch can only join edges1 while the brazing spelter can be applied over almost any area of surface4 ,welding is very successful in joining thin steel tubes while in many fittings made of sheet metal1 brazing is the only feasible operation4 ,illustration3 ,fig4 #ci4 ,chassis ,connection4 ,both methods have a common fault1 in that they are unreliable4 ,imperfect welds and brazing are not always apparent from the outside1 actual breakage of the part being necessary to determine the true nature of the joint4 ,,fuselage ,,weights4 99,distribution of ,weight994 ,the weight of a fuselage depends upon the span of the wings1 upon the seating capacity1 and upon the weight and type of the power plant4 ,the weight also varies considerably with the type of construction1 that is1 whether of truss1 veneer1 or monocoque construction4 ,a heavily powered machine1 or one carrying more than a single person1 requires heavier structural members and hence weighs more than a small single seater4 ,the amount of fuel carried also has a considerable bearing on the fuselage weight4 ,probably the best method of treating this subject is to give the fuselage weights of several types of well known machines4 ,the reader will then have at least a comparative basis for determining the approximate weight4 7,truss type only47 ,there are so many variables that the weight cannot be determined by any set rule or formula4 ,alexander ,klemin in his ,course in ,aerodynamics and ,airplane ,design says that the approximate weight of a bare wood truss type fuselage is about #aej pounds for a machine having a total weight of #b1ejj pounds4 ,for small biplane and monoplane scouts weighing approximately #a1bjj pounds total1 the bare fuselage frame will weigh about #gj pounds4 ,these figures are for the bare frame alone and without seats1 controls1 tail skids or other fittings4 ,the weights given under the column headed ,wt4 ,bare include the engine beds1 tail skids1 flooring1 cowling and body covering1 and hence exceed the bone bare estimate of ,klemin by a considerable amount4 ,the all-steel fuselage of the large ,sturtevant battle-plane 7,model ,a7 weighs #afe pounds inclusive of the steel engine bed4 ,a wooden1 wire braced fuselage of the same size and strength weighs well over #bjj pounds1 the metal fittings and wires weighing about #fj pounds alone4 ,ash is used in the wood example for the longerons4 ,the struts and diagonal members in the ,sturtevant metal fuselage are riveted directly to the longitudinals1 without fittings or connection plates4 ,the safety factor for air loads is #h1 and for the ground loads due to taxi-ing over the ground1 a safety factor of #d is used4 ,after a minute comparison of the items comprising the fuselage of the ,curtiss ,,jn#d-;,b and the ,standard ,h-#c1 ,klemin finds that the fuselage assembly of the ,standard ,h-#c amounts to #ac4f per cent of the total loaded weight1 and that the fuselage of the ,curtiss ,,jn#d-;,b is #ae4e per cent of the total4 ,tanks1 piping and controls are omitted in both cases4 ,for machines weighing about #b1ejj pounds1 ,dr4 ,j4 ,c4 ,hunsaker finds the body weight averaging #h4b per cent of the total1 this figure being the average taken from a number of machines4 ,on careful examination it will be found that the fuselage assembly 7bare7 amounts to a trifle less than the wing group for biplanes having a total weight of from #a1ijj to #b1ejj pounds4 ,the relation between the wing weight and the fuselage weight seems to bear a closer relation than between the fuselage and total weights4 ,we will set these different relations forth in the following table3 ,,percentage ,,of ,,fuselage ,,weight ,fuselage ,weight as ,percentage of the ,total ,load ,name of ,wing ,weight ,as ,plane or ,body ,body ,body ,percentage of ,total ,investigator ,assembly ,assembly ,assembly ,weight ,bare and and ,equipment ,power ,plant ,curtiss #ae4ej #ag4hf #dc4if #ad4ae ,,jn#d-;,b ,standard ,h-#c #ac4fj #ag4gj #de4dj #ad4eb ,j4,c4 #h4bj #aa4ej #cd4cj #af4ej ,hunsaker ,author's #ad4if #ag4fb #df4ff #ad4fj ,experience ,average of #ac4jf #af4ag #db4eh #ad4id ,above ,in the above table1 the column headed ,body ,assembly and ,equipment includes the body frame1 controls1 tanks and piping4 ,in the fourth column1 the radiator1 motor1 propeller1 water1 and exhaust pipe have been added4 ,for the average value it will be seen that the bare fuselage is about #a4hh per cent lower than the weight of the wings4 ,it should be noted that the wing weight given is the weight of the surfaces alone1 and does not include the weight of the interplane struts1 wires and fittings4 ,the weight of the wing surfaces as above will average about #j4ge pounds per square foot4 ,based on the above figures1 we can obtain a rough rule for obtaining the approximate weight of the fuselage1 at least accurate enough for a preliminary estimate4 ,if ,a the total area of the wings1 then the total weight of the wings will be expressed by w #j4ge;,a4 ,the weight 7f7 of the fuselage can be shown as f #ac4jf_/adid x w #j4fe;,a4 99,example994 ,the area of the ,standard ,h-#d is #edb square feet total4 ,find the approximate weight of the fuselage4 ,by the formula1 f #j4fe;,a #j4fe x #edb #ceb pounds4 ,the actual bare weight is #cjb4j pounds4 ,for several other machines1 the actual weight is greater than the weight calculated by the formula1 so that the rule can be taken as a fair average1 especially for a new type that is not as refined in detail as the ,h-#c4 ,,size ,,of ,,longerons ,the size of the longerons1 that is1 the section1 is influenced by many factors4 ,as these members must resist flying loads1 the leverage of elevator flaps1 stresses due to control wires1 landing stresses and the weight of the motor and personnel it is always advisable to itemize the loading and then prepare a diagram to obtain the stresses in the different members4 ,this latter method is a method for a trained engineer1 but an exhaustive description of the method of procedure will be found in books on the subject of ,strength of ,materials4 ,for the practical man1 ,i give the following list of longeron dimensions so that he will have at least a guide in the selection of his material4 ,the length of the fuselage and power of motor are given so that the reader can obtain sizes by comparison1 although this is a crude and inaccurate method4 ,as the longerons taper from front to back1 the sizes of the section are given at the motor end1 and also at the tail4 ,the size of the front members depends principally upon the weight of the motor and the passenger load1 while the rear longerons carry the elevator loads and the tail skid shock4 ,if the rudder is high above the fuselage it introduces a twisting movement that may be of considerable importance4 ,the loads on the stabilizer1 elevators and the vertical rudder are very severe when straightening out after a steep dive or in looping1 and the pull on the control wires exerted by the aviator at this time greatly adds to the total stress4 ,in the front of the fuselage1 the motor exerts a steady torque 7twist7 in addition to the stress due to its weight1 and to this must be added the gyroscopic force caused by the propeller when the machine is suddenly changed in the direction of flight4 ,the combination of these forces acting at different times makes the calculation very difficult4 ,in the case of the ,curtiss ,r-#d1 the front longerons taper down from the motor #a4fc x #a4be to a point directly behind the pilot's seat1 the section at the latter point being #a4be x #a4be4 ,from this point the rear longerons taper down to #a x #a at the tail4 ,at the motor1 the section is #a4fc x #a4be4 ,the longitudinals of the ,bleriot monoplane are laminated and are built up of alternate layers of spruce and ash4 ,this is an old type of machine and this practice has since been discontinued4 ,it will be noted that as the power is increased1 the size of the front longerons is generally increased1 although this is not always the case in speed machines4 ,the ,chicago ,aero ,works' ,star fuselage could easily carry a #ij horsepower motor1 although this size is not regularly installed4 99,pusher ,type ,fuselage 7,nacelle7994 ,compared with the tractor biplane and the monoplane fuselage1 the body of the pusher is very short and light4 ,the latter body simply acts as a support for the motor and personnel since the tail loads are carried by the outriggers or tail booms4 ,the motor is located at the rear end of the body and may be either of the air or water-cooled type4 ,the accompanying figure shows a typical pusher type body1 or ,nacelle as it is sometimes called4 ,the advantages of the pusher type for military service are obvious4 ,the observer or gunner can be placed immediately in the front where his vision is unobstructed1 and where the angle of fire is at a maximum4 ,illustration3 ,typical ,pusher ,body ,showing ,wings1 and ,outrigger to ,tail ,surfaces4 99,twin ,motored ,fuselage994 ,twin motored aeroplanes generally have the power plants mounted at a point about midway between the fuselage and tips of the wings4 ,in almost every case1 the power plants are of unit construction1 that is to say1 consist of the motor1 radiator and propeller complete on one support1 only the fuel and oil tanks being mounted in the fuselage4 ,the fuselage of the twin may be similar in length and general construction to that of the tractor biplane1 or it may be a short nacelle similar to that used in the pusher type4 ,in any case1 the observer can be located in the extreme front of the body4 ,an interesting and unusual construction is the body of the ,caproni ,biplane 7#aiaf74 ,a center nacelle carries the passengers1 a pusher screw being located at the rear of the central body as in the case of the pusher biplane4 ,on either side of the center are the motors driving the tractor screws1 each motor being encased in a long tractor type fuselage that also supports the tail surfaces4 ,the latter fuselage serves to streamline the motors and takes the place of the usual outrigger construction4 ,there are three bodies1 two tractor screws1 and one pusher screw4 ,somewhat similar in design is the famous ,german ,billy ,two-,tails1 this machine being equipped with two tractor type bodies4 ,a motor is located in the front of each body4 ,each fuselage is provided with accommodations for passengers1 and is long enough to support the tail surfaces4 ,the ,caproni and the ,german machine are both very large machine and heavily powered4 99,u4,s4,a4 ,sea-,plane ,specifications 7#aiaf7994 ,these government specifications cover a twin motored sea-plane with a central nacelle4 ,the body is arranged so that the forward man 7observer7 can operate the forward machine gun through a horizontal arc of at least #aej1 and through a vertical arc of at least #bgj1 with the gun at an angle of about #ge with the center line of the body4 ,the muzzle must be forward of the propeller plane4 ,the rear man 7pilot7 operates a machine gun through a vertical arc of at least #aej to the rear1 and through a vertical arc of at least #ahj1 with the gun at an angle of about #aje with the fuselage center line4 ,the muzzle must be to the rear of the plane of propeller rotation4 ,the number of stays and other important connections which extend across the plane of propeller rotation shall be reduced to a minimum4 ,it is considered advisable to incorporate in the design of the body such a structure 7in the plane and #h inches forward of propeller plane7 as will prevent a broken propeller blade from severing the main body4 ,the system used in the construction of the cage masts used on battleships is suggested1 with a number of spruce compression members in place of stay-wires4 ,the clearance of the propeller tips from the sides of the central body shall be from #e to #ab inches4 ,no part of the gas tanks shall lie in the plane of propeller rotation1 nor within a space #f inches ahead of this plane4 ,a space extending at least #i inches back from the rear of the observer's seat1 and entirely across the body1 must be left open and unoccupied in order that any desired instruments can be installed therein4 ,in the center line of the body1 a circular hole #i inches in diameter shall be cut in the floor of the observer's cock-pit1 the rear of the hole being #e inches forward of the forward edge of the observer's seat4 ,the flooring of the pilot's and observer's cockpits shall consist of spruce strips #a_/b x #a_/b spaced at #a_/b intervals along the longerons4 ,no flooring is to be placed under the seats4 ,the safety factor of the body and tail structure shall not be less than #b4e1 the air speed being taken at #ajj miles per hour with the elevator at an angle of #bj and the fixed stabilizer surface at #f4 ,all wire tension members not readily accessible for inspection and adjustment are to be single strand high tensile steel wire4 ,all tension stays that are easily accessible shall be of non-flexible stranded steel cable4 ,for turnbuckle safetying ,no4 #bj semi-hard copper wire shall be used4 ,all cable shall be well stretched before making up the connections4 ,a load equal to #bj or #cj per cent of the breaking load shall be applied for a period of from two to three hours4 ,the hard wire must undergo a bending test by bending at a right angle turn over a radius equal to the diameter of the wire1 back and forth four times each way4 ,no more than four sizes of turnbuckles shall be used on the entire aeroplane structure4 ,the strengths and size numbers of the turnbuckles will be as follows3 ,no4 #a #h1jjj lbs4 ,no4 #b #d1fjj lbs4 ,no4 #c #b1ajj lbs4 ,no4 #d #a1ajj lbs4 ,controls and fittings in the vicinity of the compasses shall1 as much as possible1 be of non-magnetic material4 ,all steel plate and forged fittings shall be protected against the action of salt water by baking enamel1 the best standard three coat process being used4 ,all covered wiring and turnbuckles shall be coated by at least two coats of ,flexible ,compound4 ,all steel tubing shall be thoroughly cleaned1 slushed with mineral oil inside1 and plugged at both ends by wood plugs impregnated with mineral oil or paraffine4 ,all steel nuts1 bolts1 pins and cotter pins shall be protected by heavy nickel plating over copper4 ,all wood members1 especially faying surfaces1 end grain butts1 scarfs and joints1 shall be protected against the access of moisture before final assembly by the best grade of varnish1 or by impregnation by paraffine4 ,all wood shall be straight grained1 well seasoned1 of uniform weight1 and free of knots1 pitch pockets1 checks or cracks4 ,spruce to be of the very highest grade of selected straight1 even grained1 clear spruce4 ,it shall be air seasoned1 preferably for two years4 ,kiln dried wood is not acceptable4 ,it is highly desirable to have all bolts1 pins1 plate fittings and turnbuckle ends made of chrome vanadium steel 7,s4 ,a4 ,e4 ,specification #f4acj71 heat treated to obtain the best physical characteristics4 ,all parts and fittings that must be bent shall be heat treated after all bending operations are completed1 and by such a sequence of treatment as will produce the desired grain and toughness1 and relieve all stresses due to the bending4 ,this includes sheet and forged steel fittings1 turnbuckle ends and bolts and pins4 ,all steel parts and fittings submitted to stress or vibration shall be heat treated in such a manner as to produce the highest possible refinement of grain and give the greatest possible resistance to alternating and vibratory stresses4 ,where plate fittings are in contact with wooden members1 sharp edges next to the wood shall be removed4 ,in making up and connecting steel fittings1 welding shall be used wherever possible4 ,if impracticable to weld1 and in such cases only1 brazing will be used1 proper heat treatment to be employed to restore strength and toughness of metal after such welding or brazing4 ,extreme care should be taken to avoid nicking or kinking any wire1 cable or fitting4 ,fittings1 sheet or forged1 must be free from sharp corners and supplied with generous fillets4 ,in general the ,s4,a4,e4 ,standards will be acceptable1 and these standards for screw threads shall be used wherever possible4 ,u4,s4 ,standard threads will be accepted where threaded into cast iron1 cast aluminum or copper alloys4 ,all nuts and pins must be provided with one or more positive and durable safety devices4 ,in general1 where it must be expected that a structural fitting will be disassembled a number of times during the life of the aeroplane1 castellated nuts with split pins1 in accordance with ,s4,a4,e4 ,standards1 shall be used4 ,wherever this is not the case1 pins or bolts shall be riveted in a workmanlike manner4 ,seats shall be securely braced against both horizontal and vertical stresses4 ,arrangement and dimensions of cock-pits shall be as nearly as practicable to that indicated by the drawings 7not published in this chapter74 ,in addition1 if practicable1 the pilot should be provided with quick release arm rests4 ,sections of best grade of khaki on each side of seats1 in which pockets are made1 should be fastened to longerons and vertical posts in such a way as to be securely in place and yet readily detachable for inspection of structural wiring and fittings4 ,safety belts shall be provided for both seats and securely fastened4 ,the belts shall safely support at any point a load of #b1jjj pounds applied as in practice4 ,rubber shock absorbers in the safety belt system are considered to be an advantage4 ,the quick release device shall be as indicated in drawings and shall reliably and quickly function4 ,seat pads shall be quickly detachable in order that they may be used as life preservers4 ,they will be filled with ,kapok or other similar material and covered with real leather to protect it against the action of salt water4 ,suitable covers shall be provided over the top of the rear end of the fuselage4 ,these must be easily removed and capable of being securely fastened in place during flight4 ,space shall be allowed in the body directly in the rear of the observer's seat for the stowage of the sea anchor4 ,when in use1 the sea anchor shall be attached by suitable and convenient fastening hooks to the two points along the lower longerons1 and at the junction of the two vertical struts in the rear of the front seat4 ,the structure must be such that it will successfully withstand the stresses imposed by the sea anchor4 ,controls shall be of the standard ,deperdussin type1 installed in the rear cock-pit only4 ,the tanks for the main supply of gasoline shall be in the fuselage and located so that the longitudinal balance will not be disturbed by the emptying of the tank during flight4 ,the above data is not in the exact form of the original specifications and is not complete1 but gives only the specifications that affect the design of the body4 ,these were picked out part by part from the original4 99,army ,specification #ajjc 7,speed ,scout7994 ,these specifications cover the design of land machines1 the extracts given here referring only to the safety factor4 ,body forward of the cockpit shall be designed for safety factor of #aj over static conditions1 with the propeller axis horizontal4 ,body in rear of cockpit shall be designed to fail under loads not less than those imposed under the following conditions3 7a7 ,dynamic loading of #e as the result of quick turns in pulling out of a dive4 7b7 ,superposed on the above dynamic loading shall be the load which it is possible to impose upon the elevators1 computed by the following formula3 ,l #j4jje;,,av1 where ,a is the total area of the stabilizing surface 7elevators and fixed surface71 and ,v is the horizontal high speed of the machine4 ,the units are all in the metric system4 7c7 ,superposed on this loading shall be the force in the control cables producing compression in the longerons4 99,fuselage ,covering994 ,disregarding the monocoque and veneer constructed types of fuselage1 the most common method of covering consists of a metal shell in the forward end1 and a doped linen covering for that portion of the body that lies to the rear of the rear seat4 ,the metal sheathing1 which may be of sheet steel or sheet aluminum1 generally runs from the extreme front end to the rear of the pilot's cockpit4 ,sheet steel is more common than aluminum because of its stiffness4 ,military machines are usually protected in the forward portions of the fuselage by a thin armor plate of about #c millimeters in thickness4 ,this is a protection against rifle bullets and shrapnel fragments1 but is of little avail against the heavier projectiles4 ,armor is nearly always omitted on speed scouts because of its weight4 ,bombers of the ,handley-,page type are very heavily plated and this shell can resist quite large calibers4 ,the fabric used on the rear portion of the fuselage is of linen similar to the wing covering1 and like the wing fabric is well doped with some cellulose compound to resist moisture and to produce shrinkage and tautness4 ,on the sides and bottom the fabric is supported by very thin1 light stringers attached to the fuselage struts4 ,on the top1 the face is generally curved by supporting a number of closely spaced stringers on curved wooden formers4 ,the formers are generally arranged so that they can be easily removed for the inspection of the wire stay connections and the control leads4 ,on some machines the top of the fuselage consists entirely of sheet metal supported on formers1 while in others the metal top only extends from the motor to the rear of the rear cockpit4 ,,chapter ,,xiii4 ,,chassis ,,construction4 99,general ,notes994 ,the chassis or landing gear carries the weight of the aeroplane when resting on or running over the ground1 and is subjected to very heavy shocks1 especially when landing4 ,it is provided with pneumatic tired wheels1 an elastic shock absorbing device1 and the structural members that connect the axle with the fuselage4 ,in some forms of landing gear1 the wheels are supplemented by long horizontal skids which serve to support the machine after the elastic shock absorbers are fully extended or when the wheels collapse4 ,the skids also protect the aeroplane in cases where the wheels run into a ditch and also prevent the machine from nosing over in a bad landing4 ,since the skids and their structural members cause a high resistance they are now seldom used except on the larger and slower machines4 ,in running over the ground1 or in making a hard landing1 part of the shock is taken up by the deflection of the tires and part by the deflection of the shock absorber4 ,the greater the movement of the tires and absorber1 the less will be the stress in the frame4 ,in the majority of cases1 the shock absorbers consist of rubber bands or cords1 these being wound over the axle and under a stationary part of the chassis members4 ,since rubber is capable of absorbing and dissipating a greater amount of energy per pound of weight than steel1 it is the most commonly used material4 ,rubber causes much less rebound or kick than steel springs4 ,the principal objection to rubber is its rotting under the influence of sunlight1 or when in contact with lubricating oil4 ,the movement of the axle tube is generally constrained by a slotted guide or by a short radius rod4 ,the design of a suitable chassis is quite a complicated problem1 for the stresses are severe1 and yet the weight and resistance must be kept at a minimum4 ,in running over rough or soft ground for the ,get off1 the shocks and vibration must be absorbed without excessive stress in the framework1 and without disturbing the balance or poise of the machine4 ,there must be little tendency toward nosing over1 and the machine must be balanced about the tread so that side gusts have little tendency in throwing the machine out of its path4 ,it must be simple and easily repaired1 and the wheels must be large enough to roll easily over moderately rough ground4 ,illustration3 ,fig #a4 ,v ,type ,chassis as ,applied to ,zens ,monoplane4 ,courtesy ,flight4 99,types of ,chassis994 ,the simplest and most extensively used landing gear is the ,vee type shown by ,fig4 #a1 and is equally applicable to monoplanes1 biplanes or triplanes4 ,primarily1 the ,vee chassis consists of two wheels1 an axle1 a rubber shock absorber1 and two sets of ,vee form struts4 ,the chassis shown by ,fig4 #a-;a is that of the ,hansa-,brandenburg and is typical of biplane chassis4 ,the winding of the rubber cord and the arrangement of the chassis struts are clearly shown4 ,the two struts are connected at the bottom by a metal fitting1 and the rubber is wound over the axle and under this fitting4 ,no guiding device is used for the axle1 the machine being freely suspended by the chord4 ,the struts are made as nearly streamline form as possible4 ,illustration3 ,fig #a;a4 ,v ,type ,chassis ,used on ,hansa-,brandenberg ,biplane4 ,fig4 #b is a front view of a typical ,vee chassis1 and ,fig4 #c is side view of the same device1 the same reference letters being used in each view4 ,the vertical struts ,c run from the fuselage at ,f to the connecting axle guide plate ,g4 ,the wheels ,w-,w are connected with the steel tube axle ,a1 and the struts are braced against side thrust by the cross-tube ,d and the stay wire braces ,b-,b4 ,in ,fig4 #c the metal fitting ,g is provided with the guiding slot ,s for the axle ,a4 ,the elastic rubber cord absorber passes over the axle and is fastened to the plate ,g by the studs ,i4 ,fig4 #d is a side view of the chassis of the ,lawson trainer1 which like many other primary training machines1 uses a front pilot wheel to guard against nosing over4 ,the rear two wheels 7,w7 are elastically supported between the ,vee struts ,c and ,f1 while the front wheel ,x is attached to the fuselage by the vertical strut ,e1 and to the rear wheel frame by the tube ,g4 ,it will be noted that the front wheel is smaller than the rear main wheels1 as this wheel carries but little load4 ,the tail skid ,t is hinged to the fuselage and is provided with elastic cord at the upper end so that the shock is reduced when the tail strikes the ground4 ,fig4 #e shown directly above the ,lawson trainer1 is the complete assembly of the ,hansa-,brandenburg already described4 ,the tail skid of the ,hansa-,brandenburg is indicated by ,t4 ,illustration3 ,figs4 #b-c4 ,typical ,v ,chassis ,with ,axle ,guide4 ,the metal shod ash skid stick is hinged to the lower face of the fuselage1 and at the upper end is attached to a stationary fuselage member through four turns of elastic cord4 ,when the skid strikes an obstacle the rubber gives and allows the tail to move in relation to the ground4 ,by this arrangement the greater part of the device is enclosed within the fuselage and1 hence1 produces little head resistance4 ,illustration3 ,fig #d4 7,below74 ,lawson ,training ,tractor ,biplane4 ,fig4 #e 7,above74 ,hansa-,brandenburg ,fighting ,biplane ,showing ,chassis and ,tail ,skid 7t74 ,fig4 #g is the skid chassis of the ,farman biplane which shows clearly the arrangement of the skids and the shock absorbing suspension4 ,a metal bridge is attached to the axle1 and a series of short rubber bands are used in connecting the axle bridge1 and the bridge on the skid4 ,a triangular tubular radius rod is attached to the axle and hinged to the skid4 ,this restrains the travel of the axle in a fore and aft direction4 ,another form of skid shock absorber is given by ,fig4 #h1 in which the rubber rings pass over a spool on the axle4 ,the guiding links or radius rods on the inside of the skids regulate the axle travel4 ,in general1 the use of a radius rod is not desirable as it transmits a percentage of the shock to the machine4 ,illustration3 ,fig4 #g4 7,left74 ,farman ,skid ,type ,chassis4 ,fig4 #h4 ,another ,type of ,skid ,chassis in ,which the ,axle ,is ,guided by a ,radius ,rod or ,lever4 ,illustration3 ,fig4 #i4 ,chassis ,details of the ,nieuport ,monoplane4 ,this ,has a ,central ,skid and ,uses an ,automobile ,type ,steel ,spring ,instead of ,rubber ,cord4 ,fig4 #aj ,is a ,detail of the ,nieuport ,spring4 7,at ,right47 ,fig4 #i is an older form of ,nieuport monoplane chassis1 a steel cross spring being used in place of the usual rubber bands4 ,this is simple1 but comparatively heavy1 and is subject to frequent spring breakage4 ,to guard against spring failure1 a long ash skid is placed under the axle4 ,the spring system is connected with the body by three sets of oval steel struts4 ,an old type of ,curtiss chassis is given by ,fig4 #aa4 ,this has been widely used by amateurs and exhibition flyers1 but requires a fairly smooth landing ground as there are no shock absorbers4 ,the only shock absorption is that due to the deflection of the tires4 ,the extreme forward position of the front wheel effectually prevents any tendency toward nosing over when landing4 ,illustration3 ,fig4 #aa4 ,an ,old ,type of ,curtiss ,exhibition ,chassis ,with ,three ,wheels4 ,illustration3 ,fig4 #ab 7,left74 ,standard ,h-#c ,shock ,absorber4 ,fig4 #ac4 7,right74 ,rubber ,cord on ,axle4 ,a ,standard ,h-#c shock absorbing system is given by ,fig4 #ab4 ,this has a bracket or hanger attached to the axle over which the elastic cord is wrapped4 ,the cord is wrapped in continuous turns between the axle hanger and the bottom of the ,vee support members4 ,as shown1 the upper streamlined bar is the axle1 while the lower is the cross bar brace which serves to hold the lower ends of the ,u's4 ,i am indebted to ,aerial ,age for this cut4 ,in order to guide the axle in a straight line in its up and down movement1 two radius links are attached between the axle and the front vertical strut4 ,one decided advantage of the ,standard construction is that the cords are wound without crossing the strands1 thus reducing cutting and wear between the cord turns4 ,fig4 #ac is a variation of ,fig4 #ab1 the cord being wound directly around spools on the axle and the lower stationary cross tube4 ,the axle is guided by a slot in the guide plate at the right1 while end motion is controlled by a radius link4 ,fig4 #ad is the double wheel arrangement of a large ,twin bombing plane4 ,two wheels are placed directly under each of the motor units so that a portion of the load is communicated to the chassis by tubes4 ,diagonal tubes transmit the body load to the chassis4 ,illustration3 ,fig4 #ad4 ,chassis for ,twin ,motored ,biplane of ,bombing ,type4 99,folding ,chassis994 ,owing to the great relative resistance of the chassis it has been suggested by many designers to provide a folding frame which will automatically fold up into the body after the machine has left the ground4 ,this would be a decided advantage but the gear is complicated and probably not altogether reliable4 99,height of ,chassis994 ,the height of the chassis is made as small as possible with a sufficient clearance for the propeller tips4 ,it is usual to have the tips of the propeller blades clear the ground by from #aj to #ab inches when the aeroplane is standing with the body in a horizontal position4 ,any smaller clearance is almost certain to result in broken blades when landing at a sharp angle or when running through high grass4 ,if the chassis is excessively high the resistance will be high and the machine is also likely to be top heavy4 ,illustration3 ,figs4 #ae-af4 ,methods of ,calculating ,wheel ,position on ,two ,wheel ,chassis4 ,this ,is an ,important ,item in the ,design of an ,aeroplane4 99,location of ,wheels994 ,the exact location of the wheels1 in a fore and aft direction1 is of the greatest importance4 ,if they are too far ahead of the center of gravity1 too much weight will be placed on the tail skid and excessive running will be required to get the tail off the ground4 ,if the wheels are too far back1 the machine will be likely to nose over when landing or running over the ground4 ,in any case1 the wheels must be well ahead of the center of gravity so that the weight will resist a forward overturning moment4 ,in the majority of orthogonal biplanes1 in which the leading edges of the upper and lower wings are on the same vertical line1 the center of the wheel is from #c to #f inches back of the leading edges4 ,in staggered biplanes the wheel center is from #f inches to one foot in front of the lower leading edge4 ,this difference is caused by the fact that the center of gravity is nearer the leading edge of a staggered wing than with the ,orthogonal type1 and hence the wheels must be further forward4 ,fig #ae 7upper diagram7 shows the conditions when the machine is running over the ground with the body horizontal4 ,the vertical line a-a passing through the center of gravity ,c ,g is a distance ,n from the center of the wheel4 ,the weight acting down has a tendency to pull the tail down1 this moment being equal to the weight of the machine multiplied by the distance ,n1 or ,w x ,n4 ,the elevator flap ,m exerts a lifting force ,ky which acts through the lever arm ,l1 and opposes the moment due to the weight4 ,the force ,k must be equal to ,k ,,wn_/,l4 ,the distance ,i is the distance of the wheel center line from the entering edge of the wing4 ,the weight on the tail skid ,s when the machine is resting on the ground will be equal to ,s ,,wn_/,m1 and this may range anywhere from #dj to #bjj pounds1 according to the size of the aeroplane4 ,fig4 #af illustrates a principle of wheel location advanced by ,capt4 ,byron ,q4 ,jones1 and published in ,aviation and ,aeronautical ,engineers1 ,nov4 #af1 #aiaf4 ,the body is shown in a horizontal position with the propeller axis ,x-,x horizontal4 ,the center of gravity is at ,g on ,x-,x1 the weight acting down as at ,p with the line prolonged meeting the ground line at ,b4 ,a line ,e-,e is a line drawn tangent to the wheels and the tail skid at ,d1 the angle of this line with the ground determining the maximum angle of incidence4 ,e-,e is the ground line when the machine is at rest4 ,for the best conditions1 ,capt4 ,jones finds that the line connecting the point of tangency ,c1 and the center of gravity at ,g1 should make an angle of #ac degrees and #aj minutes with the vertical ,,gb dropped through the center of gravity4 ,with the line ,,ga drawn perpendicular to the resting line ,e-,e1 the angle ,,bga should be #aj degrees as nearly as possible4 ,this is for a two-wheel ,vee chassis1 but with a third front wheel as with the training of type the angle ,,cgb can be made less4 ,capt4 ,jones has found that with the wheels in the above location there will be no tendency to nose over even with very poor landings1 and this method has been applied to the training machines at the ,san ,diego ,signal ,corps aviation school4 ,if the angle ,,bga is greater than #aj degrees it is difficult to taxi the machine on the ground1 this tending to make the machine spin or turn into the wind4 ,capt4 ,jones claims that a two-wheel chassis arranged according to these rules is superior to the three-wheel type for training purposes since the tendency toward spinning is less4 ,the location of the tail skid ,s should be such that the elevator and rudder surfaces are well off the ground with the skid fully deflected1 and yet the skids must be low enough to permit of the maximum angle of incidence or an angle of ,,exx #aj degrees4 ,to a certain extent1 the maximum angle of incidence determines the chassis height4 ,if the angle ,,exx is made greater than the greatest angle of incidence1 the wings can be used as air brakes in bringing the machine to a quick stop after landing4 ,the track1 or the distance between the centers of the wheels measured along the axle1 must be about #a_/g or #j4ae of the span of the lower wing4 ,this makes the track vary from #e to #g feet on the usual types1 and as high as #ae feet on the large bombing planes4 ,the track must be great enough to prevent overturning when making a landing on soft ground or with a cross wind4 ,if the track is excessive1 there will be a heavy spinning moment in cases where one wheel strikes a depression or soft spot in the ground4 99,shock ,absorbers994 ,the axle movement allowed by the elastic shock absorbers and guiding appliances averages from #e to #f inches4 ,the greater the movement1 the less will be the stresses induced by a given drop1 but in practice the movement is generally limited by considerations of chassis height and propeller clearance4 ,it can be proved that a movement of #e inches will produce a maximum stress equal to #h4f times the weight of the machine under conditions of a one-foot drop1 while with an absorber movement of #f inches the stress is reduced to #g4e times the weight4 ,this calculation takes the tire deflection into consideration4 ,with the absorber movement limited to one inch1 the stress may be as high as #ce times the weight of the machine4 ,f,w 7#b #b4gg_/x7 where ,w weight of machine in pounds1 ,f the stress produced by the fall1 and x the absorber movement in inches4 99,landing ,gear ,wheels994 ,the wheels are generally of the tangent laced wire spoke type1 and are enclosed with discs to reduce the resistance4 ,they must have very wide hubs to resist the heavy end stresses caused by landing sidewise4 ,the length of the hub should be at least twice the diameter of the tire and a greater width1 say three times the tire diameter1 is preferable4 ,the narrow hubs used on motorcycle wheels are not safe against side blows1 although they may be capable of withstanding the vertical load4 ,the wheels are rated according to the outside diameter over the tire1 and by the diameter of the tire casing4 ,a #bf x #d wheel signifies that the outside diameter is #bf inches with a casing diameter of #d inches4 ,the #bf x #d tires are used on the majority of training machines of the two-wheel type1 while a #bj x #d wheel is used for the front wheel of the three-wheel trainer4 ,two larger sizes1 #cj x #d and #cd x #d1 have also been used to some extent1 particularly on the ,ackerman spring wheels4 ,,chapter ,,xiv4 ,,estimation ,,of ,,weight4 99,effect of ,weight994 ,weight is an all important consideration and is most difficult to estimate unless one has accurate data on existing machines of the same type4 ,the total weight in flying order depends upon the useful load to be carried1 and upon the weight of the power plant4 ,the weight of the latter varies both with the useful load and with the speed1 climb1 and duration of flight4 ,the type of aeroplane determines the relative head resistance which again reflects back to the weight of the power plant4 ,the only reason for the existence of an aeroplane is to carry a certain useful load for a given distance1 and this useful load is the basis of our weight calculations4 ,the basic useful load consists of the passengers and cargo1 although in some specifications the live load may be construed as including the weight of the fuel1 oil and instruments1 and in the case of military aeroplanes1 the weight of the armament1 armor1 ammunition1 wireless and cameras4 ,for comparison1 the elements constituting the live load should always be specified4 ,for a given horsepower1 speed and climb1 it is obvious that the dead or structural weight should be at a minimum for a maximum live load capacity4 ,the dead load carried in present aeroplanes will be undoubtedly reduced in the future by the adoption of lighter and stronger materials1 better methods of bracing1 and by reductions in the weight of the power plant4 ,just as the automobile industry developed light and powerful materials of construction1 so will the aeroplane designer develop more suitable materials for the aircraft4 ,while the present power plant has been refined to a remarkable extent when compared with the older types1 it is still far from the lowest possible limit4 ,at present the complete power unit--the motor1 radiator1 propeller1 water1 etc4--will weigh from #b to #e pounds per horsepower4 ,with a given aeroplane1 the performance is determined by the total weight and power4 ,the duration and flight range can be increased by increasing the fuel weight at the expense of the passenger or cargo weight4 ,the power available for climbing is the excess of the total power of the motor over the power required for horizontal flight4 ,since the power for horizontal flight depends principally upon the weight1 it is at once evident that the weight is a regulating factor in the climbing speed4 ,in fact the climbing speed may be almost directly determined from the weight carried per horsepower at normal flight speed4 ,a fast climbing scout may weigh from #h to #ab pounds per horsepower1 while the large low climbing machine will weigh from #af to #bj pounds per horsepower1 the respective climbing speeds being approximately #a1bjj and #cej feet per minute4 99,fuel ,efficiency and ,weight994 ,the efficiency of the motor1 or its fuel consumption for a given output1 has a very marked effect upon the total weight of the aeroplane4 ,under certain conditions a very light motor with a high fuel consumption will often contribute more to the total weight than a heavier but more economical motor4 ,in short flights1 up to #c hours1 the very light rotating cylinder motor with its high fuel consumption probably gives the least total weight1 but for longer flights the more efficient and heavier water-cooled type is preferable4 ,for flights of over three hours the fuel weight is a considerable percentage of the total weight4 ,the proper motor for any machine must be selected by computing the weight of the fuel and oil required for a given duration and then adding this to the total weight of the engine and its cooling system4 99,distribution of ,weight994 ,practically the only way to predict the weight of a proposed machine is to compare it with a similar existing type4 ,after the ratio of the useful load to the total load has been determined1 the useful load of the proposed machine can be divided by the ratio factor to obtain the total weight4 ,it should be noted in this regard that if the proposed machine is much larger than the nearest existing example1 a liberal allowance must be made to compensate for the increase in the proportional weight of the structural members4 ,there have been many mathematical formulas advanced for predicting the weight1 but these are very inaccurate in the majority of cases4 ,as a rough estimate1 based on a number of successful machines1 the weight of the actual aeroplane structure without power-plant1 live load1 fuel1 oil1 or tanks1 is very nearly #cb per cent 7#j4cb7 of the total weight4 ,the remaining #fh per cent is divided up among the power-plant1 fuel and live load4 ,thus1 the aeroplane structure proper of a machine weighing #bjjj pounds total will be #bjjj x #j4cb #fdj pounds4 ,taking the weight of the power plant1 tanks and piping at #bh per cent1 the total dead load of the bare machine without fuel or oil will be #fj per cent of the total4 ,with a training aeroplane built for a #f-;hour flight1 the fuel and oil will approximate #af per cent1 so that the total percentage possible for the crew and cargo will be #bd per cent4 ,with a given live load1 the total load can now be calculated by dividing the live load by its percentage4 ,using the above value1 for example1 the total weight in order of flight with a live load of #gbj pounds becomes3 ,w #gbj_/j4bd #cjjj pounds4 ,in government specifications the total weight of the pilot and passenger are taken at #ccj pounds1 or #afe pounds per man4 ,gasoline and oil are for a #d-;hour flight4 ,a safer average figure will be #agj pounds per man1 and a fuel allowance of #f hours4 ,the floats of a seaplane or flying boat bring the percentage of the dead load much higher than with the land type of chassis4 ,the following table will give an idea as to the weight distribution expressed both in pounds1 and as a percentage of the total weight4 ,it covers a wide range of types1 varying from the training types ,curtiss ,,jn-#d;,b and the ,standard ,h-#c1 to the ,handley-,page ,giant bomber and the ,nieuport speed scout4 ,the average values found by ,hunsaker for a number of machines weighing in the neighborhood of #bejj pounds is given in the fourth column4 ,under each heading are the actual weights and the percentages of the total weight for each item4 ,items marked 7997 include both gasoline and oil4 ,mark 7,c7 is the power plant complete1 and 77 includes radiator4 99,weight ,per ,horsepower994 ,as already explained1 the weight carried per horsepower varies with the type of machine4 ,when the total weight is determined for any aeroplane1 the power requirements can be calculated by dividing the total weight by the weight per horsepower ratio4 ,a fair value for a training or exhibition machine is from #ah to #bj pounds per horsepower1 while for a very high speed machine1 such as a chaser1 the weight will be taken at #aj pounds per horsepower4 ,for two-seater fighters #af to #ah pounds is fair practice4 ,for a comparison of the horsepower-weight ratios used on different well-known machines see tables in ,chapter ,,ii4 ,thus1 if our total weight is found to be #bdjj pounds as determined from the above table1 and if this is a training machine1 the horsepower will be3 #bdjj_/bj #abj horsepower4 ,using the same total weight1 but powered for two-seater fighter conditions1 the power will be increased to #bdjj_/af #aej horsepower4 ,as a scout the power will be increased still further to #bdjj_/ajbdj horsepower4 ,as a problem in solving the weight and horsepower from the data1 we will assume that we are to design a two-seater fighter with a total useful load of #abjj pounds4 ,this load consists of the following items3 ,personnel 7#b7 #ccj pounds2 gas and oil #ejj pounds2 guns and ammunition #cgj pounds4 ,the nearest example that we have to this live load is that of the ,standard ,h-#c1 which carries #gdd pounds and in which the percentage of live load is #bh4a per cent4 ,as our machine will be somewhat larger1 we will not be far from the truth if we take the percentage as #j4bg instead of #j4bha4 ,the total weight1 in flying order1 will now be #abjj_/j4bg #dddj pounds4 ,at #af pounds per horsepower the motor will be3 #dddj_/afbgg horsepower4 ,an empirical formula for a high-speed scout was set forth in ,aviation and ,aeronautical ,engineering by ,d4 ,w4 ,douglas4 ,this is based on the horsepower unit4 ,a unit wing loading of #h4de pounds per square foot1 and a low speed of #ee miles per hour was assumed4 ,the wing section chosen was the ,u4,s4,a4-#a4 ,in the formula1 ,h horsepower3 - ,power plant weight #c ,h4 - ,chassis weight #j4g ,h4 - ,tail weight #j4be ,h4 - ,fuel for #b4be hours #a4d ,h4 - ,military load #bej pounds4 - ,tanks and piping #j4db ,h4 - ,fuselage weight #a4hd ,h4 - ,wing weight #a lb4 sq4 ft4 - ,propeller #b4h_/;,h4 - 7,total7 7#g4fa ,h #b4e_/;,h #bej7_/g4de ,weight of aeroplane fully loaded in the order of flight4 99,weight of ,wings994 ,the weight of the wings depends upon the span1 very small machines having wings that weigh only #j4ch pounds per square foot1 while the wings of very large machines may run as high as #a4a pounds per square foot4 ,for average size biplanes from #j4ge to #j4hj pounds per square foot would probably be safe--that is1 for areas ranging from #dej to #eej square feet4 ,the weight of the upper wing of the ,nieuport is #j4hae pounds per square foot1 while the lower wing 7short chord7 is #j4fdf pounds per square foot4 ,the wings of the ,standard ,h-#c trainer will average #j4gg pounds per square foot1 the lower wing and center section being heavier than the upper wing4 ,the wings of the ,curtiss ,,jn-#d;,b will average #j4ge pounds per square foot4 ,these weights do not include the interplane wires or struts1 nor the fittings4 ,the total weight of the interplane struts of the ,,jn-#d;,b1 the ,aviatic1 and machines of similar size will average from #bh to #cj pounds4 ,the ailerons will weigh about #ab pounds each4 99,weight of ,motors994 ,there is a considerable difference in the weight of air-cooled and water-cooled motors4 ,the water1 water piping1 radiators and jackets of the water-cooled motors adds considerably to the weight of the complete power plant4 ,the mountings are heavier for the water-cooled motors1 and because of the tandem arrangement of the cylinders1 the crankshaft and crankcase weigh more4 ,in taking the bare weight of the power plant all of the accessories must be included4 ,in the following table1 the bare engine includes the carbureter1 magneto1 and necessary integral accessories1 but does not include the jacket water1 mounting1 radiator1 oil in base1 water piping1 nor controls4 ,water-cooled motors are marked by 7,w7 and air-cooled by 7,a74 ,rotary air-cooled are 7,,ra71 and gallons 7,g74 ,,weights ,,of ,,aeronautical ,,motors4 ,the bare radiator will weigh from #j4dh to #j4ef pounds per horsepower1 the average being safe at #j4eb4 ,the water contained in the radiator will average #j4ce pounds per horsepower4 ,the weights of the piping and the water contained therein will be computed separately4 ,the circular sheet metal cowl used over the rotary cylinder air-cooled motor is equal to twice the square root of the motor weight1 according to ,barnwell4 ,propeller weight varies considerably with the diameter1 pitch1 etc41 but a safe rule will give the weight as #b4h ,h where ,h horsepower4 ,the tanks will weigh from #j4ge to #a4b pounds per gallon of contents1 or approximately #a_/e the weight of the contents when completely filled4 99,chassis and ,wheel ,weight994 ,the chassis of a two-wheel trainer will weigh about #ij pounds complete1 although there are chassis of training machines that weigh as much as #adj pounds4 ,the chassis of speed scouts will be from #bb to #dj pounds complete4 ,tail skids can be taken at from #f to #h pounds4 ,tangent wire wheels complete with tires are about as follows3 #bf x #d #ba pounds2 #bf x #e #bh pounds2 #bf x #c #ad pounds4 ,ackerman spring spoke wheels are estimated as follows3 #bj x #d #ag4e pounds2 #bf x #c #bb pounds2 #bf x #d #cb pounds2 #cj x #d #ce pounds2 #cd x #d #de pounds4 99,military ,loads994 ,a #bj-mile wireless outfit devised by ,capt4 ,culver weighed #dj pounds with storage batteries1 while the #abj-mile outfit weighed #fj pounds with a #ahj-watt generator4 ,the #adj-mile ,u4,s4,a4 mule-back wireless of #aiab weighs #de pounds4 ,the ,blimp specifications allow #bej pounds4 ,the ,lewis gun as mounted on the #aa ,nieuport weighs #aaj pounds1 including mount1 gun and ammunition4 ,lewis gun bare is #bf pounds4 ,the ,davis #f-pounder1 ,mark ,,iv1 weighs #ajc pounds with mounting but without ammunition1 while the same make of #c-;inch #ab-pounder weighs #bch pounds under the same conditions4 99,controls and ,instruments994 ,the ,deperdussin type controls used on the ,curtiss ,,jn-#d;,b weigh #af pounds per control1 while those installed in the ,standard ,h-#c weigh about #ac pounds4 ,an average of #ae pounds per control is safe4 ,an instrument board for the aviators' cock-pit1 fully equipped1 weighs from #bj to #bd pounds4 ,the front1 or students' instrument board will average #aj pounds4 ,pyrene extinguisher and brackets #g pounds2 ,speaking tube #c pounds2 ,oil pressure line and gage #c pounds2 ,side pockets #c pounds2 ,tool kit #aj pounds4 99,control ,surfaces994 ,the rudder1 stabilizer1 fin1 and elevator can be made so that the weight will not exceed #j4fj to #j4fe pounds per square foot4 99,general ,notes on ,weight994 ,before starting on the weight estimates of the machine the reader should carefully examine the tables in ,chapter ,,ii which give the weights1 and general characteristics of a number of modern machines4 99,weights and ,wing ,area994 ,when the weight of the machine is once determined1 the next step will be to determine the wing area4 ,for speed scouts or very large heavy duty machines the choice of a wing section must be very carefully considered4 ,for the speed scout several wings giving a minimum high speed resistance should be examined1 such as the ,eiffel #cg or the ,u4 ,s4 ,a-#a or ,u4,s4,a4-#f4 ,for the low-speed aeroplane to be designed for great lift1 a number of sections such as the ,u4,s4,a4-#d or the ,r4,a4,f4-#c should be tried for a number of speeds and angles4 ,for training machines a wing of the ,all around type such as the ,r4,a4,f4-#f should be adopted1 the structural characteristics in the case of a trainer having an important bearing on the subject4 ,if ,w weight of the machine in pounds1 ,v low speed in miles per hour1 ,a total area in square feet1 and ,kylift coefficient1 then the area becomes ,a,w_/,ky,v4 ,compensation must be made for biplane interference for aspect ratio1 and stagger as previously explained4 ,for an ordinary training machine with the usual gap_/chord ratio1 and aspect ratio1 the correction factor of #j4he may be safely employed4 99,example994 ,we will take the case of an aeroplane carrying a personnel load of #cdj pounds1 oil and gasoline #cgj pounds1 and baggage amounting to #aij pounds1 instruments #ajj pounds4 ,total live load will be #ajjj pounds4 ,taking the live load percentage as #j4cj1 the total load will be #ajjj_/j4cj #cccc pounds4 ,if the low speed is #ej miles per hour1 and the maximum ,ky of the chosen wing is #j4jjc at this speed1 the area will be ,a ,w_/,ky,v #cccc_/j4jjc x 7#ej x #ej7 #ddd square feet4 ,since this is a biplane with a correction factor of #j4he1 the corrected area will be3 #ddd_/j4he #ebc square feet4 ,the unit loading1 or weight per square foot will be3 #cccc_/ebc #f4cf pounds4 ,the corrected area includes the ailerons and the part of the lower wing occupied by the body4 99,empirical ,formula for ,loading994 ,after investigating a large number of practical biplanes1 the author has developed an expression for determining the approximate unit loading4 ,when this is found1 the approximate area can be found by dividing the total weight by the unit loading4 ,this gives an idea as to the area used in practice4 ,it was found that the unit loading increased with the velocity at nearly a uniform rate4 ,this gave an average straight line formula that agreed very closely with #abh examples4 ,if ,v ,maximum velocity in miles per hour1 and w weight per square foot1 then the unit loading becomes3 w #j4jfe,v - #j4be for the average case4 ,for high speed scouts this gives a result that is a trifle low1 the formula for a fast machine being more nearly w #j4fe,v - #j4ae1 for speeds over #ajj miles per hour4 ,a two-seat machine of average size weighs #bejj pounds1 and has a maximum speed of #ij miles per hour4 ,find the approximate unit loading and area4 ,the loading becomes3 w #j4jfe,v - #j4be 7#j4jfe x #ij7 - #j4be #e4f pounds per square foot4 ,the approximate area will be3 #bejj_/e4fj #ddf square feet4 ,if the above machine had a speed of #aaj miles per hour1 the formula would be changed for the high-speed type machine1 and the loading would become3 w #j4jfe,v - #j4ae 7#j4jfe x #aaj7 - #j4ae #g4jj pounds per square foot4 ,the required area will be3 #bejj_/g4j #cgb square feet4 ,when the unit load is also determined in this way it is a very simple matter to choose the wing section from ,ky w_/,v4 99,area ,from ,live ,load and ,speed994 ,by a combination of empirical formula we can approximate the area directly4 ,for the average size machine1 w #j4jfe,v - #j4be4 ,and the total weight ,w ,u_/#j4cb where ,u is the useful or live load4 ,since ,a ,w_/w1 then ,a ,u_/7#j4fe,v - #j4be7 x #j4cb ,u_/#j4jba,v - #j4jh4 ,thus if an aeroplane travels at #ij miles per hour and has carried a useful load of #hjj pounds 7including gas and oil71 the approximate area is3 ,a ,u_/#j4jba4,v #j4jh #hjj_/7j4jba x #ij7 - #j4jh #ddb square feet4 ,this assumes that the useful load is #j4cb of the total load and that the speed is less than #ajj miles per hour4 ,,chapter ,,xv4 ,,balance ,,and ,,stability4 99,elements of ,stability994 ,when we balance a board on a fulcrum so that it stands in a perfectly horizontal position1 the board is said to be ,in equilibrium1 or is supported at its ,center of gravity4 ,there is only one point at which a body will balance1 and this point is at the center of gravity or ,c4 ,g4 ,in an aeroplane1 the combined mass of the body1 motor1 wings1 fuel1 chassis1 tail and live load has a center of gravity or a balancing point at which the lift must be applied if the machine is to rest in equilibrium4 ,when the center of lift 7or center of pressure7 does not pass through the center of gravity of the aeroplane1 some other force must be applied to overcome the unbalanced condition4 ,when the machine is unbalanced in a fore and aft direction with the tail low1 a force must be applied by the elevator flaps that is opposite and equal to the moment of the unbalanced forces4 ,an aeroplane is stable when it is balanced in such a way that it returns to a state of equilibrium after meeting with a disturbance4 ,when disturbed1 a stable body does not usually return instantly to its position of equilibrium1 but reaches it after a series of decreasing oscillations4 ,the heavier the body1 and the more compact its form1 the longer will it oscillate about its fulcrum before coming to rest4 ,by arranging broad surfaces at the ends of the oscillating body1 a portion of the energy will be expended in creating air currents1 and the motion will be readily damped out4 ,if the damping effect is so great that the body does not swing back after once reaching the position of equilibrium1 the body is said to be dead beat1 or dynamically stable4 ,there is a great difference between the static forces that tend to return the body to a position of equilibrium and the dynamic retarding forces that tend to damp out the oscillations4 ,usually1 a body with excessive static stability is far from being stable in a true sense1 since such a body tends to oscillate longer1 and more violently1 than one in which the static restoring forces are not so strongly marked4 ,a body may be statically but not dynamically stable1 but a dynamically stable body must of necessity be statically stable4 ,static stability in calm air is determined by the location of the center of gravity1 the center of lift1 the center of propeller thrust1 the center of area of the surfaces1 and the center of the forward resistance4 ,the forces acting through these centers are3 7#a7 ,the weight2 7#b7 ,the lifting force2 7#c7 ,the propeller thrust2 7#d7 ,the resistance4 ,the weight and lift are vertical forces equal and opposite in direction4 ,the thrust and resistance are horizontal forces1 also equal and opposite in direction4 ,when all of these forces intersect at a common point1 they will completely neutralize one another and the body will be in equilibrium4 ,dynamic stability is attained by the use of large damping surfaces such as the stabilizer surface1 fins1 and the elevator4 ,these act to kill the oscillations set up by the static righting couples or forces4 ,without suitable damping surfaces the machine would soon be out of control in gusty weather since successive wind gusts will act to increase the oscillations of the righting forces until the machine will turn completely over4 ,on the other hand1 an aeroplane can be too stable and therefore difficult to steer or control in gusts because of its tendency toward changing its attitude with every gust in order to restore its equilibrium4 ,a machine should only be partially stable1 and the majority of pilots are firmly set against any form of mechanical or inherent control4 ,no matter how simple the method1 mechanical control always introduces a certain amount of mechanism that may go wrong4 ,the question of stability has already been solved to a sufficient extent4 ,a disturbance that simply changes the direction of travel is not considered an unstable force since it normally does not tend to endanger the machine4 ,nearly any machine1 equipped with any possible form of control apparatus1 tends to change its direction when being righted4 99,axes of ,stability994 ,an aeroplane has six degrees of freedom or motion4 ,three are of translation or straight line motion1 and three are of rotation about rectangular axes4 ,it can travel forward in a straight line1 rise and fall in a vertical plane1 or skid sidewise4 ,when it rolls from side to side about the fore and aft axis 7,x axis7 it is laterally unstable4 ,when pitching up and down in a fore and aft direction1 and around an axis parallel with the length of the wings 7,y axis71 the machine is said to be longitudinally unstable4 ,when swinging or ,yawing from right to left about a vertical axis 7,z axis7 it is unstable in ,yaw4 ,rolling is resisted by the ailerons1 pitching by the elevators and stabilizer1 and yawing by the vertical directional rudder4 ,lateral oscillation are damped out by the wing surfaces and by vertical surfaces or ,fins4 ,longitudinal oscillations are damped mostly by the stabilizer and elevator surfaces4 ,directional or yawing vibrations are corrected by the damping action of the vertical tail fin1 vertical rudder and the sides of the body1 the latter also serving to damp out longitudinal vibrations4 ,on an absolutely calm day1 the pilot can shut off the motor and glide down without touching the controls if the machine is longitudinally stable4 ,the glide generally starts with a few pitching oscillations1 but these gradually are damped out by the tail as soon as the machine picks up its natural gliding angle and speed1 and from this point it will continue without oscillating4 99,the ,spiral and ,nose ,dive994 ,there are two forms of instability that have not yet been fully corrected1 and both are highly dangerous4 ,one of these is known as the spiral dive or nose spin1 and the other as the straight nose dive4 ,the aeroplane in a spiral nose dive rotates rapidly about a vertical axis during the dive4 ,spiral instability resulting from lateral instability1 can be minimized by decreasing the area of the vertical rudder and by the proper placing of fins so that there is not so great an excess of vertical area to the rear of the ,c4 ,g4 ,the covered-in body acts as a fin and will be productive of spiral instability if the area is not properly distributed4 ,in the majority of cases the rear of the body is equivalent to a large fin placed to the rear of the ,c4 ,g4 ,a fin above the ,g4 ,g4 tends to reduce all spiralling4 99,stability and ,speed994 ,an aeroplane in straight horizontal flight must be driven at such an angle1 and such a speed1 that the weight is just sustained4 ,to be inherently stable the machine must always tend to increase its speed by diving should the power be cut off in any way4 ,an aeroplane that does not tend to increase its speed in this way1 ,stalls or becomes out of control4 ,any machine that will automatically pick up its gliding angle after the propeller thrust has ceased is at least partially inherently stable1 and if it does not possess this degree of stability1 other forms of stability are practically worthless4 ,the machine having the smallest1 flattest gliding angle is naturally safest in cases of power failure1 and hence the gliding angle is somewhat related to the subject of stability4 ,illustration3 ,a ,spanish ,aeroplane ,using a ,peculiar ,form of ,upper ,fin4 ,these ,fins ,also ,perform the ,duty of ,vertical ,rudders as ,well as ,acting as ,stabilizers4 ,the longitudinal stability decreases with a decrease in the speed1 the fore and aft vibrations becoming more rapid due to the decreased effect of the tail surfaces1 and to the reduction of wing lift4 ,instability at low speeds is common to all aeroplanes1 whether inherently stable or not1 and at a certain critical speed the machine becomes absolutely unstable in a dynamic sense4 ,if a machine is to be stable at low speeds1 it must not fly at too great an angle of incidence at these speeds1 and it should have a very large tail surface acting at a considerable distance from the wings4 ,hunsaker states that the lowest speed should not require more than #hj per cent of the total lift possible4 99,inertia or ,flywheel ,effect994 ,the principal weights should be concentrated as nearly as possible at the center of gravity4 ,weights placed at extreme outer positions1 as at the wing tips1 or far ahead of the wings1 tend to maintain oscillations by virtue of their flywheel effect4 ,the measure of this inertia or flywheelage is known as the ,moment of ,inertia and is the sum of the products of all the masses by the squares of their distances from the center of gravity4 ,a great amount of inertia must be met by a large damping surface or control area if the vibrations are to be damped out in a given time4 ,in twin-motored aeroplanes the motors should be kept as close to the body as the propellers will permit4 99,wind ,gusts and ,speed994 ,a machine flying at high speed is less affected by wind gusts or variations in density than a slow machine1 since the disturbing currents are a smaller percentage of the total speed4 ,in addition1 a high speed results in smaller stresses due to the gusts4 99,gyroscopic ,instability994 ,the motor gyroscopic forces do not affect the stability of a machine to any great extent1 and in twin motored aeroplanes the gyroscopic action of the propellers is almost entirely neutralized4 ,at one time the gyroscopic torque was blamed for every form of instability1 but on investigation it was found that the practical effect was negligible4 99,instability ,due ,power ,plant994 ,the power plant affects stability in a number of ways4 ,the thrust of the propeller may cause a fore and aft moment if the center line of thrust does not pass through the center of resistance4 ,this causes the machine to be held head up1 or head down1 according to whether the line of thrust is below or above the ,c4 ,g4 ,if the propeller thrust tends to hold the head up in normal flight1 the machine will tend to dive1 and assume its normal gliding velocity with the power off1 hence this is a condition of stability4 ,with the effect of the thrust neutral1 or with the thrust passing through the center of resistance1 the machine will not tend to maintain the speed1 and hence it is likely to stall unless immediately corrected by the pilot4 ,with the line of thrust above the ,c4 ,g41 the stall effect is still further increased since with this arrangement there is a very decided tendency for the machine to nose up and increase the angle of incidence when the power is cut off4 ,illustration3 ,steel ,elevator and ,rudder ,construction ,used on a ,european ,machine4 ,the ,elevators ,also ,act as ,stabilizers1 the ,entire ,surface ,turning ,about the ,tube ,spar4 ,the slip stream of the propeller has a very decided effect on the tail surfaces1 these being much more effective when the propeller slip stream passes over them4 ,with lifting tails1 or tails that normally carry a part of the load1 the stoppage of the slip stream decreases the lift of the tail and consequently tends to stall the machine4 ,non-lifting tails should be arranged so that the slip stream strikes down on the upper surface4 ,this tends to force the tail down1 and the head up in normal flight1 and when the power ceases the tail will be relieved and there will be an automatic tendency toward diving and increase in speed4 ,on a twin aeroplane1 a similar effect is obtained by making the upper tips of both propellers turn inwardly4 ,the air is thus thrown down on the tail4 ,with a single motor1 the torque tends to turn the aeroplane in a direction opposite to the rotation of the propeller4 ,lateral stability is thus interfered with when the motor is cut off or reduced in speed4 ,with right-hand propeller rotation1 for example1 the machine will be turned toward the left1 forcing the left tip down4 ,to maintain a horizontal attitude1 the left aileron must be held down by an amount just sufficient to overcome the torque4 ,in some machines one wing tip is given a permanent increase in incidence so that the down seeking tip is given permanent additional lift4 99,lateral ,stability994 ,when an aeroplane is turned sharply in a horizontal plane1 or ,yaws1 the outer and faster moving wing tip receives the greater lift1 and a lateral rolling moment is produced about the fore and aft axis4 ,in the opposite condition1 a lateral rolling moment tends to yaw or to throw the aeroplane off a straight course4 ,below a certain critical speed1 the lateral or rolling oscillations increase in amplitude1 with a strong tendency to side slip1 skid or spiral4 ,the tail fin or rudder retards the tail velocity in a side slip1 and thus turns the slipping or skidding machine into a vertical spiral or spinning nose dive4 ,this spin increases the angle of bank and hence the side slip4 ,this in turn increases the turning or yawing velocity1 and the spiral starts4 ,this tendency toward a spiral dive can be corrected by a vertical fin placed forward1 and above the center of gravity1 or by raising the wing tips4 ,an upper fin of this type will give a force that tends to break up the bank when side slip starts and thus will prevent spinning4 ,illustration3 ,sperry ,gyroscopic ,control ,system for ,automatic ,stability4 ,the ,gyroscopic ,control at the ,left ,controls the ,movements of the ,electric ,servo-,motor at the ,extreme ,right4 ,this ,motor ,operates the ,control ,surfaces ,through the ,pulley ,shown4 ,a ,small ,electric ,generator ,between the ,servo-,motor and ,gyroscope ,provides the ,current and ,is ,driven by a ,small ,wind ,propeller4 ,at normal speeds the rolling is damped down by the wing surfaces1 and can be further controlled by the application of the ailerons4 ,at the lower critical speed when the machine is stalled1 one wing tip has no more lift than the other1 and hence the damping effect of the wings and the action of the ailerons becomes negligible4 99,dutch ,roll994 ,in ,dutch ,roll1 the rolling is accompanied by an alternate yawing from right to left4 ,this is aggravated by a fin placed high above the ,c4 ,g41 and hence corrections for spiral dive conflict with corrections for ,dutch roll4 ,the rolling is accompanied by some side slip1 and the motion is stable providing that there is sufficient fin in the rear and not an excessive amount above the ,c4 ,g4 99,degree of ,stability994 ,excessive stability is dangerous unless the control surfaces are powerful enough to overcome the stable tendency4 ,since a stable machine always seeks to face the relative wind1 it becomes difficult to handle in gusty weather1 as it is continually changing its course to meet periodic disturbances4 ,this is aggravated by a high degree of static stability1 and may be positively dangerous when landing in windy weather4 99,control ,surfaces994 ,a non-lifting tail must give no lift when at a zero angle of incidence4 ,it must be symmetrical in section so that equal values of lift are given by equal positive and negative angles of incidence4 ,square edged1 flat surfaces are not desirable because of their great resistance4 ,a double cambered surface is suitable for such controls as the stabilizer1 elevator and rudder4 ,it has a low resistance1 permits of strong internal spars1 and is symmetrical about the line of the chord4 ,some tails are provided with a cambered top and a flat bottom surface so that the down wash of the wings is neutralized4 ,under ordinary conditions this would be an unsymmetrical lifting surface1 but when properly adapted to the wings the lifting effect is completely neutralized by the down wash4 ,the curvature of the section should be such that the movement of the center of pressure is as small as possible4 ,with a small movement of the center of pressure1 the surface can be accurately balanced and hinged on the center of pressure line4 ,it is desirable to have the maximum thickness of section at1 or near to the ,c4 ,p41 so that a deep spar can be used for the support of the hinge system4 ,usually the movement of the control surfaces is limited to an angle of #cj degrees on either side of the center line1 as the lift of all surfaces start to decrease after this point is reached4 ,the surface movement should be limited by the maximum lift angle of the section in any case1 since an accident will be bound to occur if they are allowed movement beyond the angle of maximum lift4 ,in locating the control surfaces1 careful attention should be paid to the surrounding air conditions so that they will not be unduly affected by the wash-down of the wings or body4 ,the effectiveness of the tail surfaces is very much reduced by bringing them close to the wings1 and the lift is always reduced by the wash of a covered fuselage4 ,the wash-down effect of the wings on the tail is proportional to the chord and not to the span1 and for this reason an increase in span does not always necessitate an increase in the length of the body4 ,an adequate damping effect requires a large surface at the end of a long lever arm4 99,balancing the ,aeroplane994 ,figs4 #a to #f show the principles involved in the balancing of the aeroplane4 ,in ,fig4 #a a number of weights #a'-b'-c' and #e,m are supported on a beam1 the load being balanced on the fulcrum point ,m4 ,the load #b' being directly over the fulcrum1 has no influence on the balance1 but load #a' at the left tends to turn the mass in a left-hand direction1 while #c' and #e,m tend to give it a right-hand rotation4 ,this turning tendency depends upon the weights of the bodies and their distance from the fulcrum4 ,the turning tendency or ,moment is measured by the product of the weight and the distance from the fulcrum4 ,if weight #a' should be #aj pounds1 and its distance ,a' from the fulcrum should be #bj inches1 then it would cause a left-hand moment of #aj x #bj #bjj inch pounds4 ,if the system is to be in balance1 then the left-hand moment of #a' should be equal to the sum of the moments of #c' and #e,m4 ,thus3 #a' x ,a 7#c' x ,b7 7#e,m x ,c'74 ,illustration3 ,figs4 #a-f4 ,methods of ,balancing an ,aeroplane ,about ,center of ,lift4 ,the application of this principle as applied to a monoplane is shown by ,fig4 #d1 in which ,x-,x is the center of pressure or lift4 ,the center of lift corresponds to the fulcrum in ,fig4 #a1 and the weights of the aeroplane masses and their distance from the center of lift are shown by the same letter as in ,fig4 #a4 ,the engine #a' is at the right of the ,c4 ,p4 by the distance ,a1 while the fuel tank #b is placed on the ,c4 ,p4 in the same way that the weight #b' in ,fig4 #a is placed directly over the fulcrum4 ,by placing the tank in this position1 the balance is not affected by the emptying of the fuel since it exerts no moment4 ,the chassis ,g acting through the distance ,e is in the same direction as the engine load4 ,the body #e with its center of gravity at ,m acts through the distance ,c1 while the weight of the pilot #c exerts a right-hand moment with the lever arm length ,b4 ,if the moments of all these weights are not in equilibrium1 an additional force must be exerted by the tail ,v4 ,fig4 #b shows an additional weight #d' that corresponds to the weight of the passenger #d in ,fig4 #e4 ,this tends to increase the right turning moment unless the fulcrum is moved toward the new load4 ,in ,fig4 #b the fulcrum ,m remains at the same point as in ,fig4 #a1 hence the system requires a new force ,p' acting up at the end of the beam4 ,if the load was in equilibrium before the addition of #d'1 then the force ,p' must be such that ,p' x ,t' #d x ,d'4 ,in the equivalent ,fig4 #e1 the center of gravity has moved from its former position at ,s to the new position at ,r1 the extent of the motion being indicated by ,u4 ,to hold this in equilibrium1 an upward force ,p must be exerted by the elevator at ,y1 the lever arm being equal to 7,t ,u74 ,fig4 #f shows the single-seater1 but under a new condition1 the center of pressure having moved back from ,x-,x to ,z4 ,to hold the aeroplane in equilibrium1 a downward force must be provided by the tail ,v which will cause a right-hand moment equal to the product of the entire weight and the distance ,u4 ,for every shift in the center of pressure1 there must be a corresponding moment provided by the elevator surface4 ,the condition is shown by the simple loaded beam of ,fig4 #c4 ,in this case the fulcrum has been moved from ,m to ,n1 a distance equal to the center of pressure movement in ,fig4 #f4 ,this requires a downward force ,p' to maintain equilibrium4 99,center of ,pressure ,calculation994 ,fig4 #g is a diagram showing the method of calculating the center of gravity4 ,the reference line ,r is shown below the elevators and is drawn parallel to the center of pressure line ,w-,w1 the latter line being assumed to pass through the center of gravity4 ,the line ,r may be located at any convenient point1 as at the propeller flange or elsewhere1 but for clearness in illustration it is located to the rear of the aeroplane4 ,the weight of each item is multiplied by the distance of its center of gravity from the line ,r1 these products are added1 and the sum is then divided by the total weight of the machine4 ,the result of this division gives the distance of the center of gravity from the line ,r4 ,thus1 if the center of gravity of the body 7#aa7 is located at 7#aj71 then the product of the body weight multiplied by the distance ,b will give the moment of the body about the line ,r4 ,the weight of the motor 7#b7 multiplied by the distance ,f gives the moment of the motor about ,r1 and so on through the list of items4 ,illustration3 ,center ,of ,gravity ,table ,the distance of the center of gravity 7or center of pressure7 from the reference line ,r is given by ,h ,k4 ,this gives the numerical value #baicej_/acge #aeif inches4 ,thus if we measure #aei4f inches from ,r toward the wings we will have located the center of gravity4 ,the location of the ,c4 ,g4 can be changed by shifting the weights of the motor1 passenger1 or other easily moved items4 ,in any case1 the ,c4 ,g4 should lie near the center of pressure4 99,tail ,lever ,arms994 ,the effective damping moment exerted by the fixed stabilizer surface 7#ab7 will be the product of its area by the distance 7,i71 measured from the center of pressure of the wing to the center of pressure of the stabilizer4 ,the lever arm of the elevator is the distance 7,h7 measured from the centers of pressure as before4 ,illustration3 ,fig4 #g4 ,method of ,determining the ,center of ,gravity of an ,aeroplane4 99,resultant ,forces and ,moments in ,flight994 ,the aeroplane is in equilibrium when all of the forces pass through a common center1 as shown by ,fig4 #h4 ,in this figure the lift 7,l71 the weight 7,w71 the line of propeller thrust 7,t71 and the resistance 7,r7 all pass through the center of gravity shown by the black dot ,c4 ,g4 ,there are no moments and hence no correction is needed from the elevator 7,t74 ,in ,fig4 #i1 the thrust and resistance pass through the center of gravity as before1 but the center of lift 7,l7 does not pass through the center of gravity1 the distance between the two being indicated by 7n74 ,this causes a moment1 the length of the lever arm 7n7 being effective in giving a right-hand rotation to the body4 ,if horizontal flight is to be had this must be resisted by the upward elevator force 7,e74 ,in ,fig4 #aj1 the lift passes through the center of gravity1 but the line of resistance lies below it by the amount 7m74 ,the thrust 7,t7 tends to rotate the machine in a left-handed direction4 ,the elevator must exert a downward force 7e7 to resist the moment caused by 7m74 ,this is a bad disposition of forces1 as the machine would tend to stall or tail-dive should the propeller thrust cease for even an instant4 ,the stability of ,figs4 #h and #i would not be affected by the propeller thrust1 as it passes through the ,c4 ,g4 in both cases4 ,in ,fig4 #aa1 the center line of thrust is below the line of resistance 7,r71 so that the thrust tends to hold the nose up4 ,should the motor fail in this case1 the nose would drop and the machine would start on its gliding angle and pick up speed4 ,in ,fig4 #ab none of the forces intersect at a common point1 the lift and weight forming a right-handed couple1 while the thrust 7,t7 and the resistance 7,r7 form a left-handed couple that opposes the couple set up by the weight and lift forces4 ,if the thrust-resistance couple can be made equal to the lift-weight couple1 the aeroplane will be in equilibrium and will need no assistance from the elevator4 ,as the weights in the aeroplane are all located at different heights1 it is necessary to obtain the center of gravity of all the loads in a vertical plane as well as horizontally4 ,thus in ,fig4 #ac the line ,c4 ,g4 is the center of gravity of the engine weight 7#a71 the wing weight 7#b71 the pilot's weight 7#c71 the chassis weight 7#d71 the fuselage weight 7#e71 and the fuel tank weight 7#f74 ,the line ,c4 ,g4 is the effective center of all these loads1 and is calculated by taking the products of the weights by the distance from a reference line such as ,r-,r4 ,the center of resistance is the effective center of all the resistance producing items such as the wings1 body1 struts1 chassis1 etc4 ,illustration3 ,figs4 #h-ae4 ,forces ,affecting the ,longitudinal ,stability of an ,aeroplane4 ,a suggestion of the method employed in obtaining the center of resistance is shown by ,fig4 #ad1 the center line of resistance ,r-,r being the resultant of the wing resistance 7,d71 the body resistance 7,b71 and the chassis resistance 7,c74 ,it will be noted that the wing resistance of biplane wings 7,w-,w'7 does not lay midway between the wings but rather closer to the upper wing1 as shown by 7,e74 ,this is due to the upper wing performing the greater part of the lift4 ,in locating the center of resistance1 the resistance forces are treated exactly like the weights in the ,c4 ,g4 determination4 ,each force is multiplied by its distance from a horizontal reference line1 and the sum of the products is divided by the total resistance4 ,as shown1 the center of resistance ,r-,r passes through the center of gravity ,c4 ,g4 ,the center of pressure line ,x-,x also contains the center of resistance4 ,a staggered biplane cell is shown by ,fig4 #ae1 the center of pressure of the upper and lower wings being connected by the line ,x-,x as before4 ,the center of resistance of the pair is shown at 7,d71 where it is closer to the upper wing than to the lower4 ,a vertical line ,y-,y dropped through the center of resistance gives the location of the center of lift4 ,as shown1 the center of lift is brought forward by the stagger until it is a distance 7g7 in front of the leading edge of the lower wing4 ,the center of lift and the center of resistance both lie on a line connecting the center of pressure of the upper and lower wings4 99,calculation of ,control ,surfaces994 ,it is almost impossible to give a hard and fast rule for the calculation of the control surfaces4 ,the area of the ailerons and tail surfaces depends upon the degree of stability of the main wings1 upon the moment of inertia of the complete machine1 and upon the turning moments4 ,if the wings are swept back or set with a stagger-decalage arrangement1 they will require less tail than an orthogonal cell4 ,all of these quantities have to be worked out differently for every individual case4 99,aileron ,calculations994 ,the ailerons may be used only on the upper wing 7#b ailerons71 or they may be used on both the upper and lower wings4 ,when only two are used on the upper wing it is usually the practice to have considerable overhang4 ,when the wings are of equal length either two or four ailerons may be used4 ,roughly1 the ailerons are about one-quarter of the wing span in length4 ,with a long span1 a given aileron area will be more effective because of its greater lever arm4 ,if a area of ailerons1 and ,a total wing area in square feet1 with ,s wing span in feet1 the aileron area becomes3 a #c4b;,a_/,s4 ,it should be borne in mind that this applies only to an aeroplane having two ailerons on the upper wing1 since a four-aileron type usually has about #ej per cent more aileron area for the same wing area and wing span4 ,for1 example1 let the wing span be #dj feet and the area of the wings be #ddj square feet1 then the aileron area will be3 a #c4b;,a_/,s #c4b x #ddj_/dj #ce4b square feet4 ,if four ailerons were employed1 two on the upper and two on the lower wing1 the area would be increased to #a4e x #ce4b #eb4h square feet4 ,as an example in the sizes of ailerons1 the following table will be of interest3 ,illustration3 ,aileron ,sizes ,table ,in cases where the upper and lower spans are not equal1 take the average span--that is1 one-half the sum of the two spans4 99,stabilizer and ,elevator ,calculations994 ,these surfaces should properly be calculated from the values of the upsetting couples and moments of inertia1 but a rough rule can be given that will approximate the area4 ,if a' combined area of stabilizer and elevator in square feet2 ,l distance from ,c4 ,p4 of wings to the ,c4 ,p4 of tail surface2 ,a ,area of wings in square feet1 and ,c chord of wings in feet1 then3 a' #j4ea;,,ac_/,l4 ,assuming our area as #dcj square feet1 the chord as #e4g feet1 and the lever arm as #bj feet1 then3 a' #j4ea;,,ac_/,l #j4ea x #dcj x #e4g_/bj #fb4e square feet1 the combined area of the elevators and stabilizer4 ,the relation between the elevator and stabilizer areas is not a fixed quantity1 but machines having a stabilizer about #bj per cent greater than the elevator give good results4 ,in the example just given1 the elevator area will be3 #fb4e_/bb #bh4da square feet1 where #b4b is the constant obtained from the ratio of sizes4 ,the area of the stabilizer is obtained from3 #bh4da x #a4b #cd4a square feet4 99,negative ,stabilizers994 ,a considerable amount of inherent longitudinal stability is obtained by placing the stabilizing surface at a slight negative angle with the wings4 ,this angle generally varies from -#b to -#f4 ,at small angles of wing incidence the negative angle of the tail will be at a maximum1 and acting down will oppose further diving and tend to head the machine up4 ,at large wing angles1 the tail will be depressed so far that the tail angle will become positive instead of negative1 and thus the lift on the tail will oppose the wings and will force the machine to a smaller angle of incidence4 ,the negative angle can thus be adjusted to give longitudinal stability within the ordinary range of flight angles4 99,stabilizer ,shapes and ,aspect ,ratio994 ,stabilizers have been built in a great number of different shapes1 semicircular1 triangular1 elliptical1 and of rectangular wing form4 ,measured at the rear hinged joint1 the span or width of the stabilizer is about #a_/c the wing span for speed scouts1 and about #a_/d the wing span for the larger machines4 ,nearly all modern machines have non-lifting tails1 or tails so modified that they are nearly non-lifting4 ,since flat plates give the greatest lift with a small aspect ratio1 and hence are most effective when running over the ground at low speeds1 the stabilizers and elevators are of comparatively low aspect4 ,in general1 an aspect ratio of #c is a good value for the stabilizer4 ,vertical rudders generally have an aspect ratio of #a1 and hence are even more effective per unit area than the stabilizers4 ,this is particularly necessary in ground running4 ,illustration3 ,aileron ,control ,diagram of ,curtiss ,,jn#d-;,b4 ,illustration3 ,elevator ,control ,diagram of ,curtiss ,,jn#d-;,b4 99,vertical ,rudders994 ,the calculation of the vertical rudders must take the moment of inertia and yawing moments into effect1 and this is rather a complicated calculation for the beginner4 ,as an approximation1 the area of the rudder can be taken from #i to #ab square feet for machines of about #dj feet span1 and from #e to #h square feet for speed scouts4 ,illustration3 ,stick ,control ,used on the ,caudron ,biplane4 ,wing ,warp ,is ,used ,instead of ,ailerons4 ,back and ,forth ,movement ,actuates ,elevator4 ,illustration3 ,german ,stick ,control ,with ,double ,grips4 ,a4 ,latch on the ,side of the ,stick ,acts on a ,sector ,so ,that the ,lever ,can ,be ,held at ,any ,point4 ,it ,is ,released by the ,pressure of the ,knees4 99,wing ,stability994 ,under wing sections1 the subject of the center of pressure movement has already been dealt with4 ,the variation of the center of pressure with the angle of incidence tends to destroy longitudinal stability since the center of pressure does not at all times pass through the center of gravity4 ,on some wings1 the camber is such that the variation in the position of the center of pressure is very little1 and hence these are known as stable wings4 ,a reflex curve in the trailing edge of a wing reduces the center of pressure movement1 and swept back wings are also used as an aid in securing longitudinal stability4 ,introducing stagger and decalage into a biplane pair can be made to produce almost perfect static longitudinal stability4 ,it should be noted that stability obtained by wing and camber arrangements is static only1 and requires damping surfaces to obtain dynamic stability4 ,illustration3 ,form of ,control ,used on the ,nieuport ,monoplane4 99,manual ,controls994 ,in flight1 the aviator has three control surfaces to operate1 the ailerons1 elevator1 and rudder4 ,in the usual form of machine the ailerons and elevator are operated by a single lever or control column1 while the rudder is connected with a foot bar4 ,in the smaller machines ,stick ,control is generally used1 the ailerons and elevator being moved through a simple lever or ,joy ,stick which is pivoted at its lower end to the floor4 ,the ,deperdussin or ,dep control is standard with the larger machines and consists of an inverted ,u form yoke on which is mounted the wheel for operating the ailerons4 99,stick ,control994 ,with the stick pivoted at the bottom1 a forward movement of the lever causes the machine to descend while a backward movement or pull toward the pilot causes the aeroplane to head up or ascend4 ,the stick is connected with the elevators with crossed wires1 so that the flaps move in an opposite direction to the ,stick4 ,moving the stick from side to side operates the ailerons4 ,illustration3 ,standard ,stick ,control and ,movements ,used in the ,u4,s4,a4 99,deperdussin ,control994 ,a ,u shaped yoke1 either of bent wood or steel tube1 is pivoted the bearers at the sides of the fuselage4 ,wires are attached to the bottom of the yoke so that its back and forth movement is communicated to the elevator flaps4 ,on the top1 and in the center of the yoke1 is pivoted a hand wheel of the automobile steering type4 ,this is provided with a pulley and is connected with the aileron flaps in such a way that turning the wheel toward the high wing tip causes it to descend4 ,pushing the yoke forward and away from the aviator causes the machine to descend1 while a reverse movement raises the nose4 ,the ,dep control is reliable and powerful but is bulky and heavy1 and requires a wide body in order to allow room for the pilot4 ,illustration3 ,foot ,rudder ,bar ,used in the ,standard ,h-#c4 ,courtesy ,aerial ,age4 99,rudder ,control994 ,foot bar control for the rudder is standard with both the stick and ,dep controls4 ,the foot bar is connected with the rudder in such a way that the aeroplane turns opposite to the movement of the foot bar in the manner of a boat4 ,that is1 pushing the right end of the bar forward causes the machine to turn toward the right4 ,illustration3 ,automatic ,control ,system 7,sperry7 ,installed in ,fuselage of ,curtiss ,tractor ,biplane4 ,,chapter ,,xvi4 ,,head ,,resistance ,,calculations4 99,effect of ,resistance994 ,resistance to the forward motion of an aeroplane can be divided into two classes1 7#a7 ,the resistance or drag due to the lift of the wings1 and 7#b7 ,the useless or ,parasitic resistance due to the body1 chassis and other structural parts of the machine4 ,the total resistance is the sum of the wing drag and the parasitic resistance4 ,since every pound of resistance calls for a definite amount of power1 it is of the greatest importance to reduce this loss to the lowest possible amount4 ,the adoption of an efficient wing section means little if there is a high resistance body and a tangle of useless struts and wires exposed to the air stream4 ,the resistance has a much greater effect on the power than the weight4 99,weight and ,resistance994 ,we have seen that the average modern wing section will lift about #af times the value of the horizontal drag1 that is1 an addition of #af pounds will be equal to #a pound of head resistance4 ,if1 by unnecessary resistance1 we should increase the drag by #aj pounds1 we might as well gain the benefit of #aj x #af #afj pounds of useful load4 ,the higher the lift-drag efficiency of the wing1 the greater will be the proportional loss by parasitic resistance4 99,gliding ,angle994 ,the gliding angle1 or the inclination of the path of descent when the machine is operating without power1 is determined by the weight and the total head resistance4 ,with a constant weight the angle is greatest when the resistance is highest4 ,aside from considerations of power1 the gliding angle is of the greatest importance from the standpoint of safety4 ,the less the resistance1 and the flatter the angle of descent1 the greater the landing radius4 ,numerically this angle can be expressed by3 ,glide ,w_/,r1 where ,w the weight of the aeroplane1 and ,r total resistance4 ,thus if the weight is #bejj pounds and the head resistance is #ejj pounds1 the rate of glide will be3 #bejj_/ejj #e4 ,this means that the machine will travel forward #e feet for every foot that it falls vertically4 ,if the resistance could be decreased to #ajj pounds1 the rate of glide would be extended to #bejj_/ajj #be1 or the aeroplane would travel #be feet horizontally for every foot of descent4 ,this will give an idea as to the value of low resistance4 99,resistance and ,speed994 ,the parasitic resistance of a body in uniform air varies as the square of the velocity at ordinary flight speeds4 ,comparing speeds of #dj and #ajj miles per hour1 the ratio will be as #dj is to #ajj #afjj3 #aj1jjj #f4be1 that is1 the resistance at #ajj miles per hour will be #f4be times as great as at #dj miles per hour4 ,the above remarks apply only to bodies making constant angle with the air stream4 ,wings and lifting surfaces make varying angles at different speeds and hence do not show the same rate of increase4 ,in carrying a constant load1 the angle of the aeroplane wing is decreased as the speed increases and up to a certain point the resistance actually decreases with an increase in the speed4 ,the wing resistance is greatest at extremely low speeds and at very high speeds4 ,as the total resistance is made up of the sum of the wing and parasitic resistance at the different speeds1 it does not vary according to any fixed law4 ,the only true knowledge of the conditions existing through the range of flight speeds is obtained by drawing a curve in which the sums of the drag and head resistance are taken at intervals4 99,resistance and ,power994 ,the power consumed in overcoming parasitic resistance increases at a higher rate than the resistance1 or as the cube of the speed4 ,thus if the speed is increased from #dj to #ajj miles per hour1 the power will be increased #ae4fc times4 ,this can be shown by the following3 ,let ,v velocity in miles per hour1 ,h ,horsepower1 ,k ,resistance coefficient of a body1 ,a ,total area of presentation1 and ,r resistance in pounds4 ,then ,h ,,rv_/#cge4 ,since ,r ,,kav1 then ,h ,,kav x ,v_/#cge ,,kav_/#cge4 99,resistance and ,altitude994 ,the resistance decreases with a reduction in the density of the air at constant speed4 ,in practice1 the resistance of an aeroplane is not in direct proportion to a decrease in the density as the speed must be increased at high altitudes in order to obtain the lift4 ,the following example given by ,capt4 ,green will show the actual relations4 ,taking an altitude of #aj1jjj feet above sea level where the density is #j4gd of that at sea level1 the resistance at equal speeds will be practically in proportion to the densities4 ,in order to gain sustentation at the higher altitude1 the speed must be increased1 and hence the true resistance will be far from that calculated by the relative densities4 ,assume a sea level speed of #ajj ft4_/sec41 a weight of #cjjj pounds1 a lift-drag ratio of ,l_/,d #ae1 and a body resistance of #dj pounds at sea level4 ,because of the change in density at #aj1jjj feet1 the flying speed will be increased from #ajj feet per second to #cej feet per second in order to obtain sustentation4 ,with sea level density this increase in speed 7#c4e times7 would increase the body resistance #c4e x #c4e #ab4be times1 making the total resistance #ab4be x #dj #dij pounds4 ,since the density at the higher altitude is only #j4gd of that at sea level1 this will be reduced by #j4bf1 or #j4bf x #dij #cfd pounds4 ,thus1 the final practical result is that the sea level resistance of the body 7#dj pounds7 is increased #i4a times because of the speed increase necessary for sustentation4 ,since the wing angle and hence the liftdrag ratio would remain constant under both conditions1 the wing drag would be constant at both altitudes1 or #cjjj_/ae #bjj pounds4 ,the total sea level resistance at #ajj feet per second is #bjj #dj #bdj pounds1 while the total resistance at #aj1jjj feet becomes #cfd #bjj #efd pounds4 ,the speed varies as the square root of the change in density percentage4 ,if ,v velocity at sea level1 v velocity at a higher level1 and d percentage of the sea level density at the higher altitude1 then v ,v_/,d4 ,when the velocity at the high altitude is thus determined1 the resistance can be easily obtained by the method given in ,capt4 ,green's article4 ,the following table gives the percentage of densities referred to sea level density4 ,altitude ,feet ,density ,percent ,altitude ,feet ,density ,percent ,sea-level #a4jj #g1ejj #j4gh #a1jjj 4#ig #aj1jjj 4#gd #b1jjj 4#ie #ab1ejj 4#ff #c1jjj 4#ia #ae1jjj 4#fa #e1jjj 4#he #bj1jjj 4#eb ,if the velocity at sea level is #ajj miles per hour1 the velocity at #bj1jjj feet will be #ajj_/j4gb #aci miles per hour1 where #j4gb is the square root of the density percentage1 or the square root of #j4eb 4#gb at #bj1jjj feet4 99,total ,parasitic ,resistance994 ,aside from the drag of the wings1 the resistance of the structural parts1 body1 tail and chassis depends upon the size and type of aeroplane4 ,a speed scout has less resistance than a larger machine because of the small amount of exposed bracing1 although the relative resistance of the body is much greater4 ,the type of engine also has a great influence on the parasitic resistance4 ,the following gives the approximate distribution of a modern fighting aeroplane3 ,body #fb percent ,landing gear #af ,tail1 fin1 rudder #g ,struts1 wires1 etc4 #ae ,the body resistance is by far the greatest item4 ,a great part of the body resistance can be attributed to the motor cooling system1 since in either case it is diverted from the true streamline form in order to accommodate the radiator1 or the rotary motor cowl4 ,the body resistance is also influenced by the necessity of accommodating a given cargo or passenger-carrying capacity1 and by the distance of the tail surfaces from the wings4 ,a body is not a streamline form when its length greatly exceeds #f diameters4 99,calculation of ,total ,resistance994 ,the nearest approach that we can make to the actual head resistance by means of a formula is to adopt an expression in the form of ,r ,,kv where ,k is a factor depending upon the size and type of machine4 ,the true method would be to go over the planes and sum up the individual resistance of all the exposed parts4 ,the parts lying in the propeller slip stream should be increased by the increased velocity of the slip stream4 ,the parasitic resistance of biplanes weighing about #ahjj pounds will average about1 ,r #j4jcf,v where ,v velocity in miles per hour4 ,biplanes averaging #bejj pounds give ,r #j4jdh,v4 ,machines of the training or #b-seater type weigh from #ahjj to #bejj pounds1 and have an average head resistance distribution as follows3 ,body1 radiators1 shields #ce4e percent4 ,tail surface and bracing #ad4i ,landing gear #ag4b ,interplane struts1 wires and fittings #bc4f ,ailerons1 aileron bracing1 etc4 #h4h ,the averages in the above table differ greatly from the values given for the high speed fighting machine1 principally because of the large control surfaces used in training machines1 and the difference in the size of the motors4 ,with the wing drag being equal to ,d ,kx ,,av1 and the total parasitic resistance equal to ,r ,,kv1 the total resistance can be expressed by ,rt ,kx,a,v ,,kv1 where ,k coefficient of parasitic resistance for different types and sizes of machines4 ,the value of ,k for training machines will average #j4jcf1 for machines weighing about #bejj pounds ,k #j4jdh4 ,scouts and small machines will be safe at ,k #j4jbh4 ,the wing drag coefficient ,kx varies with the angle of incidence and hence with the speed4 ,for example1 we will assume that the wing drag 7,kx7 of a scout biplane at #ajj miles per hour is #j4jjjae1 that the area is #bjj square feet1 and that the parasitic resistance coefficient is ,k #j4jbh4 ,the total resistance becomes3 ,r 7#j4jjjae x #bjj x #ajj x #ajj7 #j4jbh x #ajj x #ajj #cjj #bhj #ehj pounds4 ,the formula in this case would be ,r ,kx,a,v #j4jbh,v4 99,strut ,resistance994 ,the struts are of as nearly streamline form as possible4 ,in practice the resistance must be compromised with strength1 and for this reason the struts having the least resistance are not always applicable to the practical aeroplane4 ,from the best results published by the ,n4 ,p4 ,l4 the resistance was about #ab4h pounds per #ajj feet strut at #fj miles per hour4 ,the width of the strut is #a inch4 ,a rectangular strut under the same conditions gave a resistance of #ajd4d pounds per #ajj feet4 ,a safe value would be #be pounds per #ajj feet at #fj miles per hour4 ,if a wider strut is used1 the resistance must be increased in proportion4 ,with a greater speed1 the resistance must be increased in proportion to the squares of the velocity4 ,when the struts are inclined with the wind1 the resistance is much decreased1 and this is one advantage of a heavy stagger in a biplane4 ,the ,fineness ratio or the ratio of the width to the depth of the section has a great effect on the resistance4 ,with the depth equal to twice the width measured across the stream1 a certain strut section gave a resistance of #bd4h pounds per #ajj feet1 while with a ratio of #c4e the resistance was reduced to #aa4d pounds per hundred feet4 ,beyond this ratio the change is not as great1 for with a ratio of #d4f the resistance only dropped to #aa4b pounds4 99,radiator ,resistance994 ,for the exact calculation of the radiator resistance it is first necessary to know the motor power and the fuel consumption since the radiator area1 and hence the resistance1 depends upon the size of the motor and the amount of heat transmitted to the jacket water4 ,an aeronautic motor may be considered to lose as much through the water jackets as is developed in useful power1 so that on this basis we should allow about #a4f square feet of radiation surface per horsepower4 ,this figure is arrived at by ,j4 ,c4 ,hunsaker and assumes that the wind speed is #ej miles per hour 7#gc feet per second74 ,the most severe cooling condition is met with in climbing at low speed1 and it is here assumed that #ej miles per hour will represent the lowest speed that would be maintained for any length of time with the motor full out4 ,for a racing aeroplane that will not climb for any length of time1 one-half of the surface given above will be sufficient1 and if the radiator is placed in the propeller slip stream it can be made relatively still smaller as the increased propeller slip at rapid rates of climb partially offsets the additional heating4 ,in the above calculations1 ,hunsaker does not take any particular type of radiator into consideration1 merely assuming a smooth cooling surface4 ,the ,rome-,turney ,company states that they allow #a4jh square feet of cooling surface per horsepower for honeycomb radiators1 and #j4he square feet for the helical tube type4 ,the surface referred to means the actual surface measured all over the tubes and cells1 and does not refer to the front area nor the exterior dimensions of the radiator4 ,while a radiator may be made #be percent smaller when placed in the slipstream1 the resistance is increased by about #be per cent1 with a very small saving in weight1 hence the total saving is small1 if any4 ,side mounted radiators have a lower cooling effect per square foot than those placed in any other position1 owing to the fact that the air must pass through a greater length of tube than where the broad side faces the wind4 ,in the radiator section tested by ,hunsaker1 there were about #fd square feet of cooling surface per square foot of front face area1 but for absolute assurance on this point one should determine the ratio for the particular type of radiator that is to be used4 ,the ,auto ,radiator ,manufacturing ,corporation1 makers of the ,flexo copper core radiators1 have published some field tests made under practical conditions and for different types and methods of mounting4 ,the four classes of radiators described are3 7#a7 ,front ,type1 in which the radiator is mounted in the end of the fuselage2 7#b7 ,side ,type1 mounted on the sides of the body2 7#c7 ,overhead ,type1 mounted above the fuselage and near the top plane2 7#d7 ,over-,engine ,type1 placed above and connected directly to the motor1 as in the ,standard ,h-#c4 ,the following table gives the effectiveness of the different mountings in terms of the frontal area required per horsepower and the cooling surface1 the area being in square inches 7,front face area of radiator74 ,area in wind of type 7#c7 is half the calculated frontal area since one core lies behind the other3 ,taking the value of the ,rome-,turney honeycomb radiator as #fj square feet of cooling surface per horsepower1 the frontal area per horsepower will be #j4jafi square feet1 assuming that the radiator is approximately #f inches thick4 ,this amounts to #b4dc square inches of frontal area per horsepower4 99,example994 ,find the approximate frontal area of a ,rome-,turney type honeycomb radiator used with a motor giving #ajj brake-horsepower4 ,find ,resistance at #ej miles per hour 7#gc feet per second74 ,class of ,mounting ,square ,inches ,cooling ,surface ,per ,h4,p ,per ,h4,p4 ,square ,inch ,front ,type #d4jj #aag4jj ,side ,type #g4bj #ajd4jj ,overhead ,type #b4gj #aab4jj ,over-,engine ,type #e4jj #aba4jj 99,solution994 ,area ,a #j4jafi ,,hp #j4jafi x #ajj #a4fi square feet4 ,the honeycomb portion of surface for a square radiator of the above area will measure #af4b x #af4b4 ,allowing a #a-;inch water passage or frame all around the core1 the side of the completed square radiator will measure #af4b #a #ah4b4 ,the diameter of a circular radiator core of the same #a4fi x #add area will be #ag4d inches1 since ,d #a4fix#add_/j4ghed4 ,adding the water passage1 the overall diameter becomes #ag4d #a #a #ai4d inches4 ,the round honeycomb front radiator used on the #ajj horsepower ,curtiss ,baby ,scout measures #bj inches4 ,hunaker found the resistance of a honeycomb radiator to be ,r#j4jjjhad ,,av1 there being #d honeycomb cells per square inch4 ,a area of radiator in square feet1 and ,v velocity in feet per second4 ,adopting1 for example1 a speed of #gc feet per second1 and an area equivalent to a #ai4d-;inch diameter circular radiator as above1 the total resistance becomes3 ,r #j4jjjhad ,,av #j4jjjhad x #c4ax 7#gc x #gc7 #ac4cb pounds1 at #ej ,m4 ,p4 ,h4 where ,a #c4a square feet4 99,resistance of ,chassis994 ,disc wheels 7,enclosed spokes7 have a resistance of about one-half that of open-wire wheels4 ,the ,n4 ,p4 ,l4 and ,eiffel have agreed that the resistance of a wheel approximating #bf x #d has a resistance of #a4g pounds at #fj miles per hour 7,disc type74 ,for any other speed1 the wheel resistance will be ,r #a4g ,v_/#cfjj1 where ,v speed in miles per hour4 ,we must also take into consideration the axle1 chassis struts1 wiring1 shock absorbers1 etc4 ,the itemization of the chassis resistance1 as given by the ,n4,p4,l4 for the ,b4,e4-#b biplane is as follows 7#fj miles per hour73 ,wheels #b7;a7#a4ge pounds #c4e pounds ,axle #b4j ,chassis struts and connections #a4a ,total chassis resistance7#c7fj ,,mph4 #f4f pounds ,at any other speed1 the resistance for the complete chassis can be given by the formula ,r #f4f,v_/#cfjj4 ,this allowance will be ample1 as the ,b4 ,e4-#b is an old type and is equipped with skids4 99,interplane ,resistance994 ,the interplane struts and wires are difficult to estimate by an approximate formula1 the only exact way being to figure up each item separately from a preliminary drawing4 ,the resistance varies with the form of the strut or wire section1 the length1 and the thickness4 ,the fact that some of the struts lie in the propeller slipstream1 and some outside of it1 makes the calculation doubly difficult4 ,the only recourse that we have at present is to analyze the conditions on the ,b4 ,e4-#b4 ,with struts approximating true streamline form1 a great percentage of the total resistance is skin friction1 and as before explained1 this item varies at a lesser rate than the square of the speed4 ,according to a number of experiments on full size biplanes averaging #aijj pounds1 it has been found that the interplane resistance 7,struts1 wires and fittings7 amounts to about #bd per cent of the total parasitic head resistance of the entire machine1 the drag of wings not being included4 ,the maximum observed gave #bi per cent and the minimum #ae per cent4 ,the resistance of the interplane bracing of speed scouts will be considerably less in proportion1 as there are fewer exposed struts and cables on this type1 the resistance probably averaging #ae per cent of the total head resistance4 ,based on these figures the resistance of the interplane bracing can be expressed by the following formula1 in which ,i resistance of interplane bracing in pounds1 and ,v translational speed in miles per hour3 ,i #j4jji ,v 7,for two-place biplanes weighing #aijj pounds74 ,i #j4jjed,v 7,for biplane speed scouts or racing type biplanes74 99,strut ,resistance994 ,the above estimate includes wiring1 strut fittings1 etc41 complete1 and also takes the effect of the slipstream into consideration4 ,a more accurate estimate can be made on the basis of strut length4 ,to obtain this unit value we have recourse to the ,b4 ,e4-#b tests4 ,the translational speed in #fj miles per hour 7#hh feet per second7 and the slipstream is taken at #be feet per second4 ,this gives a total velocity in the slipstream of #aac feet per second4 ,the struts are #a inches wide1 and vary in length from #c' #j to #f' #j4 ,in the slipstream the increased velocity increases the resistance of the items by #fd per cent4 ,total running length #aaj'-j4 ,total resistance #aj4ha pounds4 ,the resistance per foot #aj4ha_/aaj #j4jii pounds4 99,resistance of ,wire and ,cable994 ,in this estimate we will take the resistance given in the ,b4 ,e4-#b tests1 since values are given in the slipstream as well as for the outer portions4 ,in the translational stream there is #bdj' #j of cable1 #gj' #j of ,no4 #ab solid wire1 and #eb turnbuckles1 the total giving a resistance of #ch4aj pounds4 ,in the slipstream there is #ej' #j of cable and #cj' #j of solid wire with a resistance of #aa4jj pounds4 ,the total wire and cable resistance for the wings is therefore #di4aj pounds4 ,the resistance of the wire and cable combined is #j4abg pounds per running foot4 99,summary of ,interplane ,resistance994 ,the total interplane resistance includes the struts1 wires1 cables and turnbuckles1 a portion of which are in the slipstream4 ,since the total head resistance of the entire machine 7,b4,e4-#b7 is #adj pounds at #fj ,m4 ,p4 ,h41 and the interplane resistance #aj4ha #di4aj #ei4ia pounds1 the relation of the interplane resistance to the total resistance is #dc per cent4 ,this is much higher than the average 7#bd per cent71 but the ,b4,e4-#b is an old type of machine and the number of struts and wires were much greater than with modern aeroplanes4 99,control ,surface ,resistance994 ,the resistance of the control surfaces is a variable quantity1 since so much depends upon the arrangement and form4 ,another variation occurring among machines of the same make and type is due to the various angles of the surfaces during flight1 or at least during the time that they are used in correcting the attitude of the machine4 ,with the elevator flaps or ailerons depressed to their fullest extent1 the drag is many times that with the surfaces in neutral1 and as a general thing the controls are depressed at the time when the power demand is the greatest--that is1 on landing1 flying slow1 or in getting off4 ,ailerons in neutral can be considered as being an integral part of the wings when they are hinged to the wing spar4 ,in the older types of ,curtiss machines the ailerons were hinged midway between the planes and the resistance was always in existence1 whether the ailerons were in neutral or not4 ,wing warping1 in general1 can be assumed as in the case where the wings and ailerons are combined4 ,with ailerons built into the wings1 the resistance of the ailerons1 and their wires and fittings1 can be taken as being about #d per cent of the total head resistance4 ,with the aileron located between the two wings1 the resistance may run as high as #bj per cent of the total4 ,like the ailerons1 the elevator surfaces and rudder are variable in attitude and therefore give a varying resistance4 ,in neutral attitude the complete tail1 consisting of the rudder1 stabilizer1 elevator1 fin and bracing1 will average about #ae per cent of the total resistance1 it being understood that a non-lifting stabilizer is fitted4 ,with lifting tails the resistance will be increased in proportion to the load carried by the stabilizer4 ,in regard to the tail resistance it should be noted that these surfaces are in the slipstream and are calculated accordingly1 although the velocity of the slipstream is somewhat reduced at the point where it encounters the tail surfaces4 ,the total tail resistance of the ,b4 ,e4-#b is given as #c4c pounds4 99,resistance of ,seaplane ,floats994 ,the usual type of seaplane with double floats may be considered as having about #ab per cent higher resistance than a similar land machine4 ,some forms of floats have less resistance than others1 owing to their better streamline form1 but the above figure will be on the safe side for the average pontoon4 ,basing our formula on a #ab per cent increase on the total head resistance1 the formula for the floats and bracing will become3 ,rt #j4jjdcf,v where ,r#a resistance of floats and fittings4 99,body ,resistance994 ,this item is probably the most difficult of any to compute1 owing to the great variety of forms1 the difference in the engine mounting1 and the disposition of the fittings and connections4 ,the resistance of the pilot's and passenger's heads1 wind shields1 and propeller arrangement all tend to increase the difficulty of obtaining a correct value4 ,aeroplanes with rotary air-cooled motors1 or with large front radiators have a higher resistance than those arranged with other types of motors or radiator arrangements4 ,probably the item having the greatest influence on the resistance of the fuselage is the ratio of the length to the depth1 or the fineness ratio4 ,in tractor monoplanes and biplanes1 of the single propeller type1 the body is in the slipstream1 and compensation must be made for this factor4 ,if it were not for the motor and radiator1 the tractor fuselage could be made in true dirigible streamline form1 and would therefore present less resistance than the present forms of practical bodies4 ,the necessity of placing the tail surfaces at a fixed distance from the wings also involves the use of a body that is longer in proportion than a true streamline form1 and this factor alone introduces an excessive head resistance4 ,the ideal ratio of depth to length would seem to range from #a to #e4e or #a to #f4 ,the fineness ratio of the average two-seat tractor is considerably greater than this1 ranging from #a to #g4e or #h4e4 ,a single-seat machine of the speed-scout type can be made much shorter and has more nearly the ideal proportions4 ,the only possible way of disposing of this problem is to compare the results of wind tunnel tests made on different types of bodies1 and even with this data at hand a liberal allowance should be made because of the influence of the connections and other accessories4 ,eiffel1 the ,n4 ,p4 ,l41 and the ,massachusetts ,institute of ,technology have made a number of experiments with scale models of existing aeroplane bodies4 ,it is from these tests that we must estimate our body resistance1 hence a table of the results is attached1 the approximate outlines being shown by the figures4 ,as in calculating the resistance of other parts1 the resistance of the body can be expressed by ,r ,kx,a,v1 where ,kx coefficient of the body form1 ,a ,cross-sectional area of body in square feet 7,area of presentation71 and ,v velocity in miles per hour4 ,the area ,a is obtained by multiplying the body depth by the width4 ,the area of presentation of a body #b' #f wide and #c' #j deep will be #b4e x #c #g4e square feet4 ,the experimental data does not give a very ready comparison between the different types1 as the bodies not only vary in shape and size1 but are also shown with different equipment4 ,some have tail planes and some have not2 two are shown with the heads of the pilot and passenger projecting above the fuselage1 while the remainder have either a simple cock-pit opening or are entirely closed4 ,the presence of the propeller in two cases may have a great deal to do with raising the value of the experimental results4 ,the propeller was stationary during the tests1 but it was noted that the resistance was considerably less when the propeller was allowed to run as a windmill1 driving the motor4 ,this latter condition would correspond to the resistance in gliding with the motor cut off4 ,in all cases1 except the ,deperdussin1 the bodies are covered with fabric1 and the sagging of the cloth in flight will probably result in higher resistance than would be indicated by the solid wood or metal model used in the tests4 ,the pusher type bodies give less resistance than the tractors1 but the additional resistance of the outriggers and tail bracing will probably bring the total far above the tractor body4 ,in the accompanying body chart are shown #g representative bodies3 7a7 ,deperdussin ,monocoque ,monoplane ,body1 a single-seater2 7b7 ,n4 ,p4 ,l4-#e ,tractor ,biplane ,body1 single-seater2 7c7 ,b4 ,f4-#cf ,dirigible ,form1 without propeller or cock-pit openings2 7d7 ,b4 ,e4-#c4 ,two-,place ,tractor ,body1 with passenger and pilot2 7e7 ,curtiss ,,jn ,type ,tractor ,body1 with passengers1 chassis and tail2 7f7 ,farman ,pusher type1 with motor1 propeller and exposed passengers2 7g7 ,n4 ,p4 ,l4 ,pusher ,body1 bare4 ,body 7a7 was tested with a #a_/e scale model at a wind tunnel speed of #bh meters per second1 the resistance of the model being #j4cgg kilograms 7#j4hc pounds74 ,body 7d7 in model form was #a_/af scale and was tested at #bj4e miles per hour1 at which speed the resistance was #j4jafe pounds4 ,model 7e7 was #a_/ab scale and was tested at #cj miles per hour4 ,these varying test speeds1 it will be seen1 do not allow of a very accurate means of comparison4 ,the resistance of model 7e7 was #j4acfe pounds at the specified wind-tunnel air speed4 ,the speeds given in the above table are simply translational speeds1 and are not corrected for slipstream velocity4 ,with a slipstream of #be per cent1 increase the body resistance by #dj per cent4 ,it would be safe to add an additional #aj per cent to make up for projecting fittings1 baggy fabric1 and scale variations4 ,since a body of approximately streamline form has a considerable percentage of skin friction1 scale corrections for size and velocity are even of more importance than with wing sections4 ,no wind-tunnel experiments can determine the resistance exactly because of the uncertainty of the scale factor4 ,the resistance as given in the table is also affected by the proximity of the wing and tail surfaces1 and by projections emanating from the motor compartment4 ,it will be noted that the dirigible form ,b4,f4-#cf is markedly better than any of the others1 being almost of perfect streamline form4 ,the nearest approximation to the ideal form is ,n4,p4,l4-#e1 which has easy curves1 low resistance1 and is fairly symmetrical about the center line4 ,because of their small size1 the pusher bodies or nacelles have a small total resistance1 but the value of ,kx is high4 ,illustration3 ,chart ,showing ,forms of #g ,typical ,aeroplane ,fuselage 99,problem994 ,find the resistance of a ,curtiss ,tractor ,type ,,jn body with a breadth of #b' #f and a depth of #c' #c1 the speed being #ij miles per hour4 ,the slipstream is assumed to be #be per cent1 with an additional #aj per cent for added fabric loss1 etc4 ,illustration3 ,typical ,stream ,line ,strut ,construction4 99,solution994 ,the cross-sectional area #b' #f x #c' #c ,a #h4ac square feet4 ,the velocity of translation is #ij ,m4 ,p4 ,h41 or ,v #hajj4 ,the value of the resistance coefficient is taken from the table1 ,ko-#j4jjbgc4 ,the total resistance ,r ,kx,a,v #j4jjbgc x #h4ac x #hajj #agh4b pounds4 ,since a slipstream of #be per cent increases the resistance by #dj per cent1 the resistance in the slipstream is #aghb x #a4d #bdi4dh pounds4 ,the addition of the #aj per cent for extra friction makes the total resistance #bdi4dh x #a4a #bgd4dc pounds4 ,the resistance of this body1 used with twin motors1 would be #agh4b x #a4a #aif4jb1 but as a tractor with the body in the slipstream1 the resistance would be equal to #bgd4dc pounds as calculated above4 ,,chapter ,,xvii4 ,,power ,,calculations4 99,power ,units994 ,power is the rate of doing work4 ,if a force of #aj pounds is applied to a body moving at the rate of #cjj feet per minute1 the power will be expressed by #aj x #cjj #cjjj foot-pounds per minute4 ,as the figures obtained by the foot and pound units are usually inconveniently large1 the ,horsepower unit has been adopted4 ,a horsepower is a unit that represents work done at the rate of #cc1jjj foot-pounds per minute1 or #eej foot-pounds per second4 ,thus if a certain aeroplane offers a resistance of #bjj pounds1 and flies at the rate of #fjjj feet per minute1 then the work done per minute will be equal to #bjj x #fjjj #a1bjj1jjj foot-pounds4 ,since there are #cc1jjj foot-pounds of work per minute for each horsepower1 the horsepower will be3 #abjjjjj_/ccjjj #cf4c4 ,as aeroplane speeds are usually given in terms of miles per hour1 it will be convenient to convert the foot-minute unit into the mile per hour unit4 ,if ,h horsepower1 ,r resistance of aeroplane1 and ,v miles per hour1 then ,h ,,rv_/#cge1 the theoretical horsepower1 without loss4 ,if an aeroplane flies at #ajj miles per hour and requires a propeller thrust of #cjj pounds1 then the horsepower becomes3 ,h ,,rv_/#cge #cjj x #ajj_/cge #hj horsepower4 ,this is the actual power required to drive the machine1 but is not the engine power1 as the engine must also supply the losses due to the propeller4 ,the propeller losses are generally expressed as a percentage of the total power supplied4 ,the percentage of useful power is known as the ,efficiency4 ,the efficiency of the average aeroplane propeller will vary from #j4gj to #j4hj4 ,if e propeller efficiency expressed as a decimal1 the motor horsepower becomes3 ,h ,,rv_/#cge;e4 ,to obtain the motor horsepower1 divide the theoretical horsepower by the efficiency4 ,using the complete formula for the solution of an example in which the flight speed is #ajj ,m4 ,p4 ,h41 the resistance #bbe pounds and the efficiency #j4ge1 we have3 ,h ,,rv_/#cge;e #bbe x #ajj_/cge x #j4ge #hj horsepower4 99,power ,distribution994 ,since power depends upon the total resistance to be overcome1 part of the power will be used for driving the lifting surfaces and a part for overcoming the parasitic resistance4 ,the power required for driving the wings depends upon the angle of incidence1 since the drag varies with every angle4 ,the wing power varies with every flight speed1 owing to the changes in angle made necessary to support the constant load4 ,the power for the wings will be least at the speed and angle that corresponds to the greatest lift-drag ratio4 ,owing to the low value of the ,l_/,d at very small and very large angles1 the power requirements will be excessive at extremely low and high speeds4 ,as the parasitic resistance increases as the square of the speed1 the power for overcoming this resistance will vary as the cube of the speed4 ,it is the parasitic resistance that really limits the higher speeds of the aeroplane1 since it increases very rapidly at velocities of over #fj miles per hour4 ,the total power at any speed is the sum of the wing power and power required for the parasitic resistance4 ,owing to variations in the wing drag and resistance at every point within the flight range1 it is exceedingly difficult to directly calculate the total power at any particular speed4 ,the wing drag and the resistance should be calculated for every speed1 and then laid out by a graph or curve4 ,the minimum propeller thrust1 or the minimum total resistance1 occurs approximately at the speed where the body resistance and wing drag are equal4 ,the minimum horsepower occurs at a low speed1 but not the lowest speed1 and this will differ with every machine4 ,illustration3 ,fig4 #a4 ,power ,chart of ,bleriot ,monoplane1 ,with ,outline of ,wing ,section4 ,the ,results ,were ,taken ,from ,full ,size ,tests ,made by the ,english ,government4 ,fig4 #a is a set of performance curves drawn from the results of tests on a full size ,bleriot monoplane4 ,at the bottom the horizontal row of figures gives the horizontal speed in feet per second4 ,the first column to the left is the horsepower1 and the second column is the resistance or drag in pounds4 ,the four curves represent respectively the body resistance1 wing or plane resistance1 horsepower1 and total resistance4 ,the horizontal line ,,av shows the available horsepower4 ,it will be noted that the body resistance increases steadily from #i pounds at #ej feet per second1 to #ahj pounds at #ajj feet per second4 ,the wing resistance1 on the other hand1 decreases from #cej pounds at #ef feet per second to a minimum of #acj pounds at #hc feet per second4 ,it will be noted that the angles of incidence are marked along the wing-drag curve by small circles4 ,the incidence is #f at #ge feet per second1 and #d at a little less than #he feet per second4 ,the available horsepower ,,av is #db4 ,this is shown as a straight line1 although in the majority of cases it is slightly curved owing to variations in power at the higher speeds1 and to variations in the propeller efficiency4 ,at #ij feet per second the actual horsepower curve crosses the line of available horsepower ,,av4 ,beyond this point horizontal flight is no longer possible1 as the power requirements would exceed the available horsepower4 ,it will be noted that the lowest total resistance occurs near the point where the body and wing resistance curves intersect1 or in other words1 where the body and wing resistance are equal4 ,the minimum horsepower takes place at #fc feet per second1 or at a point nearly #a_/c between the lowest flight speed and the highest speed attained by the available horsepower in horizontal flight 7#ij ft_/sec74 ,the actual range of flight speeds is limited to points between the intersection of the ,horsepower required curve1 and the ,available horsepower curve4 ,by increasing the propeller efficiency1 or by increasing the power of the motor1 the available horsepower line is raised and the flight range increased4 99,horsepower ,for ,climbing994 ,up to the present we have only considered horizontal flight4 ,the power available for climbing is the difference between the power required to maintain horizontal flight at any speed1 and the actual horsepower that can be delivered by the propeller4 ,thus1 if the actual power delivered by a motor through the propeller is #he horsepower1 and the power required for horizontal flight at that speed is #de1 then we have3 #he-de #dj horsepower available for climbing4 ,since the difference between the driving power and the power required for horizontal flight is less at extremely low and high speeds1 it is evident that we will have a minimum climbing reserve at the high and low speeds4 ,consulting the power curve for the ,bleriot monoplane1 we see that the power required at #ef feet per second is #dj horsepower1 and at #he feet per second it is #ch horsepower4 ,at the low speed we have a climbing reserve of #dd-dj #d ,h4 ,p41 and at the higher speed #dd-ch #f ,h4 ,p4 ,the maximum available horsepower ,,av is #dd horsepower4 ,the minimum horizontal power required is found at #fc feet per second1 the climbing reserve at this point being #dd-bh #af horsepower4 ,at #ee feet per second1 and at #ij1 we would not be able to climb1 as we would only have sufficient power to maintain horizontal flight4 ,if ,w total weight of aeroplane1 c climbing speed1 and ,h horsepower reserve for climbing1 then the climbing speed with a constant air density will be expressed by3 c #ccjjj;,h_/,w4 ,assuming that the weight of the ,bleriot monoplane is #hjj pounds1 and that we are to climb at the speed of the greatest power reserve 7#af horsepower71 our rate of climb is3 c #ccjjj;,h_/w #ccjjj x #af_/hjj #ffj feet per minute4 ,it should be understood that this is the velocity at the beginning of the climb4 ,after prolonged climbing the rate falls off because of diminishing power and increasing speed4 ,much depends upon the engine performance at the higher altitudes1 so that the reserve power for climb usually diminishes as the machine rises1 and hence the rate of climb diminishes in proportion4 ,the following table taken from actual flying tests will show how the rate of climb decreases with the altitude4 ,these machines were equipped with #aej ,h4 ,p4 ,hispano-,suisa motors4 ,it will be noted that the ,s4 ,p4 ,a4 ,d4 and the ,bleriot hold their rate of climb constant up to #ghjj feet altitude1 which is a feat that is undoubtedly performed by varying the compression of the engine4 ,besides increasing the power1 the rate of climb can also be increased by decreasing the weight of the aeroplane4 99,maximum ,altitude994 ,the maximum altitude to which a machine can ascend is known as its ,ceiling4 ,this again depends on both the aeroplane and the motor1 but principally on the latter4 ,it has been noted that machines having the greatest rate of climb also have the greatest ceiling4 ,thus the ceiling of a fast climbing scout is higher than that of a larger and slower machine4 ,based on this principle1 a writer in ,flight has developed the following equation for ceiling1 which1 of course1 assumes a uniform decrease in density4 ,let ,h maximum altitude1 h the altitude at any time t after the start of the climb1 and a the altitude after a time equal to twice the time t1 then3 ,h h _/ 7#b - a_/h7 ,approximate values of h and a may be had from the following table1 which are the results of a test on a certain aeroplane3 99,time99 7,minutes7 #j4j #b4e #e4j #g4e #aj4j #ab4e #ae4j #ag4e #bj4j #bb4e 99,altitude99 7,feet7 #j4jccjj #faej #hgcj #ajgfj #abfaj #adaij #aeecj #affej #agfjj ,if we assume that the height is #ajgfj feet after the first #aj minutes1 and that the altitude after twice this time 7#bj minutes7 is #affej feet1 then the maximum ceiling attained will be3 ,h h _/ 7#b - a_/h7 #ajgfj _/ #b - #affej_/ajgfj #bc1ggj feet4 ,the use of this formula requires that the climb be known for certain time intervals before the ceiling4 99,gliding ,angle994 ,the gliding angle of the wings alone is equal to the lift-drag ratio at the given angle4 ,the best or ,flattest gliding angle is1 of course1 the best lift-drag ratio of the wing--say on the average about #a in #af4 ,the gliding angle of the complete machine is considerably less than this1 owing to the resistance of the body and structural parts4 ,this generally reduces the actual angle to less than #ab1 and in most cases between #f and #h4 ,expressed in terms of degrees1 tan ,r_/,w where ,r head resistance and ,w weight in pounds4 ,fig4 #b is a diagram giving the gliding force diagram4 ,the plane descends along the gliding path ,,ac1 making the angle of incidence 774 ,when in horizontal flight1 the lift is along ,,ol and the weight is ,,ow4 ,when descending on the gliding path the lift maintains the same relation with the wing1 but the relative angle of the weight is altered4 ,the weight now acts along ,,og4 ,the drag is represented by ,,od1 with the propeller thrust ,,op equal and opposite to it4 ,with the weight constant1 the lift ,,ol is decreased by the angle so that the total life ,l ,w cos 4 ,the action of the weight ,w produces the propelling component ,,op that gives forward velocity4 ,the line ,,ab is the horizontal ground line4 ,if the total lift-drag ratio is #h1 then the gliding angle will be #a in #h1 or measured in degrees1 tan ,r_/,w #a_/h #j4abe4 ,from a trigonometric table it will be found that this tangent corresponds to an angle of #g - #aj'4 ,it should be noted that ,r is the total resistance and not the wing-drag4 ,illustration3 ,fig4 #b4 ,gliding ,angle ,diagram ,showing ,component of ,gravity ,that ,causes ,forward ,motion4 ,the ,gliding ,angle ,depends ,upon the ,ratio of the ,resistance to the ,weight4 99,complete ,power ,calculations994 ,knowing the total weight and the desired speed1 we must determine the wing section and area before we start on the actual power calculations4 ,this can either be determined by empirical rules in the case of a preliminary investigation1 or by actual calculation by means of the lift coefficients after the approximate values are known4 ,sustaining a given weight1 we can vary the angle1 area1 wing section1 or the speed1 the choice of these items being regulated principally by the power4 ,given a small area and a great angle of incidence1 we can support the load1 but the power consumption will be excessive because of the low value of the ,l_/,d ratio at high angles4 ,if small area is desired1 a large value of ,ky due to a high lift-wing section is preferable to a low lift wing at high angles4 ,in general1 the area should be so arranged that the wing is at the angle of the maximum lift-drag ratio at the rated speed4 ,a low angle means a smaller motor1 less fuel1 and hence a lighter machine4 ,this selection involves considerable difficulty1 and a number of wing sections and areas must be tried by the trial and error method until the most economical combination is discovered4 ,illustration3 ,graphical ,gliding ,diagrams of ,several ,aeroplanes ,recorded in ,british ,army ,contest of #aiab4 ,the first consideration being the total weight1 we must first estimate this from the required live load4 ,this can be estimated from previous examples of nearly the same type4 ,say that our required live load is #ffj pounds1 and that a live load factor of #j4cj is used4 ,the total weight now becomes #ffj_/j4cjbbjj pounds4 ,to make a preliminary estimate of the area we must find the load per square foot4 ,an empirical formula for biplane loading reads3 w #j4jfe,v - #j4be where ,v maximum speed in ,m4 ,p4 ,h41 and w load per square foot4 ,if we assume a maximum speed of #ij ,m4 ,p4 ,h4 for our machine1 the unit loading is w 7#j4jfe x #ij7 - #j4be #e4f pounds per square foot4 ,the approximate area can now be found from #bbjj_/e4f #cic square feet4 7,call #cij47 ,the minimum speed is about #dh per cent of the maximum1 or #dc ,m4 ,p4 ,h4 ,we can now choose one or more wing sections that will come approximately to our requirements by the use of the basic formula1 ,ky w_/,v4 ,at high speed1 ,ky #e4f_/7ij x #ij7 #j4jjjfia4 ,at low speed1 ,ky #e4f_/7dj x #dj7 #j4jjcjcj4 ,we must choose the most economical wing between these limits of lift1 and on reference to our wing section tables we find3 ,it would seem from the above that the chosen area is a little too large1 as the majority of the ,l_/,d ratios at high speed are poor1 the best being #aa4jj of the ,u4,s4,a4-#a4 ,the angles are small1 being negative in most cases at high speed4 ,while the lift-drag of the ,r4,a4,f-#c is very good at low speed1 it is very poor at high1 hence the area for this section should be reduced to increase the loading4 ,the ,r4,a4,f4-#f and the ,u4,s4,a4-#a show up the best1 for they are both near the maximum lift at low speed and have fair ,l_/,d ratios at high speed4 ,it will be seen that for the best results there should be a series of power curves drawn for the various wings and areas4 ,this method is too complicated and tedious to take up here1 and so we will use ,u4,s4,a4-#a1 which does not really show up so bad at this stage4 ,both the ,r4,a4,f4-#f and the ,u4,s4,a4-#a have been used extensively on machines of the size and type under consideration4 ,while we require ,ky #j4jjcjcj1 and ,u4,s4,a-#a gives #j4jjcafe1 we will not attempt to utilize this excess1 as it will be remembered that we should not assume the maximum lift for reasons of stability4 ,the wing-drag at high speed will be #bbjj_/aa4j #bjj pounds1 and at low speed it will be3 #bbjj_/aj4d #baa pounds4 ,since the maximum ,l_/,d is #ag4h at #c1 where ,ky is #j4jjacc1 the least drag will be3 #bbjj_/ag4h #abd pounds4 ,this least drag will occur at ,v ,v#e4f_/jjjacc #fe ,m4 ,p4 ,h4 ,the wing drag for each speed must now be divided by the correction factor #j4he1 which converts the monoplane values of drag into biplane values4 ,since this is practically constant it does not affect the relative values of ,kx in comparing wings1 but it should be used in final results4 ,for this type of machine we will take the total parasitic resistance as r #j4jcf,v4 ,at #ij ,m4,p4,h41 r #j4jcf x #ij x #ij #bia4f pounds4 ,at #fe ,m4 ,p4 ,h41 the resistance is3 #j4jcf x #fe x #fe #aeb4a4 ,at the extreme low speed of #dc ,m4 ,p4,h4 we have r - #j4jcfx#dc x #dc #ff4ef pounds4 ,the total resistance 7,r7 is equal to the sum of the wing-drag and the parasitic resistance4 ,at #ij ,m4 ,p4 ,h4 the total resistance becomes #bjj #bia4f #dia4f pounds4 ,at #fe ,m4,p4,h4 the total is #abd #aeb4a #agf4a1 and at #dc ,m4,p4,h4 it is #baa #ff4ef #bgg4ef pounds4 ,the horsepower is computed from ,h ,,rv_/#cge;e1 and at #ij ,m4 ,p4 ,h4 this is 3 ,h #dia4f x #ij_/cge x #j4hj #adg4e ,h4 ,p4 where #j4hj is the assumed propeller efficiency4 ,at #fe ,m4 ,p4 ,h4 the horsepower drops to ,h #agf4a x #fe_/cge x #j4h #ch4a ,h4 ,p41 assuming the same efficiency4 ,in the same way the ,h4 ,p4 at #dc ,m4 ,p4 ,h4 r is #ci4h4 ,a table and power chart should be worked out for a number of sections and areas according to the following table4 ,the calculations should be computed at intervals of #e ,m4 ,p4 ,h41 at least the lower speeds4 ,wing drag is not corrected for biplane interference3 99,weight and ,power994 ,the weight lifted per horsepower varies in the different types of aeroplanes1 this difference lying principally in the reserve allowed for climbing and horizontal speed4 ,a speed scout may carry as little as #h pounds per horsepower1 while a slow two-seater may exceed #bj pounds per horsepower4 ,a rough estimate of the horsepower required may be had by dividing the total weight by the weight per horsepower ratio for that particular type4 ,thus if the unit ,h4 ,p4 loading is #af pounds and the total weight is #cbjj1 then the horsepower will equal #cbjj_/af #bjj horsepower4 ,assuming that the live load w' is #j4cb of the total weight ,w1 then ,w w'_/#j4cb4 ,if m lbs4 per ,h4,p41 then ,h ,w_/m or ,h w'_/#j4cbm4 ,taking the case of a training machine where m #bj1 and the live load is #fdj pounds1 the approximate horsepower will be3 ,h w'_/#j4cbm #fdj_/j4cb x #bj #ajj horsepower4 ,a speed scout carrying #cbj pounds useful load1 with m #aj1 will require ,h #cbj_/j4cb x #aj #ajj horsepower4 ,,chapter ,,xviii4 ,,propellers4 99,principles and ,use of ,propellers994 ,a propeller converts the energy of the engine into the thrust required to overcome the resistance of the aeroplane4 ,to maintain flight the thrust1 or force exerted by the propeller1 must always equal the total resistance of the aeroplane4 ,a total resistance of #djj pounds requires a propeller thrust of #djj1 and as the resistance varies with the speed1 the engine revolutions must be altered correspondingly4 ,the propeller is the most complicated and least understood element of the aeroplane1 and we can but touch only on the most elementary features4 ,the inclined blades of the propeller throw back an airstream1 the reaction of which produces the thrust4 ,the blades can also be considered as aerofoils moving in a circular path1 the lift of the aerofoils corresponding to the thrust of the propeller4 ,the reactions in any case are quite complicated and require the use of higher mathematics for a full understanding4 99,pitch and ,velocity994 ,when in action the propeller rotates1 and at the same time advances along a straight line parallel to its axis4 ,as a result1 the tips of the propeller blades describe a curve known as ,helix or screw-thread curve4 ,the action is very similar to that of a screw being turned in a nut4 ,for clearness in explanation we will call the velocity in the aeroplane path the ,translational velocity1 and the speed of the tips in their circular path as the ,rotational velocity4 ,when a screw works in a rigid nut it advances a distance equal to the ,pitch in each revolution1 the pitch of a single threaded screw being equal to the distance between the threads4 ,since the propeller or ,air screw works in a fluid1 there is some slip and the actual advance does not correspond to the ,pitch of the propeller blades4 ,the effective pitch is the distance traveled by the propeller in one revolution4 ,the actual pitch or the angle of the blades must be greater than the angle of the effective helix by the amount of slip4 ,if ,n ,revolutions per minute1 ,p effective pitch in feet and ,v translational velocity in miles per hour1 then ,v ,,np_/#hh4 ,with an effective pitch of #e feet1 and #abjj revolutions per minute1 the translational velocity of the aeroplane will be3 ,v #abjj x #e_/hhfh4b miles per hour4 ,illustration3 ,excelsior ,propeller1 an ,example of ,american ,propeller ,construction4 ,this ,propeller ,is ,built ,up of ,laminations of ,ash4 ,the actual pitch of the blades would be from #ae to #be per cent greater than the effective pitch because of the slip4 ,to have thrust we must have slip4 ,with the translational velocity equal to the blade-pitch velocity1 there is no airstream accelerated by the blades1 and consequently there is no thrust due to reaction4 ,the air thrown to the rear of a propeller moves at a greater speed than the translation when thrust is developed1 and this stream is known as the slipstream4 ,the difference between the translational and slipstream velocity is the slip4 ,the angle of the blade face determines the pitch4 ,the greater the angle of the blade with the plane of propeller rotation1 the greater is the pitch4 ,this angle is measured from the chord of the working face of the table1 or from that side faced to the rear of the blade4 ,in the majority of cases the working face is flat4 ,the front face is always heavily cambered like a wing section1 with the greatest thickness about one-third the chord from the entering edge4 ,as in the case of the wing1 the camber is of the greatest importance4 ,a uniform pitch propeller has a varying blade angle1 smallest at the tip and increasing toward the hub4 ,with a uniform pitch propeller1 every part of the blade travels through the same forward distance in one revolution1 hence it is necessary to increase the angle toward the hub as the innermost portions travel a smaller distance around the circle of rotation4 ,theoretically1 the angle at the exact center would be #ij degrees4 ,the blade angles at the different points in the length of a uniform pitch propeller are obtained as follows3 ,draw a right angle triangle in which the altitude is made equal to the pitch1 and the base is equal to #c4adaf times the propeller diameter4 ,the angle made by the hypotenuse with the base is the blade angle at the tip4 ,divide the base into any number of equal spaces and connect the division points with the upper angle4 ,the angles made by these lines with the base are the angles of the different blade sections4 99,blade ,form994 ,the blade may be either straight-sided or curved4 ,in the latter case the most deeply curved edge is generally the entering edge1 and the maximum width is about one-third from the tip4 ,much care is exercised in arranging the outline so that the center of pressure will not be located in an eccentric position and thus harmfully distort the blade when loaded4 ,if this is not attended to1 the pitch will vary according to the load4 ,in one make of propeller the blade is purposely made flexible so that the pitch will accommodate itself correctly to different flight speeds and conditions4 ,this1 however1 is carefully laid out so that the flexure is proportional throughout the blade to the changes in the load4 ,illustration3 ,the ,lang ,propeller1 ,having ,straight ,edges1 ,slightly ,tapering ,toward the ,tips4 ,the ,tips ,are ,sheathed ,with ,thin ,copper for ,protection ,against ,spray4 ,this ,outline ,is ,often ,known as the ,normale4 ,type ,from the ,french ,propeller ,first ,using ,this ,outline4 ,illustration3 ,a ,paragon ,propeller ,with a ,curved ,leading ,edge4 ,the ,maximum ,width ,is ,about ,one-,third the ,blade ,length from the ,tip and o4 ,toward the ,tip ,so ,that ,it ,is ,very ,narrow at the ,outer ,end4 ,the ,steel ,propeller ,flange ,is ,shown in ,place on the ,hub4 99,propeller ,diameter994 ,the largest propellers are the most efficient4 ,the propeller should be as large as can be safely swung on the aeroplane4 ,large1 slow revolution propellers are far superior to the small high speed type4 ,it is more economical to accelerate a large mass of air slowly with a large diameter than to speed up a small mass to a high velocity4 ,the diameter used on any aeroplane depends upon the power plant1 propeller clearance1 height of chassis and many other considerations4 ,approximately the diameter varies from about #a_/c the span on small speed scouts1 to #a_/e or #a_/f of the span on the larger machines4 99,air ,flow994 ,the greater part of the air is taken in through the tips1 and is then expelled to the rear4 ,this condition prevails until the blade angle is above #de degrees1 and from this point the flow is outward4 ,owing to the great angles at the hub1 there is little thrust given by the inner third of the blade1 the air in this region being simply churned up in a directionless mass of eddies4 ,at the tips the angle is small and the velocity high1 which results in about #hj per cent of the useful work being performed by the outer third of the blade4 ,in some aeroplanes a spinner cap is placed around the hub to reduce the churning loss and to streamline the hub4 ,the blade section is very thick at the hub for structural reasons4 ,the ,disc area of a propeller is the area of the circle swept out by the blades4 ,it is the pressure over this area that gives the thrust1 and in some methods of calculation the thrust is based on the mean pressure per square foot of disc area4 ,the pressure is not uniformly distributed over the disc1 being many times greater at the outer circumference than at the hub4 ,the average pressure per square foot depends upon the blade section and angle4 ,because of the great intensity of pressure at the circumference1 the effective stream is in the form of a hollow tube4 99,number of ,blades994 ,for training1 and ordinary work1 two-bladed propellers are preferable1 but for large motors where the swing is limited1 three or four blades are often used4 ,a multiple-bladed propeller absorbs more horsepower with a given diameter than the two-blade type4 ,in general1 a four-bladed propeller revolving slowly may be considered more efficient than the two-blade revolving rapidly4 ,where the swing and clearance are small1 a small four-blade may give better results than a larger and faster two-blade4 ,a three-blade often shows marked superiority over a two-blade even when of smaller diameter1 and the hub of the three-blade is much stronger than the four-blade1 although neither the three or four is as strong as the two-blade type4 99,effects of ,altitude994 ,at high altitudes the density is less1 and consequently the thrust is less with a given number of revolutions per minute4 ,the thrust can be maintained either by increasing the speed1 or by increasing the pitch4 ,for correct service at high altitudes the propeller should undoubtedly be of the variable pitch type1 in which the pitch can be controlled manually1 or by some automatic means such as proportional blade flexure4 99,effects of ,pitch994 ,driven at a constant speed1 both the thrust and horsepower increase with the pitch up to a certain limiting angle4 ,for a given horsepower the static thrust depends both on the diameter and the pitch4 ,if the pitch is increased the diameter must be decreased in proportion to maintain a constant speed4 ,as the pitch is regulated by the translational speed and revolutions1 the static thrust of a high speed machine is very small4 ,as the translational speed increases1 the pitch relative to the wind is less1 and consequently the thrust will pick up until a certain limiting speed is reached4 99,thrust and ,horsepower994 ,the calculation for thrust and power are very complicated1 but the primary conditions can be given by the following3 ,let ,v the pitch velocity in feet per minute1 ,t thrust in pounds1 and ,h horsepower1 then ,h ,,tv_/#ccjjj;,e from which ,t #ccjjj;,,he_/,v1 the efficiency being designated by ,e4 ,since the pitch velocity is ,,np1 where ,n revs4 per minute and ,p pitch in feet1 then ,t #ccjjj;,,he_/,,pn4 ,assuming a #e-;foot pitch1 #abjj revs41 the efficiency #j4ge1 and the horsepower #ajj1 the thrust will be3 ,t #ccjjj x #ajj x #j4ge_/e x #abjj #dab4e pounds4 ,the pitch in this case is the blade pitch1 and the great uncertainty lies in selecting a proper value for ,e4 ,this may vary from #j4gj to #j4he4 ,the diameter is also an unknown factor in this primitive equation4 99,materials and ,construction994 ,the woods used for propeller construction are spruce1 ash1 mahogany1 birch1 white oak1 walnut1 and maple4 ,up to #ej ,h4 ,p4 spruce is suitable1 as it is light1 and strong enough for this power4 ,in ,europe walnut and mahogany are the most commonly used1 although they are very expensive4 ,birch is very strong and comparatively light for its strength1 and can be used successfully up to #abe horsepower4 ,ash is strong1 light and fibrous1 but has the objectionable feature of warping and cannot withstand moisture4 ,maple is too heavy for its strength4 ,white oak1 quarter-sawed1 is the best of propeller woods and is used with the very largest engines4 ,it is strong for its weight and is hard1 but is very difficult to work and glue4 ,for tropical climates1 ,southern poplar is frequently used as it has the property of resisting heat and humidity4 ,one-inch boards are rough dressed to #g_/h inch and then finished down to #ac_/af or #c_/d inch4 ,after a thorough tooth planing to roughen the surface for the glue1 they are thoroughly coated with hot hide glue1 piled together in blocks of from #e to #aj laminations1 and then thoroughly squeezed for #ah hours in a press or by clamps until the glue has thoroughly set4 ,only the best of hide glue is used1 applied at a temperature of #adj;,f4 and at a room temperature of #ajj4 ,the glue must never be hotter1 nor the boards cooler than the temperatures stated4 ,the propeller after being roughed out is left to dry for ten days so that all of the glue stresses are adjusted4 ,if less time is taken1 the propeller will warp out of shape4 ,the propeller is worked down within a small fraction of the finished size and is again allowed to rest4 ,after a few days it is finished down to size by hand1 is scraped1 and tested for pitch1 tracking and hub dimensions4 ,the finish is glossy1 and may be accomplished by several coats of spar varnish or by repeated applications of hot boiled linseed oil well rubbed in1 finishing with three or four coats of wax polish4 ,there should be at least #e applications of linseed oil1 the third coat being sandpapered with ,no4 #j paper4 ,the wood should be scraped to dimension and must not be touched with sandpaper until at least two coats of varnish or oil have been applied4 ,the wood must be absolutely clear and straight grained1 and without discolorations4 ,the boards must be piled so that the edge of the grain is on the face of the blades1 and the direction of the annular rings must be alternated in the adjacent boards4 ,illustration3 ,plan and ,side ,elevation of the ,s4,p4,a4,d4 ,speed ,scout4 ,courtesy ,aerial ,age4 ,,chapter ,,xix4 ,,operation ,,and ,,training4 99,self-,training994 ,in the early days of aviation1 there were few schools1 and these were so expensive to attend that the majority of the aeronautical enthusiasts taught themselves to fly on home-made machines4 ,while this was a heroic method1 it had the advantage of giving the student perfect confidence in himself1 and if his funds were sufficient to outlast the crashes1 it resulted in a finished and thorough flyer4 ,in general1 this process may be described as consisting of two hours of practice followed by a week or more of repairing4 ,the present-day beginner has many advantages4 ,he has the choice of many excellent schools that charge a reasonable tuition1 and where the risk of injury is small4 ,he has access to the valuable notes published in the aeronautical magazines1 and the privilege of consulting with experienced aviators4 ,the stability and reliability of the planes and the motors have also been improved to a remarkable degree1 and the student no longer has to contend with a doubtful aeroplane construction nor with the whims of a poorly-constructed motor4 99,training ,methods994 ,in the majority of ,american schools1 the instructor accompanies the student in the first flights4 ,the controls are ,dual1 or interconnected1 so that the instructors' controls act in unison with those of the student1 thus giving the latter an accurate knowledge of the movements necessary for each flight condition4 ,after the first few flights the instructor can relax his controls at times so that the student can take charge4 ,this continues until the student has shown the ability to handle the machine alone under ordinary conditions and is then ready for his first ,solo or flight alone4 ,the first solo is a critical period in his training1 for when once in flight he is beyond all human aid4 ,at the navy training school at ,pensacola1 the student is first taken for a ride with one of the instructors without giving him access to the controls4 ,this is simply to give the student an experience in the sensation of flight4 ,after this he is taken for a series of short flights on a dual control machine1 the instructor gradually allowing him to take charge to a greater and greater extent as he develops the ,air feel4 ,during this time the intricacies of the maneuvers are also gradually increased1 so that after about ten hours of this sort of work he is allowed to take his first solo4 ,it has been found that the average student will require from #aj to #bj hours of dual control instruction before he is fit to fly alone4 ,when his work has proven satisfactory he is then allowed to fly in rough weather1 execute spirals1 and attempt high altitude and long distance flying4 ,some instructors believe in showing what can be performed in the air from the very beginning4 ,during the first dual flights1 the pilot indulges in dives1 vertical banks1 side slip1 or even looping4 ,after an experience of this sort1 the student is far more collected and easy during the following instructions in simple straight flying4 ,if this preliminary stunt flying has a very material effect on the nerve of the student it may be taken for granted that he is not adapted for the work and can be weeded out without further loss of time4 ,if he is of the right type1 this rough stuff has a beneficial influence on his work during the succeeding lessons4 ,during this time numerous landings are made1 for it must be understood that this is one of the most difficult features of flying4 ,with #ae minute lessons1 at least #f landings should be made per lesson4 ,a second method of instruction1 and to the author's mind the most desirable1 is by means of the ,penguin or ,roller4 ,this is a low-powered machine with very small wings--so small that it cannot raise itself from the ground4 ,by running the penguin over the ground1 the student learns how to manage his engine and to steer with his feet4 ,in this way he obtains a certain delicacy of touch without endangering either himself or an expensive machine4 ,after he has progressed satisfactorily on this machine he graduates to a faster penguin or else to a very slow aeroplane with which he can actually leave the ground4 ,since the second penguin1 or the slow aeroplane are much faster than the first machine1 the student finds that the sensitiveness of the rudder and controls are greatly increased4 ,they require more careful handling than in the first instance1 and the slightest mistake or delay will send the machine skidding4 ,the aeroplanes used at this stage are very low-powered1 and are capable of rising only a few feet from the ground1 but they give the student an opportunity of learning the aileron and tail controls in comparative safety4 ,the same result can be obtained with a standard aeroplane by a permanent set in the throttle control1 and by adjusting the stabilizer surface4 ,the beginner is allowed to work only during calm weather1 as the low speed and small lifting capacity is likely to cause an accident if the machine is caught by a side or following gust4 ,he only learns how to get the machine off the ground1 to keep the tail up and hold it in a straight line for a few seconds4 ,the man taught by the penguin method is alone when he first leaves the ground1 and hence is generally more self-reliant than one who has been ,spoon fed4 ,his experience in handling the controls has made his movements instinctive1 so that when he first actually flies he is in a better position to analyze the new problems before him4 ,it is a better and cheaper method for the school as the breakage is less expensive and allows the unfit students be weeded out before they cause damage to themselves or to the school property4 99,ground ,instruction994 ,before attempting flight1 the student should be thoroughly versed in the principles an constructional details of the aeroplane and the aeronautic motor4 ,he should know how to take down1 time and repair every type of motor with which he is likely to come into contact4 ,he should be able to tell at a glance whether the machine is rigged or trued up properly1 and have a general knowledge of the underlying principles of aerodynamics4 ,the study of these subjects is the function of the ground school4 ,at this school the student should learn the assembling and adjusting of the aeroplane structure and its balance4 99,types ,suitable for ,pilots994 ,there is a great diversity of opinion as to the type of man best suited for flying4 ,in this country the government requirements regarding age and physical condition are very exacting1 while in ,europe it has been found that physical condition is not an index to a man's ability as a pilot4 ,many of the best ,french pilots were in such bad shape as to be rejected by the other branches of the army4 ,our men are well under #cj years of age1 while in ,european service there are many excellent pilots well over #dj4 ,it is almost impossible to tell from external appearances whether a man can become a good pilot4 ,in general he must be more intelligent and better educated than the average infantryman4 ,he should not be subject to an attack of ,nerves1 nor become easily rattled1 for such a man courts disaster in flying4 ,many exhibition flyers of reputation have proved absolute failures in military service4 ,a knowledge of mechanics will be of great benefit and has been the salvation of many a pilot in active service4 ,automobile or motorcycle experience is particularly valuable4 ,recklessness1 or a dare-devil sort of a disposition1 are farthest from being qualifications for an aviator4 ,such a man should not be permitted to fly1 for he is not only a constant menace to himself but to everyone else concerned4 99,learning to ,fly ,alone994 ,it is with the greatest hesitancy that the author enters into a ,ground course of flight instruction4 ,i can1 however1 list the principal things to avoid and some of the things to do1 but this will never take the place of actual field instruction and experience4 ,the first and last thing to remember is to ,proceed slowly and with caution4 ,never try a new stunt until you are absolutely sure that you have thoroughly mastered the preliminary steps in straight flying4 ,over-confidence at the beginning is almost as bad as no confidence at all1 and the greatest difficulty met with by instructors during the first solo flights is to keep the student from imitating the maneuvers of the more experienced flyers4 ,spend plenty of time rolling or ,grass-cutting before attempting to leave the ground4 ,be sure that you can handle the rudder with accuracy1 and at fairly high speeds before attempting to lift4 ,a few days spent in sitting in the machine 7motor dead71 and acquainting yourself with the controls is excellent practice and certainly is not a loss of time4 ,with the machine in the hangar1 move the controls for imaginary turns1 dips and other maneuvers so that the resistance1 reach and limit of control movement will come more naturally when the machine is moving4 ,during the ground rolling period1 the elevator or stabilizer should be set so that it is impossible to leave the ground1 and the motor should be adjusted so that it cannot develop its full thrust4 ,this will provide against an accidental lift4 ,be easy and gentle in handling the controls1 for they work easily1 and have powerful effect at high speeds4 ,the desperate fervor with which the beginner generally yanks at the joystick is generally the very reason for his accidents4 ,do not start off at full speed without first getting used to the effect of the controls4 ,learn to find the location of the various devices so that you can reach them without looking or without fumbling4 99,the ,first ,straight994 ,by adjusting the stabilizer and elevators so that the latter has a greater degree of freedom1 and by changing the motor so that it can be run at a slightly higher speed1 we are in a position to attempt our first flight4 ,be careful that the adjustment will limit the climb of the machine1 and choose only the calmest of weather4 ,it should be remembered that the aeroplane will get off the ground at a lower speed than that required for full flight at higher altitudes1 this being due to the cushioning effect between the wings and the earth4 ,a machine traveling at a speed capable of sustaining flight at a few feet above the earth will cause it to stall when it is high enough to lose this compression4 ,the adjustment should be such that the machine cannot rise above this ,cushion1 and in this condition it is fairly safe for the beginner4 ,in making the first runs under the new conditions of adjustment1 the student should learn to manipulate the elevators so that they will hold the tail up in the correct position1 that is1 with the chord of the wings nearly horizontal4 ,do not allow the tail skid to drag over the ground further than necessary4 ,at this point the student should be strapped in the seat by a quick-detachable safety belt4 ,now comes the test4 ,get under full headway with the tail well up1 taking care to run against the breeze4 ,the speed increases rapidly1 then the motion and jar seem softer1 and the motor ceases to roar so loudly4 ,there is now a very distinct change in the note of the motor4 ,you are off4 ,at this point a very peculiar illusion takes place1 for your elevation of a few feet seems about a thousand times greater than it really is4 ,with this impression the student usually tries to correct matter by a sudden forward push on the control lever causing fine dive and a smash4 ,it must be borne in mind that only the slightest movement of the controls should be made1 and if this does not prove sufficient after a moment or so1 advance them still further but very gently4 ,sudden movements must be avoided4 ,at first the ,hops should not extend over a hundred yards or so until the student is sure of his controls4 ,little by little they can be increased in length and height4 ,he should practice for some time before attempting a flight of more than a mile4 ,by this time1 the student will have learned that the landing is by far the most difficult feature in flying1 and he should practice this incessantly before trying flights in windy weather4 ,the machine should be headed directly into the wind1 both in getting off and in landing1 especially in the latter case1 as a sudden following gust will tend to stall a machine or upset it4 ,with a head wind1 the lift is maintained at a low speed and hence is an aid in a safe landing4 ,when flying in still air there is little if any use for the ailerons1 but in gusts the student will need their aid in maintaining lateral balance4 ,after the rudder and elevator controls have been well learned the effect of the ailerons can be tried4 ,gusty or squally weather must be avoided at this point in the training1 and no turns should yet be attempted4 ,when the student attains heights greater than a few feet he should take great care in obtaining a sufficient ground speed before trying to get off1 for if lifted before the full flying speed is attained it is likely to stall4 ,fast climbing at sharp angles is dangerous unless a sufficient ground speed has been attained4 ,sustentation is due to forward speed1 and this must not be forgotten4 ,the quickest climb for getting over trees and other obstructions is obtained by gaining full speed on the ground before the climb begins1 as the power of the engine is aided by the momentum of the machine4 ,in landing in small fields it is necessary to bring the machine to rest as soon as possible1 and this stopping distance depends to a great extent upon the attitude of the machine when it first touches the ground4 ,if it is landed so that the chassis wheels and tail skid strike the ground simultaneously1 the incidence is so great that the wings act as air brakes4 ,on landing1 the angle in any case should be quickly increased past the angle of maximum lift4 ,the lift is much reduced and the drag is increased by quickly pulling the control toward the aviator4 ,this also reduces the tendency toward nosing over4 ,a normal landing in a large field can be affected by first starting down at the normal gliding angle1 and when from twenty to thirty feet above the ground the elevator control is pulled back so that the machine will describe a curve tangent to the ground4 ,in student's practice the curve should not be exactly tangent to the ground1 but tangent to a level two or three feet above the ground4 ,the machine is now losing speed1 and to prevent settling the elevator should be pulled back a trifle4 ,the speed continues to decrease until it settles down through the small remaining distance with the elevator full back4 ,the points of support should strike simultaneously4 ,it is difficult for the beginner to make this sort of a landing1 as there always seems to be an uncontrollable desire to jam the machine down on the ground4 ,if a puff of wind happens to strike the machine when a few feet off1 the student becomes rattled by the suddenly increased elevation and jams her down doubly hard4 99,wind ,flying994 ,the nature of wind at low altitudes is determined to a great extent by the contour of the ground4 ,eddies are caused by trees1 embankments1 fences1 small hills1 etc41 which tend to disturb the equilibrium or change the course of the aeroplane4 ,as the altitude increases1 the effects of these obstructions are less pronounced1 until at from #bjjj to #cjjj feet the effect is practically negligible4 ,winds that may be ,bumpy near the ground are fairly regular when #cjjj feet is attained4 ,at the higher altitudes the velocity increases1 and if the machine is flying against the wind the progress will naturally be much slower at the higher altitudes4 ,when starting in a strong wind it is advisable to attain an altitude of at least #cjj to #djj feet before turning4 ,turning in with the wind carries the possibility of a drop or stall4 ,a short gust striking the machine1 head on1 tends to retard the velocity in regard to the earth1 but in reality increases the relative air speed and thus causes the machine to climb momentarily4 ,a prolonged head gust may produce a stall unless corrected by the elevator or met with by reserve power4 ,a rear gust reduces the relative wind velocity and tends to make the machine stall1 although there are a few cases where the gust velocity has been great enough to cause a precipitate drop4 ,the higher the speed1 the less the danger from rear gusts4 ,the gusts are much more pronounced with low winds1 say winds of about #e to #ae miles per hour1 and hence it is usually more tricky to fly in a wind of this velocity than with a higher wind4 ,it is not the speed of the wind so much as it is its variation from the average velocity4 ,one should start to work on a bump at the moment it first starts to appear4 ,when flying with the wind1 the total speed in regard to the earth is the sum of the wind speed and the aeroplane speed4 ,when flying against it is the difference between the aeroplane and air speeds4 ,thus1 if the air speed of the aeroplane is #fj miles per hour1 the speed in regard to the ground will be #ge miles per hour with a following wind of #ae miles per hour1 and #de miles per hour when flying against a #ae-mile wind4 ,the speed when flying across the wind would be represented by the diagonal of a parallelogram1 one side of which represents the aeroplane speed1 and the other side the wind speed4 ,the angle of the diagonal is the angle at which the machine must be pointed4 ,when viewed from the ground1 an aeroplane in a cross wind appears to fly sideways4 99,turning994 ,after the beginner is able to maintain longitudinal and lateral balance on straight away flights1 he next attempts turns4 ,at first1 the turns must be of great radius4 ,as the radius is gradually shortened1 the effects of centrifugal force become greater1 increasing the tendency toward skidding or outward side slip4 ,to prevent skidding1 the outer wing tip must be raised so that the lift will oppose the centrifugal force4 ,the shorter the turn1 and the faster it is made1 the greater will be the banking angle4 ,should the bank be too steep1 the gravitational force will pull the machine down1 and inwardly in a direction parallel to the wings4 ,this is known as an ,inner side slip4 ,the banking may be performed by the natural banking tendency of the aeroplane or may be assisted by depressing the aileron on the outer wing tip4 ,unless the speed is well up to normal1 the machine will be likely to stall and drop on a turn1 as the head resistance is much greater under these conditions4 ,for safety one should take a short downward glide before starting the turn1 so that the speed will surely be sufficient to carry it around the turn4 ,a turn should never be attempted when climbing unless one has a great reserve power4 ,the combined effects of the turning resistance1 and absorption of energy due to the climb1 will be almost certain to stall the machine4 ,there are banking indicators on the market which will prove of great service4 ,these operate on the pendulum principle and indicate graphically whether the aeroplane is being held at the correct angle of bank4 99,proper ,flight ,speed994 ,an aeroplane should always be provided with an air speed meter1 giving the speed of the machine in relation to the air4 ,when flying with the wind the pilot is likely to be confused by the tremendous ground speed at which his machine is flying4 ,while the machine may be moved at a fast clip in regard to the earth1 it may be really near the stalling speed4 ,this error is particularly dangerous when one turns in with the direction of the wind1 after flying against it for some time4 ,the sudden increase in the earth speed1 when fully in with the wind1 always creates a sudden desire to throttle down at the very time when the relative air speed has already been greatly reduced by the turn4 ,stalling due to this cause has resulted in many accidents1 and the beginner should always attain an altitude of a least #ejj feet before he tries turning in with a strong wind4 ,an accurate speed indicator eliminates this danger to a great extent1 but it should be proved that the instrument itself is accurate before too much reliance is placed on it4 ,before the advent of the indicator1 pilots were compelled to estimate the speed by the sense of feel1 some depending upon the feel of the wind pressure on their faces1 and others by the relative resistance offered to the movement of the control surfaces4 ,the sense of ,air feel developed by the late ,lincoln ,beachey was marvelous1 for without instruments he would repeatedly climb nearly into a stall when only #ej feet from the ground1 and then recover with his chassis nearly dragging in the weeds4 99,gliding 7,fr4 ,vol ,plan7994 ,gliding is a descent along an inclined path without power1 and is possible with any aeroplane4 ,by suitably inclining the wings with the horizontal1 gravity is made to produce a forward propelling component that moves the machine forward at the expense of a loss in altitude4 ,the angle of the gliding path made with the horizontal is known as the ,gliding angle1 and indicates the efficiency of the aeroplane1 for with machines having very low head resistance the angle is very flat1 and more nearly approaches the horizontal4 ,the best or flattest gliding angle is an inherent feature of the aeroplane design1 and this cannot be exceeded by any effort on the part of the pilot4 ,it is generally expressed in terms of the ratio of the descent to the forward distance traveled1 thus a gliding angle of #aj means that the aeroplane travels #aj feet horizontally for every foot of descent4 ,any angle steeper than the flattest angle can be produced by pushing forward on the elevator controls1 thus depressing the elevator tips4 ,a very flat gliding angle is a most important feature from the standpoint of safety1 as it determines the extent of the area within which a landing can be made with a dead engine4 ,if the gliding angle is taken as #ab1 and the height is #bjjj feet1 then the radius of the circular area in which a landing is possible is #bjjj #ab #bdjjj feet1 and the diameter is twice this or #dh1jjj feet1 so that we can land anywhere within a distance of over #i miles4 ,if the best gliding angle of the machine were only #aj1 this will be reduced to #bjjj #aj #bjjjj feet1 hence our chance of choosing a safe landing space would be cut down in proportion4 ,the best gliding angle corresponds to a certain speed and wing angle1 and must be determined by experiment1 but in many machines the adjustment of the weight is such that the machine automatically picks up the best glide as soon as the motor is cut off1 and needs but little correction by the elevators4 ,such a machine is dived slightly when the motor is cut out1 and then after a few oscillations settles down and travels steadily along the proper gliding path4 ,in trying to improve this performance1 the speed indicator and incidence indicator should be carefully watched so that neither the stalling angle nor the stalling speed are approached4 ,the best glide angle corresponds to the best flight speed and will be increased if the incidence is much below or above the incidence for the most economical flight speed4 99,vertical ,nose ,dive994 ,when the aeroplane is diving vertically1 nose down1 the center of pressure movement in some machines may oppose the elevators1 thus making it difficult to straighten out into the horizontal4 ,if pulling full back on the elevator control does not remedy matters1 the control should then be quickly reversed so that there is a momentary tendency to throw the machine over on its back4 ,this breaks up the lock1 and when accomplished1 the controls should be again pulled back to bring the machine into the horizontal with the elevators in the original straightening out position4 ,the momentum swings the machine out and against the locking position1 thus aiding the controls in overcoming the moment of the ,c4 ,p4 ,illustration3 ,typical ,gliding ,angle ,diagram ,showing ,path ,inclination of ,deperdussin ,monoplane4 99,tail ,spin 7,spinning ,nose ,dive7994 ,spinning is due to side slipping or stalling1 and sooner or later every pilot gets into this position either through accident or intention4 ,if an accident1 it may be due to the design of the aeroplane through an improper distribution of the vertical surfaces1 or again it may be caused by very steep banking without an equivalent rate of turning4 ,incorrect manipulation of the ailerons when the machine is near stalling speed1 or when gliding in a spiral of gradually decreasing radius1 also causes this result4 ,at any rate1 the side slip and stall are the final cause of spin4 ,in ,stunt flying1 where a spin is desired1 one of the quickest methods of getting a spin is to pull the controls all the way back and push the rudder hard over in the desired direction of spin with the motor shut off4 ,another way to get a spin with lots of ,pep in it1 is pull the stick clear back with the motor on1 and climb until the machine is stalled1 then rudder over hard with the controls still held back4 ,the aeroplane will now fall over on its side in the direction of the rudder1 and assisted by the motor which has again cut in after the peak of the climb1 will give all the spin that any critic could ask for4 ,after the stall occurs1 the motor should be throttled down for it is likely to strain the plane or even break it4 ,there are several ways of coming out of the spin4 ,probably the best way1 and the one that causes the least loss of altitude1 is to keep the controls pulled back all the way1 and rudder in the opposite direction to the spin 7,motor cut out74 ,the rudder will stop the spin1 and the elevator will cause the plane to level out of the dive simultaneously1 but the controls should be put into neutral as soon as leveled out or there will be another spin started in the opposite direction4 ,a very common method used by exhibition flyers is first put the controls into neutral1 and rudder opposite to the spin until it stops turning and it is then put into a nose dive4 ,the straight nose dive can then be easily corrected by pulling back on the controls until it levels out4 ,this latter method develops an excessive speed and requires a high altitude4 ,when the aeroplane is overbanked at normal speed1 and the turn is not correspondingly rapid1 the plane will slip down sideways into an ,inside side slip4 ,the strong upward wind against the side of the body will turn the nose into a dive1 the nose drops1 and the tail will then start to swing around in a circle larger than the circle described by the nose--the dive continuing4 ,when much below the normal flight speed1 or near the stalling point1 the inner ailerons are not as effective when making a sharp turn for their velocity is much reduced4 ,when fully depressed1 the inner ailerons give very little lift toward righting the machine but add to the drag and tend to spin the machine around with the inner tips acting as a center of rotation4 ,the outer ailerons are very effective and because of the high speed of these tips1 there is a strong banking tendency that eventually will result in side slip and a spin if the pilot is not experienced4 ,either the spin due to overbanking1 or that due to low speed may be straightened out according to instructions already given4 ,when a turn is attempted at low speed near the ground1 the student generally fails to bank up sufficiently through fear of striking the ground with the lower wing tip1 and therefore gets into an outward side slip4 ,in the frantic effort to keep the low wing up and off the ground he depresses the low aileron to the full1 thus increasing the drag on the low side and starting the spin4 ,very much to his surprise he finds that this actually drops the low tip further instead of raising it as the outer tip is now speeding around at a tremendous clip1 and the outer lift is increasing the bank against his will4 ,given time1 and altitude1 the plane will bank up until it stands on end1 and in any event a bad side slip results1 and the fun is on4 ,if near the ground as assumed1 either the side slip or the resulting nose dive will soon terminate matters4 ,the moral to be derived from this experience is to keep up to speed in making a turn1 to maintain a safe altitude1 and in case the speed should fall off1 to depress the 99outer aileron994 ,the outer aileron will resist the spin if depressed1 as the drag acts against the spin1 and the bank thus obtained will act against the outer side slip1 without destroying the velocity of the machine as a whole4 ,in turning at stalling speed1 the aileron effects are reversed1 and as soon as straightened out the engine should be opened up so that the speed will be increased and the landing made as easy as possible4 ,if the fin and rudder surface is not sufficient for the machine1 little is gained by turning the rudder to an angle greater than #ae1 and in such cases it is much more effective when held parallel to the wind4 ,if correction has been started before the spin has developed great rapidity1 the rudder can first be turned to check the rotation and then turned back parallel to the wind4 ,it is always best to shut off the engine when getting out of a tail spin1 especially if the engine rotation is in the direction of the spin1 since the motor torque aids the spin and acts against the controls4 ,in case of a smash there is no danger from fire with the engine cut out4 99,stunt ,flying994 ,when the student has had #bj hours or more of solo flying1 and is capable of performing the ordinary maneuvers with confidence and accuracy1 he is in a position to undertake stunt flying under the directions of a good instructor in a dual control machine4 ,this tremendously increases the confidence of the student if gone about in the right way1 and in his after flying experience enables him to get out of tight places that would otherwise often prove impossible4 ,there is no doubt but what stunt flying has decreased the percentage of accidents when properly taught1 and that ,pegoud's original stunt of looping the loop has been one of the greatest steps in the advancements of aeronautics that we have had1 if only for the fact that it taught the flyer that there was no flying attitude so bad but what there was a solution for it4 99,flying ,upside ,down994 ,with the machine on its back1 then wings are very inefficient1 and it is impossible to maintain horizontal flight in this position1 and the machine is also very unstable4 ,it should really be called gliding instead of flying since the aeroplane constantly loses altitude along an inclined gliding path4 ,the distance that a machine can be glided in this way depends upon the skill of the pilot1 and it will also be found that upside down flight with a large dihedral is more difficult than with straight wings4 ,the upside down flight begins with a glide to gain speed1 the path being about #bj with the horizontal1 and this speed gain is imperative since it requires both the power of the motor and the momentum of the machine to overcome the sharp climb for the turnover4 ,illustration3 ,upside ,down ,glide ,diagram1 ,showing ,successive ,positions of ,aeroplane4 ,after sufficient speed has been attained1 the controls are pulled back for a climb at about a #fj angle1 as between 7,a7 and 7,c71 this maneuver being best performed with the gliding path 7,c-,d7 against the wind4 ,with the control pulled back at 7,a71 the rudder is thrown over sharply in the desired direction of the turnover1 and this will turn the machine over as indicated by at 7,b71 the machine finally getting on its back at the peak of the climb 7,c74 ,with the machine on its back1 reverse rudder to stop the overturning1 and when the wings are horizontal1 the rudder should be put in neutral to hold it in this position4 ,at 7,c7 the motor is shut off1 and the glide continued to 7,d7 where it is leveled out by a backward pull on the controls4 ,this should always be performed at an altitude well over #bjjj feet4 ,illustration3 ,looping ,diagram ,showing ,successive ,positions of ,machine4 99,looping994 ,this is probably the easiest of all stunts outside of the spiral glide4 ,it starts with about a #bj glide as at 7,a7 to increase the velocity 7,motor on71 and at the beginning of the loop at 7,b71 the control lever is pulled back slowly4 ,the controls must be pulled back faster and faster as the plane approaches the top of the loop1 a steady pull producing nearly the correct effect because of the decreasing elevator resistance as the machine reaches the top of the loop at 7,c74 ,at the top1 the lever should be clear back and must be held in this position until at the bottom 7,d7 where the machine leaves the loop along the inclined path 7,d-,e7 ,at 7,d71 the stick is pushed slowly forward to neutral1 gradually bring the machine into the horizontal4 ,the loops must always be made when flying into the wind1 and the faster they are made the better1 for there is less strain on the frame and speed also prevents the motor from cutting out at the top of the loop4 ,illustration3 ,a ,few ,straight ,loops and ,backward ,reverse ,loops ,performed by ,niles4 ,illustration3 ,photograph of ,night ,looping by ,charles ,niles4 ,the ,machine was ,provided with ,railroad ,flares which ,left the ,trace or ,path of the ,aeroplane on the the ,dry ,plate4 99,immelmann ,turn994 ,this maneuver was originated by the ,german flyer ,immelmann1 and is much used in combat by both the ,allied and ,german armies1 for it subjects the enemy to a maximum field of fire and enables the machine to make a quick getaway with a single seat machine4 ,with the enemy machine at 7,x71 and with our machine provided with two machine guns1 it will be seen that the enemy is under the fire of either the rigid front gun or the pivoted cock-pit guns through nearly three-quarters of the twisting loop4 ,the pivoted gun which fires over the top wing is the most effective as it can reach the enemy machine 7,x7 at 7,a71 7,b71 7,d7 and 7,e71 the only blind spots occurring during the climb from 7,b7 to 7,d7 as indicated by the partly rolled over position at 7,c74 ,illustration3 ,successive ,positions in ,immelmann ,turn1 ,enemy ,machine ,either ,being at ,y or ,x4 ,it begins with the usual power glide 7,motor on7 at 7,a7 in order to gain speed1 and at the beginning of the #fj at 7,b7 the elevator controls are pulled back and the rudder given a quick turn to the extreme position in the direction of the desired turnover4 ,the rudder action turns the machine over on its back at the peak of the climb at 7,d7 without the use of ailerons4 ,at the top 7,d71 the rudder is thrown to the opposite direction to stop the roll over and is then brought back to neutral to hold the machine flat on its back4 ,the elevator controls are held back until the machine comes out of the reverse loop extending from 7,d7 to 7,e7 and until it leaves on the horizontal at 7,f74 ,as the object is to get away quick1 the finish along 7,e-,f7 should be made with the wind1 and preferably should be started across wind4 ,motor should be throttled down from 7,d7 to 7,e7 to prevent coming out with excessive speed4 ,illustration3 ,positions in ,turn ,over1 the ,machine ,continuing to ,rotate in the ,same ,direction from ,b to ,d4 99,the ,roll-,over994 ,the start of this stunt is exactly like the start of the upside down glide or the ,immelmann1 while the finish is a sort of reversed ,immelmann1 the machine being straightened out without going around a loop4 ,when at the top of the turnover climb1 the rudder is not reversed and straightened out as in the ,immelmann1 but a little rudder is kept on so as to continue the turnover and bring the plane out on the horizontal4 ,the rudder action is assisted by a slight application of the aileron while the elevator control is pushed forward after the machine leaves the peak of the climb4 ,i am indebted to ,lieutenant ,charles ,w4 ,keene for suggestions on the ,immelmann and roll over1 and to the late ,lieutenant ,r4 ,c4 ,saufly of the ,u4 ,s4 ,navy for other items on training4 ,illustration3 ,flying ,upside ,down ,with a ,bleriot ,monoplane4 ,the ,plane is ,far ,too ,low to ,recover ,its ,normal ,position1 and as a ,result1 the ,glide ,ended ,fatally4 ,illustration3 ,an ,aeroplane ,equipped with the ,light ,boat ,hull ,shown1 in this ,figure is ,known as a ,flying ,boat4 ,it ,differs from the ,seaplane1 as the ,floats or ,pontoons of the ,latter ,do ,not ,enclose the ,passenger and ,pilot4 ,,chapter ,,xx4 ,,aeronautical ,,motors4 99,general ,notes994 ,it is assumed that the reader understands the principles of the automobile motor and its accessories1 for a minute description of gas-engine principles does not fall within the scope of this book4 ,if more information is desired on this subject1 the reader is referred to the author's ,practical ,handbook of ,gas1 ,oil and ,steam ,engines4 ,only those features peculiar to aeronautic motors will be discussed in this chapter4 99,aeronautic ,requirements994 ,the principal requirements of an aeronautic motor are light weight1 low oil and fuel consumption1 reliability and compactness4 ,the outline as viewed from the shaft end is also very important1 for the motor must be mounted in a narrow streamline body4 ,the compression pressures are much higher than those employed on auto motors1 and the speed is generally lower4 ,with one or two exceptions the four-stroke cycle has been universally adopted4 ,aeronautic service is a severe test for the motor4 ,from the start to the finish of a flight1 the aeroplane motor is on a steady grind1 loaded at least to #ge per cent of its rated power4 ,the foundations are light and yielding and the air density varies rapidly with changes in the altitude4 ,as the fuel and oil require an expenditure of power for their support1 the fuel consumption becomes of great importance1 especially in long flights4 ,because of the heavy normal load the lubricating system must be as nearly perfect as it is possible to make it4 ,a motor car runs normally at from #aj to #be per cent of its rated horsepower1 while the aero motor may develop as high as #ge per cent to #ajj per cent for hours at a time4 ,a car engine of #fgb cubic inches displacement is rated at #fe horsepower1 while the same size aero engine has a rating of #aed4 ,on the basis of normal output1 this ratio is about #g to #a1 and taking the weight of the aero motor as one-half that of the auto type1 the true output ratio becomes #ad to #a4 ,up to the time of a complete overhaul 7#ej hours71 and at #ajj miles per hour1 the average distance traveled by the aero motor is #ejjj miles4 ,the equivalent motor car mileage is #be1jjj1 and the duration is about #ajjj hours4 ,this suggests the necessity for improved materials of construction4 ,even on the present aeronautic motors the fiber stress in the crank-shaft ranges from #abj1jjj to #adj1jjj pounds per square inch against the #hj1jjj-pound stress used in auto shafts4 ,the crank case of an aeronautic motor must be particularly rigid to withstand the stresses due to the light mounting1 and this demands a higher grade metal than that ordinarily used with automobiles4 ,unlike the car engine1 quality comes first and price is a secondary consideration4 99,cooling ,systems994 ,both the air and water cooling system is used1 the former for light fast aeroplanes such as speed scouts1 and the latter for the larger and more heavily powered machines4 ,even in some types of speed scouts the air-cooled motor has been displaced by the water-cooled1 owing to the fact that the air-cooler cannot be built satisfactorily for outputs much greater than #aaj horsepower4 ,by increasing the revolutions of the stationary water-cooled type an increase in power may be had with the same cylinders1 but in the case of the rotary air-cooled type the speed is limited by the centrifugal forces acting on the cylinders4 ,illustration3 ,a #f-;,cylinder ,hall-,scott ,motor ,installed in a ,martin ,biplane4 ,while the weight of the radiator1 water and piping increase the weight of the water-cooled motor very considerably1 the total weight is not excessive4 ,when the fuel is considered1 the total weight is below that of the rotary when long flights are attempted4 ,the radiator and water add complication and are a source of danger4 ,the radiators increase the head resistance and add very considerably to the maintenance cost4 ,illustration3 ,a ,motor ,installation in a ,pusher ,type ,biplane1 ,showing the ,motor at the ,rear and the ,double ,radiator ,sections ,over the ,body4 ,each type of cooling has its limitations1 and it is hoped that an improvement in cooling may be had in the near future4 ,this system should primarily reduce the size and resistance of the power plant1 and if possible the weight1 although the latter is a secondary consideration4 ,at present the cooling system prevents even an approach to the true streamline form of the body4 99,propeller ,speed994 ,for the best results1 the propeller speed should not exceed #abjj revolutions per minute1 and for structural reasons this is generally limited to #aejj ,r4 ,p4 ,m4 ,this at once puts a limiting value on the output of a given size engine unless a gear down arrangement is used4 ,it should be understood1 between certain limits1 that the power output increases roughly as the speed4 ,with direct drive arrangements in which the propeller is mounted directly on the end of the engine shaft1 the motor revs4 are necessarily the propeller revs41 and the only way of increasing the speed is by increasing the length of the stroke or by gearing down4 ,an increase in stroke adds rapidly to the weight by increasing the cylinder length1 length of connecting rod1 length of crank throws1 etc4 99,horsepower ,rating994 ,at present there are many methods of calculating the horsepower of gasoline engines4 ,formula applying to auto or boat motors does not apply to flight conditions1 for the aero motor is essentially a high compression type and has a greater output per unit of displacement4 ,it is not practical to give the rated horsepower as the maximum output possible under ideal conditions1 for this would give no idea as to the practical capabilities except by long tedious calculation4 ,the brake horsepower would give no overload capacity at a fixed propeller speed1 and the conditions are entirely different from those regulating the rating of auto motors4 ,the latter can be forced up to the wrecking speed1 or many times the normal automobile speed of #cj miles per hour4 ,as aero engines are generally well kept up1 and well tuned at all times1 the rated horsepower may be taken from #ae to #bj per cent below that of the maximum brake horsepower4 ,in geared-down motors1 the gear efficiency is still to be considered4 ,the question of the quality of the mixture1 and barometric pressure1 also enter into the problem whether the power is rated on the maximum obtained with a rich mixture1 or is calculated from the output at the maximum efficiency4 ,a writer in ,aviation suggests that the rated horsepower be taken as #ie per cent of the power developed at a point midway between the maximum output1 and the output at the greatest efficiency4 ,barometric pressure to be #cj inches and the revolutions #abjj4 ,owing to the great diversity in the bore-stroke ratio1 a power formula must include the bore and stroke4 ,this makes the ,s4,a4,e4 formula for auto motors impossible4 ,a formula is proposed by a writer in ,aviation4 ,the writer has checked this up with the published performance of several well-known aeronautical motors4 ,h ,b,,snr_/#ab1ejj ,where ,b bore in inches1 ,s stroke in inches1 ,n number of cylinders1 ,r ,crankshaft revolutions per minute1 and ,h rated horsepower4 ,this applies only to the four-stroke cycle type4 99,power and ,altitude994 ,the power drops off rapidly with an increase in altitude unless corrections are made for compression and mixture4 ,with constant volume1 the decreased density causes decreased compression4 ,as the weight of air taken in per stroke is reduced1 this also reduces the amount of fuel that can be burned per stroke4 ,by holding the compression constant through adjustment of the clearance or valve motion1 a fairly constant output can be had through a wide range of altitudes4 ,a compression of #aae pounds per square inch 7commonly used7 is difficult to handle with a light construction1 but this pressure must be obtained if the output is to be kept within practical limits4 ,engines having a compression ratio of as high as #f are running satisfactorily at sea level1 this ratio giving a mean effective working pressure of #acd pounds per square inch4 ,with this ratio the engine cannot be used with full open throttle at sea level for more than #aj or #ae minutes without causing damage to the shaft1 bearing and valves4 ,at about #aj1jjj feet the compression is normal4 ,at great altitudes carburetion has become a great problem1 and as aerial battles have already taken place at elevations of #bj1jjj feet1 it is quite possible that future motors will be equipped with some device that will force a measured fuel charge into the cylinders4 ,the air necessary for the combustion will also have to be pumped in by some means4 99,weight ,per ,horsepower994 ,the weight per horsepower of the engine is a very loose term since so much depends upon the equipment included in the weight4 ,as many as #bj items may be considered as being in the doubtful list1 and among these are the radiator water1 piping1 mounting1 propeller hub1 oil in sump1 wiring1 self-starter1 etc4 ,the only true unit weight is that obtained by taking the plant complete 7ready to run71 with the cooling system1 gasoline for an hour's flight1 and the oil4 ,the weight of the bare engine signifies nothing4 ,the weights of the various items used on well known motors are given in a table under the chapter ,weight ,calculations4 ,while the bare weight of a certain engine may be very low per brake horsepower1 an excessive fuel consumption will often run the effective weight up and over that of a type in which the bare weight is far greater4 ,the weight of the engine per horsepower1 including the magneto and carbureter1 will run from #b4b to #e4j pounds1 according to the type4 ,illustration3 ,two ,examples of ,cowls ,used ,over ,rotary ,cylinder ,motors 7,air ,cooled74 99,fuel ,consumption994 ,the fuel consumption of water-cooled motors varies from #j4dh to #j4fe pounds per horsepower hour1 an average of #j4f being safe4 ,the fuel consumption of a rotary air-cooled motor will range from #j4f to #j4ge4 ,the oil consumption varies from #j4ah gallons per horsepower in the air-cooled type to #j4jce with the water-cooled stationary motor4 99,radiators994 ,owing to extremes in the temperature of the air at different altitudes1 the radiating surface should be divided into sections so that a constant cooling effect can be obtained by varying the effective surface of the radiator4 ,the temperature can also be controlled by an automatically regulated by-pass which short circuits a part of the radiator water at low temperatures4 ,constant water temperature has much to do with the efficiency and general operation of the motor1 and there will be only one temperature at which the best results can be obtained4 ,illustration3 ,typical ,radiators4 ,a7 ,side or ,top ,type4 ,illustration3 ,typical ,radiators4 7,b7 ,front ,type4 ,hunsaker finds that #j4hc square feet of actual cooling surface per horsepower is correct at #fj ,m4 ,p4 ,h41 while others give a value of about #ajj square foot under similar conditions4 ,the front or projected area varies with the thickness of the radiator1 the thicknesses varying from #b to #e inches4 ,the ,livingston radiator gives a cooling surface of #ej square inches per square inch of front surface4 ,the total cooling effect depends upon the speed1 the location in regard to the slipstream1 and the position on the body4 ,a radiator maker should always be consulted when making the final calculations4 ,see ,chapter ,,xvi4 99,fuel ,tanks and ,piping994 ,the fuel tanks may be of copper1 aluminum or tin-coated steel1 and all joints should be welded or riveted4 ,never depend upon solder1 as such joints soon open through the vibration of the engine4 ,gasoline should not come into contact with steel1 nor the zinc used on galvanized iron4 ,splash plates are provided to keep the fluid from surging back and forth while in flight4 ,all gas should be supplied to the engine through a filter or strainer placed in the main gas line4 ,the valves in the fuel lines should be provided with stopcocks1 so arranged that they can be closed from the pilot's seat4 ,in general1 the carbureters should be fed by gravity from an overhead service tank1 this tank being supplied from the main reservoir by air pressure or a gasoline pump4 ,the air can be compressed by a pump on the engine or by a paddle driven pump operated by the airstream1 and as a rule the latter is preferable1 as it can be operated with the aeroplane gliding and with the engine dead4 ,air pressure systems are likely to fail through leaks1 while with a good gasoline pump conditions are much more positive4 ,the gravity service tank should be located so that it will feed correctly with the aeroplane tilted at least #cj degrees from the horizontal4 ,illustration3 ,two ,views of the ,monosoupape ,gnome ,rotary ,cylinder ,motor4 ,this ,motor ,has #i ,cylinders ,arranged ,radially ,around the ,crankshaft and ,develops #ajj ,horsepower4 ,the ,cylinders ,are ,air ,cooled4 ,the gasoline piping should be at least #e_/af inch inside diameter1 and should be most securely connected and supported against vibration4 ,to guard against crystallization at the point of attachment1 special flexible rubber hose is generally used4 ,this must be hose made specially for this purpose1 as ordinary rubber hose is soon dissolved or rotted by gasoline and oil4 ,air pockets must be avoided at every point in the fuel and oil system4 ,illustration3 ,hall-,scott ,big ,six ,aeronautical ,motor of the ,vertical ,water-cooled ,type4 #abe ,horsepower4 99,rotating ,cylinder ,motors994 ,the first rotating cylinder motor in use was the ,american ,adams-,farwell1 a type that was soon followed by the better known ,french ,gnome4 ,other motors of this type are the ,clerget1 ,le,rhone1 ,gyro and ,obereusel4 ,they are all of the air-cooled type--cooled partly by the revolution of the cylinders about the crank-shaft1 and partly by the propeller slipstream4 ,while the pistons slide through the cylinder bore1 the rotating cylinder motor is not truly a reciprocating type1 as the pistons do not move back and forth in regard to the crank shaft4 ,the cylinders revolve about the crank shaft as a center1 while the pistons and connecting rods revolve about the crank pin1 the difference in the pivot point causing relative1 but not actual1 reciprocation4 ,illustration3 ,hall-,scott #d-;,cylinder ,vertical ,water-cooled ,motor4 #hj-ij ,horsepower4 ,the original ,gnome motor drew in the charge through an inlet valve in the piston head4 ,the gas passed from the mixer1 through the hollow crank-shaft1 and then into the crank-case4 ,the exhaust valve was in the cylinder head4 ,this valve arrangement was not entirely satisfactory1 and the company developed the ,monosoupape or ,single valve type4 ,the #ajj ,h4 ,p4 ,monosoupape ,gnome has #i cylinders1 #d4c x #e4i4 ,the total weight is #bgb pounds and the unit weight is #b4gb pounds per horsepower4 ,it operates on the four-stroke cycle principle4 ,the gas consumption is #ab gals4 per hour1 and it uses #b4d gals4 of castor oil4 ,the cylinders and cooling fins are machined from a solid steel forging1 weighing #hh pounds4 ,the finished cylinder weighs #e4e pounds after machining4 ,the walls are very thin1 probably about #a_/af inch1 but they stand up well under service conditions4 ,illustration3 ,sturtevant ,v ,type #h-;,cylinder ,water ,cooled ,aeronautical ,motor4 ,this ,motor ,is ,provided ,with a ,reduction ,gear ,shown at the ,rear of the ,crankcase4 ,assuming the piston to be on the compression stroke1 the ignition will occur from #ae to #bj before the top dead center4 ,moving down on the working stroke1 and at #he from top dead center1 the exhaust valve begins to open1 and the exhaust continues until the piston returns to the upper dead center4 ,with the valve still open1 pure air now begins to enter through the exhaust valve and continues to flow until the valve closes at #fe below the bottom center4 ,still descending1 the piston forms a partial vacuum in the cylinder1 until at #b before the lower center the piston opens the ports and a very rich mixture is drawn in from the crank case4 ,this rich mixture is diluted to the proper density by the air already in the cylinder1 and forms a combustible gas4 ,the upward movement of the piston on the compression stroke closes the ports and compression begins4 ,the mixture enters the crank case through a hollow shaft1 with the fuel jets near the crank throws4 ,a timed fuel pump injects the fuel at the proper intervals4 ,illustration3 ,dusenberg #d-;,cylinder ,vertical ,water ,cooled ,motor ,with ,reduction ,gear4 ,four ,valves ,are ,used ,per ,cylinder4 ,note ,peculiar ,valve ,motion4 99,curtiss ,motors994 ,the ,curtiss motors are of the water-cooled ,v type1 with #f to #h cylinders per row4 ,these are probably the best known motors in ,america and are the result of years of development1 as ,curtiss was the first to manufacture aero motors on a practical scale4 ,illustration3 ,curtiss ,type ,,ox-#e ,eight ,cylinder ,aeroplane ,motor 99,hall-,scott ,motors994 ,these motors are made by one of the pioneer aeronautical motor builders1 and have met with great favor4 ,they are of the vertical water-cooled type1 and with the exception of minor details and weight are very similar in external appearance to the automobile motor4 ,four and #f-;cylinder types are built4 99,sturtevant ,motors994 ,these are of the ,v water-cooled type1 and are provided with or without a reducing gear4 ,at least one model is provided with lined aluminum cylinders4 99,dusenberg ,motor994 ,this is a four-cylinder1 water-cooled1 vertical motor with a very peculiar valve motion4 ,the valves are operated by long levers extending from the camshaft4 ,two inlet1 and two exhaust valves1 are used per cylinder4 ,the motor is generally furnished with a reducing gear4 99,roberts ,motor994 ,this is a solitary example of the two-stroke cycle type1 and has been used for many years4 ,it is simple and compact1 and is noteworthy for the simplicity of its oiling system4 ,the oil is mixed with the gasoline1 and is fed through the carbureter4 ,this is one of the many advantages of a two-stroke cycle motor4 99,table of ,aeronautical ,motors994 ,the following table will give an idea as to the general dimensions of ,american aeronautical motors3 99,the ,liberty ,motor994 ,the necessity of speed and quantity in the production of aeronautical motors after the declaration of war caused the ,government to seriously consider the design of a highly standardized motor4 ,this idea was further developed in a conference with representatives of the ,french and ,british missions on ,may #bh1 #aiag1 and was then submitted in the form of sketches at a joint meeting of our allies1 the ,aircraft ,production ,board1 and the ,joint ,army and ,navy ,technical ,board4 ,the speed with which the work was pushed is remarkable1 for on ,july #crd1 the first model of the eight cylinder type was delivered to the ,bureau of ,standards4 ,work was then concentrated on the #ab cylinder model1 and one of the experimental engines passed the #ej hour test ,august #be1 #aiag4 ,it is of the ,v type with the cylinder blocks at an angle of #de degrees instead of #fj degrees as in the majority of #ab cylinder ,v motors4 ,this makes the motor much narrower and more suitable for installation in the fuselage1 and in this respect is similar to the arrangement of the old ,packard aviation motor4 ,it has the additional advantages of strengthening the crank case4 ,the bore and stroke is #e x #g as in the ,hall-,scott models ,a-#e and ,a-#g4 ,the cylinders combine the leading features of the ,german ,mercedes1 the ,english ,rolls-,royce1 ,lorraine-,dietrich1 and ,isotta-,fraschini4 ,steel cylinder walls are used with pressed steel water jackets1 the latter being applied by means of a method developed by the ,packard ,company4 ,the valve cages are drop forgings1 welded to the cylinder heads4 ,the camshaft and valve gear are above the cylinder head as in the ,mercedes1 but the lubrication of the parts was improved upon by the ,packard ,company4 ,the crankshaft follows standard #ab cylinder practice except as to the oiling system1 the latter following ,german practice rather closely4 ,the first system used one pump to keep the crankcase empty delivering the oil to an outside reservoir4 ,a second pump took the oil from the reservoir and delivered it to the main crankshaft bearings under pressure4 ,the overflow from the main bearings traveled out over the face of the crank throw cheeks to a ,scupper1 which collected the excess for crank pin lubrication4 ,in the present system1 a similar general method is followed except that the pressure oil is not only fed to the main crankshaft bearings1 but also through holes in the crank cheeks to the crank pins instead of by the former scupper feed4 ,a special ,zenith carburetor is used1 that is particularly adapted to the ,liberty motor4 ,a ,delco ignition system of special form is installed to meet the peculiar cylinder block angle of #de degrees4 ,this ignition is of the electric generator type and magnetos are not used4 ,several ,american records have been broken by the new motor1 and it is reported to have given very satisfactory service1 but full details of the performance are difficult to obtain owing to the strict censorship maintained in regard to things aeronautic4 ,the motor is particularly well adapted to heavy bombing and reconnaissance type machines1 or for heavy duty4 ,it is reported that the use of the motor has been discontinued on speed scouts1 although further developments along this line may not have been reported4 ,the following gives the principal characteristics of the ,liberty motor1 issued by the ,national ,advisory ,committee for ,aeronautics4 ,year ,horse-power ,weight ,weight ,per ,gasoline ,h4 ,p4 7,model7 ,pounds ,h4 ,p4 ,hour #aiag #djj #hja #b4jj #j4ej #aiah #dcb #hjh #a4ij #j4dh #aiah #dej #hbe #a4hj #j4df ,the motors listed are all #ab cylinder models1 and the output and unit weights are based on a crank-shaft speed of #ahjj ,r4 ,p4 ,m4 ,the #e x #g bore and stroke give an output of #cg4e horsepower per cylinder in the latest model4 ,in #aiag1 the ,liberty motor was #fe per cent more powerful1 and #bh per cent lighter1 than the average stock motor in service during that year4 ,,chapter ,,xxi4 ,,glossary ,,of ,,aeronautical ,,words4 ,in the following list are the most common of the aeronautical words and phrases4 ,many of these words are of ,french origin1 and in such cases are marked ,fr4 ,in cases of ,english words1 the ,french equivalents follow in parentheses4 ,when a ,french word or term is given it is in italics1 unless it is in common use in this country4 ,words marked 7997 are the revisions adopted by the ,national ,advisory ,board of ,aeronautics at ,washington1 ,d4 ,c41 and include the term ,airplane1 which was intended to supplant the more common ,aeroplane4 ,these revisions have not met with universal adoption1 for the older words are too well established to admit of change4 ,a ,,absolute ,,units4 ,units given in terms of mass4 ,for expression in terms of pounds 7,gravitational units7 they must be multiplied by some factor involving the value of gravitation4 ,thus1 to convert units of mass into pounds1 the mass must be multiplied by the value of gravitation1 #cb4af being the average figure taken for this quantity4 ,to convert the absolute lift factors given by the ,n4,p4,l4 into pounds per square foot per mile per hour1 multiply the absolute value by ,o4#jje;,,iv4 ,,absolute ,,zero4 ,the temperature at which heat ceases to exist4 ,this is #dfa degrees below the ,fahrenheit zero1 or #bgc degrees below the ,centigrade zero4 ,,accelerate4 ,to increase in speed4 ,,acier 7,fr47 ,steel4 ,,aerodonetics4 ,a word originated by ,lanchester to denote the science of stability4 ,,aerocurve4 ,see ,,aerofoil4 ,,aerofoil499 ,a thin wing-like structure designed to obtain lift by the reaction of moving air upon its surfaces4 ,,aerodynamics4 ,a science investigating the forces produced by a stream of air acting upon a surface4 ,,aerodynamic ,,resistance4 ,the resistance caused by turbulence or eddies4 ,,aerodrome4 ,a flying field4 ,this word was also used by ,langley to describe an aeroplane4 ,,aerostat4 ,a lighter than air machine4 ,,aerostatics4 ,the science of lighter than air machines1 or devices sustained by flotation4 ,,aeroplane4 7,fr4 ,l',avion47 ,a heavier than air craft sustained by fixed wing surfaces driven through the air at the same velocity as the body of the machine4 ,auxiliary surfaces are provided for stabilizing1 steering1 and for producing changes in the altitude4 ,the landing gear may be suitable for either land or water1 although in the latter case it is generally known as a ,seaplane4 ,the ,committee equivalent is ,airplane4 ,,aileron499 ,a movable auxiliary surface used in maintaining lateral balance4 ,,aile 7,fr47 ,wing4 ,,airboat4 ,an aeroplane provided with a light boat hull in which the pilot and passenger are enclosed4 ,,aircraft499 ,any form of craft designed for the navigation of the air4 ,this includes aeroplanes1 balloons1 dirigibles1 helicopters1 ornithopters1 etc4 ,,airplane499 ,see aeroplane4 ,,airship4 ,a lighter than air craft provided with means of propulsion4 ,,air-,,screw4 ,see ,,propeller4 ,,altimeter499 ,an instrument used for determining the height of aircraft above the earth4 ,,altitude4 ,height of aircraft above sea level--generally given in feet4 ,,amphibian4 ,an aeroplane equipped with landing gear for both land and water4 ,,anemometer499 ,an instrument for measuring the velocity of the wind4 ,,angle ,,of ,,incidence4 ,the angle made by a surface or body with an air stream4 ,in the case of curved wings1 the angle is measured from the chord of the curve4 ,,angle ,,of ,,attack499 ,see ,angle of ,incidence4 ,,angle ,,of ,,entry4 ,the angle made with the chord of a wing section by a line drawn tangent to the upper curved face1 and at the front edge4 ,,angle ,,of ,,trail4 ,the angle made by a line drawn tangent to the upper surface at the trailing edge4 ,,anemograph4 ,an instrument used for graphically recording the velocity of air currents4 ,,apteroid ,,aspect4 ,a wing is in apteroid aspect when the narrow edge is toward the wind4 ,,aretier ,,arriere 7,fr47 ,see ,trailing ,edge4 ,,aretier ,,avant 7,fr47 ,see ,leading ,edge4 ,,arbre 7,fr47 ,shaft4 ,,aspect ,,ratio499 ,the ratio of the wing span to the chord 7length divided by width74 ,,atterrissage 7,fr47 ,landing ,gear4 ,,attaches 7,fr47 ,fastenings4 ,,auxiliary ,,surface4 ,a surface used for stability or for the control of the aeroplane4 ,,aviaphone4 ,an electric system of communication between the passenger and pilot4 ,,avion 7,fr47 ,see ,aeroplane4 ,,axis ,,of ,,pitch4 ,the axis taken parallel to the length of the wings1 and through the center of gravity4 ,this is sometimes called the ,y axis4 ,,axis ,,of ,,roll4 ,an axis passing fore and aft parallel to the center line of the propeller4 ,this axis is sometimes called the ,x axis4 ,,axis ,,of ,,yaw4 ,a vertical axis1 passing through the center of gravity1 around which the machine swings when being steered in a horizontal direction under the action of the rudder4 ,this is the ,z axis4 ,b ,,balsa ,,wood4 ,a very light wood obtained from ,south ,america4 ,it is lighter than cork4 ,,balloon499 ,a form of aircraft of the lighter than air type comprising a gas bag and car4 ,it is not provided with a power plant1 and depends upon the buoyancy of the gas for its sustentation4 ,a balloon restrained from free flight by means of a cable is known as a ,captive balloon4 ,a kite balloon is an elongated form of captive balloon1 fitted with a tail to keep it headed into the wind1 and is inclined at an angle so that the wind aids in increasing the lift of the gas4 ,,ballonet499 ,a small air balloon within the main gas bag of a balloon or dirigible used for controlling the ascent or descent1 and for keeping the fabric of the outer envelope taut when the pressure of the gas is reduced4 ,the ballonet is kept inflated with air at the required pressure1 the air being controlled by a valve or by regulating the speed of the blower4 ,,bank499 ,to incline the wings laterally when making a turn so that a portion of the lift force will be opposed to the centrifugal force4 ,,barograph499 7,fr4 ,barographe47 ,an instrument used for recording pressure variations in the atmosphere4 ,the paper charts on which the records are made are used for determining the altitude of aircraft4 ,,barometer4 ,an instrument used for measuring variations in the atmospheric pressure1 but is not provided with a recording mechanism as in the case of the barograph4 ,,beaume4 ,a scale of density or a hydrometer unit used in measuring the density of fluids4 ,on the ,beaume scale water is #aj4jj1 while on the ,specific gravity scale water is #a4jj4 ,the ,beaume scale is generally used for gasoline and oils4 ,,bending-,,moment4 ,the moment or ,leverage that tends to bend a beam4 ,,bequille 7,fr47 ,tail ,skid4 ,,berceau de ,,moteur 7,fr47 ,engine ,bed4 ,,bias ,,laid ,,fabric4 ,fabric laid on the wing structure with the seams at an angle with the ribs4 ,,biplace 7,fr47 ,two ,seater4 ,,biplane499 7,fr4 ,biplan47 ,an aeroplane with two superposed lifting surfaces4 ,,body4 ,see ,,fuselage4 ,,body ,,rails4 ,see ,,longerons4 ,,bois 7,fr47 ,wood4 ,,bois ,,creus 7,fr47 ,hollow wood construction4 ,,bomber4 ,an aeroplane used for bombing operations4 ,,boom4 ,the fore and aft beams running from the wings to the tail in a pusher type biplane4 ,,bord de ,,attacque 7,fr47 ,entering or leading edge4 ,,bord de ,,sortie 7,fr47 ,trailing edge4 ,,blade1 ,,propeller4 7,fr4 ,pale-,helice47 ,,boulon 7,fr47 ,bolt4 ,,boussole 7,fr47 ,compass4 ,,bras de ,,aile 7,fr47 ,wing ,spar4 ,,brevet 7,fr47 ,flying permit or license4 ,,brakes1 ,,air4 ,small adjustable flaps used in increasing the head resistance during a landing1 thus decreasing the speed4 ,,burble ,,point4 ,the angle at which the lift of a wing section reaches a maximum4 ,,buoyancy4 ,the static force due to a difference in density4 ,the difference in density between the gas in a balloon envelope and the outside air determines the sustaining or buoyant force of a balloon4 ,,bus4 ,a slow fairly stable aeroplane used in training schools4 ,c ,,cable4 7,fr4 ,cable47 ,a wire rope built up of a number of small strands4 ,,cabre'4 99 7,fr47 ,a flying attitude in which the angle of incidence is larger than normal with the tail well down4 ,,camber499 ,the convexity1 or rise of a lifting surface1 measured from the chord of the curve4 ,it is usually given as the ratio of the maximum height of the curve to the length of the chord4 ,top camber refers to the upper surface1 and bottom camber to the lower surface4 ,,cabane 7,fr47 ,the center struts rising from the top of the body to the upper wing1 or the short struts used for the bracing of the overhanging portions of a biplane wing4 ,usually cabane denotes the center cell struts4 ,,canard 7,fr47 ,a machine in which the elevator and stabilizer are in front4 ,the canard type flies ,tail first4 ,,capot 7,fr47 ,cowl or motor hood4 ,,captive ,,balloon499 ,see ,balloon4 ,,capacity499 ,the lifting capacity is the maximum flying load of an aircraft4 ,the carrying capacity 7live load7 is the excess of the lifting capacity over the dead weight of the aeroplane1 the latter including the structure1 power plant and essential accessories4 ,,carlingue 7,fr47 ,cock-pit4 ,,cata-,,hedral4 ,a negative dihedral1 or wing arrangement1 where the wing tips are lower than the center portion4 ,,catapult4 ,a device for launching an aeroplane from the deck of a ship or other limited space4 ,the first ,wright machines were launched with a catapult4 ,,cell4 7,fr4 ,cellule47 ,the space included between adjacent struts of a biplane4 ,the space between the center struts is the ,center ,cell4 ,,ceiling4 ,the maximum altitude to which an aeroplane can ascend4 ,,ceinture de ,,surete 7,fr47 ,safety ,belt4 ,,center ,,of ,,pressure 7,c4 ,p4799 ,the point of application of the resultant of all aerodynamic forces on an aeroplane wing4 ,if the wing is supported at the center of pressure it will be in equilibrium4 ,,center ,,of ,,gravity4 ,the point at which an aeroplane will balance when freely suspended4 ,,center ,,of ,,buoyancy499 ,the point at which the resultant of all the buoyant forces act4 ,,charniere 7,fr47 ,hinge4 ,,chassis4 ,the landing wheels and their frame4 ,this is also called the ,landing gear in ,english1 or the ,train de ,atterrissage in ,french4 ,the chassis carries the load when resting on the ground or when running over the surface4 ,,chord499 ,this has two meanings4 ,the chord is the width of a wing or its shortest dimension4 ,the chord is also the straight line drawn across the leading and trailing edges of a wing section4 ,,chaser4 7,fr4 ,avion de ,chasse47 ,a small1 fast machine used in scouting or fighting4 ,this type is also known as a ,speed scout4 ,,chara-,a-,,banc 7,fr47 ,a two seater aeroplane in which the pilot and passenger are seated side by side4 ,,cloche 7,fr47 ,a type of control column used on the old ,type ,,xi ,bleriot4 ,,cock-,,pit4 ,the part of the body occupied by the pilot or passenger4 ,the openings in the body cut for entrance and exit are the ,cock-pit ,openings4 ,,commandes ,a ,,pont 7,fr47 ,control bridge or ,deperdussin yoke4 ,,compte ,,tours 7,fr47 ,tachometer or speed indicator4 ,,components4 ,the individual forces that make up a total resultant force4 ,,controls499 7,fr4 ,commandes47 ,the complete system used for steering1 elevating1 balancing1 and speed regulation4 ,when controls are operated by hand they are known as ,manual ,controls4 ,,control ,,bridge4 7,fr4 ,commandes ,a ,pont47 ,the ,u shaped lever used with the ,deperdussin control system4 ,sometimes known as the ,yoke4 ,,control ,,stick4 7,fr4 ,manche ,a ,balai47 ,a simple control lever capable of being moved in four directions for elevation1 depression and lateral balance4 ,,control ,,surfaces4 ,the adjustable surfaces used for directing and balancing aircraft4 ,on an aeroplane these are represented by the rudder1 elevator1 and ailerons4 ,,contreplaque 7,fr47 ,three-ply wood4 ,,corde 7,fr47 ,cord or wire4 ,,cord ,a ,,piano 7,fr47 ,piano or solid hard wire4 ,,cord ,,winding4 7,fr4 ,transfil47 ,a winding wrapped around wooden struts to prevent splintering or complete fracture4 ,,cosse 7,fr47 ,thimble for cable connections4 ,,couss ,,in 7,fr47 ,cushion4 ,,covering1 ,,wing4 7,fr4 ,entoilage47 ,the fabric used in covering the wing structure4 ,,critical ,,angle499 ,the angle of attack or incidence at which the lift is a maximum4 ,,cowl4 7,fr4 ,capot47 ,the metal cover surrounding a rotary cylinder motor4 ,,croisillons 7,fr47 ,bracing wires4 ,d ,,damping4 ,the reduction of oscillation or vibration by the resistance of the stabilizing surfaces4 ,,dead ,,load4 ,the weight of the structure1 power plant1 and essential accessories4 ,,dead ,,water4 ,the wake directly in the rear of a moving body or surface4 ,de ,,chasse 7,fr47 ,see ,,chaser4 ,,decalage499 ,the difference in the angle of incidence between the upper and lower wings of a biplane4 ,,demoiselle ,,type4 ,a small monoplane type developed by ,santos ,dumont4 ,,density4 ,the specific weight1 or the weight per cubic foot4 ,,diedre 7,fr47 ,dihedral angle4 ,,derive 7,fr47 ,fin4 ,,dihedral ,,angle4 7,fr4 ,diedre47 ,when the tips of the wing are higher than at the center1 the two wing halves form an angle4 ,the included angle between the two halves1 taken above the surface1 is known as the ,dihedral angle4 ,,dipping ,,front ,,edge4 ,a wing section in which the leading edge is well bent down below the rest of the lower surface4 ,,dirigible499 ,a lighter than air craft in which sustentation is provided by a gas bag4 ,it differs from a balloon in having a power plant1 and is thus capable of flying in any desired direction regardless of the wind4 ,,disc ,,area ,,of ,,propeller499 ,the total area of the disc swept out by the propeller tips4 ,,discontinuity4 ,interruption in direction1 or breaks in stream line flow4 ,a body causing eddies or turbulence causes ,discontinuous flow4 ,the surface separating the eddies and the continuous stream is called a ,surface of ,discontinuity4 ,,displacement4 ,the volume or space occupied by a floating body4 ,,double ,,camber4 ,a wing section in which both the top and bottom surfaces are given a convex camber or curvature4 ,,dope4 7,fr4 ,enduit47 ,a solution used for protecting and stretching the wing fabric4 ,,drag4 ,the resistance offered to the forward motion of a surface or body moving through the air4 ,as defined by the ,advisory ,committee this is the total resistance offered by the craft and includes both the resistance of the wings and body4 ,this conception is confusing1 hence the author has considered drag as being the forward resistance of the wings alone4 ,the resistance of the structure is simply called the ,head resistance1 and the sum of the resistances is the ,total resistance4 ,this nomenclature was in existence before the ,advisory ,board proposed their definition4 ,,drift4 ,as defined by the ,advisory ,board1 the drift is the horizontal resistance offered by the wings alone4 ,this is confusing since previous works defined ,drift as the amount by which an aircraft was driven out of its normal path by wind gusts4 ,according to usage1 ,drift is the sidewise deviation from the normal flight path4 ,,drag ,,wires4 ,the bracing wires used for resisting the drag stresses set up in the wing4 ,,drift ,,indicator4 ,an instrument for indicating the amount by which an aircraft is blown out of its path by side winds4 ,,dual ,,control4 ,a double system of control that can be operated both by the pilot and passenger4 ,,dutch ,,roll4 ,a combined side roll and fore and aft pitch4 ,the machine rolls from side to side in combination with an up and down motion of the nose4 ,,dynamic ,,pressure4 ,the pressure due to the impact of an air stream4 ,e ,,eccentric ,,load4 ,a load acting to one side of the center line of a beam or strut4 ,,ecole 7,fr47 ,school4 ,,ecrou 7,fr47 ,nut4 ,,eddy4 ,an irregularly moving mass of air caused by the breaking up of a continuous air stream1 or by ,discontinuity4 ,,efficiency4 ,the efficiency of a lifting surface is generally expressed by the ratio of the lift to the drag1 or the ,lift-drag ratio4 ,the efficiency of a propeller is the ratio of the work usefully applied to the air stream in regard to the power supplied to the propeller4 ,,elevator499 ,the hinged horizontal tail surface used for maintaining longitudinal equilibrium and for ascent or descent4 ,,empennage 7,fr47 ,the group of tail surfaces1 including the elevator and stabilizer4 ,,enduit 7,fr47 ,dope4 ,,engine ,,rotation4 ,according to the ,advisory ,board1 an engine is turning in right-hand rotation when the output shaft stub is turning anti-clockwise4 ,,engine ,,bearers 7,,bed74 7,fr4 ,berceau du ,moteur74 ,the timbers or fuselage members upon which the engine is fastened4 ,,engine ,,spider or ,,bracket4 7,fr4 ,arraignee ,support de ,moteur47 ,a perforated metal support for a rotary cylinder motor4 ,,entering ,,edge4 7,fr4 ,bord ,d',attaque or ,aretier ,avant47 ,the front edge1 or air engaging edge1 of an aerofoil or lifting surface4 ,it is also called the ,leading ,edge4 ,,entoilage 7,fr47 ,wing fabric or covering4 ,,envelope4 ,the gas bag of a balloon or dirigible4 ,,essieu 7,fr47 ,axle4 ,,envergure 7,fr47 ,wing span4 ,,expanding ,,pitch4 ,a system in which the pitch increases or expands towards the tips of the propeller4 ,f ,,fabric1 ,,wing4 7,fr4 ,entoilage47 ,the cloth used for covering the wing and control surface structures4 ,,fairing4 7,fr4 ,fusele47 ,wood coverings used to streamline steel struts or other structural members4 ,,ferrules4 ,sheet steel caps used for the ends of the interplane ,struts4 ,,fin4 7,fr4 ,derive47 ,a fixed vertical stabilizing surface used for damping out horizontal vibration and oscillations4 ,,fineness ,,ratio4 ,the ratio of the maximum length to the width of a streamline body4 ,,fittings4 7,fr4 ,ferrures1 ,godets47 ,the metal parts used for making connections between the structural parts of an aeroplane4 ,,fixed ,,tail4 7,see ,,stabilizer47 ,,flaccid ,,blade ,,propeller4 ,a propeller having a cloth covered frame work on which the fabric is free to adjust itself to the air pressure4 ,,flaps1 ,,elevator4 7,fr4 ,volets de ,profondeur47 ,see ,,elevator4 ,,flexible ,,shaft4 7,fr4 ,transmission flexible47 ,used for tachometer drive4 ,,flooring4 7,fr4 ,plancher47 ,,flasque ,d',,helice 7,fr47 ,propeller flange4 ,,foot ,,lever4 7,fr4 ,palomnier47 ,the foot lever generally used to operate the rudder4 ,,formers4 ,supports used in giving a certain outline to the fuselage4 ,the formers are attached to the fuselage frame and in turn support small stringers on which the fabric is fastened4 ,,frictional ,,wake4 ,the following current of air in the rear of a moving body or surface4 ,because of the friction1 a portion of the air is drawn in the direction of the motion4 ,,fuselage4 ,a structure1 usually enclosed1 which contains and streamlines the power plant1 passengers1 fuel1 etc4 ,sometimes called the ,body4 ,,fuselage ,,biplane4 ,see ,,tractor ,,biplane4 ,,fusiform4 ,of streamline form4 ,g ,,gap4 ,the vertical distance between leading edges of the superposed planes of the biplane or triplane4 ,,gliding4 7,fr4 ,vol ,plan47 ,with an aeroplane the weight of the machine can be made to provide a forward component that will allow the machine to descend slowly 7without power7 along an inclined line4 ,this line is known as the ,gliding ,path4 ,,gliding ,,angle4 ,the angle made by the gliding path with the horizontal is known as the gliding angle4 ,this may be expressed in degrees or in the units of horizontal distance traveled per foot of fall4 ,,glider4 ,a small form of aeroplane without a power plant1 which is capable of gliding down from an elevation in the manner of an aeroplane4 ,with a proper direction and velocity of wind it can be made to hold a constant altitude and can be made to hover over one spot continuously4 ,,gouvernail 7,fr47 ,rudder4 ,,guy ,,wire4 ,a bracing wire4 ,h ,,hard ,,wire4 ,a solid tempered wire of high tensile strength used for aeroplane bracing systems4 ,h4,t4 ,,wire4 ,another expression for hard or high tensile strength wire4 ,,head ,,resistance4 ,the resistance of the structural parts of an aircraft4 ,in an aeroplane1 the head resistance is the sum of the resistances of the body1 stays1 struts1 chassis1 tail1 rudder1 elevators1 etc42 in fact1 this includes everything with the exception of the wing drag4 ,,helicopter4 ,a type of direct lift machine in which sustentation is performed by vertical air screws or propellers4 ,,helix4 ,a geometrical curve formed by the combined advance and revolution of a point4 ,,helice 7,fr47 ,propeller or screw4 ,,helice ,,tractive 7,fr47 ,tractor propeller4 ,,hydroaeroplane4 ,see ,,seaplane4 ,,hollow ,,wood ,,construction4 7,fr4 ,bois ,creus47 ,,hood ,,of ,,engine4 7,fr4 ,capot47 ,,hydrometer4 ,an instrument for measuring the density of liquids4 ,i ,,icthyoid4 ,fish or stream lined shape4 ,,inclined ,,plane4 ,a plane inclined to the wind stream so that the energy of the air stream is broken up into the two components of lift and drag4 ,,inclinometer4 ,an instrument used for determining the angle of the flight path4 ,,incidence4 ,see ,,angle ,,of ,,incidence4 ,,incidence1 ,,negative4 ,the angle formed with the air stream when front edge of the lifting surface dips below the apparent flight path4 ,,inherent ,,stability4 ,stability due to some fixed arrangement of the main or auxiliary surfaces4 ,a machine that requires mechanism or moving parts for its stability is automatically but not inherently stable4 ,,interference4 ,the crowding of the airstream in the gap of a biplane or triplane causes the surfaces to ,interfere1 and results in a loss of lift4 ,j ,,joy ,,stick4 ,see ,,control ,,stick4 ,,jamb de ,,force 7,fr47 ,bracing strut4 ,,jante 7,fr47 ,rim of wheel4 ,k ,,kite ,,balloon4 ,see ,,balloon4 ,,kilometer4 ,french metric unit of distance4 ,one kilometer equals ,o4#fba statute mile or ,o4#ecif nautical mile4 ,,kilogram4 ,metric unit of weight4 ,one kilogram equals #b4bje ,avoir4 pounds4 ,,knockout ,,hub4 ,an aeroplane chassis wheel hub provided with removable bronze bushings4 ,,keel ,,plane ,,area499 ,the total effective side area of an aeroplane which tends to prevent skidding or side slipping4 ,l ,,lateral ,,stability4 ,stability about the fore and aft axis4 ,l',,avion 7,fr47 ,aeroplane4 ,,laminated4 ,built up in a series of layers4 ,,leeway499 ,the angular deviation from a given course due to cross currents of wind4 ,,leading ,,edge4 ,see ,,entering ,,edge4 ,,lift4 ,the vertical component of the forces produced on an aerofoil by an air current4 ,,lift ,,coefficient4 ,the lift per unit of area at a unit velocity 7,ky74 ,the ,american lift coefficient is the lift in pounds per square foot at one mile per hour4 ,,lift ,,capacity4 ,see ,,capacity4 ,,live ,,load4 ,the live load generally includes the passengers1 pilot1 fuel1 oil1 instruments1 and portable baggage1 although in some cases the instruments are included in the dead load4 ,the live load is the difference between the total lift and the dead load4 ,,loading 7,,unit74 ,the unit loading is the load carried per square foot of wing surface1 or is equal to the total weight divided by the area4 ,,longerons4 ,the principal fore and aft structural members of the fuselage4 ,,longitudinals4 ,see ,,longerons4 ,,longitudinal ,,stability4 ,stability in a fore and aft direction about the ,y axis4 ,m ,,mass4 ,the quantity of matter4 ,is equal to the weight in pounds divided by the gravitation1 or generally to the weight divided by #cb4af4 ,,mandrin de ,,bois 7,fr47 ,wood spar4 ,,marouflage 7,fr47 ,strut taping with fabric bands4 ,,manche ,a ,,balai 7,fr47 ,control stick4 ,,manette 7,fr47 ,throttle4 ,,mar1 ,,montant 7,fr47 ,interplane struts4 ,,metacenter499 ,the point of intersection of a straight vertical line passing through the center of gravity of the displaced fluid or gas1 and the line that formerly was a vertical through the center of gravity before the body was tipped from its position of equilibrium4 ,there is a different metacenter for each position of a floating body4 ,,monoplane4 7,fr4 ,monoplan47 ,a type of aeroplane with a single wing surface4 ,,monocoque ,,body 7,fr47 ,a body built up in tubular form out of three-ply wood1 thus virtually forming a single piece body4 ,,monoplace 7,fr47 ,single seater4 ,,monosoupape 7,fr47 ,single valve ,gnome motor4 ,,montgolfier 7,fr47 ,hot air balloon4 ,,multiplane4 ,an aeroplane having the main lifting surface divided into a number of parts4 ,n ,,nacelle4 ,the body or fuselage of an aeroplane or dirigible4 ,it generally signifies a dirigible body4 ,the short fuselage of a pusher type is often called the nacelle4 ,,natural ,,stability4 ,see ,,inherent ,,stability4 ,,negative ,,ailerons4 ,ailerons making a negative angle with the wind when in normal flight4 ,the negative incidence of the ailerons is decreased on the low side and increased on the high side so that the high side is pushed down4 ,this decreases the drag on the lower1 inner wing in making a turn1 and therefore does not tend to stall the machine4 ,,nervures 7,fr47 ,wing ribs4 ,,normal ,,plane4 ,a flat plane placed with its surface at right angles to the air stream4 ,,normal ,,pressure4 ,the pressure at right angles to the surface of a plane4 ,,non-,,lifting ,,tail4 ,a stabilizing surface arranged so that it carries no load in normal flight4 ,,nosing4 ,the member used for the entering edge of the wing4 ,,nose4 ,the front end of the aeroplane4 ,,nut4 7,fr4 ,ecru47 ,o ,,obliteur ,,rings 7,fr47 ,the special piston rings used on the ,gnome motor4 ,,orthopter4 ,any type of wing flapping machine4 ,,ornithopter4 ,a wing flapping machine that imitates bird flight4 ,,orthogonal ,,biplane4 ,a biplane with the upper and lower leading edges in line4 ,,osmosis4 ,the transfer of hydrogen or other gas through a balloon envelope by a molecular process4 ,this must not be confused with leakage due to holes4 ,,outrigger4 ,see ,boom4 ,o4,w4,l4 ,,type4 ,a type of machine adapted for use over ,water and ,land4 ,p ,,pancake4 ,a straight vertical drop due to stalling4 ,,path ,,of ,,flight4 ,the path of the center of gravity of an aircraft in reference to the air4 ,,palonnier 7,fr47 ,foot bar or lever4 ,,panels4 ,the wing sections included between adjacent struts4 ,,patin1 ,,patinnage 7,fr47 ,skids4 ,,parasol ,,type4 ,a monoplane in which the wing is located above the body4 ,,penguin4 ,a training machine which cannot leave the ground4 ,,personnel4 ,pilot and passengers4 ,,petrol4 ,an ,english term for gasoline4 ,,phillip',s ,,entry4 ,see ,,dipping ,,front ,,edge4 ,,pilot4 ,the operator of aircraft4 ,,pilot ,,balloons4 ,small balloons sent up to determine the direction of the wind4 ,,pitch4 ,the forward distance traveled through by one revolution of the propeller4 ,,pitching4 ,a fore and aft oscillation1 first heading up and then diving4 ,,pisciform4 ,fish form4 ,,pique1 ,,vol 7,fr47 ,dive4 ,,plafond 7,fr47 ,ceiling or maximum altitude obtainable4 ,,plan ,,central 7,fr47 ,center panel4 ,,plancher 7,fr47 ,flooring4 ,,plan ,,fixe de ,,queue 7,fr47 ,stabilizer surface4 ,,plan de ,,derive 7,fr47 ,stabilizing fin4 ,,pitot ,,tube4 ,an instrument for measuring the velocity of an air current4 ,,pontoon4 ,seaplane floats4 ,,poignee 7,fr47 ,handle4 ,,pompe 7,fr47 ,pump4 ,,pompe ,a ,,pression 7,fr47 ,pressure pump4 ,,poulie 7,fr47 ,pulley4 ,,propeller4 7,fr4 ,helice47 ,a device used in converting the energy of a motor into the energy required for the propulsion of an aircraft4 ,it consists of two or more rotating blades which are inclined in regard to the relative wind1 and hence they act as rotary aeroplanes in creating a tractive force4 ,,propeller ,,rotation4 ,the direction of rotation is determined when standing in the slip stream4 ,,pneu 7,fr47 ,pneumatic tire4 ,,pterygoid ,,aspect4 ,a wing flying with the long edge to the wind is said to be in ,pterygoid ,aspect4 ,,pusher ,,type4 ,an aeroplane with the propeller in the rear of the wings4 ,,pylon4 ,a marking post on an aeroplane course4 ,p ,,race ,,of ,a ,,propeller4 ,the air stream thrown by the propeller4 ,,radial ,,motor4 ,a motor with the cylinders arranged in radial lines around the crankcase4 ,,raked ,,tips4 ,the tips are arranged at an angle with the wing so that the span of the trailing edge is greater than that of the leading edge4 ,,rayons 7,fr47 ,spokes4 ,,reflex ,,curve4 ,an aerofoil in which the trailing edge is given an upward turn4 ,,remous 7,fr47 ,a downward current of air4 ,,reservoir 7,fr47 ,tank4 ,,reservoir ,,sous ,,pression 7,fr47 ,pressure tank4 ,,resultant4 ,the total force resulting from the application of a number of forces4 ,,retreat4 ,back swept wings with the tips to the rear of the wing center4 ,,ribs4 ,the fabric forming member of the wing structure4 ,,rudder1 ,,vertical4 ,a control surface used for steering in a horizontal plane4 ,,roll4 ,oscillation about the fore and aft axis4 ,s ,,screw4 7,fr4 ,helice47 ,see ,,propeller4 ,,seaplane499 ,an aeroplane equipped with floats or pontoons for landing on water4 ,,scout ,,type4 ,see ,,chaser4 ,,service ,,tank4 ,the fuel tank feeding directly into the carburetors4 ,,set ,,back ,,wings4 ,a type of wing in which the leading edge is inclined backward as in the ,mann biplane4 ,the trailing edge is straight4 ,,shock ,,absorbers4 ,an elastic device on the chassis or landing gear that absorbs vibration by allowing a limited axle movement4 ,,side ,,slip499 ,sliding down sideways1 and toward the center of a turn4 ,this is due to an excessive angle of bank4 ,,siege 7,fr47 ,seat4 ,,similitude1 ,,laws ,,of4 ,the drag or resistance of a small aerodynamic body does not increase in direct proportion with the area and speed4 ,the laws governing the relation between a model and a full size machine are known as the laws of ,similitude4 ,,skids499 7,fr4 ,patin1 ,pattinage47 ,long wood or metal runners attached to the chassis to prevent the nosing over of a machine when landing1 or to prevent it from dropping into holes or ditches on rough ground4 ,it also acts when the wheels collapse4 ,,skid ,,curtains4 ,vertical side curtains or surfaces provided to reduce the skidding action on turns or to prevent side slip4 ,,skidding499 ,sliding sideways away from the center of the turn4 ,it is due to insufficient banking on a turn4 ,,skin ,,friction4 ,the resistance caused by the friction of the air along a surface4 ,,slip499 ,applied to propeller action1 the slip is the difference between the actual advance of an aircraft and the theoretical advance calculated from the product of the mean pitch and the revolutions per minute4 ,when the propeller is held stationary1 the slip is said to be #ajj percent4 ,,slip ,,stream4 ,the wind stream thrown by a propeller4 ,,soaring ,,flight499 ,the sustentation of a wing surface due to wind currents and without the expenditure of other power4 ,soaring flight is performed by gulls1 buzzards and vultures1 but no practical machine has yet been built that will fly continuously without the aid of power4 ,,span4 7,fr4 ,envergure47 ,the length or longest dimension of a wing1 generally taken at right angles to the wind stream4 ,,spar4 7,fr4 ,bras ,d',aile47 ,the main wing beams that transmit the lift to the body4 ,,spokes4 7,fr4 ,rayon47 ,,spread499 ,see ,,span4 ,,stability499 ,the property of an aircraft that causes it to return to a condition of equilibrium after meeting with a disturbance in flight4 ,,stagger499 ,the advance of the leading edge of the upper wing over that of the lower wing4 ,,stabilizer499 7,fr4 ,stabilisateur47 ,a horizontal tail surface 7fixed7 used for damping out oscillations and for promoting longitudinal stability4 ,,stalling499 ,the condition of an aeroplane that has lost the speed necessary for steerage way or control4 ,,stalling ,,angle4 ,see ,,critical ,,angle4 ,,steering ,,wheel4 7,fr4 ,volant47 ,,statoscope499 ,an instrument for detecting a small rate of ascent or descent4 ,used principally with balloons4 ,,stay ,,wire4 7,fr4 ,tendeur47 ,a wire or cable used as a tie to hold members together1 or to give stiffness to a structure4 ,,step499 ,a break in the form of a float or flying boat bottom4 ,,streamline4 ,a form of body that sets up no turbulence or eddies in passing through air or liquid4 ,,strut499 7,fr4 ,mar1 ,montant47 ,a compression member used in separating the upper and lower wings of a biplane1 or the longerons of the fuselage4 ,,sweep ,,back4 ,see ,,retreat4 ,t ,,tachometer4 7,fr4 ,compte ,tours47 ,an instrument for directly indicating the revolutions per minute4 ,,tail499 7,fr4 ,queue47 ,the rear part of an aircraft to which usually are attached the rudder1 stabilizer1 and elevator4 ,,tail ,,skid4 7,fr4 ,bequille47 ,a flexibly attached rod which holds the tail surfaces off the ground1 and breaks the landing shocks on the tail structure4 ,,tail ,,boom4 ,see ,,boom4 ,,tail ,,dive4 ,a very dangerous backward dive4 ,,tail ,,spin4 ,a condition in which the tail revolves about a vertical line passing through the center of gravity4 ,,tandem ,,planes4 ,a form of aeroplane in which the wings are placed one after another4 ,,taube4 ,an old type of ,german or ,austrian aeroplane with back swept wing tips4 ,,taxi4 ,to run along the ground4 ,,thimble4 7,fr4 ,cosse47 ,an oval grooved metal fitting used for the protection of a cable loop at the point of attachment4 ,,three-,,ply4 7,fr4 ,contreplaque47 ,a wood sheet composed of three layers of wood glued together1 the line of grain crossing at each joint4 ,,thrust4 ,the propulsive force exerted by a propeller4 ,,thrust ,,deduction499 ,the reduction of thrust due to a reduction of pressure under the stern of the aircraft4 ,,tirant 7,fr47 ,bracing tubes4 ,,torque4 ,the turning force or moment exerted by the motor4 ,,toile 7,fr47 ,linen4 ,,torque ,,warp4 ,the amount of warp1 or permanent set in the ailerons necessary to overcome the torque or twisting effect of the motor4 ,in some machines the torque is overcome by changing the angle of incidence at the wing tips4 ,,tractor ,,biplane4 ,a type of aeroplane in which the propeller is placed in front of the wings so that it pulls the machine along4 ,,trailing ,,edge4 ,the edge of a wing at which the air stream leaves the surface4 ,,train ,d',,atterrissage 7,fr47 ,landing gear4 ,,transfil 7,fr47 ,cord winding on the struts4 ,,triplane4 7,fr4 ,triplan47 ,an aeroplane with three superposed wings4 ,,turbulence4 ,the eddies or discontinuity caused by a body or surface passing through the air4 ,u ,,useful ,,weight4 ,the difference between the total lift and the dead load4 ,this comprises the pilot and passenger1 the weight of the fuel1 baggage and instruments4 ,,unit ,,loading4 ,the weight per square foot of main wing surface4 ,v ,,vol ,,plane 7,fr47 ,see ,,glide4 ,,vol ,,pique 7,fr47 ,see ,,dive4 ,,volant 7,fr47 ,steering wheel4 ,,vernis 7,fr47 ,varnish4 ,,vril 7,fr47 ,spinning nose dive4 ,,volets de ,,profondeur 7,fr47 ,elevator flaps4 ,w ,,warp ,,control499 ,lateral control obtained by twisting the wing tips4 ,,washout4 ,decreased camber or incidence toward the wing tips4 ,,weather-,,cock ,,stability4 ,stability in the line of travel1 or with the relative wind1 so that the machine always tends to head into the wind4 ,,whale ,,type4 ,a speed type biplane in which the body entirely fills the gap between the upper and lower wings4 ,,whirling ,,table4 ,a testing device in which a model wing or body is placed at the end of a revolving arm4 ,,wings499 7,fr4 ,aile47 ,the main supporting surfaces of an aeroplane4 ,,working ,,face4 ,the face of a propeller blade lying next to the slip stream4 ,,wake ,,gain499 ,due to skin friction and eddies1 a moving aircraft drags a certain amount of the surrounding air with it4 ,this reduces the effective resistance of the hull and increases the effective pitch of a pusher propeller since the latter acts on a forward moving mass of air4 ,this is ,wake gain4 ,illustration3 ,launching with ,catapult from ,deck of ,battleship