,transcriber's ,note ,italic text displayed as3 italic ,bold text displayed as3 bold ,,learning ,,to ,,fly ,,in ,,the ,u4 ,s4 ,,army ,mc,graw-,hill ,book ,co4 ,inc4 ,,publishers ,,of ,,books ,,for ,coal ,age ,illustration3 ,decoration ,electric ,railway ,journal ,electrical ,world ,illustration3 ,decoration ,engineering ,news-,record ,american ,machinist ,illustration3 ,decoration ,the ,contractor ,engineering ,mining ,journal ,illustration3 ,decoration ,power ,metallurgical ,chemical ,engineering ,electrical ,merchandising ,illustration3 ,a ,,group ,,of ,u4,s4 ,,army ,,student ,,aviators4 ,frontispiece ,,learning ,,to ,,fly ,,in ,,the ,u4 ,s4 ,,army ,a ,,manual ,,of ,,aviation ,,practice ,,by ,e4 ,n4 ,,fales ,,formerly ,,assistant ,,professor ,,of ,,mechanical ,,engineering ,,chair ,,of ,,aeronautics1 ,,university ,,of ,,illinois ,,first ,,edition ,,second ,,impression ,mc,g,r,a,w-,,hill ,,book ,,company1 ,,inc4 #bci ,,west #ci,,th ,,street4 ,,new ,,york ,,london3 ,,hill ,,publishing ,,co41 ,,ltd4 #f #h ,,bouverie ,,st41 ,e4 ,c4 #aiag ,,copyright1 #aiag1 ,,by ,,the ,,mcgraw-,,hill ,,book ,,company1 ,,inc4 ,,the ,,maple ,,press ,,york ,,pa ,,preface ,this book is primarily intended for non-technical readers2 and for the student aviators who1 called from non-technical occupations1 must cram themselves at short notice with the gist of airplane flying2 and who must omit everything except the outstanding fundamentals4 ,the desired essentials are here given without sacrificing accuracy to brevity4 ,it has been necessary to omit many technical details of interest to the aeronautical engineer1 to whose needs other larger textbooks are adapted as a complete survey of technical aeronautics4 ,in brief1 the book presents the main principles of aviation1 such as the aviator must know in order properly to understand his airplane1 keep it trued up1 and operate it in cross-country flights as well as at the flying field4 ,out of the #bjjj aeronautical books now in existence1 a few are adapted to use as textbooks for the present need1 but none give the particular and abridged information in tabloid form such as must be adopted for the best time economy of these students4 ,it is by the kind permission of ,professor ,e4 ,a4 ,holbrook1 ,mr4 ,o4 ,s4 ,beyer1 and ,mr4 ,c4 ,m4 ,hebbert that chapters ,,vi to ,,xi have been included4 ,acknowledgment and full credit is due them as co-authors4 ,chap4 ,,vi1 ,,vii1 and part of ,chap4 ,,xi were prepared by ,prof4 ,e4 ,a4 ,holbrook2 ,chap4 ,,ix1 ,x1 pages #aeb-aeg of ,chap4 ,,viii1 and pages #agc-agg of ,chap4 ,,xi were prepared by ,mr4 ,o4 ,s4 ,beyer2 ,chap4 ,,viii1 pages #acc-aeb1 was prepared by ,mr4 ,c4 ,m4 ,hebbert4 ,in the ,chapter on 8,history of ,aviation0 only those experiments are treated which have a bearing on flight today2 this chapter is to be used in conjunction with the ,chapter on 8,principles of ,flight10 especially as regards controlling the airplane4 ,the question of ,airplane ,motors has not been touched1 because to do it justice would unduly increase the size of this volume1 and because adequate treatises on the subject are available4 ,dec4 #abth1 #aiag4 ,,contents ,,page ,,preface vii ,,chapter ,i4 ,history of ,aviation #a ,,ii4 ,types of ,military ,airplanes and ,uses #ah ,,iii4 ,principles of ,flight #ci ,,iv4 ,flying the ,airplane #hj ,v4 ,cross-country ,flying #hi ,,vi4 ,the ,rigging of ,airplanes--,nomenclature #aac ,,vii4 ,materials of ,construction #abj ,,viii4 ,erecting ,airplanes #acc ,,ix4 ,truing up the ,fuselage #aeh ,x4 ,handling of ,airplanes in the ,field and at the ,bases ,previous to and ,after ,flights #aff ,,xi4 ,inspection of ,airplanes #agc ,,learning ,,to ,,fly ,,in ,,the ,u4 ,s4 ,,army ,a ,,manual ,,of ,,aviation ,,practice ,,chapter ,i ,,history ,,of ,,aviation ,that part of the history of ,aviation which has especial interest for aviators is of recent date1 and extends back only two dozen years4 ,of course efforts have been made toward manflight ever since the early sixteenth century1 when ,leonardo da ,vinci invented the parachute and became the first patron of aeronautics2 between the time of this famous artist and the present many experimenters have given their attention to the problem1 but previous to the last decade of the nineteenth century nothing practical was achieved4 ,then1 with the perfection of the steam engine and the development of the gasoline engine1 there came inducement to sound experimentation1 bringing forth such well-known figures as ,maxim1 ,langley1 ,lillienthal and ,chanute4 ,the work of each of these men is an interesting story by itself1 especially that of ,langley1 who approached the matter from a strictly scientific viewpoint1 established testing apparatus and built successful self-propelled steam models years before the ,wright brothers reported their independent successes4 ,he reproduced his models to full scale with every expectation of success1 but failed1 due to exhaustion of his capital4 ,langley's ,experiments in ,aerial ,navigation4--,in all the history of aerial navigation one of the most romantic stories is that describing the scientific researches begun in #ahhg by ,langley and culminating in #ahif in the first really successful case of mechanical flight using a prime mover2 continuing up to #aijc when this first successful machine1 a model of #ab-;ft4 span1 was reproduced to full scale and manned for its trial flight by a human pilot2 and ending with the destruction of this full-sized machine on launching1 so that ,langley missed the glory of being the actual discoverer of manflight only by a hair's breadth1 dying shortly afterward of a broken heart1 as is conceded by those who knew him4 ,if this full-scale machine had performed as successfully in #aijc as it actually did after being rebuilt and partly remodelled a decade later by the ,curtiss company1 ,langley would have antedated the first successful flight made by the ,wright brothers by a narrow margin of about #b months4 ,illustration3 7,courtesy ,s4 ,s4 ,mc,clure ,co47 ,,fig4 #a4--,the ,langley steam model flying machine4 ,it flew a mile in #ahif1 the first successful airplane to fly with a prime mover4 ,lillienthal 7,germany1 #ahid74--;,but omitting details regarding the early experimenters we will consider only that part of the history of aviation most important to the prospective aviator4 ,we will confine ourselves to the sequence of gliding and power experiments begun by ,lillienthal1 carried forward by ,chanute and brought to completion by the ,wrights4 ,illustration3 7,courtesy ,jas4 ,means' 8,aeronautical ,annual407 ,,fig4 #b4--,lillienthal's biplane glider in flight1 #ahid4 ,note4--7a7 ,arched wings2 7b7 fixed tail2 7c7 method of balancing by swinging legs4 ,illustration3 7,courtesy ,jas4 ,means' 8,aeronautical ,annual407 ,,fig4 #c4--;,chanute's biplane glider1 #ahif4 ,note improvement in rigidity by bridge-type trussing4 ,lillienthal was the first man to accomplish successful flights through the air by the use of artificial wing surfaces4 ,after many years of experiment and study of soaring birds he constructed rigid wings which he held to his shoulders and which1 after he had gained considerable velocity by running forward downhill1 would catch the air and lift his weight completely off the ground4 ,the wings were arched1 for he observed this was the case in all birds2 flat wings proved useless in flight1 and suggested a reason for the failure of previous experimenters4 ,to these rigid wings ,lillienthal fastened a rigid tail2 the wings and the tail comprised his 8glider40 ,there were no control levers and the only way the operator could steer was to shift the balance by swinging his legs one way or the other4 ,lillienthal constructed an artificial hill for his gliding so that he could coast downward for some distance without striking the ground and he was able to accomplish many glides of a couple of hundred yards in length4 ,chanute 7,chicago1 #ahif74--;,chanute's experiments in gliding were quite similar to ,lillienthal's and were made on the sand dunes along ,lake ,michigan outside of ,chicago4 ,his apparatus was more strongly constructed1 being of trussed biplane type1 a construction suggested to him by his experience in bridge building1 and one which persists today as the basis of strength in our present military biplanes4 ,the ,wright ,brothers1 #aija4--,lillienthal was killed in a glide1 having lost control of his apparatus while some distance above the ground4 ,the ,wright brothers read of his death and commenced thinking over the whole problem4 ,lillienthal's method of balancing his large apparatus by the mere effect of swinging his legs appeared to them as a very inadequate means of control4 ,they came to the conclusion that the immediate problem in artificial flight was the problem of stability1 which they felt should be solved by an entirely different means than that employed by ,lillienthal and ,chanute4 ,the work already done had demonstrated without question that support in the air had been established2 with the addition of controllability the ,wrights looked forward to doing something worth while in the way of artificial flight4 ,to improve ,lillienthal's method of shifting the weight1 they conceived the idea of leaving the pilot in an immovable position in the glider1 and instead of obliging him to shift his weight this way and that1 they proposed to manipulate the surfaces of the wings themselves by means of levers under the pilot's control1 so that the same result of balancing could be obtained by quite a different and superior method4 ,they set out1 therefore1 deliberately to solve the whole question of airplane stability4 ,there was the fore and aft or horizontal stability1 for which ,lillienthal had swung his legs forward and backward2 there was in addition the sidewise or lateral stability for which ,lillienthal had swung his legs to left and right4 ,the fundamental requirements to be met were that during flight the glider should be kept in its proper attitude without diving or rearing up1 and without rolling into an attitude where one wing tip was higher than the other1 i4e41 the machine was to be kept level in both directions4 ,illustration3 ,first ,wright glider4 ,with front elevator1 shown flying empty as a kite4 ,final ,wright glider4 ,with rudder and elevator4 ,note right wing warped downward to raise right wing tip4 ,a successful downhill glide4 ,pilot lies prone on bottom wing4 ,,fig4 #d4 ,fore and ,aft ,control4--,after some preliminary trials the ,wrights found that the fore and aft balance could be controlled by an elevator or horizontal rudder1 supported on outriggers on the front of the airplane1 and operated by a lever4 ,if the pilot found the glider pitching too much downward1 and tending toward a dive1 he would tilt the elevator upward by moving the lever1 thus turning the glider back into its proper attitude4 ,this elevator in modern machines is back of the airplane1 a better place for it than was chosen by the ,wrights4 ,it may be said that their chief reason for first putting it in front was that they could see it there and observe its effect4 ,they soon realized that the rear location gave easier control1 and they acted accordingly4 ,lateral ,control4--,after satisfying themselves regarding fore and aft control1 the ,wrights took up lateral control4 ,their problem was to devise a means for keeping the span of the wings level so that when for any reason one wing tip should sink lower than the other1 it could be at once raised back to its proper position4 ,lillienthal had tried to do this by swinging his legs toward the high side2 the shifted weight restoring the position4 ,the ,wrights1 to obviate this inadequate method1 bethought themselves to restore equilibrium by means of the wind itself rather than by gravity4 ,they observed an interesting maneuver employed by a pigeon which seemed to secure its lateral balance in exactly the way they wanted2 this bird was seen to give its two wings each a different angle of attack1 whereat one wing would lift more forcibly than the other1 thereby rotating the bird bodily in any desired amount or direction about the line of flight as an axis4 ,to copy this bird apparatus in a ,wright glider1 it was found sufficient to alter the angle of the wing tips only1 leaving the chief part of the supporting surface in its original rigid position4 ,in other words1 the wing tips were to be warped2 the one to present greater angle of attack1 the other less angle1 exactly as in the case of the pigeon4 ,suppose the airplane to develop a list to the left1 the wing on that side sinking1 the pilot was to increase the angle at the tip of this left-hand wing by moving the warping lever1 and at the same time decrease the angle of the right-hand wing by the same lever4 ,he was to hold this position until the airplane was righted and brought back to level position4 ,this arrangement proved to have the effect anticipated and maintained stability easily on a glider much larger than ,lillienthal ever managed with his leg-swinging method4 ,directional ,control4--,we have now followed the development by the ,wrights of airplane control as regards3 #a4 ,fore and aft or 8pitching0 motion1 accomplished by an elevator operated by lever4 #b4 ,lateral or 8rolling0 motion accomplished by wing warping operated by a second lever4 ,these were the only controls used in the earliest gliders4 ,it remains to consider the third element of control1 viz3 #c4 ,the directional or 8yawing0 control1 which is accomplished by an ordinary vertical rudder operated by a third lever4 ,the ,wrights found the warping had all the effect anticipated but had also certain secondary and undesirable effects4 ,whenever they applied the warping lever to correct the rolling motion1 the glider responded as far as rolling control was concerned1 but at the same time would 8yaw0 or swerve out of its course to right or left4 ,this was a serious complication4 ,for1 in the moment of swerving1 the high wing which they desired to depress would advance faster than the low wing1 and solely by its higher velocity tended to develop a greater lift and thereby neutralize the beneficial effect of the warp4 ,in many of their early glides1 because of pronounced swerving1 the warp effect was entirely counteracted and failed to bring the glider back to level2 with the result that one wing tip would sink1 at the same time swinging backward until the machine was brought to the ground4 ,no amount of controlling could prevent this4 ,after much bewilderment on this point1 the ,wrights observed that whenever a wing tip was warped to a large angle its resistance became relatively greater and it slowed up while the opposite side went ahead4 ,they at once hit upon the idea of a rudder1 previously considered unnecessary1 which they believed could be turned in each case of yawing just enough to create a new and apposing yawing force of equal magnitude4 ,they therefore attached a rudder at the rear1 connecting its tiller ropes to lever ,no4 #b1 and giving this lever a compound motion so that one hand could operate either warp or rudder control independently 7or simultaneously in proper proportion to eliminate the yawing tendency above mentioned74 ,this combination is the basis of the ,wright patents and is essential in airplanes of today4 ,great success now ensued in their gliding experiments2 the machine was always in perfect control2 could be manipulated in any desired manner2 turned to right or left1 or brought down to earth with safety4 ,thus were the three elements of control applied by the ,wrights to their glider and the problem apparent in ,lillienthal's death was solved4 ,the next step was to install a power plant able to maintain forward speed without resorting to coasting downhill by gravity2 and therefore capable of producing a horizontal flight4 ,in developing a power flyer aside from the question of control the proper design was arrived at as follows3 ,efficiency of ,wings4--,the ,wrights knew from ,langley and ,chanute that flat wings were inefficient and useless1 and curved wings essential2 they did not know whether the amount of curvature mattered much4 ,to find this out by trials in gliding would be slow and expensive4 ,they adopted a better way--the wind-tunnel method1 wherein small-scale models were tested and compared for efficiency in a blast of air4 ,they made their wind tunnel #af in4 in diameter and created a powerful air blast through it by means of an engine-driven fan4 ,small models of wings were placed in the center of this confined air blast1 mounted on a balance arm which projected into the tunnel from the outside4 ,the air forces and efficiency of the models were thus measured4 ,a large variety of shapes were tested and one was selected as best of all from the standpoint of curvature and rounded wing tips4 ,this shape was adopted in their flyer1 and though on a much larger scale fulfilled the predictions made for its efficiency in the indoor wind-tunnel experiments4 ,the ,wright glider was1 of course1 a biplane model4 ,they tested a small #f-;in4 model biplane and found that the two wings together were less efficient than either wing by itself4 ,however1 other considerations1 such as rigidity of trussing1 decided them to adopt the biplane rather than a monoplane arrangement4 ,low ,resistance to ,forward ,motion4--,the ,wrights used their wind tunnel also in choosing for the struts of their airplane a shape which would present least head resistance to forward motion4 ,they found that a square strut had a resistance which could be decreased by changing the shape to resemble a fish4 ,the resistance of the pilot himself was decreased by making him lie prone1 face downward on the bottom wing4 ,propeller ,efficiency4--,although little data on the subject of propeller efficiency was available to the ,wrights1 they were able to arrive at a very creditable design wherein two propellers were used1 driven from a single motor1 and rotating one each side of the pilot4 ,the mechanical difficulties which have since embarrassed the use of two propellers were less with the ,wrights because they were dealing with smaller horsepowers than are in use today2 they therefore were able to realize a very high propeller efficiency4 ,motor4--,when the ,wrights were ready to apply a motor to their glider1 they found it impossible to secure one light enough1 and had to set about building one themselves4 ,they adopted a four-cylinder type1 water-cooled1 and their aim was to save weight and complication wherever possible4 ,their first motor gave about #ab hp41 which was raised to a higher and higher figure by subsequent improvements until it reached #bj hp4 ,in its earliest stages it was able to give sufficient power for short horizontal flights4 ,means of ,starting and ,landing4--,one reason the ,wrights could use such low horsepower was that they employed auxiliary starting apparatus to get up original speed4 ,they knew that less horsepower was necessary to fly an airplane after it was once in the air than was necessary to get it into the air at the start1 and they therefore rigged up a catapult which projected their airplane forward on a rolling carriage with great force at the start1 so that all the motor had to do was to maintain the flight in air4 ,the ,wright airplane had at first no landing wheels1 and was provided only with light skids on which it could make a decent landing4 ,present-day airplanes1 of course1 have wheels on which to roll both at starting and at landing and their motors are powerful enough to eliminate the necessity for a starting catapult4 ,illustration3 7,courtesy ,american ,technical ,society and ,scientific ,american ,supplement47 ,,fig4 #e4--;,details of ,bleriot ,,xi monoplane4 ,bleriot's ,contribution to ,aviation4--,bleriot experimented a great many years before he attained success and did so years after the ,wrights had successfully flown4 ,but when he did obtain success1 his great ingenuity produced features of design which were a decided step forward4 ,he added a body to the airplane and produced a machine which instead of being a pair of wings with various appendages1 was a body to which wings were attached1 giving a more shipshape and convenient arrangement4 ,the motor1 instead of being located beside the pilot as in the ,wright machine1 was put in the very front of the body ahead of the pilot where it was not likely to fall on him in case of a smash4 ,this location of the motor entailed the use of a single propeller at the front1 a 8tractor0 screw as it was called1 less efficient than the double propeller of the ,wrights1 but better from the standpoint of mechanical convenience4 ,the body of a ,bleriot1 which was quite similar to the body of any bird in its general arrangement1 projected to the rear in a tapering form and carried at the rear a rudder and elevator4 ,the motor1 pilot and tanks were thus enclosed within the body and away from the wind4 ,bleriot's contributions were then1 better location of the motor1 adaptation of the body or 8fuselage10 elimination of the front elevator and substitution of the rear elevator4 ,nieuport and ,fokker's ,contribution to ,aviation4--,a further advance on ,bleriot's design was made by ,nieuport and later by ,fokker4 ,the former utilized the fuselage principle of ,bleriot and enclosed the whole framework1 front and back1 to give a stream-line form1 and even went so far as to make wind-tunnel experiments from which he was able to choose a very efficient fuselage shape as well as wing and strut efficiency4 ,illustration3 7,from ,hayward's 8,practical ,aeronautics407 ,,fig4 #f4--,nieuport monoplane4 ,representing an advance in speed1 due to covered stream-line body4 ,,chapter ,,ii ,,types ,,of ,,military ,,airplanes ,,and ,,their ,,uses ,modern ,airplanes ,combining ,best ,features of ,previous ,experiments4--,the modern airplane1 of which the ,curtiss training machine used at the ,u4 ,s4 ,aviation ,schools is typical1 is a combination of the best features referred to above4 ,it is of the biplane type for1 as shown by ,chanute1 rigid trussing is thus possible1 an advantage sufficient to offset the slight loss of efficiency which exists in the biplane4 ,the landing gear consists of two wheels provided with shock absorbers2 the body is of the general stream-line type1 enclosed from front to back1 containing comfortable seats for the passengers and enclosing the motor and tanks away from the wind4 ,the motor is at the front where1 in an accident1 it will not be on top of the pilot4 ,the warping effect is obtained by hinging flaps at the wing tips1 the same effect being obtained while at the same time leaving the whole wing structure rigid and strong rather than flexible and weak1 as was the case in the early warping type of machines4 ,military ,airplanes of ,today4--,in the modern airplane1 therefore1 we see that matters of efficiency1 to which the ,wrights gave great attention1 have been sacrificed in favor of convenience1 particularly in favor of power and speed4 ,this is the effect of military demands for airplanes where power1 speed1 and ability to climb fast are vital requirements4 ,to escape from or to destroy an enemy1 high speed and ability to climb fast are1 of course1 prerequisites4 ,moreover1 from the standpoint of safety in maneuvering it is desirable to have a reserve of power and speed4 ,therefore1 the design of military machines has tended in a given direction up to the present4 ,new considerations have arisen on this account1 such as for instance the question of landing4 ,fast machines in general make high-speed landings1 and are for that reason dangerous4 ,the original ,wright machines were built to land at such a slow speed that ordinary skids were sufficient to take the shocks4 ,nowadays the high-powered airplane is likely to come to grief in landing more than at any other time4 ,the question of stability in flight has of recent years been treated mathematically and experimentally1 using of course the fundamental system of 8three axes control0 first applied by the ,wrights4 ,it has been found that by properly proportioning the tail surfaces and properly arranging the wings and center of gravity1 any desired degree of stability may be obtained1 such that a machine may be made almost self-flying or1 if preferred1 may be made very sensitive4 ,all of the above features of design have had consideration in the latest types of military airplanes4 ,observe the high speed of the latest speed scouts1 where power is concentrated exclusively on speed and climbing ability and landing speed is dangerously high4 ,we see the advent of the triplane scout1 which is an attempt to secure slow landing speed combined with high flying speed4 ,we see machines with the motor and propeller in the rear1 or with two motors1 one to each side of the body out in the wings1 the object being to avoid interference of the propeller with the range of gun fire4 ,in short1 we see the effect of many military considerations on the design of the airplane4 ,it will be interesting at this point to survey what are these military uses of the airplane4 ,aerial ,fighting4--,fighting in the air is the most spectacular use to which military airplanes have been put4 ,the first requirements in a fighting airplane are speed and climbing ability and these must be obtained at all costs1 because speed and climb are weapons of defense and offense second only in value to the gun itself4 ,the concentration of motive power for speed and climb requires that as little weight as possible be used2 and therefore the fastest fighters are designed to carry only one person and are very light and of course very small4 ,it is usual to have one gun fixed to the body and firing through the propeller in the case of a tractor1 and a second adjustable aim gun pointing upwards over the top wing4 ,this gives the pilot a chance to fire a round at the enemy while 8sitting on his tail0 or following from behind2 and then when diving below the enemy the second gun is available for shooting overhead4 ,these very high-speed fighters are difficult to land1 due to their speed1 and are suitable only for the highest-trained pilots4 ,directing ,artillery ,fire4--,the friendly airplane is sent out over the enemy's positions1 soars above the target1 sends back signals by wireless to the friendly battery regarding the effect of fire2 practically dictating the success of artillery operations4 ,reconnaissance4--,the friendly airplanes go out1 usually in squads for the sake of protection1 and observe by means of photographs or vision size of enemy troops1 batteries1 trenches1 lines of communication1 etc42 report the situation to headquarters as a source of daily photographic record of the operations of the enemy1 to such an extent that any change of the enemy's position can be analyzed4 ,of course the value of reconnaissance is lessened when the enemy disguises his gun emplacements1 etc4 ,in reconnaissance machines it is important to have two persons1 one to steer and the other to scan the countryside4 ,the reconnaissance machine is therefore a two-place type which may or may not have armament4 ,it need not be so fast1 especially when convoyed by fighting speed scouts4 ,the two-place machines are frequently used for fighting1 in which case the pilot will have a gun fixed to the body and shooting through the propeller1 and the passenger1 especially in ,german machines1 will also have a gun mounted in the turret so that it may be shot in a variety of directions by the passenger4 ,bomb ,dropping4--,this maneuver requires squad flights to be of great value4 ,the fundamental characteristic of a bombing airplane is its ability to carry great weight4 ,such machines are of comparatively large size and not particularly fast4 ,weight carrying is of course incompatible with speed and climbing ability and therefore the bombing machine must be a compromise if it is to have any reasonable speed4 ,it may be said that airplanes compare very unfavorably with dirigible balloons for bomb raids because the latter are able to carry several tons of bombs as against the airplane's quarter of a ton4 ,locating ,submarines4--,for coast patrol or submarine spotting1 the airplane is an important factor1 for from an airplane it is possible to see for a considerable depth into the water1 and to locate hostile submarines4 ,training ,student ,aviators4--,the training machine on which prospective aviators secure their flying instruction may be considered as a type in which great speed and power is not essential1 but in which reliability and ease of control is desirable4 ,the typical military training airplane in this country is a single-motor tractor of moderate horsepower 7about #ajj7 having of course the seats in tandem and furnished with dual control so that operation may be from either pilot's or passenger's seat4 ,the dual-control system of training which prevails in this country differs from the ,french method of starting the pupil out alone to try his wings2 it enables the pilot to keep a constant eye upon the pupil's control manipulations and to correct them instantly whenever they are in error before any damage is done4 ,a possible improvement in the dual-control training machine will be the substitution of side by side seats for tandem seats4 ,at present1 communication is difficult due to the great noise of the motor2 but with the adoption of side by side seats such as is used in naval training schools1 the pilot and pupil will be able to communicate to better advantage4 ,illustration3 ,,fig4 #g4--,u4 ,s4 training airplane1 dual control 7,curtiss ,,jn-#d74 ,speed #dc to #gb mi4 per hr42 climbing ability #cjj ft4 per min42 #ij h4p42 weight fully loaded #a1hij lbs4 ,types of ,airplanes4--,to suit the foregoing purposes flying machines exist in seven distinct different shapes at the present time1 namely3 monoplanes1 biplanes1 triplanes1 single-motor tractors1 single-motor pushers1 double-motor machines and marine airplanes4 ,the last four types may be either monoplanes1 biplanes or triplanes4 ,in order to understand the adoption of one or the other type for military use1 it is well to run over the characteristics of the seven types mentioned4 ,monoplanes4--,the simplest form of airplane is the monoplane which is fashioned after the manner of a bird 7see ,fig4 #cd74 ,there are two things to say in favor of the monoplane3 first1 that the passengers have an unobstructed view forward and range of gun fire upward because there is no wing above them2 second1 the aerodynamic efficiency of the monoplane is superior to any other type4 ,but when the bird design is applied to a man-carrying apparatus1 it becomes impracticable to construct spars to take the place of the bird's wing bones2 and therefore to give the wings proper strength it becomes necessary to truss them with numerous tension wires stretching from the running gear out to various portions of the wings4 ,there are also wires running from a vertical mast above the body to a point on the top part of the wing2 these wires1 while they give the wing no added strength during a flight1 are necessary in order that the shock of landing shall not break the wings off sharp at the shoulder4 ,it is characteristic of monoplane construction that from a point below the body and also from a point above the body a number of heavy wires run outward to various points on the wings2 and it may be said that the strength to be secured from this construction is not all that could be desired4 ,biplanes4--,the biplane is an improvement over the monoplane from the latter standpoint2 in the biplane there are two parallel surfaces separated by vertical sticks or struts1 thus forming parallelograms which are susceptible of being trussed by means of tension-wire diagonals in a manner familiar and well understood in case of bridges4 ,it is possible to build up biplane wings of great rigidity and strength by this system1 much more easily than in case of monoplanes4 ,however1 the biplane type is from the standpoint of efficiency inferior to the monoplane4 ,this is due to the fact that the vacuum above the bottom wing which is so necessary for high duty is somewhat interfered with by the upper wing2 thus while in a biplane the upper wing operates about as efficiently as it would operate in a monoplane1 yet the lower wing has its efficiency materially reduced and the resulting overall efficiency of a biplane compared area for area with the monoplane is about #he per cent4 as great4 ,however1 recent developments of the airplane have more or less put efficiency in the background and as a result today the biplane is more popular than the monoplane4 ,in addition to the greater strength of biplane wings their span may be less than the monoplane for the same supporting area4 ,this makes them less unwieldy4 ,moreover1 for certain reasons a biplane machine of high speed may be landed at a lower speed than equivalent monoplanes4 ,triplanes4--,what is true of the biplane is more true in almost every item of the triplane1 that is1 it is comparatively strong1 compact1 and of low landing speed1 but of reduced efficiency4 ,illustration3 ,,fig4 #h4--,u4 ,s4 speed scout triplane1 single seater4 7,curtiss ,model ,s#c71 #ee to #aae mi4 per hr42 climbing ability #ijj ft4 per min42 #ajj h4p42 weight fully loaded #a1cbj lbs4 ,single-,motor ,tractors4--,the single-motor tractor received its name simply because the propeller is in front and draws the machine forward2 but this location of the propeller necessitates a distinct type of airplane1 wherein the power plant is located at the very nose of the machine4 ,the tractor type has the pilot and passenger located in or to the rear of the wings in order that their weight may balance the weight of the motor4 ,this means that the view and range of fire of the passengers is obstructed in a forward direction by the wings1 and in machines such as the ,u4 ,s4 training machine1 the passenger1 who is practically in the center of the wings1 can not look directly upward nor directly downward4 ,moreover1 as concerns gun fire1 the propeller of a tractor obstructs the range straight ahead4 ,in the tractor the tail is supported at the rear and on the same body which contains the motor and passengers2 this body constitutes a stream-line housing for the machinery1 seats1 etc41 and therefore has low wind resistance4 ,the tractor is a very shipshape design1 compact and simple and is at present the prevailing type on the ,european war front4 ,however1 it has disadvantages which are only overcome in other types4 ,one of these disadvantages is of course the obstruction to range of gun fire4 ,the present practice in fighting airplanes is simply to shoot the gun straight through the circle of rotation of the propeller on the assumption that most of the bullets will get through and that those which hit the shank of the propeller blade will be deflected by proper armoring4 ,an attempt is made to insure that all the shots will get through by connecting the gun mechanism mechanically to the motor shaft in such a way that bullets will be discharged only at the instant when their path is unobstructed by a propeller blade4 ,this practice is possible of course only in guns which are fixed immovably to the airplane4 ,illustration3 ,,fig4 #i4--;,fuselage diagram1 ,curtiss 8,r#d0 reconnaissance biplane4 ,speed #dh to #ij mi4 per hr42 climbing ability #djj ft4 per min42 #bjj h4p42 weight fully loaded #c1bde lbs4 ,illustration3 ,,fig4 #aj4--;,an ,american pusher biplane design4 ,crew in front1 motor and propeller in the rear1 tail support on outriggers4 ,single-motor ,pusher ,airplanes4--,the pusher type has popularity because the propeller and motor rotate to the rear of the passenger1 who takes his place in the very front of the body and has an open range of vision and gun fire downward1 upward and sideways4 ,another point in favor of the pusher is that the oil and fumes of the motor do not blow into his face as in the case of the tractor4 ,the disadvantage of the pusher is that the motor1 being located behind the pilot1 will be on top of him in the case of a fall4 ,another disadvantage is that the body can not be given its shipshape stream-line form because to do so will interfere with the rotation of the propeller4 ,therefore1 the body is abruptly terminated just to the rear of the wings and it is just long enough to hold the passenger and the motor1 the propeller sticking out behind4 ,the tail surfaces are then attached to the airplane by means of long outriggers springing from the wing beams at points sufficiently far from the propeller axis so as not to interfere with the propeller4 ,illustration3 ,,fig4 #aa4--,u4 ,s4 army battle plane4 ,two #ajj h4p4 motors2 speed #he mi4 per hr4 ,double-motor ,machines4--,in order to combine the advantages of the tractor and pusher types and eliminate their disadvantages1 the double-motor machines have been developed4 ,in these there is no machinery whatever in the body either in front or back1 and the passengers may take seats at the extreme front as is desirable4 ,the body then tapers off to the rear in stream-line form and supports the tail surfaces4 ,the power plants are in duplicate and one is located to each side of the body out on the wings4 ,it is customary to enclose each of these two motors in a casing so that the whole power plant presents a more or less stream-line shape to the wind1 the propellers projecting from the front or rear of these stream-line shapes4 ,it may be said that in the double-motor airplane it makes very little difference whether the propeller is in front or behind so that while a 8twin-motor0 machine may be more accurately specified as a 8twin-motor pusher0 or a 8twin-motor tractor10 it is usually sufficient indication of a machine's characteristics to call it a twin-motor machine4 ,by adopting this twin-motor form we bring in new disadvantages4 ,one of these is due to the fact that the heavy motors are now located some distance from the center of gravity of the machine4 ,this requires stronger supporting members between the motor and the body4 ,it also makes the lateral control comparatively logy for now the heavy masses are far from the center of gravity1 resisting the pilot's efforts to use the lateral control4 ,the second disadvantage in the twin-motor type results from possible stoppage of either motor4 ,in this case1 of course1 the propelling force is some distance off center and is also reduced to one-half its value requiring energetic exercise of the control wheel to maintain equilibrium4 ,it is reported1 however1 that twin machines can continue to fly and even climb with only one motor running4 ,in this country the twin-motor type has not developed as was hoped at first1 and on the ,european firing lines it is not so numerous as the single-motor tractor type4 ,marine ,airplanes4--,the possibility of mechanical flight having once been established and wheels having been applied to the airplane so that it could start from and land on the ground1 the logical next step was to substitute some form of boat for the wheels so that flights could be made over the water4 ,experiments were made in ,france by ,m4 ,fabre in this direction and in this country by ,g4 ,h4 ,curtiss4 ,the latter1 in his flight down the ,hudson from ,albany to ,new ,york1 equipped his airplane with a light float to provide against forced landing in the river4 ,pursuing this general idea he made some experiments under the auspices of ,alexander ,graham ,bell's ,aerial ,experiment ,association1 in which a canoe was substituted for the wheels1 and in which an attempt was made to start from the surface of the water4 ,success did not come at first and this plan gave no satisfaction4 ,curtiss next turned his attention to the hydroplane type of boat and made a series of experiments at ,san ,diego4 ,the hydroplane appeared to be much better adapted to his purpose than the canoe had been1 and he was able to obtain success4 ,illustration3 ,,fig4 #ab4--,thomas ,type ,h4 ,s4 seaplane4 ,double pontoons4 ,speed #dg to #hb mi4 per hr42 climbing ability #bgj ft4 per min42 #ace h4p42 weight1 fully loaded #b1fjj lbs4 ,illustration3 ,,fig4 #ac4--;,curtiss ,model ,f flying boat4 ,speed #de to #fe mi4 per hr42 climbing ability #aej ft4 per min42 #ij h4p42 weight fully loaded #b1ajj lbs4 ,the ,hydro-airplane 7or 8,seaplane074--,from analogy to the airplane one might at first imagine that a suitable hydroplane would have a wide span and fore and aft length2 but such proportion would give a very poor stability on the water1 and would require auxiliary hydroplanes in the same way that an airplane requires auxiliary guiding surfaces4 ,so ,curtiss1 with his customary eye for simplicity and convenience1 adopted a type of hydroplane which had the general proportions of an ordinary boat1 i4e41 was long and narrow1 thus obviating the necessity of auxiliary hydroplanes at the tail of the machine4 ,to prevent the machine's tipping over sidewise1 8wing pontoons0 were attached at the lower wing tips to prevent capsizing4 ,illustration3 ,,fig4 #ad4--;,building a flying boat hull4 ,note wing stumps and hydroplane fins4 ,illustration3 ,,fig4 #ae4--,method of hoisting a marine airplane aboard ship4 ,the ,flying ,boat4--,in the early hydro-airplane1 which was thus developed1 the motor and pilot were above in the usual position in the wings1 while the hydroplane itself was a considerable distance below the wings4 ,thus there was a good deal of head resistance4 ,curtiss set about reducing this head resistance as far as possible and tried to incorporate the pilot's seat with the hydroplane pontoon4 ,the outcome of his endeavor was that he developed a boat with a tapering stern4 ,the pilot1 gasoline tanks1 etc41 are located inside of the hull2 the tapering stern provides a backbone to which the tail surfaces can be readily attached2 the wings fixed to the sides of the hull in a manner analogous to the wing fastenings of the modern military airplane2 and the motor alone remains exposed to the wind4 ,this is the flying boat2 its action on the water is analogous to the action of the hydroplane for the bottom of this boat hull is made in hydroplane form2 indeed1 in the latest types of flying boat1 the hydroplane area is increased by extending it to right and left of the boat hull4 ,the flying boat is an ingenious combination1 wherein the characteristics of the hydroplane are combined with the seaworthiness of the ordinary boat1 and at the same time wind resistance is reduced to a minimum4 ,the hydro-airplane remains in use1 however1 being preferable to the flying boat for certain purposes1 and often is termed seaplane4 ,future of the ,airplane4--,in order to be commercially successful and have a commercial future after the war1 the following weak points in airplane design must be rectified4 #a4 ,motor4--,airplane motors are imperfect and unreliable at present and there must be considerable progress before this type of motor which is very light and delicate can be considered as reliable or can be made in large enough quantities to cut down the cost4 #b4 ,landing4--,the necessity of landing at considerable speed1 say #dj to #ej miles per hour1 requires a wide flat space1 such as is not easy to find1 and if the present type of airplane is to become commercially numerous1 a large number of landing fields must be developed all over the country4 #c4 ,danger4--,the airplane is by no means so dangerous as the public has been led to think from the exploits of the daredevil circus performers of the past #aj years2 with careful manipulation it will make trips day after day without any damage4 ,however1 it is not a foolproof machine and there remains an element of danger on this account1 which it is hoped will one day be eliminated4 ,future ,uses of the ,airplane4--,future uses of the airplane are many after the war is over4 ,the postal service of several governments are considering this means of mail delivery2 the sports use as in the past will continue to flourish2 express carrying may be expected in inaccessible countries where railroads and roads do not give access and where high-speed delivery by countless airplanes would aid materially in the development of newly opened countries4 ,for airplane transportation will require no expensive right-of-way1 rubber-tire renewals1 etc4 ,minor uses of airplanes are on such duties as forest-fire patrol1 working at life-saving stations1 etc4 ,american ,airplane ,industries4--,the magnitude of the airplane industry in this country is great1 although not so great as in ,europe4 ,leading business men have invested in this industry with the firm belief that it will become a profitable one1 irrespective of war4 ,we see a number of leading bankers and also automobile manufacturers in various parts of the country putting their money into this new industry4 ,now that a great demand has sprung up on our side of the water for airplanes1 we will expect to see this industry increase more rapidly still4 ,the only result can be1 from all the interest and importance attached to aviation1 that after the war is over1 large commercial uses will develop which will offer employment to those who go into the work at this time for military reasons4 ,no one can predict exactly what turn the situation will take1 but there is every indication that aviation has graduated from the primary class of experimental work and is to be considered now as an industry along with the automobile business1 motor-boat business1 etc4 ,,chapter ,,iii ,,principles ,,of ,,flight ,support of an ,airplane by ,its ,wings4--,an airplane is supported just as definitely as though on top of a post1 and by the same law1 namely reaction4 ,if you try to sweep the air downward with a wing held at a slight angle1 the air just before it consents to be pushed downward1 delivers a momentary reaction which is upward4 ,if you have a bag of air in your hand it exerts no push upward of course2 but the minute you give it a quick push downward it resists1 due to its inertia1 thus delivering an upward 8reaction0 against your hand4 ,whenever you move anything1 it reacts an amount just equal to the force that is moving it2 if you move a bullet out of a gun1 just before starting the bullet reacts and you have 8kick40 ,if you should shoot a thousand guns downward1 the reaction would be considerable1 and for the instant might be sufficient to support heavy weight4 ,the airplane is a device for pushing downward millions of little bullets1 made out of air and exceedingly small and light4 ,the wing of an airplane sweeps through these bullets1 or molecules1 of air like a horizontal plow1 wedges the particles downward in vast numbers and in a continual stream1 making up in amount what is lacking in weight1 so that as long as the airplane rushes along1 there are many thousands of cubic feet of air forced down beneath its wings1 delivering up a reaction that results in complete support for the machine4 ,this reaction is just as definite and secure as though the machine were supported from the ground on wheels1 but it disappears entirely when the airplane is at rest4 ,part of the whir of a training machine as it glides back to earth is made by the air driven downward from the wings2 the same phenomenon may be noticed when a bat flies close to your ears at night1 and if you were a few feet below the airplane as it flew1 you would feel the rush of air driven downward from its wings 7see ,fig4 #af74 ,the net result of all the reactive pushes from this air is lift4 ,it may amount to several pounds for every square foot of the wing surface4 ,this is all that need be said about why the air supports an airplane2 all you have to remember is that as long as you have the forward sweeping movement1 you will have the lift4 ,the forward movement is absolutely essential1 however1 and to maintain it requires a lot of horsepower and gasoline4 ,for it is by means of the engine and propeller that this forward movement is maintained4 ,the engine is a device for creating forward movement--the propeller drives the machine ahead in exactly the same way as is the case in a torpedo1 or steamboat4 ,illustration3 ,,fig4 #af4--,relative path of air particles past an airplane4 ,this diagram illustrates the general downward trend of the stratum of air met by the wings4 ,lift4--,assuming that we have all the forward motion needed1 let us now investigate the lift that results4 ,experimenters such as the ,wrights and others have found out how to get this lift most conveniently4 ,lift depends upon the four following factors3 #a4 ,area4 #b4 ,density of air4 #c4 ,angle of incidence4 #d4 ,speed of motion4 #a4 ,relation of ,area of ,wings to ,support4--,consider a small wing2 suppose it to be held by hand outside a train window in a given attitude1 its area being #a sq4 ft4 ,it tends to lift a certain amount1 say #e lb4 ,now increase its size to #b sq4 ft4 and it will lift with #aj-lb4 force1 tending to get away from your grasp4 ,rule3 ,when only the area of a wing is changed1 its lift varies with the area4 ,if1 as above mentioned1 you can get #e lb4 of lift from each square foot of wing surface1 you can by the same sign get #aj-lb4 of lift from #b sq4 ft4 ,and if you have #ejj sq4 ft4 of surface you can get #bejj lb4 of lift4 ,illustration3 ,,fig4 #ag4--;,diagram showing that in fast airplanes wings are small2 in slow airplanes wings are large4 7,above7 ,small wings2 speed #aae mi4 per hr42 for fighting4 ,one seat4 7,below7 ,large wings2 speed #hj mi4 per hr42 for reconnaissance4 ,two seats4 ,regarding area of wing surface1 the pilot does not have to worry in a flight since he can do nothing to change it anyway4 ,all he needs to know is that in different airplanes small wing area accompanies high speed and small weight-carrying capacity1 as in the case of the ,fokker and ,sopwith speed scouts 7see ,fig4 #ag74 ,conversely1 large wing areas are used for heavy load carrying and slow speed 7see ,fig4 #ah74 ,speed and weight-carrying capacity thus appear to be antagonistic and can not both be attained with efficiency1 but only at the expense of enormous power4 ,the incompatibility between high speed and weight carrying keeps the designer busy in efforts toward a reconciliation4 ,illustration3 ,,fig4 #ah4--;,diagram showing use of large wings for heavy airplanes1 and small wings for light airplanes4 #b4 ,density4--,the second factor affecting the lift is the character of the air itself4 ,i refer to the density of the air4 ,the heavier each particle of air becomes1 the more reaction it can furnish to the wing that drives it downward2 so on days when the barometer is high the wing will lift more than on other days4 ,now the air is heaviest1 or most dense1 right near the ground2 because in supporting the #ej miles or so of air above it1 it becomes compressed and has more weight per cubic foot4 ,therefore1 the wing gets more lift at a low altitude than at a high4 ,some airplanes will fly when low down but won't fly at all high up4 ,in ,mexico1 for instance1 when the punitive expedition started out they were already at an altitude of several thousand feet above sea level4 ,the airplanes had been built for use at places like ,new ,york and ,england1 close to sea level1 and when our army officers tried to fly with them in ,mexico1 they would not fly properly1 and the factory had to redesign them4 ,regarding density1 the pilot should know that for a low density he should theoretically get a high speed4 ,as density decreases1 high up in the air1 the speed tends to increase1 and moreover he gets more speed for the same amount of gasoline4 ,unfortunately1 at an altitude the motor power falls off1 so that nowadays the speed is not faster high up than low down2 but when the motor builders succeed in designing their motors to give the same horsepower at #bj1jjj ft4 as they do on the ground1 airplanes will be able to reach terrific speed by doing their work above the clouds4 ,it is found desirable to give large wings to airplanes which are going to fly at high altitudes1 so as to offset the lack of density by an increase in area1 thus leaving the angle range--that is1 the speed range--as large as possible4 ,the army airplanes in ,mexico mentioned above were simply given a new set of larger wings to offset the lower air density in ,mexico1 and thereafter flew better4 #c4 ,angle of ,incidence4--,the angle of incidence is defined as the angle between the wing-chord and the line of flight4 ,the line of flight is the direction of motion of the airplane1 and is distinct from the axis of the airplane which corresponds with the line of flight only for a single angle of incidence4 ,if the line of flight is horizontal1 the airplane may be flying tail-high1 tail-level1 or tail-low2 that is1 its axis may have varying positions for a given line of flight4 ,this is true1 if the line of flight is inclined1 as in climbing4 ,it is a mistake to confuse the line of flight with the axis of the machine4 ,the angle of incidence of the wings of the ,u4 ,s4 training machine may have any value from #ae down4 ,when the angle is smaller the lift of the wings is smaller4 ,consider the model wing held out of a train window2 if its front edge is tilted up to an angle of #ae with the line of motion it will lift say #a lb42 if reduced to a #aj angle1 it will lift less1 say lb4 ,a model of the training-machine wing could be tilted down to an angle several degrees less than zero before its lift disappeared1 because it is a curved1 not a flat wing2 this angle would be the 8neutral-lift0 angle2 notice then that ,o is not a neutral-lift angle1 and therefore may be used in flight4 ,if the model wing were tilted up to an angle greater than #ae1 the lift would not increase any more1 but would be found to decrease4 ,for this wing1 #ae is called the critical1 or 8,stalling0 angle1 beyond which it is unwise to go4 #d4 ,velocity4--,if the model wing which is imagined to be held out of the car window1 is held now in a fixed position at a given angle of incidence1 any change of the train's speed will result in a change of lift2 should the speed rise from #cj miles per hour to double this value1 the lift would increase enormously1 fourfold in fact4 ,lift varies as the square of the speed4 ,thus any increase or decrease of speed results in a great increase or decrease of lift4 ,interdependence of ,angle of ,incidence and ,velocity4--,the four factors above mentioned all contribute to the lift2 if in an airplane wing each factor be given a definite value1 the resulting lift is determined according to the formula3 ,l ,kr,a,v#b where ,l is lift4 ,k is a coefficient referring to the angle4 ,a is the area4 ,v is the velocity4 r is the density4 ,two only of these quantities change materially in flight1 the angle and the velocity2 the lift itself remains substantially the same under most normal circumstances4 ,the angle always changes simultaneously with the velocity1 increasing when the velocity decreases4 ,thus the drop of lift due to velocity decrease is balanced by gain of lift due to angle increase1 and the lift remains unchanged when speed changes4 ,speed change then requires that the pilot alter the angle of incidence simultaneously with the throttle2 so there are two things to do1 unlike the case of the automobile where only the throttle is altered4 ,minimum ,speed4--,when1 in slowing up an airplane1 the angle of incidence reaches the #ae limit1 no further decrease of speed is allowable2 therefore1 the critical angle determines the minimum limit of speed4 ,if for any reason the machine exceeds the #ae limit1 it must speed up to gain support2 that is1 the pilot has to increase angle and speed simultaneously instead of oppositely4 ,efficiency of ,airplane ,wings4--,i said at the beginning of this chapter that the airplane was a device for pushing down an enormous quantity of air4 ,a certain amount of force has to be furnished in order to keep the airplane moving1 and this force is furnished by the engine and propeller4 ,the propeller by giving a certain amount of push in a horizontal direction to the airplane wing enables this wing to extract from the air ten or twenty times this amount of push in a vertical direction2 that is1 the airplane wing will give you #aj lb4 or more of lifting in exchange for #a lb4 of push4 ,illustration3 ,,fig4 #ai4 ,lift and ,drift4--,lift is perpendicular to line of flight1 drift is parallel4 ,angle of ,incidence4--,wing in position shown has angle of #e if moving in direction 8,a10 #aj if in direction 8,b20 and a negative angle of #d if moving in direction 8,c40 ,in the last case it is moving along its neutral-lift-line1 lift becomes zero4 ,the propeller push is necessary to overcome the drift or resistance of the wings to forward motion4 ,it appears then that the airplane wing as it moves through the air has two forces on it1 one acting straight up and called 8lift10 the other acting straight back and called 8drift0 7see ,fig4 #ai74 ,the lift is several times greater than the drift1 and the situation is quite analogous to that of a kite1 which rises upward in the air due to its lift but at the same time drifts backward with the wind due to its drift4 ,in the case of the kite the string takes up an angle which just balances the joint effect of the lift and drift4 ,the efficiency of an airplane wing is indicated by the ratio of lift to drift1 and for a given lift1 the efficiency is best1 therefore1 for small drift4 ,if the lift is #aijj lb4 and the wing drift #aij lb41 ,wing efficiency ,lift or weight_/,wing drift #aijj_/aij #aj ,factors ,determining ,best ,efficiency4--,it goes without saying that an airplane wing should attain the best efficiency it can1 and there are several ways of doing this4 ,the first relates to the question of angle of incidence2 we have already discussed the effect of angle on lift1 but when we come to discuss its effect on efficiency we find that there is only one angle at which we can get the best efficiency4 ,this is a small angle1 about #c to #f2 at this angle the lift is nowhere near as much as it would be at #aj or #ae1 but the drift is so small compared to the lift that it is found desirable in airplanes to employ these small angles for normal flight4 ,as the angle increases above this value of maximum efficiency1 the efficiency drops off1 and when you get up to the stalling angle1 the efficiency becomes very low indeed 7see ,fig4 #bj74 ,illustration3 ,,fig4 #bj4--,wing characteristics4 ,curves showing lift1 drift1 efficiency1 and center of pressure travel of typical training-airplane wing1 as determined in ,aerodynamical ,laboratory4 ,the second way to get good efficiency is to choose the shape of the wings properly4 ,for instance1 early experimenters tried to get results with flat wings1 and failed completely1 for the flat wing proved to be very inefficient4 ,when it was observed that birds had curved wings1 this principle was applied to early experiments and then for the first time man was able to obtain support in a flying machine4 ,the fundamental principle of efficiency in wings is that they must be curved1 or cambered1 as it is sometimes called4 ,this is because as the wing rushes onward it wants to sweep the air downward smoothly and without shock1 as can be done only when the wing is curved 7see air flow1 ,fig4 #ba74 ,illustration3 ,,fig4 #ba4--;,efficiency of curved and flat wing4 7a7 ,air flow past curved wing is smooth without much eddying2 7b7 air flow past flat wing produces eddies above it4 ,the question of wing curvature is exceedingly important then2 we find that the curvature of its upper surface is particularly so4 ,we notice that airplane wings all have a certain thickness in order to enclose the spars and ribs2 it is not necessarily a disadvantage for them to be thick1 due to the fact that the upper curve of the wing does most of the lifting anyway1 and the lower side is relatively unimportant4 ,you can make the lower surface almost flat1 without much hurting the effect of the wing1 so long as the upper surface remains properly curved4 ,however1 the upper surface must be accurately shaped1 and is so important that in some machines we find cloth is not relied on to maintain this delicate shape1 but thin wood veneer is used 7,i refer to the front upper part of the wing74 ,in general1 then1 wings are thick toward the front and taper down to a thin trailing edge4 ,illustration3 ,,fig4 #bb4--;,diagram of vacuum and pressure on airplane wings4 ,note in biplane reduced vacuum on bottom wing4 ,you may wonder how it was found that the upper surface of the wing was the most important2 and ,i will say that this was one of the interesting discoveries of the early history of aerodynamics4 ,people at first thought that a wing sweeping through the air derived its support entirely from the air which struck the bottom of the wing1 and they assumed that if the bottom of the wing were properly shaped1 the top did not matter2 that is1 all the pressure in the air was delivered up against the bottom surface4 ,but a ,french experimenter conceived the idea of inserting little pressure gages at various points around the wing4 ,he found1 it is true1 that there was considerable pressure exerted in the air against the bottom of the wing2 but he found a more surprising fact when he measured the condition above the wing4 ,when he applied his gage to the upper surface of the wing1 it read backward1 that is1 showed a vacuum1 and a very pronounced one4 ,he found that there was a vacuum sucking the top part of the wing upward twice as hard as the pressure underneath was pushing2 so that two-thirds of the total lift on this wing was due to vacuum above it 7see ,fig4 #bb74 ,in the diagram the shaded area on top of the wing represents vacuum above1 that below the wing represents pressure beneath4 ,illustration3 ,,fig4 #bc4--,wings of small and large aspect ratio ,aspect ,ratio4--,the third factor in wing efficiency has to do with the plan shape4 ,it was early found that square wings were not much good1 and that if you made them wide in span like those of a bird1 the efficiency was best 7see ,fig4 #bc74 ,aspect ratio is the term which gives the relation of the span to the fore and aft dimension of the wing1 and this relation is usually equal to six or so4 ,the reason why large aspect ratios are advantageous is as follows3 ,the tips of all wings are inefficient1 because they allow the air to slip sideways around the ends1 and there is all the trouble of disturbing this air without extracting any considerable lift from it4 ,in a wide-span wing these inefficient wing tips are only a small percentage of the total area1 but in a small-span wing they may be an important consideration 7see ,fig4 #bd74 ,illustration3 ,,fig4 #bd4--;,diagram illustrating aspect-ratio effect4 ,arrows show direction of air flow past plate2 note that air escapes sideways around sides of plate4 ,this phenomenon occurs at the tips of all airplane wings and accounts for small efficiency of narrow-span wings4 ,wing ,arrangements4--,all the foregoing remarks in this chapter have applied only to a single wing4 ,they apply in general to double or triple wings 7biplanes and triplanes71 but the matter of arranging multiple wings affects the efficiency4 ,the monoplane with its single layer of wings is the most efficient type of flying machine4 ,we find if we arrange wings into the biplane shape that the presence of the upper wing interferes with the vacuum formed above the lower wing1 and the efficiency decreases 7see ,fig4 #bb74 ,the same is true of the triplane and the quadruplane arrangement4 ,if all we wanted in airplanes was efficiency1 we would use monoplanes1 but the biplane is pretty popular now in spite of its low efficiency2 this is because it can be much more strongly trussed than the monoplane1 and also because of the fact that sufficient area may be secured with less span of wings4 ,it may be said that the low efficiency of the biplane can be somewhat relieved by spacing the upper and lower wings at a considerable distance apart2 but if they are spaced at a distance much greater than the chord1 it requires extra long struts and wires1 and the resistance and weight of these will offset the advantage of wider spacing2 so that practically biplane-wing efficiency may be taken as #he per cent4 of monoplane efficiency4 ,it remains to mention the tandem arrangement1 used in all airplanes1 where the tail is a tandem surface in conjunction with the wings4 ,a surface located in the position of an airplane tail is at a disadvantage and shows low efficiency for flight purposes4 ,this is because the main wings deflect the air downward and when the tail comes along it meets air which has a more or less downward trend1 instead of encountering fresh1 undisturbed air 7see ,fig4 #af74 ,resistance of an ,airplane to ,motion4--,earlier in this chapter the support of an airplane was explained and it was seen that the weight was exactly equalled by the lift or support2 it was also explained that the production of this lift required considerable force in moving the wings rapidly through the air4 ,it is not only the wings1 however1 which require force to overcome the resistance to motion4 ,in order to have any wings at all it is unfortunately necessary to supply also struts1 wires1 etc41 for bracing these wings1 also a motor and seat for the passenger1 which are usually included inside a fuselage1 also wheels for landing and various control surfaces4 ,none of these accessories to the wings contribute material lift1 but they involve a large amount of resistance which is therefore a dead loss4 ,note carefully that there are two distinct sorts of resistance3 7#a7 that of the wings1 which is the necessary price paid for securing lift2 7#b7 that of all the rest of the machine1 in return for which nothing beneficial is received1 and which therefore has sometimes been called 8parasite0 or 8deadhead0 resistance4 ,in a typical training machine the total resistance to be overcome if forward motion is maintained is as follows3 7,see ,fig4 #bf47 ,at #gb miles per hour3 ,wings #afj lb4 ,deadhead ,fuselage #ge resistance ,wiring #gj ,struts #bj #aie ,miscellaneous ,balance #cj ------ ,total #cee lb4 ,at a speed of #eg miles per hour3 ,wings #aeh lb4 ,deadhead resistance #acj ------ ,total #bhh lb4 ,at a speed of #dc miles per hour3 ,wings #cej lb4 ,deadhead resistance #abe ------ ,total #dge lb4 ,it is seen that the above resistance values total to the highest figure at the lowest speed1 and that the lowest value of resistance occurs at an intermediate speed2 the resistance decreases as the speed decreases from #gc to #eg miles per hour2 but a further decrease in speed finds the resistance running up rapidly so that at minimum speed the resistance is very great again4 ,this is due to the fact that at high speeds the deadhead resistance exceeds that of the wings but at slow speeds although the deadhead resistance is very small1 the wings being turned up to a large angle within the air1 have a resistance which is at its maximum4 ,this seems clear enough when we remember that the lift of the wings remains the same as the angle decreases 7and speed goes up7 but that the efficiency of the wings increases so that the wing resistance is a smaller fraction of the lift at high speed than at low speed4 ,cause of ,resistance4--,wing resistance1 which is affected1 as mentioned previously1 by the wing curvature1 can not be decreased unless new and improved sorts of wings are invented4 ,as to deadhead resistance1 it may be decreased in future by methods of construction which eliminate unessential parts4 ,in a high-speed airplane in this country an attempt was made to eliminate the wires altogether and most of the struts 7because the wiring is one of the largest single items of deadhead resistance72 so far the attempt has failed for structural reasons4 ,in the monoplane type of airplane of course the struts are eliminated1 which is an advantage from the standpoint of resistance4 ,illustration3 ,,fig4 #be4--;,diagram illustrating advantage of stream-line shape4 ,note large eddy disturbance and vacuum behind round shape1 causing high resistance4 ,as long as struts1 wires1 etc41 are used at all1 the minimum resistance can be secured by giving them a proper 8stream-line0 shape4 ,the stream-line shape is one in which the thickest part is in front and tapers off to a point in the rear1 like a fish4 ,if1 for instance1 we take round rods instead of the struts of the training machine above mentioned and having the same thickness1 the resistance might be #hj lb4 instead of #bj lb42 and if we take a rod whose shape is elliptical with its axes in a ratio of #a to #e the resistance might be #dj lb4 instead of #bj lb42 and if we took the stream-line struts out of the training machine and put them back sharp edge foremost1 the resistance would be increased4 ,the advantage of the stream-line shape is that it provides smooth lines of flow for the air which has been thrust aside at the front to flow back again without eddies to the rear4 ,this is not possible in the case of the round strut1 behind which will be found a whirl of eddies resulting in a vacuum that tends to suck it backward4 ,by fastening a stream-line tail behind the round rod the eddies are greatly reduced1 as is the vacuum4 ,the wires of the airplane are subject to the same law and if the training machine above mentioned had stream-line wires instead of round wires we might expect them to have less than #gj lb4 resistance4 ,the fuselage should always be given as nearly a stream-line shape as the presence of the motor and tanks will permit2 and it must all be inclosed smoothly in 8doped0 fabric in order that the air-flow phenomena may operate4 ,as for the wheels1 they must of necessity be round1 but by enclosing them with fabric the air flow past them is more easy and the resistance may be halved4 ,total ,resistance4--,the necessity has been explained of discriminating between wing and deadhead resistance2 if we are talking about wings we may ignore everything except the wing resistance 7commonly called 8wing drift071 but if we are talking about the whole airplane1 we then must refer to the total resistance1 which includes all the others and is overcome by the propeller thrust4 8,skin-friction0 resistance has not been mentioned nor need it be more than to say that any surface moving through air attributes part of its resistance to the actual friction of the air against it1 and therefore should be as smooth as possible4 ,motor ,power ,required for ,flying4--,the reason resistance interests us is that motor power is required to propel the airplane against it2 more and more power as the resistance and speed increase4 ,obviously1 the power required is least when the resistance is small1 i4e41 when the speed is intermediate between minimum and maximum4 ,it takes more power to fly at minimum speed than at this intermediate speed4 ,of course it also takes more power to fly at maximum speed1 where again the resistance is high4 ,maximum ,speed4--,ordinarily1 for moderate speeds1 airplanes have a margin of power at which the throttle need not be opened wide2 should speed be increased the resistance and horsepower required will increase steadily until the throttle is wide open and motor 8full out20 this establishes the maximum speed of an airplane2 there is no margin of power1 no climb is possible4 ,the only way to increase speed is to use the force of gravity in addition to the motor force4 ,it may be interesting to know what is the maximum possible speed in the case of a vertical dive with the motor shut off2 it will be about double the maximum horizontal speed as may be readily seen from the fact that the thrust in the direction of motion is now no longer horizontal and equal to the resistance but is vertical and equal to the weight of the machine2 that is1 the thrust may be increased fivefold1 and the speed resulting will be increased correspondingly1 if the motor be running in such a vertical dive the velocity may be slightly increased though at this speed of motion the propeller would not have much efficiency4 ,there is danger in such high speeds2 the stresses in the machine are increased several times merely by the increased resistance1 and if the angle of incidence should be suddenly brought up to a large value at this high speed the stress would again be increased so that the total stress increase theoretically might be as high as fourteen times the normal value1 thus exceeding the factor of safety4 ,it is for such reasons that the maximum strength is desirable in airplanes2 holes must not be carelessly drilled in the beams but should be located if anywhere midway between the top and bottom edges1 where the stress will be least2 initial stresses1 due to tightness of the wires1 should not be too great4 ,climbing ,ability4--,climbing ability refers to the number of feet of rise per minute or per #aj min4 ,in order to climb1 extra horsepower is required beyond that necessary for more horizontal flight4 ,the machine can1 for instance1 fly at #ef miles per hour at which speed it requires #dc hp4 ,if now the throttle is opened up so as to increase the horsepower by #bb1 making a total of #fe hp41 the machine will climb at the rate of #chj ft4 per minute1 maintaining approximately the same flight speed4 ,if instead of #fe hp41 it were #ed hp4 the speed of climb would be about one-half of the #chj1 or #aij ft4 per minute2 the flight speed again remaining approximately as before2 that is1 any margin of horsepower beyond the particular value of horsepower required may be used for climbing without material change of the flight speed4 ,it is necessary here to state that lift does not increase during climb2 and while for the instant that a climb commences there may be1 due to acceleration1 more lift on the wings than balances the weight1 this does not remain true after a steady rate of climb is reached4 ,to illustrate1 in a wagon drawn uphill by horses the wheels which support the wagon do not exert any more support than on the level1 and the entire force to make the wagon ascend is supplied through extra hard pulling by the horses4 ,thus in a climbing airplane the propeller furnishes all the climbing force and lift is no greater than in horizontal flight4 ,in fact1 the actual lift force may be even less1 as the weight of the airplane is partly supported by the propeller thrust which is now inclined upward slightly4 ,to secure maximum climbing ability1 we must determine at what velocity the margin of motor power is the greatest4 ,in the above-mentioned machine we know that the horsepower required for support is least for a speed of near #ee miles per hour1 and it is near speed where therefore the excess margin of power is greatest and at which climbing is best done4 ,an airplane designed chiefly for climbing must have low values of motor power necessary for support1 namely1 must have small resistance1 therefore small size1 therefore small weight4 ,illustration3 ,,fig4 #bf4--,performance curves for typical training airplane4 ,gliding ,angle4--,gliding angle denotes the angle at which the airplane will glide downward with the motor shut off and is spoken of as #a in #e1 #a in #f1 etc41 according as it brings the airplane #a mile down for each #e1 #f1 etc41 miles of travel in the line of flight4 ,the gliding angle of a machine may be found by dividing the total resistance into the weight3 ,gliding angle ,weight_/,total resistance4 ,in the above-mentioned airplane it is one in #f4f when the resistance is #bhh lb41 that is1 when the speed is #eg miles per hour4 ,at any other speed the resistance increases and hence the gliding angle decreases4 ,hence the importance of putting the airplane into its proper speed in order to secure the best gliding angle4 ,the ,propeller4--,the propeller or 8screw10 by screwing its way forward through the air1 is able to propel the airplane at the desired velocity4 ,regarding principles of propeller action the matter can be hastily summarized in the following brief lines4 ,the propeller blades may be regarded as little wings moving in a circular path about the shaft2 and they have a lift and drift as do the regular wings4 ,the lift is analogous to the thrust2 to secure this thrust with least torque 7drift7 the blades are set at their most efficient angle of incidence1 and while the blade appears to have a steep angle near the hub1 it actually meets the air in flight at the same angle of incidence from hub to tip4 ,propeller ,pitch4--,pitch is best defined by analogy to an ordinary wood-screw2 if the screw is turned one revolution it advances into the wood by an amount equal to its pitch4 ,if the air were solid1 a propeller would do the same1 and the distance might be #h ft41 say4 ,actually the air yields1 and slips backward1 and the propeller advances only #f ft4 ,its 8slip0 is then #h minus #f1 equals #b ft41 or #be per cent4 ,such a propeller has an #h-;ft4 pitch1 and a #be per cent4 slip4 ,this 8slip stream0 blows backward in a flight so that the tail of an airplane has air slipping past it faster than do the wings4 ,hence the air forces at the tail are greater than might be expected4 ,the rudder and elevators therefore give a quicker action when the propeller is rotating than when1 as in the case of a glide1 it is not4 ,illustration3 ,,fig4 #bg4--,washout in left-wing tips4 ,washout4--,due to torque of the motor1 the airplane tends to rotate in the opposite direction to the propeller4 ,this tendency may be neutralized by giving one wing tip a smaller angle of incidence1 called 8washout10 so that the machine normally tends to neutralize the torque-effect4 ,,principles ,,of ,,airplane ,,equilibrium ,illustration3 ,,fig4 #bh4--;,balances of forces in an airplane4 ,weight forward of lift1 thrust below resistance4 ,thrust equals resistance1 weight equals lift4 ,introductory4--,under this head will be discussed3 7a7 features of airplane design which tend to maintain equilibrium irrespective of the pilot2 7b7 matters of voluntary controlling operations by the pilot4 ,as regards 7a7 the tendency of the airplane toward inherent stability acts to oppose any deviation from its course whether the pilot so desires or not4 ,the more stable is a machine1 the less delicately is it controlled1 and the present consensus of opinion among pilots is that a #ej-ej compromise between stability and controllability is the best thing4 ,in questions of airplane equilibrium the starting point is the center of gravity2 obviously1 if the center of gravity were back at the tail or up at the nose there would be no balance2 the proper place for it is the same spot where all the other forces such as thrust1 lift and resistance act2 there it is easy to balance them all up4 ,but it is not always easy to bring the line of thrust and the line of total resistance into coincidence1 because the line of thrust is the line of the propeller shaft and when this is high up as in the case of some pushers it may be several inches above the line of resistance4 ,and as the thrust is above the resistance there is a tendency to nose the machine down2 to balance which the designer deliberately locates the center of gravity sufficiently far behind the center of lift so that there is an equal tendency to tip the nose upward2 and all four forces mentioned completely balance each other4 ,but things may happen to change the amount or position of these forces during flight1 and if this does happen the first thing to do is to restore the balance by bringing in a small new force somewhere4 ,in an actual airplane this small restoring force is supplied at each critical moment first1 by the tail1 etc41 of the airplane and second1 by voluntary actions of the pilot4 ,the center of gravity of any airplane may be determined easily by putting a roller under it and seeing where it will balance1 or by getting the amount of weight supported at the wheels and tail1 according to the method of moments4 ,longitudinal ,stability4--,longitudinal stability has to do with the tendency of an airplane to maintain its proper pitching angle4 ,it was said above that the four forces of lift1 resistance1 thrust and weight always exactly balanced due to their size and their position4 ,now the first consideration about longitudinal stability is that while the centers of gravity and other forces remain in a fixed position1 the center of lift changes its position whenever the angle of incidence 7that is the speed7 is changed4 ,the phenomenon of shift of center of pressure applies only to the wings and to the lift 7the position of center of resistance remains practically fixed at all angles74 ,note the effect on center of pressure position of a change of wing angle 7see ,fig4 #bj74 ,the wing used on the ,u4 ,s4 training machine has a center of lift which is about in the middle of the wing when flying at a small angle of maximum speed2 but if the angle is increased to the stalling angle of #ae1 the center of pressure moves from midway of the wing to a point which is about one-third the chord distance of the wing from the front edge4 ,the lift may travel about foot1 and it is equal in amount to the weight of the machine 7that is1 nearly a ton71 and the mere effect of changing the angle from its minimum to its maximum value therefore tends to disturb the longitudinal equilibrium with a force which may be represented as #a ton acting on a lever arm of ft4 ,suppose that the airplane is balancing at an angle of #b so that the center of gravity coincides with the center of lift for this angle2 now if a gust of wind causes the angle to increase for an instant to #b1 the center of lift will move forward and tend to push the front edge of the wing up1 thus increasing the angle further to #b4 ,then the center of lift1 of course1 moves further forward to accommodate the increase of angle1 and in a fraction of a second the wing would rear up unless it were firmly attached to the airplane body and held in its proper position by the tail4 ,similarly if for any reason the proper angle of #b were decreased1 the same upset would follow1 only this time tending to dive the wing violently to earth4 ,this tendency is neutralized in an airplane by the 8,penaud ,tail ,principle40 ,there are certain shapes of wings in which the center of pressure travels in the reverse direction2 a flat plate1 for example2 or a wing having its rear edge turned up so that the general wing shape is like a thin letter 8,s40 ,such wings as these would not tend to lose their proper angle1 because when the angle is changed for any reason the center or pressure in these wings moves in just the manner necessary to restore them to their proper position2 but these wings are inefficient and are not in present use on airplanes4 ,illustration3 ,,fig4 #bi4--;,diagrams illustrating theory and application of longitudinal dihedral angle4 ,the ,penaud ,tail ,principle4--,rule4--,the horizontal tail must have a smaller angle of incidence than the wings4 ,the upsetting force above mentioned must be met by a strong opposite righting force1 and this latter is furnished by the horizontal tail surface4 ,in the angle of equilibrium of #b above mentioned1 the flat horizontal stabilizer will perhaps have no force acting on it at all because it is edgewise to the air and its angle of incidence is zero4 ,when the angle of the wing increases to #b and the lift moves forward tending to rear it up1 the wing being rigidly fastened to the body pushes the tail downward so that the tail now begins to have a small lift force upon it due to its angle of 2 and this newly created force1 though small1 acts at such a long lever arm that it exceeds the rearing force of the wing and will quickly restore the airplane to #b4 ,this action depends upon the principle of the ,penaud ,tail or longitudinal 8,dihedral0 which requires that the front wings of an airplane make a larger angle with the wind than the rear surface4 ,this principle holds good even when we have rear surfaces which actually are lifting surfaces in normal flight1 the requisite being that the wings themselves shall in such cases be at an even greater angle than the tail4 ,no mention has been made of the elevator control1 because its action is additional to the above-mentioned stability4 ,the elevator is able to alter the lift on the tail2 such alteration requires1 of course1 immediate change of angle of the wings so that equilibrium shall again follow2 and this equilibrium will be maintained until the lift at the tail is again altered by some movement of the elevator control4 ,thus the elevator may be considered as a device for adjusting the angle of incidence of the wings4 ,the air through which the wings have passed receives downward motion1 and therefore a tail which is poised at zero angle with the line of flight may actually receive air at an angle of -#b or -#c4 ,in the above case we would expect an actual downward force on the tail1 unless this tail is given a slight arch on its top surface 7for it is known that arched surfaces have an angle of zero lift which is negative angle74 ,longitudinal ,control4--,steering up or down is done by the elevator1 which as explained above is merely a device for adjusting the angle of incidence of the wings4 ,the elevator controls like all the other controls of an airplane depend for their quick efficient action upon generous speed2 they can not be expected to give good response when the machine is near its stalling speed4 ,the elevators like the rudder are located directly in the blast of the propeller and in case the speed of motion should become very slow1 the elevators may be made to exert considerable controlling force if the motor is opened up to blow a strong blast against them4 ,this is good to bear in mind when taxying on the ground because if the motor is shut off at the slow speed of motion the elevator and rudder will lose their efficacy4 ,the propeller blast1 due to a #be per cent4 slip1 adds #be per cent4 of apparent speed to those parts which are in its way1 and therefore the tail forces are affected as the square of this increase1 that is1 the forces may be #ej per cent4 greater with the propeller on than off4 ,lateral ,stability4--,this depends upon the keel surface or total side area of an airplane4 ,the keel surface includes all the struts1 wires1 wheels1 wings1 as well as body1 against which a side wind can blow4 ,skidding and side-slipping have the same effect as a side wind1 and the resulting forces acting against the side of the machine should be made useful instead of harmful4 ,this is done by properly proportioning the keel or side surface4 ,if keel surface is low1 the side force will rotate the airplane about its axis so that the windward wing sinks2 if high1 so that it rises4 ,but if the keel surface is at just the right height 7i4e41 level with the center of gravity7 the side forces will not rotate the machine at all and will simply oppose the skidding without upsetting equilibrium4 ,illustration3 ,,fig4 #cj4--;,diagram showing effect on lateral stability of dihedral angle and non-skid fins4 7a7 ,machine flying level4 7b7 ,machine tips and side-slips3 excess pressure is created on windward wing and fins1 7c7 ,machine has side-slipped and rotated back to level4 ,lateral ,dihedral4--,now when an airplane appears to have its keel-surface center too low1 the easiest way to raise it level with the center of gravity is to give the wings a dihedral angle1 that is make them point upward and outward from the body4 ,thus their projection1 as seen in a side view1 is increased1 and the effect is to add some keel surface above the center of gravity1 thus raising the center of total keel surface4 ,a further advantage of the lateral dihedral is that any list of the airplane sideways is automatically corrected 7see ,fig4 #cj74 ,the low wing supports better than the high wing1 because a side slip sets in1 hence will restore the airplane to level position4 ,non-,skid-,fins4--,where for the above-mentioned purposes an excessive dihedral would be needed1 resort may be had to non-skid-fins erected vertically edgewise to the line of flight above or beneath the topwing4 ,these are used in marine machines to balance the abnormally large keel surface of the boat or pontoon below4 ,lateral ,control4--,by means of ailerons1 lateral control is maintained voluntarily by the pilot2 the aileron on the low tip is given a greater angle of incidence while on the high tip a less angle of incidence thus restoring the proper level of the machine4 ,notice that the efficacy of the ailerons depends upon speed of motion of the airplane1 irrespective of propeller slip because the propeller slip does not reach the ailerons4 ,therefore1 at stalling speeds the ailerons may not be expected to work at their best1 and when lateral balance is upset at slow speeds it is necessary to dive the machine before enough lateral control can be secured to restore the balance4 ,illustration3 ,,fig4 #ca4--;,deperdussin control4 ,system used in ,u4 ,s4 training airplanes4 ,directional ,stability4--,directional stability has to do with the tendency of an airplane to swerve to the right or left of its proper course4 ,to maintain directional stability the 8vertical stabilizer0 is used1 which acts in a manner analogous to the feather on an arrow4 ,thus in case of a side slip the tail will swing and force the airplane nose around into the direction of the side slip so that the airplane tends to meet the relative side wind 8nose-on0 as it should4 ,the vertical stabilizer should not be too large1 however1 as then any side pressure due to deviation from a rectilinear course will cause the machine to swerve violently2 the wing which is outermost in the turn will have preponderance of lift due to its higher speed2 that is1 the airplane will get into a turn where there is too much bank and a spiral dive may result4 ,directional ,control4--,the rudder gives directional control in exactly the same way that it does on a boat2 it should be said1 however1 that the rudder is sometimes used without any intention of changing the direction1 that is1 it is used simultaneously with the ailerons as a means of neutralizing their swerving tendency4 ,the ailerons1 of course1 at the same time that they restore lateral balance create a disadvantageous tendency to swerve the machine away from its directional course2 that is what the rudder must neutralize4 ,moreover1 the rudder is frequently used against side winds to maintain rectilinear motion4 ,banking4--,banking combines the lateral and directional control1 which should be operated simultaneously so as to tilt the machine and at the same time maintain the radius of turn4 ,the wings are tilted in a bank because in going around a curve of a certain radius the weight of the machine creates a centrifugal force in a horizontal direction and if the curved path is to be maintained this centrifugal force must be neutralized2 and this is done by inclining the force of lift inward until it has a horizontal component equal to the centrifugal force4 ,that is why the angle of bank must be rigidly observed1 or else the inward component of the lift will change4 ,now as soon as the wings bank up1 the lift force is no longer all vertical and therefore may not be enough to support the weight of the machine4 ,to offset this have plenty of motor power for speed in a bank2 and do not try to climb while banking4 ,it is better to bank too little than too much2 too little results in skidding which may be easily cured2 too much results in side slipping inward and if the tail surface is too great in this latter case1 a spiral dive may result--so look out for over banking4 ,it is better for the beginner in banking to move his ailerons first and then move the rudder2 for if he moves the rudder first there will be skidding outward1 forward speed will drop and a stall may result4 ,on high angles of banking1 over #de1 it should be noted that the elevators are now more nearly vertical than horizontal and operate as a rudder2 similarly the rudder's function is reversed1 and to turn down the rudder will be used4 ,damping in an ,airplane4--,above have been mentioned the restoring forces which tend toward airplane equilibrium4 ,now these restoring forces tend to push the machine back to equilibrium and even beyond in exactly the same way that gravity causes a pendulum to swing about its point of equilibrium4 ,this can sometimes be noticed in the case of an automobile when travelling at high speed along country roads where a sort of slow oscillation from side to side may be noticed due to the forceful maintenance of equilibrium of the body in its forward motion4 ,this oscillation in an airplane would be serious unless there were means of damping it out and these means are3 first1 the wings2 second1 the tail surfaces2 third1 the weight and inertia of the machine itself4 ,regarding inertia it should be said that a machine with weight distributed far from the center of gravity1 such as the double-motor airplane has a large tendency to resist the rolling motions associated with lateral stability4 ,but from the same sign airplanes with large moment of inertia are difficult to deviate from any given attitude1 and therefore have the name of being 8logy40 ,the proper proportioning of an airplane's parts to secure first1 the restoring forces2 second1 the proper damping force2 third1 the proper amount of moment of inertia1 is a very delicate matter and beyond the scope of the present chapter4 ,,chapter ,,iv ,,flying ,,the ,,airplane ,starting ,off4--,the first thing to do before starting off in an airplane is to inspect carefully everything about the machine and assure yourself that it is in perfect condition4 ,when all is ready to start turn the machine directly against the wind2 this is done in order that the rise from the ground may be more quickly made with the assistance of the wind under the wings1 and it has a more important advantage in the fact that if you try to get off the ground across the wind the machine will be very hard to balance4 ,birds also take the air directly against the wind even though for the moment this carries them in a direction toward some supposed enemy1 and it is a fundamental principle in airdromes4 ,keep the machine pointed into the wind for the first #bjj ft4 of altitude 7and similarly in landing face the wind when within #bjj feet of the ground74 ,in case the engine should fail before a height of #bjj ft4 is reached1 never turn down wind as this is extremely dangerous4 ,assistance will be had for the start from the mechanics1 or if away from the airdrome from bystanders4 ,have each assistant in his proper place before starting the engine2 one is to start the propeller and the rest to hold back the machine until ready to let go4 ,illustration3 7,from 8,how to ,instruct in ,flying407 ,,fig4 #cb4--;,airplane in flying position just after starting4 ,this cut also illustrates proper landing attitude1 since airplane is just skimming the ground4 ,in order to get off the ground you will want good engine power2 it takes considerable thrust to accelerate an airplane on the ground to its flying speed2 in fact the first flying machine of the ,wrights had to use an auxiliary catapult to furnish the thrust necessary to get them into the air4 ,making sure that the motor is giving full power raise the hand as a signal to the attendants to remove the chocks and let go4 ,as you start rolling forward push the control lever forward which will raise the tail off the ground and place the wings edgewise to the wind while they will not offer resistance to the acquiring of good rolling speed4 ,within a few seconds the machine will have attained on the ground a velocity not less than the low flying speed2 it will not rise1 however1 until the tail is lowered by pulling the lever back4 ,when the necessary rolling speed is attained pull the lever softly backward2 the tail at once drops1 the wings increase their angle and lift and the machine will rise1 the lever being held in a fixed position 7see ,fig4 #cb74 ,the distance between the point of starting and rising will be #ajj yd4 or more and will occupy from #e to #aj sec4 depending on the wind4 ,the change from flying position to climbing position is only a slight modification involving only a slight pulling back of the control lever and holding it in fixed position2 the motor may in some machines simply be opened out when its increased power will make the machine rise2 however1 there is only one speed at which the climb will be fastest and therefore it is well to know what is the proper speed for climbing2 the motor is then opened out full and the airplane operated to give the proper speed corresponding4 ,the pupil should rise to the height of at least #ajj ft41 as any less is useless and nothing will be learned from landing4 ,in the case of cross-country flying the pilot will rise to the height of #bjjj ft41 circling over the field rather than flying off in a straight line so that preparatory to his start he always has the flying field in reach4 ,illustration3 7,from 8,how to ,instruct in ,flying407 ,,fig4 #cc4--;,airplane in gliding position1 approaching a landing4 ,note that its attitude relative to line of flight is similar to 8flying position10 line of flight however being inclined4 ,landing4--,proper landing is the most important thing in airplane flying4 ,the pilot in turning his machine downward toward a landing spot from flight will choose a distance from the field equivalent to the proper gliding angle of his machine4 ,if the gliding angle is #a in #g he must not turn downward any further from the field than a distance greater than seven times his altitude or he will fall short4 ,it is safer to come closer to the field before turning downward for two reasons3 first1 because you may not be gliding at the best gliding angle2 second1 because you can always kill extra height by a spiral or two better than you can regain it4 ,have height to spare when landing4 ,to come down throttle down the engine and push the lever softly forward until the proper gliding angle is obtained 7,fig4 #cc74 ,the reason for throttling down the engine is3 first1 that you do not need its thrust when you are coasting down because gravity furnishes all the necessary velocity2 second1 if you glide or dive with the motor wide open high speed will result1 resulting in strains on the machine especially on the moment of leveling out again2 third1 at this high speed the controls become stiff to operate4 ,illustration3 ,,fig4 #cd4--;,attitudes of an airplane in flight4 ,maintain the proper gliding speed to within #e miles an hour of what it ought to be as it is the speed which determines the proper gliding angle4 ,the revolution counter will indicate what the speed is or the air-speed meter may be used4 ,arrange to come on to the field facing directly into the wind1 which may be observed by watching smoke or flags below4 ,in landing against the wind you are again copying the practice of the birds4 ,when you come to within #ae ft4 of the ground pull the lever softly back until the machine is in its slow-flying position1 which should be attained #e ft4 above the ground 7,fig4 #cd74 ,hold the stick at this position of horizontal flying2 no further movement of the lever is necessary except to correct bumps1 for which purpose it would be held lightly for instant action4 ,the aileron control must be used here to keep the machine level and it may be necessary to operate the rudder after touching the ground in order to avoid swerving2 in fact some machines are provided with a rear skid which steers for this purpose4 ,in rolling just after landing keep the tail as close to the ground as possible without causing undue bumping1 so that the maximum resistance of the wings may be presented to the air and the machine be slowed up rapidly4 ,some machines are fitted with brakes on the wheels to assist in the quick retardation of the roll4 ,landing is one of the biggest problems in aviation and is a hard thing to learn because it is done at a high speed especially in the fast military machines such as the ,fokker1 ,nieuport1 etc4 ,landing is more of a problem than it used to be in the early days when1 for instance1 the ,wrights were able to land without any wheels at all on mere skids because their machines were not fast4 ,the following are examples of bad landings3 #a4 ,the pancake results from allowing the machine to get into its rising position when it is landing 7,fig4 #ce74 ,there will be a perpendicular bounce and on the second bounce the running gear will break4 ,in order to get out of an imminent pancake open up the engine to keep machine flying1 put the machine into a flying position1 then throttle down again and land4 #b4 ,another type of pancake results from bringing the machine out of its gliding position at a point too far above the ground when the machine will drop due to lack of speed and break the running gear4 ,to avoid this open motor full1 thus regaining speed and flying position2 afterward throttle down and reland4 ,illustration3 7,from 8,how to ,instruct in ,flying407 ,,fig4 #ce4--;,bad landing1 ,type #a--the 8pancake0 landing4 ,line of flight is downward2 angle of incidence large1 hence speed is slow2 but there is too much downward momentum and landing gear will break4 ,should line of flight arrow point upward1 airplane as shown would then be in climbing position4 #c4 ,a third type of bad landing results from failure to turn the machine out of its glide at all1 so that it glides straight downward until it touches the ground4 ,this is the most dangerous case of all the bad landings4 ,to cure it open up the engine after the first bounce1 regaining flying speed before the second bounce2 then reland4 ,illustration3 7,from 8,how to ,instruct in ,flying407 ,,fig4 #cf4--;,bad landing ,type #d--machine not level4 ,wheels do not touch ground at same time1 and one may smash4 #d4 ,if at the moment of landing the rudder is turned causing machine to swerve1 or if the machine is not level1 a side strain will be placed upon the landing gear and the wheels will buckle 7,fig4 #cf74 ,,chapter ,v ,,cross-,,country ,,flying ,cross-country flying differs from ordinary airdrome flying in that it takes you a long way off from your landing field4 ,on the airdrome your chief anxiety is to learn how to fly1 how to work the controls1 how to bank2 but in cross-country work1 you are supposed to have all the technique of airplane operation well in hand1 so that you do not have to think much about it4 ,in cross-country flying1 then1 your chief anxiety will be to arrive at your destination and to be constantly searching out available landing fields in case of engine failure4 ,the first cross-country flight you make may be a short1 easy one1 in which there are plenty of available landing places1 and on which you will be able to make a regular reconnaissance report4 ,further experience in cross-country work will involve more and more difficult trips1 until you will think nothing of flying1 for example1 on long raiding tours over unfamiliar enemy country4 ,equipment4--,knowing that you may have to land far away from any headquarters1 you must take a complete set of tools and covers for the airplane4 ,your clothing need not be different from usual1 and will comprise helmet1 goggles1 leather suit1 and gloves4 ,do not forget your handkerchief1 which you frequently need to clean off your goggles4 ,the instruments needed on a cross-country trip are3 a compass1 which should be properly adjusted before starting and the variation angle noted4 ,a wrist watch is necessary2 ordinary dashboard clocks go wrong on account of the vibration4 ,take an aneroid barometer with adjustable height reading4 ,of course you will depend upon a revolution indicator1 for no matter how experienced a pilot may be in 8listening out0 faulty engine operation1 after a long flight his ear loses its acuteness1 and he will fall back on the revolution indicator for assistance4 ,the air-speed meter1 whether of the ,pitot type or pressure-plate type1 will prove invaluable in flying through clouds or mist when the ground is obscured4 ,also the inclinometer is able to give the angle of flight when the earth is not visible1 although the speed indicator usually is sufficient to give the angle of flight1 for an increase of speed means downward motion and decrease of speed means upward motion4 ,additional instruments may be used4 ,map4--,the map is essential for cross-country work4 ,it should be tacked on to the map board if the flight is short1 but made to run on rollers if the flight is long4 ,in the latter case the map is in the form of a single long strip1 while your flight may be full of angles2 therefore you will have to practice using this sort of map1 in which the corners of your flight are all drawn as straight lines4 ,the scale of maps may be #b or #d miles to the inch for long flights4 ,this scale is sometimes spoken of as a fractional figure2 that is1 #b miles to the inch is the same as #a_/abg1jjj scale4 ,the map should be studied most carefully before the start of the trip4 ,the course which you propose to fly should be marked out on it2 all available landmarks which could be of service as guides should be distinctly noticed and marked on the map where necessary4 ,these landmarks will in case there is no wind enable you to make your trip without using the compass at all1 and in case of wind1 are essential as a check on the compass4 ,mark off the distance in miles between consecutive points of your course4 ,mark the compass bearing of each leg of this course4 ,as landmarks towns are the best guides1 and they should be underscored on the map1 or enclosed in circles4 ,it is customary not to fly actually over towns4 ,railways are very good assistance to finding your way1 and these should be marked on the map in black wherever they approach within #aj miles of the course4 ,mark water courses with blue color1 and roads with red4 ,landmarks4--,only practice can make a pilot good at observing the various features of the ground beneath him4 ,the various features which can be used as guides are those which are most visible4 ,after towns1 railways come next in importance4 ,their bridges1 tunnels1 etc41 make good landmarks4 ,on windy days when relying on the compass1 it will be well to keep in sight of a railway even if this be the longer way around1 because the railway gives a constant check upon the compass bearing4 ,in this case you will have noted on your map a general magnetic bearing of the railway1 which bearing you can readily compare with your compass reading4 ,moreover1 the railway is good in case you become involved in a fog or mist for a time4 ,it should be remembered1 however1 that on most of the maps no distinction is made between one and two-track roads2 also that it is easy to make mistakes where branch lines are not shown on the map because they are dead ends leading to private quarries1 etc41 and may be taken for junctions4 ,railways sometimes seem to end abruptly1 which means that you are looking at a tunnel4 ,water is visible from a great distance4 ,cautions to be observed are that after a heavy rain small flooded streams may take on the appearance of larger bodies of water or lakes1 which you will have difficulty in reconciling with the map4 ,small rivers are often overhung with foliage1 and to follow them in all their curves will waste a lot of time4 ,the use of roads as guides may be governed by the fact that paved roads are usually main roads1 and telegraph wires may be expected along them4 ,in the newer parts of the ,united ,states the system of laying out roads provides a very useful means of gaging distances2 ,i refer to the section system which is in use1 for instance1 in ,illinois1 where there is a road every mile running north and south1 so that the entire country is cut up into squares #a mile on each side1 with occasional roads of course at -mile and -mile points4 ,navigation by ,landmarks4--,in all cases of cross-country flying the pilot will have two independent systems of maintaining his proper directions3 first1 the computed compass bearing2 second1 the use of landmarks whose position is known4 ,in comparing his computed course with the course actually indicated by passing over these landmarks the rule should be made that1 in case of doubt when a landmark is not distinctly recognized1 take the compass course2 there are many chances that a landmark may be altered or even removed without being so recorded on the pilot's map1 whereas the errors of the compass of course are presumably understood by the pilot who has secured every opportunity to check it when passing previous landmarks4 ,it is important to note the time of completing successive stages of the flight1 that is when passing over predetermined landmarks4 ,time is a very uncertain condition to ascertain in airplane flying for it seems to pass quickly on calm days but slowly when the journey is rough4 ,if the pilot does not check the time interval between successive objects he is quite likely to expect the next before it is really due4 ,landing ,fields4--,next to the ever-present worry which the pilot has regarding the perfect operation of his engine1 the most important thing about cross-country flying is that wherever he may be he must have available a landing field within gliding distance in case his engine defaults4 ,the question is of course immediately raised1 8,what if there is no landing field within gliding range80 ,the answer to this is that the pilot will instinctively learn to keep his eyes open for landing possibilities every minute of his progress whether he expects to use them or not2 in cross-country flying the lookout for fields is first and foremost in his mind2 if there are no fields1 it is up to him to pick out a spot of ground which is the least objectionable for a landing4 ,in the ,state of ,illinois the question of landing fields is almost non-existent1 because there are large1 flat fields and pastures in almost every square mile of the farming district1 and a cross-country flight from ,rantoul to ,chicago could have no terrors for the beginner as regards the choice of a landing ground4 ,when it comes to a cross-country flight like ,ruth ,law's1 from ,chicago to ,new ,york1 these favorable conditions begin to disappear after the middle of the journey1 that is1 east of ,buffalo4 ,the most ideal condition for cross-country flying would be one like that on the ,london-,edinburgh route1 where landing grounds are so frequent that by flying at a height of a couple of miles the pilot can free his mind completely of the worry of suitable landing places2 but in the ,united ,states we have very few established airdromes1 and the only approach to the ,london-,edinburgh route is the ,st4 ,louis-,new ,york route1 where the jumps are approximately #aej miles2 namely1 ,st4 ,louis1 ,champaign1 ,indianapolis1 ,dayton1 ,sandusky1 ,erie1 ,hammondsport1 ,philadelphia1 and ,new ,york4 ,that is why long cross-country trips are such an adventure in this country and such an ordinary affair in ,england4 ,the beginner will have special difficulty in training his mind to pick out available landing places2 first of all because the earth looks so different from the sky that it is only with practice a beginner learns the shades and hues of color which mean certain kinds of ground1 or learns to spot the different features of flat and hilly country4 ,even for an accomplished pilot it is hard to tell whether a field is good or bad from a height of over #ajjj ft42 and as it is dangerous to fly this low over unknown territory1 you can at once see what is meant by the worry of scanning the countryside for available fields4 ,choose the best field that you can get1 having a smooth surface and being easy to get out of in all directions4 ,the following considerations are intended as a guide to what constitute the best field1 in case you have a choice between several possibilities4 #a4 ,choose a field near a town if possible1 or failing that1 near a main road or at least a good road4 ,remember that a field which appears to be near a town from the air may actually turn out to be a long walk after you have landed there and find that there are various trips to be made to and fro between your chosen landing spot and the town for the purpose of securing ropes1 gasoline1 supplies1 etc4 ,if you land near a main road there will probably be telegraph wires along it1 which are undesirable in the case of a small field and wind direction such that you have to rise off the field over the telegraph wires4 ,it is often hard to distinguish between main roads and minor roads1 and it will be wise to look for the number of vehicles on any road in determining whether or not it is the main road4 #b4 ,the best field is a stubble field1 and is most numerous of course in the fall when the crops are in4 ,it will have a lightish brown color when seen from a height1 and is pretty sure to be smooth1 without ditches or mounds4 ,grass land is next best1 but is often full of mounds4 ,plowed1 furrow fields are to be avoided4 ,it might be said that stubble fields will be hard to get out of after a wet night4 ,vegetable and corn fields have a dark green appearance which the pilot must learn to distinguish from grass pastures1 etc4 ,if you choose pasture land1 remember that in summer evenings the farm animals will generally be lying down near the hedges4 #c4 ,avoid river valleys for landing over night1 as there is liable to be a fog in the morning4 #d4 ,any field which has been previously used for landing with success by an army officer can be wisely chosen4 ,the final determination of landing field characteristics can be made when your airplane has descended to a height of #ajjj ft4 off the ground1 and in case you are not making a forced landing and your engine is still going1 you can check up your estimate by descending to this level4 ,proper ,dimensions of ,fields and ,airdromes4--,there are three kinds of flying fields4 ,one is the airdrome which is used exclusively for flying1 and may be as large as a mile square2 very few of these will be found in cross-country flights in the ,united ,states4 ,second1 there is what is called the 8one-way0 field1 a long1 narrow1 open space which is usable when the wind blows parallel to its length4 ,third1 there is the 8two-way0 field1 which has two sufficiently long runways at right angles to each other4 ,a two-way field is very much better than a one-way field1 inasmuch as you can always head within #de of the wind1 whereas in a one-way field an extreme case would be #ij4 ,moreover1 two-way fields1 such as the crescent-shaped field at ,dayton1 ,ohio1 sometimes permit of almost universal direction of flight4 ,the two-way field may be crescent-shaped1 ,t-shaped1 or ,l-shaped4 ,an ,l-shaped field should have each arm #bjj by #cjj yd4 ,under certain conditions there may be buildings located inside or outside the angle which do no harm aside from creating eddies in case of strong wind4 ,a ,t-shaped field should also have its arms #cjj by #bjj yd4 in size4 ,regarding the size of fields it can be said that1 while the ,,jn-#d machine will rise off the ground after a run of #ajj yd4 or so1 a field of this length is of course not big enough for frequent use1 especially if bordered by trees1 telegraph lines1 fences1 and so forth4 ,a field for temporary use should be at least #bjj by #bjj yd41 about #i acres4 ,if obstructions at the edges are more than #e ft4 high add to this #bjj yd4 a distance equal to twelve times the height of the obstruction4 ,for a permanent field #cjj yd4 is the minimum dimension necessary for clearing obstacles and must be increased if the trees exceed #ej ft4 in height4 ,this minimum dimension assumes hard ground and the possibility of starting in any direction4 ,training fields are mile square or more4 ,whatever field is used either temporarily or permanently by the pilot should be absolutely familiar to him over every inch of its surface4 ,the adjacent country should also be absolutely familiar to him from the standpoint of possible forced landings which he may have to make during his flight2 he should make a habit of informing himself as to all the woods and hills1 etc41 which can affect air currents in the neighborhood of the field from which he is going to start4 ,guide ,posts on ,airdromes4--,some fields have pot holes in them1 and these holes should be marked in each case with a large high red or yellow flag4 ,do not use short1 small flags1 as they will frequently be invisible to pilots taxying on the ground4 ,all telephone wires1 etc41 should have large blankets or other suitable signals hung over them to warn the pilot away4 ,commonly accepted marks for designating a landing spot on airdromes are as follows3 ,for day use a large letter 8,t0 lying on the ground1 made out of white cloth strips #ae by #c ft4 ,this letter ,t is shifted with the wind so that its long leg always points in the direction of the wind and the pilot will therefore have nothing to do in landing but approach the letter 8,t0 from the bottom1 so to speak4 ,for night flying a system of four flares is used1 so arranged that the pilot in making a proper landing will pass flare ,a on his left2 within #ej yd4 further on1 flare ,b2 then #ajj yd4 further on1 flare ,c1 also on his left4 ,in passing flare ,c he will have a fourth flare1 ,d1 #ej yd4 to his right4 ,that is to say1 the four flares make the outline of a letter 8,l0 and the pilot approaches the letter having the long leg on his left4 ,the flares may be made by putting half a gallon of gasoline into a pail4 ,this will burn for #cj min4 and will be visible #h miles away4 ,sometimes at night instead of flares white sheets can be spread on the ground and a shaded lamp used to illuminate the sheets4 ,all searchlights on the landing field should point in the direction of landing4 ,all other lights within a distance of a mile should be extinguished1 and red lamps should be used at danger points4 ,on moonlight nights the same signals and guides may be used as in the daytime4 ,pegging ,down an ,airplane4--,in landing for the night do not stay up until it gets dark but choose a landing place which will allow you to come down #a hr4 before dark2 this amount of time will be needed for laying up the machine over night4 ,as you come to the landing ground note the time so that you can compute the actual duration of your flight in your report1 then make a good landing4 ,taxy the machine to the spot where you intend to leave it over night1 such as the lee of a hedge1 etc42 or if there is no choice of position taxy the machine to the approximate location from which you will make your start next morning2 this will save trouble when you get ready to start4 ,dismount from your machine1 lift up the tail enough to leave the wings edgewise to the wind1 the machine1 of course1 facing the wind1 and jack up the tail in this position by the use of any convenient prop4 ,lash the control wheel or joy stick fast in a fixed position so that the wind can not flap the control surfaces around and damage them4 ,choose a sunken trench if possible in which the wheels may be sunk2 if the wind is going to blow and there is no sunken trench it will be wise to dig one so that the effect of the wind on the airplane will be lessened4 ,if the trench is not necessary1 at least put chocks under the wheels4 ,peg down the wings and the tail to stakes driven into the ground using rope if you can get some or lacking this in an emergency fence wires which you can secure by means of your wire cutters4 ,do not lash tightly enough to induce strains in the framework of the machine4 ,next1 fill up the tanks if a supply of gasoline or oil is available4 ,put the covers on the propellers1 engine1 cowls1 etc41 in order that rain and dew shall do no damage to these parts4 ,the wings and body are varnished waterproof and will not be seriously damaged by a little moisture2 to avoid the collection of moisture in the wings small eyelet holes are sometimes set in the wings at the trailing edge to let out the water4 ,of course1 you will engage a guard to watch the machine all night2 see that a rope is strung around the airplane to keep off the crowd which may collect4 ,,aerial ,,navigation ,effect of ,wind4--,navigating in an airplane is complicated only on account of the fact that there is a wind blowing which may not be in the desired direction4 ,while on the sea navigation is simple through the assistance of the magnetic compass 7because side winds can not materially drift the ship sideways71 in the air this is not the case2 for if the pilot using the compass points the nose of the airplane directly north while a west wind is blowing1 this wind will cause the machine to drift in an easterly direction so that in an hour of flight the airplane will be off its course by an amount equal to distance which the wind travels in #a hr42 and the joint result of the motion of the airplane forward and the motion of the wind sideways will cause the machine to drift in a northeasterly direction at a speed quite different from its rated velocity1 and in this case somewhat larger4 ,victor ,carlstrom in his ,chicago-,new ,york flight found while he was over ,cleveland that a side wind was deviating his course #ag away from what it should be1 and if he had not had such landmarks as the shore of ,lake ,erie for guidance he might easily have lost considerable time4 ,the question of making allowance for this wind drift is very important where there are no landmarks1 as in the case of night flying1 flying over the sea1 or flying over the clouds2 and the only way the pilot can make allowances for these conditions is to figure them out before he starts from the airdrome1 and plan to circumvent them4 ,that is to say1 the pilot in flight has no means1 aside from visual observation of the ground1 to determine whether or not the wind is blowing him off his course4 ,he must determine the whole situation before he starts1 and the process of doing so is as follows4 ,graphical ,method for ,determining ,direction to ,steer4--,the pilot will ascertain from the weather vane and anemometer of the airdrome 7#a7 the velocity and 7#b7 the direction of the wind1 7#c7 the speed of the airplane he is to fly1 7#d7 the compass bearing of the actual course which he desires to follow4 ,with this data it is possible to construct a simple diagram and to determine the direction to be steered and the actual velocity which will result in the proposed journey4 ,a draftsman's scale1 protractor and dividers1 a pencil and a piece of paper are the necessary equipment4 ,when the wind blows at an angle with the desired course it is necessary to steer the airplane in such a direction that its own forward motion will neutralizer the side effect of the drift of the wind from moment to moment4 ,the problem is to determine this direction for steering1 as it is not known4 ,we are not concerned with distances in this problem1 for the direction is going to be the same whether our flight is of #ajj or #bjj miles4 ,we are1 however1 vitally concerned with velocities2 and we will assume that the velocity of the airplane is known to be #ge miles per hour1 and from observation on a local anemometer the velocity of the wind is known to be #bj miles an hour4 ,we also know1 of course1 the direction of the wind1 which should be given in terms of an angle whose other leg points directly north4 ,now if the flight is to be made at a height of #bjjj ft41 as is usual in cross-country flight over average country1 we will find that the speed of wind will increase as we rise up2 moreover1 that its direction will change4 ,in the present case the wind will be #hh per cent4 higher in #bjjj ft4 than it is on the ground2 that is to say1 the velocity at the altitude we are going to use is twenty times #a4hh1 or about #ch miles per hour4 ,moreover1 as the height increases the direction of the wind changes1 shifting around always in a clockwise direction as the height increases1 in the present case shifting around #af from its ground direction4 7,the change of velocity and direction for various heights is indicated on the subjoined table47 ,thus a west wind becomes at a height of #bjjj ft4 a slightly northwest wind1 or1 to be exact1 blows from a direction which is #gd west of north4 ,our treatment of the problem then has for starting points3 velocity of wind1 #ch miles per hour2 direction of the wind1 #gd west of north2 velocity of airplane #ge miles per hour2 desired direction of flight 7which has been determined by laying out on the map and reading the compass bearing with the protractor71 say #fj east of north4 ,in #a hr4 of flight the machine would travel in this unknown direction a distance of #ge miles were it not for the wind1 but for every hour of such flying the wind is blowing it #ch miles sideways2 and the desired direction must be such that its joint effect1 together with the #ch mile sideways wind1 will leave the machine exactly on its proper course at the end of the hour4 ,on the map or piece of paper denote the starting point by ,a 7see ,fig4 #cg74 ,from ,a draw a line parallel to the wind 7that is to say1 #gd west of north71 and let this line represent1 to any convenient scale1 the speed of the wind1 #ch miles per hour4 ,the far end of the line may be called ,b1 and may be given an arrow to represent the direction of wind4 ,now draw on the map a line from ,a to the desired destination 7,c71 giving it1 of course the proper compass bearing4 ,take the dividers1 and with ,b as a center1 describe an arc at such distance as to represent #ge miles per hour1 the speed of the machine2 this arc will intercept the line ,,ac at ,d1 and ,,bd then gives the direction to steer1 for it is that direction which will permit the airplane in #a hour exactly to neutralize the sidewise drift of the wind4 ,the distance ,,ad on this diagram can be measured off and will give the actual velocity of movement along the line of flight in miles per hour4 ,notice that it is #ig miles per hour1 quite different from the speed of the airplane4 ,illustration3 ,,fig4 #cg4--;,graphical method for determining direction to steer to counteract wind-drift4 ,assuming that the pilot has determined the proper angle toward which the airplane nose must be pointed1 has maintained this angle throughout his flight by means of the compass and has safely reached his objective2 for the return trip this diagram must be completely reconstructed 7unless the wind is exactly parallel to his course74 ,the pilot should not make the mistake in returning to the starting point of steering the airplane nose in a direction exactly opposite to the outward trip2 the reader may make this clear to himself by drawing the return diagram and comparing it with the outward-bound diagram4 ,to summarize flying when a cross wind is blowing1 it will be said that the direction of actual travel will not be the direction indicated by the axis of the airplane2 and that therefore while in a picture of the situation the airplane appears to skid sideways along the whole course it must be borne in mind that actually there is no skidding whatever but the air is meeting the airplane in normal manner4 ,the situation is analogous to that of a fly going from one side to the other of the cabin of a moving ship1 where the actual course through space of the fly is an apparent skid1 due to the resultant of its own and the ship's movement4 ,,variation ,,of ,,velocity ,,and ,,direction ,,with ,,height 7#be miles per hour wind7 ---------------------------------------- ---------------------------------------- ---------------------------------------- ,height in feet ,at surface #ejj #ajjj #bjjj #cjjj #djjj #ejjj ---------------------------------------- ---------------------------------------- ---------------------------------------- ,velocity change in per cent #ajj #ace #agb #ahh #aif #bjj #bjj ---------------------------------------- ---------------------------------------- ---------------------------------------- ,clockwise deviation in degrees #j #e #aj #af #ai #bj #ba ---------------------------------------- ---------------------------------------- ---------------------------------------- ,effect of ,wind on ,radius of ,action4--,not only is the direction of flight altered by the wind but also the radius of action from a standpoint of gasoline capacity is altered4 ,in the above machine the gasoline capacity is sufficient for #c hr4 of flight4 ,how far can it go across country and return before the gasoline is used up8 ,always allow hr4 gasoline for climbing and for margin2 this leaves #c hr41 which at #ge miles an hour is #bbe miles1 or #aab miles out and #aab miles back4 ,now suppose that a flight is to be made across country directly in the teeth of a #dj-mile wind2 the radius of flight will be altered as indicated by the following calculation3 ,speed outward is obviously #ge minus #dj or #ce miles per hour4 ,speed on the return trip is obviously #ge plus #dj or #aae miles per hour--#c4bi times as fast--and occupying a time which may be designated by the letter x4 ,the time on the outward trip may be designated by #c4bix1 a total time of x #c4bix which we know equals #ahj min4 before the gas runs out4 ,solve the equation x #c4bix #ahj and we find that x is equal to #db min41 that is1 the return trip requires #db min41 and the outward trip requires #ach min4 ,the distance covered on the outward trip is then #ach_/fj of #ce1 which equals #hj4e miles4 ,the radius is then reduced from #aab miles to #hj4e miles4 ,in cases where the wind is not parallel to the line of flight the actual velocity of course can not be obtained by adding up the airplane and wind velocities1 but must be obtained by the graphical method mentioned above2 thenceforward the calculation is the same4 ,effect of ,height4--,of course if one has to fly in the teeth of a wind and can choose one's own altitude1 it is desirable to fly low where the head wind has its smaller velocity1 and when flying with the following wind to rise to considerable altitudes4 ,the proper height at which to fly will be about #aejj to #cjjj ft41 for cross-country trips over ordinary country2 but may be increased when the wind is unsteady or decreased when there are low-lying clouds4 ,the steadiness as well as the speed of the wind increases with the height4 ,the character of the country should be carefully investigated from the profile maps before starting2 all hilly parts should be marked on the map as a warning against landing4 ,contour is not readily distinguished from a height of #bjjj ft4 and for this reason points may be indicated on the map where poor landing places make it desirable to fly high4 ,the character of the country or the scarcity of landing places may make it advisable to fly at high altitudes for the following reasons3 7#a7 in case of engine failure a good margin of height is necessary to provide length of glide to reach distant landing places2 7#b7 there is then plenty of space for righting the airplane in case of bumps1 side slips1 etc42 7#c7 eddies or local currents due to inequalities of the ground do not exist to great heights2 7#d7 landmarks can be better distinguished from high altitudes because the vision is better 7however1 one must never trust to landmarks only in navigating but should constantly use a compass if only as a check1 and especially in passing through clouds74 ,having selected in advance the proper height to use during the trip climb to this height in circles2 note the direction of wind drift meanwhile to check up your estimate4 ,pass directly over the point of departure and when over it point the nose of the airplane for a moment directly toward the desired objective 7which can be done with the aid of the magnetic compass72 select some distant object which is dead ahead1 and therefore directly in the course2 then head the nose of the machine up into the wind just enough so that the direction of movement will be straight toward this distant object4 ,the direction of the nose of the machine thus set by a method distinct from the graphical method above mentioned should exactly correspond1 however1 with the calculated direction2 and thus a means of checking is obtained4 ,effect of ,fog4--,the effect of fog upon navigating an airplane is that it prevents the use of landmarks in aiding the pilot2 also that it upsets the pilot's sense of level4 ,these two effects are1 of course1 independent of the fact that proper landing places are obscured1 with resultant peril in case of engine failure4 ,therefore1 a fog should be avoided whenever possible2 when one comes up1 the airplane should descend1 and should never attempt to get above it1 as in certain localities it may turn out to be a ground fog4 ,if the fog is very bad1 land at the earliest opportunity4 ,it is on account of fog that the pilot avoids river valleys where frequently there is a haze from the ground up to a height of #gjj ft41 preventing the view of proper landing places in case of necessity4 ,effect of ,clouds on ,navigation4--,flying in or above the clouds is a similar case1 inasmuch as landmarks can not be seen4 ,it is not wise to go above the clouds when on the sea coast1 as offshore winds may1 unknown to the pilot1 carry him out to sea2 and any flight over the sea which is to a distance greater than the safe return gliding distance is1 of course1 perilous4 ,navigation by ,means of the ,drift ,indicator4--,the drift indicator is an instrument for determining directly the side drift of an airplane4 ,it enables the pilot by looking through a telescope at the ground to determine exactly what his direction of motion is with relation to the ground4 ,the telescope is mounted vertically and is rotatable about its own axis2 it has a cross-hair which appears in the field of view during the pilot's observation of the ground4 ,as the airplane speeds overhead objects on the ground will appear through the telescope to slip backward in the given direction2 and when accustomed to the use of this instrument the pilot can rotate the telescope until the cross-hair is exactly parallel to the apparent line of motion of objects on the ground4 ,the telescope cross-hair is parallel to the axis of the airplane normally and the scale attached to the telescope will in this case read zero4 ,when the pilot rotates the telescope so that the cross-hair becomes parallel to the relative backward motion of the ground the scale will read something different from zero and will give the angle between the actual line of motion and the axis of the airplane4 ,such a drift indicator is1 of course1 useful only when the ground is visible4 ,the pilot knowing the angle between the airplane axis and the line of motion and therefore knowing the deviation between the supposed course and the actual course is able to make corrections and steer the machine in its proper direction4 ,this may be done by altering the 8lubber-line0 or his compass just enough to offset the side drift of the machine2 after which the desired course may be followed by simply keeping to the proper compass bearing4 ,an instrument has been devised wherein the rotation of the drift-indicator telescope simultaneously alters the lubber-line zero4 ,the operator then has merely to take an occasional observation of the apparent drift line of the ground1 which observation automatically shifts the lubber-line and navigation proceeds as if there were no side wind blowing whatever4 ,knowing the angle between the direction of movement and the airplane axis1 the pilot may then compute the speed of motion in a manner analogous to the graphical method previously mentioned2 or he can make use of a chart for the determination of this speed4 ,navigation over ,water4--,in flying over water the presence of waves is a valuable guide to the aviator1 for he knows that these waves extend in a direction normal to the wind4 ,moreover1 he knows that the velocity of the waves bears some relation to the velocity of the wind4 ,in order to estimate the velocity of the waves it is only necessary to know their wave length1 that is1 the distance between two consecutive wave crests4 ,the rule is that for a wave length of #aj ft4 the velocity is #aj miles per hour1 and will vary as the square root of this wave length2 that is1 if the wave length is half1 the velocity will be #aj divided by the square root of #b1 or #g4a miles per hour4 ,,chapter ,,vi ,,the ,,rigging ,,of ,,airplanes ,object4--,the object of this chapter is to teach the elementary principles of correct rigging4 ,it is not expected that the student will become an expert mechanic1 but with this treatment as a basis and through practice he will be able to judge whether or not a machine is correctly and safely rigged4 ,in other words1 he will not have to depend on someone else's judgment as to whether panels1 wires1 controls1 struts1 etc41 of a machine are in good order1 but he will be able to observe understandingly that they are4 ,if the engine goes wrong he can land1 if the rigging goes wrong he is in great difficulty4 ,moreover1 if the rigging is wrong1 speed is lessened and the stability is uncertain4 ,the first thing to be learned in rigging is a knowledge of the peculiar terms which have come into use in aeronautics defining different parts of the machines4 ,our present list of terms is derived1 partly from ,french1 partly from ,english1 and partly from ,american terms4 ,thus different names may refer to the same part4 ,,nomenclature #a4 ,tractor4--,an airplane that is pulled through the air by a propeller situated in front of the machine1 is called a tractor4 #b4 ,pusher4--,if the propeller is back of the main lifting planes the machine is called a pusher4 #c4 ,fuselage or ,body4--,the main body of the airplane in which the pilot sits and to which the landing gear1 motor1 controls1 and sustaining surfaces are fixed4 ,a small body1 especially in pusher types of machines1 is called a ,nacelle4 #d4 ,cockpit4--,the openings and space in the fuselage where pilot or observer sits4 #e4 ,stream-line ,body4--,the shape of a body or part which permits a regular flow of air around and along it with the least resistance1 in other words with minimum1 obstruction and eddying4 #f4 ,fairing4--,building up a member or part of the plane with a false piece that it may have a stream-line body4 #g4 ,wings1 ,planes1 ,panels4--,the main supporting surfaces of an airplane are called wings1 although the terms planes and panels are probably as frequently used and even preferred by many4 ,the term panel refers properly to a section of the wings with the included struts and wires4 ,the small panel directly above the body is called the engine section panel or the center panel1 while the panels to the right and left of the body or fuselage are called the main panels4 ,the main panels are the right and left panels as seen from the seat4 ,each main panel may be subdivided into the inner wing bay1 the outer wing bay1 and the overhang4 #h4 ,landing ,gear1 ,chassis or ,undercarriage4--,the wheels and the struts and wires by which they are attached to the fuselage4 #i4 ,horizontal ,stabilizer or ,horizontal ,fin4--,the horizontal fixed tail plane4 #aj4 ,vertical ,stabilizer or ,vertical ,fin4--,the small vertical fixed plane in front of the rudder4 #aa4 ,rudder4--,the hinged surface used to control the direction of the aircraft in the horizontal plane4 ,as with a boat1 for steering or 8yawing0 or changing its direction of travel4 #ab4 ,elevator or ,flap2 ,flippers4--,a hinged horizontal surface for controlling the airplane up and down1 usually attached to the fixed tail plane2 for pitching the machine or 8nosing up0 and 8nosing down40 #ac4 ,tail or 8,empennages40--,a general name sometimes applied to the tail surfaces of a machine4 #ad4 ,mast or ,cabane4--,the small vertical strut on top of the upper plane used for bracing the overhang4 #ae4 ,ailerons4--,movable auxiliary surfaces used for the control of rolling or banking motion4 ,other definitions are that they are for the lateral control or for maintaining equilibrium4 ,when they are a part of the upper plane they are sometimes called wing flaps4 #af4 ,landing ,wires or ,ground ,wires 7,single74--,the single wires which support the weight of the panels when landing or on the ground4 #ag4 ,flying ,wires1 or ,load ,wires 7,double74--,the wires which support the body or fuselage from the planes when in flight4 #ah4 ,drift ,wires4--,the horizontal wires which lead from the nose of the fuselage to the wings and thus keep them from collapsing backward4 ,for the same reason the wings have interior drift wires4 #ai4 ,diagonal ,wires4--,any inclined bracing wires4 #bj4 ,skids4--7a7 ,tail ,skid4--,the flexible support under the tail of the machine4 7b7 ,wing ,skid4--,the protection under the outer edge of the lower wing4 7c7 ,chassis ,skids4--,skids sometimes placed in front of the landing gear4 #ba4 ,horns1 or ,control ,braces4--,the steel struts on the controls to which the control wires are attached4 #bb4 ,struts2 ,wing ,struts4--,the vertical members of the wing trusses of a biplane1 used to take pressure or compression1 whereas the wires of the trusses are used to take pull or tension4 ,there are also fuselage struts and chassis struts4 #bc4 ,spar or ,wing ,bars4--,the longitudinal members of the interior wing framework4 #bd4 ,rib 7,wing74--,the members of the interior wing framework transverse to the spars4 #be4 ,the ,longerons or ,longitudinals4--,the fore and aft or lengthwise members of the framing of the fuselage1 usually continuous across a number of points of support4 #bf4 ,engine 7,right and ,left ,hand74--,in the ordinary tractor machine1 when viewed from the pilot's seat a right-handed engine revolves clockwise and right-handed4 #bg4 ,propeller4-- #bh4 ,pitch 7,propeller74--,the distance forward that the propeller would travel in one revolution1 if there were no slip1 that is1 if it were moving in a thread cut at the same inclination as the blade4 ,pitch angle refers to the angle of inclination of the propeller blade4 #bi4 ,slip4--,slip is the difference between the actual travel forward of a screw propeller in one revolution and its pitch4 #cj4 ,dope4--,a general term applied to the material used in treating the cloth surface of airplane members to increase strength1 produce tautness1 and act as a filler to maintain air and moisture tightness4 ,usually of the cellulose type4 #ca4 ,controls4--,since there are three axes or main directions about which an airplane may turn or rotate it follows that three controlling devices are required4 ,these are3 7#a7 the elevator for pitching2 7#b7 the rudder for steering or yawing2 7#c7 the ailerons for lateral1 rolling or banking control4 ,the term controls is a general term used to distinguish the means provided for operating the devices used to control speed1 direction of flight and attitude of the aircraft4 #cb4 ,cotter ,pins4--,must be on every nut4 #cc4 ,castelled ,nuts4--,admit cotter pins4 #cd4 ,turnbuckles4--,must be well and evenly threaded and locked with safety wires4 #ce4 ,safety ,wires4--,for locking turnbuckles and hinge pins4 #cf4 ,shackle and ,pin4-- #cg4 ,hinge ,connections4-- #ch4 ,leading ,edge or ,entering ,edge4--,the front edge of a plane4 #ci4 ,trailing ,edge4--,the rear edge of a plane4 #dj4 ,stagger4--,the horizontal distance that the entering edge of the upper wing of a biplane is ahead of the entering edge of the lower wing4 #da4 ,dihedral ,angle4--,a term used to denote that the wings are arranged to incline slightly upward from the body toward their tips4 ,the angle made with the horizontal by this inclination of the wing is called the dihedral angle4 #db4 ,angle of ,incidence4--,the angle at which a wing is inclined to the line of flight4 #dc4 ,decalage4--,difference in angle of incidence between any two distinct aerofoils on an airplane4 #dd4 ,chord4--,distance between the entering edge and trailing edge of a wing measured on a straight line touching front and rear bottom points of a wing4 #de4 ,camber4--,the depth of the curve given to a sustaining surface such as a wing4 ,thus it will be observed that the planes are not straight in cross-section but are concave slightly upward4 ,the depth of this concavity is the camber4 ,another way of expressing this is that camber is the greatest distance between the surface of a wing and its chord line4 #df4 ,gap4--,the distance between the lower and upper wings of a biplane4 #dg4 ,spread4--,the distance over all from one wing tip to the other wing tip4 #dh4 ,aerofoil4--,a general name applied to any wing or lifting surface of an airplane4 #di4 ,deadhead ,resistance4--,each part of an airplane against which the wind strikes offers a resistance against being moved through the air4 ,this is called the deadhead resistance or the parasite resistance4 ,it is for the purpose of lessening this resistance that the parts of a machine are stream-lined4 ,remember that force or power must be applied to overcome this resistance and the lessening of such resistance decreases the power necessary4 ,a parallel illustration is to think of the power necessary to push a board sideways through water4 #ej4 ,drift4--,when the air strikes the inclined wing of an airplane its force has two components4 ,one part called the lift 7see #eb7 acts up and tends to lift the machine4 ,the other part1 called drift1 tends to push the machine backward4 ,this drift must also be overcome by applying power enough to drive the machine forward4 #ea4 ,total ,resistance4--,sometimes called drag4 7#di7 ,deadhead resistance added to 7#ej7 drift1 gives the total forces opposing the forward movement of the airplane4 ,this is called the total resistance and is overcome by the thrust of the propeller4 #eb4 ,lift4--7,see #ej74 ,the upward or vertical part of the air pressure acting against the wings1 and which is utilized to lift or support the airplane4 #ec4 ,center of ,gravity4--,the point of balance of an airplane which may be otherwise defined as the point through which the mass of an airplane acts4 ,if the weight is too far forward the machine is nose-heavy4 ,if the weight is too far behind the center of lift the machine is tail-heavy4 #ed4 ,aspect ,ratio4--,the ratio of span to chord of a wing or any other aerofoil4 #ee4 ,gliding ,angle 7,volplane74--,the angle made to the horizontal by the flight path of an airplane with the engine shut off2 e4g41 an airplane is #ajjj ft4 high1 when its engine fails4 ,suppose its gliding angle is #a in #f4 ,therefore1 in still air it can glide #fjjj ft4 forward4 ,the general term glide refers to flying without power4 #ef4 ,the ,angle of ,best ,climb4--,the steepest angle at which an airplane can climb4 #eg4 ,stability4--,the property of an airplane to maintain its direction and to return easily to its equilibrium or balance with a minimum of oscillation4 ,this is sometimes called dynamical stability4 ,an airplane may have 7first7 inherent stability1 which is the stability due to the arrangement and disposition of its fixed parts4 ,it may also have stability with regard to any one of the three directions in which it may move4 ,these are named as follows3 7#a7 directional stability1 with reference to the vertical axis2 7#b7 lateral stability with reference to the longitudinal 7or fore and aft7 axis2 7#c7 longitudinal stability1 stability with reference to the lateral 7or thwartship7 axis4 #eh4 ,flying ,position4--,refers to the position of the fuselage when flying4 ,with the ,curtiss ,,jn-#d machines in this position the top longerons are horizontal and level both ways4 ,the engine bearers are also level1 and the wings have an angle of incidence of #b4 #ei4 ,capacity4--,the weight an airplane will carry in excess of the dead load 7dead load includes structure power plant and essential accessories74 #fj4 ,flight ,path4--,the path of the center of gravity of an aircraft with reference to the air4 #fa4 ,stalling4--,a term describing the condition of an airplane which from any cause has lost the relative speed necessary for support and controlling1 and referring particularly to angles of incidence greater than the critical angle4 #fb4 ,sweepback4--,the horizontal angle 7if any7 that the leading edge of a machine makes with the crosswise or lateral axis of an airplane4 #fc4 ,nose ,dive or ,vol-pique4--,a dangerously steep descent1 head on4 ,,chapter ,,vii ,,materials ,,of ,,construction ,the materials of construction for airplanes should be of such material1 size and form as to combine greatest strength and least weight4 ,with metal parts in particular it may be necessary to substitute less strong material for the sake of getting non-corrosive qualities1 ability to withstand bending1 ductility or ease of bending1 etc4 ,with wood1 absence of warping is important as well4 ,the materials which are considered are the following3 wood1 steel1 including wires2 special metals as aluminum1 brass1 monel metal1 copper1 etc41 and also linen and dope4 ,strength of ,materials4--,it is important in a general way to understand the terms used in speaking of strength of materials4 ,thus we may have strength in tension1 strength in compression1 or strength in shearing1 bending and torsion4 ,some material fitted to take tension will not take compression1 as for example wire2 some material1 as bolts1 are suited to take shear1 etc4 ,in general all material for airplanes has been carefully tested and no excess material is used above that necessary to give the machine the necessary strength4 ,tension4--,this means the strength of a material which enables it to withstand a pull4 ,thus wires are used where strength of this kind is required4 ,compression4--,this refers to strength against a pressure4 ,wire has no strength for this purpose1 and wood or sometimes steel is used4 ,shearing4--,refers to strength against cutting off sideways4 ,thus the pull on an eyebolt tends to shear the eyebolt1 or the side pull on any bolt or pin tends to shear the pin4 ,bending4--,in bending material the fibres on the outside tend to pull apart2 those on the inside tend to go together4 ,thus on the outside we have tension1 and on the inside compression4 ,along the center line there is neither tension or compression1 it is the 8neutral axis40 ,torsion4--,torsion is a twisting force1 such as an engine propeller shaft receives4 ,testing for ,strength4--,if a wire is an inch square in cross-section and breaks when a load of #aej1jjj lb4 is hung on it1 we say that the strength of the wire is #aej1jjj per square inch4 ,smaller wires equally strong have a strength of #aej1jjj lb4 per square inch also1 but they in themselves will not support a load of #aej1jjj lb4 but only the fraction of that1 according to the fraction of a square inch represented by their cross-section4 ,in the same way1 a square inch of wood under a compressive load may break at #ejjj lb4 ,if1 however1 the piece of wood is long in proportion to its thickness1 it will bend easily and support much less weight4 ,for example1 a perfectly straight walking cane could perhaps have a ton weight put on it without breaking but if the cane were not set squarely or if it started to bend it would immediately break under the load4 ,these cases illustrate the importance of having struts perfectly straight1 not too spindling and evenly bedded in their sockets4 ,some training machines are built with a factor of safety of #ab4 ,that is to say1 the breaking strength of any part is twelve times the ordinary load or stress under which the piece is placed4 ,it should be remembered1 however1 that under any unusual condition in the air1 such as banking1 etc41 extra strains are placed on the parts and the factor of safety is much less than #ab4 ,factor of safety of #ab thus does not mean exactly what it does in other engineering work1 where allowances are made for severe conditions4 ,the so-called factor of safety of #ab in airplane work is probably no greater than a factor of safety of #b or #c in regular engineering work4 ,there are three all-important features in the flying machine construction1 viz41 lightness1 strength and extreme rigidity4 ,spruce is the wood generally used for parts when lightness is desired more than strength1 oak1 ash1 hickory and maple are all stronger1 but they are also considerably heavier1 and where the saving of weight is essential1 the difference is largely in favor of the spruce4 ,this will be seen in the following condensed table of ,u4 ,s4 ,government ,specifications4 ---------------------------------------- ---------------------------------------- ------------------ ,weight per ,modulus of ,compression ,wood cubic foot1 rupture1 strength1 pounds 7#ae pounds per pounds per moisture7 square inch square inch ---------------------------------------- ---------------------------------------- ------------------ ,hickory #ej #af1cjj #g1cjj ,white ,oak #df #ab1jjj #e1ijj ,ash #dj #ab1gjj #f1jjj ,walnut #ch #aa1ijj #f1ajj ,spruce #bg #g1ijj #d1cjj ,white ,pine #bi #g1fjj #d1hjj ---------------------------------------- ---------------------------------------- ------------------ ,a frequently asked question is3 8,why is not aluminum or some similar metal1 substituted for wood80 ,wood1 particularly spruce1 is preferred because1 weight considered1 it is much stronger than aluminum1 and this is the lightest of all metals4 ,in this connection the following table will be of interest4 ---------------------------------------- ---------------------------------------- ---------------------------------------- ------ ,weight in ,tensile ,compression ,material cubic feet1 strength per strength per sq4 in pounds sq4 in pounds pounds ---------------------------------------- ---------------------------------------- ---------------------------------------- ------ ,spruce #bg #g1ijj #d1cjj ,aluminum #afb #ae1jjj #ab1jjj ,brass 7sheet7 #eaj #bj1jjj #ab1jjj ,steel 7tool7 #dij #ajj1jjj #fj1jjj ,nickel steel #dhj #ajj1jjja ,copper 7sheet7 #edh #cj1jjj #dj1jjj ,tobin bronze 7,turnbuckles7 444 #hj1jjj ,monel metal #edj #ij1jjj #cj1jjj ---------------------------------------- ---------------------------------------- ---------------------------------------- ------ ,wood4--,present practice in airplane construction is to use wood for practically all framing1 in other words1 for all parts which take pressure or compression4 ,although wood is not as strong for its size as steel and therefore offers more air resistance for the same strength yet the fact that frame parts must not be too spindling1 in other words1 that they must have a certain thickness in proportion to their unsupported length1 has led to the use of wood in spite of the greater strength of steel4 ,some airplanes1 however1 as the ,sturtevant1 are constructed with practically a steel framing4 ,it should be borne in mind that any piece or kind of wood will not answer for framing1 and more especially for repair parts4 ,there is a tremendous difference in the strength and suitability among different woods for the work4 ,for instance1 a piece of wood of cross or irregular grain1 one with knots1 or even one which has been bored or cut or bruised on the outside1 may have only half or less the strength of the original piece4 ,air drying doubles the strength of green wood1 proper oven drying is better yet4 ,notice how the ends of each piece are ferruled1 usually with copper or tin4 ,this is to prevent the bolt pulling out with the grain of the wood1 and also prevents splitting and end checking and gives a uniform base on which the pressure comes4 ,it is generally advised not to paint wood as it tends to conceal defects from inspection4 ,so varnish only4 ,wrapping wooden members with linen or cord tightly and doping this1 both to make waterproof and to still further tighten1 increases the resistance to splitting4 ,the absence of warping tendencies determine often what wood to choose4 ,the selection of lumber and detection of flaws is a matter of experience and should be cultivated4 ,it is1 however1 nothing more than the extension of the knowledge that leads a man to pick out a good baseball bat4 ,woods4--#a4 ,spruce4--,should be clear1 straight-grained1 smooth and free from knot holes and sap pockets1 and carefully kiln-dried or seasoned4 ,it is about the lightest and for its weight the strongest wood used4 ,it is ordinarily used as a material for spars1 struts1 landing gear1 etc41 as it has a proper combination of flexibility1 lightness and strength4 #b4 ,white ,pine4--,a very light wood used for wing ribs1 and small struts4 #c4 ,ash4--,springy1 strong in tension1 hard and tough1 but is considerably heavier than spruce4 ,used for longerons1 rudder post1 etc4 #d4 ,maple4--,used for small wood details1 as for blocks connecting rib pieces across a spar or for spacers in a built-up rib4 #e4 ,hard ,pine4--,tough and uniform and recommended for long pieces1 such as the wooden braces in the wings4 #f4 ,walnut1 ,mahogany1 ,quarter-sawed ,oak4--,the strength1 uniformity1 hardness and finishing qualities make these woods favorites for propeller construction4 #g4 ,cedar ,wood4--,is used occasionally for fuselage coverings or for hull planking in hydroplanes as it is light1 uniform and easily worked4 ,veneers1 or cross-glued thin layers of wood1 are sometimes used for coverings4 ,laminated or built-up wooden members have been much used for framing and for ribs and spars4 ,the engine bearers are always of wood on account of vibration and are also laminated4 ,in lamination the wooden strut is built up of several pieces of wood carefully glued together4 ,the grains of the different layers run in different directions1 consequently a stronger and more uniform stick often is secured4 ,the objection to laminated pieces comes from the weather causing ungluing4 ,laminated pieces should be wrapped in linen or paper and freshened with paint or varnish from time to time4 ,forms4--,attention should be called to the hollowed form of many of the wooden members4 ,in any beam or strut1 material at the center of the cross-section is of far less value in taking the load than the material away from the center4 ,therefore1 to secure greatest strength with least weight1 it is permissible to lighten wooden members if done understandingly4 ,steel4--,there is a tremendous difference in the strength1 wearing and other desirable qualities among different steels and irons4 ,for airplane work none but the best qualities are allowed4 ,for this reason the use of ordinary iron bolts 7as stove bolts7 or metal fastenings or wire not standardized and of known qualities should not be permitted4 ,the airplane is no stronger than its weakest fitting4 ,this does not mean that the hardest and strongest steel must necessarily be used1 as ease of working and freedom from brittleness may be just as important qualities1 but the steel on all metal fittings should be of high-grade uniform stock4 ,a ductile1 not too easily bent1 mild carbon steel is usually recommended for all steel plate1 clips1 sockets and other metal parts4 ,if any parts are required to be tempered or hardened it must be remembered that they become brittle and can not afterward be bent without annealing or softening4 ,tool or drill steel is a name given to uniform or rather reliable grades of steel adapted to heat treatment as tempering or annealing4 ,often the bolts1 clips1 nuts1 pins1 devices and other fittings are of special heat-treated nickel steel which must not be heated locally for bending or for attachment4 ,such work seriously weakens the steel4 ,the steel is often copper-or nickel-plated and enamelled to prevent rusting4 ,do not forget that the proper material may be twice as strong as other material which looks the same but which has not received special treatment4 ,wires4--,only the highest grade of steel wire1 strand and cord is allowable4 ,manufacturers1 as ,roebling of ,trenton1 ,n4 ,j41 manufacture special aviator wire and cord1 which is given the highest possible combination of strength and toughness1 combined with ability to withstand bending1 etc4 ,steel wire ropes for airplane work are divided into three classes as follows3 #a4 ,the solid wire #a wire 7as piano-wire grade7 and known as aviation wire4 #b4 ,the strand stay1 consisting either of #g or #ai wires stranded together and known as 8aviator strand40 ,flying and landing wires on ,curtiss4 #c4 ,cord or ,rope ,stay4--,seven strands twisted together forming a rope1 each strand being of #g or #ai wires and known to trade as aviator cord4 ,the wires are either tinned or galvanized as protection against rust1 etc4 ,ordinarily galvanizing is used1 but hard wires and very small wires are injured by the heat of galvanizing and they are therefore tinned4 ,no4 #a4 ,the single wire is the strongest for its weight4 ,single wires will not coil easily without kinking and are easily injured by a blow1 therefore their use is confined to the protected parts of the machine such as brace wires in the fuselage and in the wings4 ,the strand stay 7,no4 #b7 of #g or #ai wires is generally used for tension wires1 as it is more elastic 7can be bent around smaller curve7 without injury1 as the flying and landing wires on the ,curtiss4 ,the smaller strands usually have #g wires1 the larger ones #ai wires4 ,no4 #c4 ,the ,tinned ,aviator ,cord4--,the #g by #ai cord is used for stays on foreign machines4 ,it is #a times as elastic as a solid wire of the same material4 ,on the ,curtiss it is used for control wires4 ,for steering gear and controls extra flexible aviator cord is also recommended4 ,this has a cotton center which gives extra flexibility and is used for steering gear and controls4 ,it is #b times as elastic as a single wire4 ,although wire strands or cords are not quite as strong for the same size as a single wire they are preferred for general work1 being easier to handle and because a single weak spot in one wire does not seriously injure the whole strand4 ,especial care is necessary to avoid using common steel wires1 or strands which have a frayed or broken wire1 or wire that has been kinked and then straightened or wire that has been locally heated or wire that has been bruised4 ,all these factors weaken steel rope much more than is supposed ordinarily4 ,wire ,fastening or ,terminal ,connections4--,wire terminals are of four classes3 #a4 ,ferrule and dip in solder1 then bend back the end4 ,with or without thimble2 used on single wires or on strand2 #ej to #id per cent4 as strong as the wire4 #b4 ,thimble and ,end ,splicing4--,the splice must be long and complete4 ,used on cable2 #hj to #he per cent4 as strong as the strand2 breaks at last tuck in the splice4 #c4 ,socket4--,nearly #ajj per cent4 strong4 #d4 ,end ,wrap and ,solder4--,simple and serviceable2 not used for hard wire4 ,present practice is rather toward elimination of acid and solder1 imperfect bends1 flattening of cable on bends1 and toward care in avoiding all injury as kinking to wire1 strand and cord due to unskillful handling of material in the field4 ,other ,metals4--,other metals as aluminum1 brass1 bronze1 copper1 monel metal 7copper and nickel7 are used for certain airplane fittings for the reasons of lightness1 non-corrosive qualities1 or ease of bending1 etc4 ,the trouble with these metals is that they are not uniform and reliable in strength and in an important part the great strength combined with minimum weight given by steel is not equalled by any of these metals4 ,aluminum is used on the engine hood and also for control levers and for the backs of the seats4 ,in other words1 for parts and castings which require light metal construction1 but which are under no particular stress4 ,tin and copper are used for ferrules of wire joints and for tankage4 ,copper or brass wire are used for safety wires4 ,special ,tobin bronze is used for turnbuckles as the part must not only be strong but free from any tendency to rust4 ,monel metal 7nickel #fj per cent41 copper #ce per cent41 iron #e per cent47 is strong and has the special property of being acid- and rust-resisting4 ,it has been used for metal fittings and even for wires and for the water jacket of the motor4 ,until more strength tests show greater uniformity of strength1 it is to be recommended with caution4 ,in dealing with metals like steel1 it should be remembered that they are subject to crystallization and fatigue4 ,repeated jarring may cause a bar of steel to break easily at a particular point1 when the metal is said to have crystallized there4 ,fatigue of a metal may be defined as loss of springiness which may come from repeated bending and which lessens the strength of metal4 ,above all1 however1 corrosion of steel must be guarded against4 ,the above points should be clear1 as in airplane work you are dealing with a structure which is safe with perfect materials and workmanship4 ,the factor of safety1 however1 is not great enough to permit carelessness1 or defective material4 ,linen4--,the almost universal wing covering is fine1 unbleached ,irish linen1 stretched rather loosely on the wing frames and then treated with dope4 ,the linen used weighs #c to #d oz4 per square yard1 and should have a strength with the length of the cloth or 8warp0 of at least #fj lb4 per inch of width4 ,the strength in this direction is slightly greater than that taken crosswise of the cloth or on the filler or weft4 ,there is a gain of strength and tautness by varnishing or 8doping40 ,in general1 it is desirable to have wing material which will not sag easily and have the fabric yield rather than break4 ,this often reduces stress and saves complete failure4 ,dope4--,the linen must be coated with a more or less waterproof dope4 ,some form of cellulose acetate or nitrate with more or less softening material is used and to these some suitable solvent as acetone is added4 ,the cellulose acetate or nitrate in the dope acts as a waterproof sizing1 shrinks the cloth tight1 and prevents it from changing in tightness due to moisture4 ,spar varnish protects this layer from peeling and makes the wing more waterproof4 ,in service1 varnish or dope must be applied every few weeks4 ,the ,u4 ,s4 ,army practice calls for four coats of cellulose nitrate dope followed by two coats of spar varnish to prevent inflammability4 ,cellulose nitrate is more elastic and durable than the acetate but is also more inflammable4 ,commercial dopes with various desirable properties are3 ,cellon1 ,novavia1 ,emaillite1 ,cavaro1 ,titanine1 etc4 ,,footnotes3 #a ,but has very high elastic limit4 ,,chapter ,,viii ,,erecting ,,airplanes ,airplanes shipped from the manufacturer or from another field almost always suffer more or less from shipment or packing4 ,care must be exercised in unpacking in order not to do any more damage4 ,boxes should be placed with the part marked 8,top0 uppermost4 ,cables and wires must be handled carefully in order not to bend or twist them4 ,every bent or kinked wire or damaged turnbuckle must be replaced1 or at least brought to the attention of an inspector4 ,the order of erection is as follows3 #a4 ,assemble landing gear to fuselage and align landing gear before putting on main panels4 #b4 ,assemble tail4 #c4 ,assemble engine section and align before attaching main panels4 #d4 ,assemble main panels4 #a4 ,landing ,gear ,assembly to ,fuselage4--,the landing gear is assembled by mounting the wheels on the axle1 and bolting wheels in place4 ,the fuselage should now be elevated to receive the landing gear4 ,this may be accomplished in one of two ways--either by tackle or by shims and blocking4 ,for either method1 first connect up the tail skid4 ,this is accomplished by pinning up the front end of the skid to the spring-fitting1 and then pinning in the other end to the tail-post socket4 ,if block and tackle are used to raise the fuselage1 pass a line under the engine-bed supports or sills just to the rear of the radiator4 ,to this line attach hook of block4 ,to avoid damaging or crushing some part do not attach lifting device to any other point4 ,with the fuselage now resting on its attached tail skid1 lift the front end until the lower longeron clips clear the landing gear4 ,when the clips on the longerons line up with the clips on the ends of the struts of the landing gear the bolts are passed down through the holes thus aligned4 ,this places the nuts on the down side of the connection thus facilitating assemblies and inspection of connections4 ,the castellated nuts are then put on the bolts and drawn up tight1 until the drilled hole in the bolt is visible through the castle of the nut4 ,then insert cotter-pin and spread the two leaves backward over the nut4 ,this locks the nut in place4 ,when the landing gear has been completely assembled to the fuselage1 the tail of the machine should be elevated and supported by a horse and blocking until the upper longeron is level4 ,this can be determined by placing a spirit level on the upper longeron at the tail or on the two engine-bed sills in machines where these sills are parallel to the top longeron1 as in ,curtiss ,,jn-#d;,b4 #b4 ,horizontal ,stabilizer4--,after the upper longeron is levelled up1 the horizontal stabilizer is assembled to the tail of the fuselage4 ,the horizontal stabilizer is fastened by means of bolts in the top longeron and the tail post4 ,the nuts are all drawn up tight and cotter-pinned4 ,the vertical stabilizer is next erected in place4 #c4 ,vertical ,stabilizer4--,the vertical stabilizer is now fastened to the horizontal stabilizer1 first by means of the bolt which passes up through the forward part of the horizontal stabilizer and then by means of the flexible stay lines running from the top of the vertical stabilizer4 ,the forward bolt passes through the clip at the lower front point of the vertical stabilizer4 ,draw the nuts up tight and lock with cotter-pins4 ,flexible wire cables are attached to vertical stabilizer1 and turnbuckles are used to align and tighten cables4 ,the vertical stabilizer is further aided in its alignment by the bolt clip at its toe and by the double clip at its heel4 ,this rear double clip passes over the two bolts which are attached to the tail post and which hold down the horizontal stabilizer4 #d4 ,rudder4--,the control braces are first attached to the rudder4 ,these braces are so placed that the upper tips point toward the hinge line4 ,in this fashion the holes will match up4 ,the rudder is mounted on the tail post and vertical stabilizer by means of the hinges4 ,the hinge pins are inserted in the hinges1 and cotter-pins passed through the drilled holes in the bottom of the pins4 ,the cotter-pins should be spread backward as usual4 #e4 ,elevators or ,flaps4--,these are first equipped with the control braces which are also arranged so that the upper tips point toward the hinge line4 ,the elevators are mounted to the horizontal stabilizer by means of the hinges and hinge pins4 ,the hinge pins are kept in their bearings by the cotter-pins1 inserted through the drilled holes in the bottom of the hinge pins4 #f4 ,panel ,assembly4--,the panels are now to be assembled4 ,before the main panels can be connected to the fuselage1 the engine section panel must be erected4 ,engine ,section ,panel4--,the engine section struts are first set into place in their sockets on the engine section4 ,then the whole thing is lifted up to place and the four struts are set into their sockets on the upper longeron4 ,the bracing wires are attached and the engine section aligned by means of them 7see alignment74 #g4 ,main ,panels4--,the main panels are now to be assembled to the machine4 ,there are two methods for accomplishing this3 first1 assemble panels1 struts and wires1 before attaching to fuselage2 second1 assemble the upper plane to the engine section1 and complete assembly4 ,the first method is the most advantageous1 since it permits the setting of the main panels at the correct stagger and dihedral1 and does not require as much adjustment as the second method1 which will be omitted4 ,assembling ,panels ,together ,before ,fastening ,them to ,fuselage4--,all the main struts will be found to bear a number4 ,these numbers run from #a to #h1 on ,curtiss ,,jn-#d4 ,the numbers on the ,standard run from #a to #ab including the center section struts4 ,the method used in numbering the posts is as follows3 ,starting at post ,no4 #a1 with the outer post1 on the left-hand side of the pilot1 as he faces his direction of travel1 the posts are numbered successively from ,no4 #a to ,no4 #d2 ,nos4 #a and #b being on the left side and ,nos4 #c and #d being on the right side4 ,the rear posts are similarly numbered from ,no4 #e to ,no4 #h1 ,nos4 #e and #f being on the left and ,nos4 #g and #h being on the right4 ,this system of numbering does not include the engine section struts4 ,the plan shows the system graphically 7see ,fig4 #ci74 ,the system of marking also insures that the struts are not inverted in their sockets4 ,this is accomplished by painting the number on the strut1 so that when viewed from the pilot's seat1 all numbers can be read1 i4e41 the numbers are painted on that side of the strut intended to face the fuselage4 ,if a strut is inverted by mistake1 it can thus be quickly detected4 ,the procedure of assembling panels is as follows3 #a4 ,the upper left-wing panel is first equipped with mast1 by inserting the mast into its socket on the upper surface of the wing4 ,the mast wire is then connected up to the clips to the right and left of the mast4 ,adjust the tension in this wire1 by means of turnbuckles1 until the spar becomes straight4 #b4 ,stand the upper left-wing panel and lower left-wing panel on their 8leading0 or 8entering0 edges1 properly supporting the panels in cushioned blocks to prevent damage to the nose4 ,space the panels apart1 at a distance approximately equal to the length of the struts4 #c4 ,next connect up the diagonal cross wires4 ,these must be loosely connected up1 to permit the easy entering of the posts into the sockets4 ,the wires are connected before the posts or struts are set in place1 since with the latter in place1 the connecting of the wires to the lugs of the sockets is accomplished only with difficulty4 ,after these wires are thus connected1 insert the posts and bolts into place4 #d4 ,connect up closely the 8landing0 7single7 wires1 and 8flying0 7double7 wires of the outer bay to hold the wings together as a unit4 ,the outer bay is thus completely wired1 though but loosely4 #e4 ,the posts that are used for this left side are1 according to the diagram1 ,no4 #a1 ,no4 #b1 ,no4 #e1 ,no4 #f4 ,no4 #a is the outer front2 ,no4 #b is the inner front2 ,no4 #e is the outer rear2 ,no4 #f the inner rear4 #f4 ,the wings1 as above assembled1 are now erected to the fuselage4 ,extreme care should be exercised in transferring the wings to the fuselage1 not to strain or break them4 ,in carrying the wings1 use wooden boards placed under the wings1 and block up under the wing beams 7which can be easily located71 so that these take the strain of the load4 ,do not attempt handling assembled wings1 using the posts as carriers2 or by attachments to the trailing or leading edges4 ,the wings should be suitably supported temporarily by suitable sling at the outer upper post point 7not beyond this point7 or by a horse1 properly blocked under lower wing at outer lower post point 7not beyond this point7 during fitting of wing to machine4 ,the wings will have the approximate stagger if assembled as above1 since the posts are in place1 and the tension cross wires are adjusted to almost correct length when shipped4 ,insert the hinge pins through the hinges as now coupled up1 lower hinges first4 ,the machine is now ready for alignment1 perhaps the most important of the rigger's duties4 ,alignment of ,airplanes4--,the proper alignment of a machine largely determines the flying qualities of that machine4 ,the alignment of the fuselage should be done at the factory or in the repair shop4 ,however1 the alignment of the whole machine depends upon the correctness of the fuselage4 ,directions for aligning and checking fuselage are1 therefore1 given4 ,the order in which the different parts of a machine should be aligned is as follows3 #a4 ,alignment of landing gear4 #b4 ,alignment of center section4 #c4 ,alignment of leading edge4 #d4 ,getting both wings the same height4 #e4 ,dihedral angle1 if any4 #f4 ,alignment of trailing edge 7angle of incidence74 #g4 ,stagger4 #h4 ,droop4 #i4 ,tightening and safetying all wires4 #aj4 ,length of struts1 positions and fittings1 warp in planes4 #aa4 ,alignment of ailerons4 #ab4 ,alignment of stabilizer4 #ac4 ,alignment of elevator flaps4 #ad4 ,alignment of rudder4 ,the tail of the machine should be raised until the fuselage is nearly horizontal before starting the alignment4 #a4 ,alignment of ,landing ,gear4--,when a machine is being assembled1 it is easier to align the landing gear before the wings are put on4 ,take the weight off the landing gear by supporting the fuselage on sawhorses4 ,the axle should be parallel with the lateral axis of the machine4 ,the center of the axle should be directly under the center of the fuselage4 ,this can be secured by either of two methods3 7a7 ,by ,measuring ,cross ,distances4--,loosen and tighten the cross wires until the cross distances are exactly the same4 ,take all measurements from similar points on the fittings to which the wires are attached4 7b7 ,with ,level and ,plumb ,bob4--,level the fuselage crosswise4 ,mark the exact center of the fuselage and drop a plumb bob4 ,mark the exact center of the axle4 ,adjust the cross wires until the plumb bob is over the center of the axle4 ,tighten the wires until fairly tight1 and safety them4 #b4 ,alignment of the ,center ,section4--,when assembling a machine1 the center section should be aligned before the wings are put on4 ,when a machine is already assembled1 the first thing to do is to loosen all wires except the landing wires4 ,this is very important1 for if one wire is tightened against another wire1 an unnecessary and possibly a dangerous strain may be put upon some member4 ,the bracing wires connecting tops of center section struts should be tight enough to hold the shape of the center section when bracing wires are tightened up4 ,illustration3 ,,fig4 #ch4--;,center section and undercarriage alignment4 7a7 ,machines ,having ,no ,stagger4--,in machines having no stagger1 the struts of the center section should be perpendicular to the propeller axis4 ,as the upper longerons are usually parallel to the propeller axis1 they may be used as a base line4 ,align one side of the center section first1 then the other side1 and lastly the front4 ,from a point at the lower end of one of the front center section struts 7the center of a bolt head for example71 measure forward on the longeron a certain distance4 ,from the same point 7center of bolt head7 measure back on the longeron exactly the same distance4 ,move the upper end of the strut forward or backward by loosening one of the bracing wires and tightening the other1 until the distance from the two points on the longerons to some point on the center line at the top of the strut 7center of bolt head7 are exactly the same4 ,the strut will then be perpendicular to the propeller axis4 ,tighten both wires evenly until fairly tight4 ,measure the cross distances 7the diagonal distances between similar points at the upper and lower ends of the front and rear struts71 and align the other side of the center section until its cross distances are the same as those on the opposite side4 ,align the front of the center section by loosening one cross wire and tightening the other1 until one cross distance is exactly the same as the other cross distance4 7b7 ,machines ,having ,stagger4--,in machines having stagger1 the shape and position of the center section strut fittings usually determines the amount of stagger the machine was designed to have 7,fig4 #ch-;a74 ,the ,,jn-#d has #aj-;in4 stagger1 i4e41 a plumb line dropped from the leading edge of upper panel should be #aj-;in4 from leading edge of lower panel4 ,adjust the wires on one side of the center section until the struts and that side are in their correct positions as shown by the shape of the fittings4 ,tighten the wires1 measure the cross distances1 and adjust the wires on the other side of the center section until the cross distances are exactly similar to the first set4 ,a more accurate method is to drop a plumb line from the leading edge of the center section and adjust until the line is at the correct distance ahead of the point on the fuselage where the leading edge of the lower wing meets it4 ,this point may be determined by measuring the distance from the inside of the front hinge to the leading edge of the lower wing and then laying off this distance on the body from the front of the hinge on the lower longeron4 ,better still1 if the hinges are at the same distance from the leading edge on both top and bottom wings1 the plumb line may be dropped from the front side of the hinge on the center section and the stagger measured back to the hinge on the lower longeron 7,fig4 #ch-;b74 ,this has the advantage of setting the plumb line out far enough to clear the fuselage4 ,also the measurements are easily made4 ,next1 adjust the two front wires until one cross distance is exactly the same as the other cross distance 7,fig4 #ch-;c74 #c4 ,alignment of ,leading ,edge4--7a7 ,upper ,plane4--,the leading edges of the upper and lower planes of one wing should next be made perfectly straight4 ,by standing on a step ladder1 placed #ae to #bj ft4 to one side1 and sighting along the leading edge of the upper plane1 any bow or warp can be easily seen4 ,this should be straightened out by loosening or tightening the front landing wires4 ,the edge should be brought in exact line with the leading edge of the center section4 7b7 ,lower ,plane4--,after the leading edge of the upper plane has been made straight1 sight along the leading edge of the lower plane4 ,if there is no warp in the plane1 this edge should also be straight4 7c7 ,align the opposite wing in the same manner4 #d4 ,getting ,both ,wings the ,same ,height4--,place a small tack exactly in the middle of the leading edge of the center panel4 ,measure from this tack to similar points at the lower ends of the intermediate and outer struts 7,fig4 #ci74 ,make these distances the same on each side by raising or lowering one wing or the other1 or by raising one wing and lowering the other wing1 all the while keeping the leading edges of both wings perfectly straight4 #e4 ,dihedral4--,the method of setting the wings of a machine at a dihedral angle is as follows3 ,place two tacks in the leading edge of the upper plane1 one tack near the tip of each wing and exactly the same distance out from the tack in the center section4 ,stretch a string tightly between the two outer tacks1 until there is no sag in the string4 ,a dihedral angle of #agh means that each wing has been raised #a4 ,to set the wings of a machine at a dihedral angle of #agh for example3 7a7 ,find the natural sine of #a 7#j4jage74 7b7 ,multiply this by the distance in inches between the center tack and one of the outer tacks4 ,the result will give the rise1 in inches1 of the string over the tack in the center section4 ,raise the wings equally1 keeping the leading edges perfectly straight1 until the proper rise shows over the center section4 ,illustration3 ,,fig4 #ci4--;,alignment diagrams4 #f4 ,alignment of ,trailing ,edge 7,angle of ,incidence74--7a7 ,lower ,plane4--,the trailing edge should be brought parallel to the leading edge4 ,this can be done by bringing the rear spar in line with the leading edge4 ,stand squarely in front of the center of the machine #ae to #bj ft4 away4 ,sight under the leading edge of the lower plane2 move forward or backward until the fittings under the rear spar are just visible4 ,raise or lower the trailing edge by loosening or tightening the rear landing wires1 until all of the fittings on the rear spar appear equally under the leading edge4 7b7 ,upper ,plane4--,after aligning the trailing edge of the lower plane1 place a ladder in front of the center of the machine1 and sight under the leading edge of the upper plane4 ,if there is no warp in this plane1 the trailing edge should align with the leading edge4 ,the objection to this method is that since there are no fittings next the body on the rear spar1 there is room for considerable error in the angle of incidence4 ,reversing the process and finding the angle of incidence at each set of struts secures the alignment of the trailing edge and removes the liability to error4 ,to set wings at correct angle of incidence proceed as follows 7,fig4 #ci73 ,place the airplane in rigging position1 i4e41 level up the top longeron or engine bearers4 ,set the corner of the straight-edge against the center of the rear spar1 level up the straight-edge1 and measure from the top of the straight-edge to the center of the front spar or to the lowest point of the leading edge4 ,this must be done next the body and under each set of struts4 7,it is useless to make such a measurement between the struts because of possible warping of the wings47 ,unless the wings have a washout or washin the measurements must agree1 thus making the angle of incidence the same all along the wing4 ,then the trailing edge must necessarily be parallel to the leading edge4 #g4 ,stagger4--,the stagger should be the same all along the wing as it is for the center section4 ,with the machine in rigging position drop a plumb line from the leading edge of the upper wing in front of each set of struts4 ,the distance from the plumb line to the lower edge should equal the stagger4 ,if there is too much1 tighten the diagonal wire running from the lower rear socket to the upper front socket1 being sure that the other diagonal wire is loosened somewhat4 ,for too little stagger tighten the latter and loosen the former wire4 ,check up the dihedral and alignment of the trailing edges to see if these have been disturbed while setting the stagger4 ,if not1 the droop may be put in4 #h4 ,droop4--,to correct for the torque of the propeller1 one wing of a machine is slightly drooped4 ,in single-motored tractor types1 if the propeller turns to the right1 when looking from the rear1 the left wing is drooped1 and vice versa4 ,the outer rear landing wire of the wing to be drooped should be loosened until the trailing edge1 between the outer and intermediate struts1 appears to be about an inch 7for machines of not more than #ajj hp47 lower than the rest of the trailing edge4 ,the practice with the ,curtiss ,,jn-#d;,b is to loosen the inner rear landing wire on the left wing in4 and loosen the outer rear landing wire in4 after the angle of incidence and stagger have been adjusted so that corresponding wires on the right and left wings are the same length4 #i4 ,tightening and ,safetying ,all ,wires4--7a7 ,after the wing is drooped1 all flying wires should be tightened to the same tension1 and just taut enough to take out all sag4 7b7 ,next tighten all drift or cross wires between the front and rear struts to the same tension4 7c7 ,drift wires from the wings to the fuselage1 and from the wings to the landing gear1 if any1 should be tightened last4 7d7 ,safety all turnbuckles4 ,a wire too loose will vibrate when the machine is in the air4 ,the flying and drift wires should be so tightened that when they take the weight of the machine in the air1 there will be no sag in the landing wires4 #aj4 ,length of ,struts1 ,positions of ,fittings1 ,warp in ,planes4--,the above instructions are given for machines that are true1 that is1 machines having no bends1 warps1 or bows in the spars and leading or trailing edges4 7a7 ,similar struts should be of the same length4 7b7 ,similar fittings occupying similar positions should be spaced the same4 ,if difficulties are encountered in getting the measurements to tally1 check up the lengths of the struts and the positions of the fittings4 7c7 ,if the planes of a machine are warped1 the machine should be so aligned that the warp is equally divided between both planes4 #aa4 ,alignment of ,ailerons4--,before aligning ailerons1 place the shoulder yoke or wheel controlling the ailerons in the center of its path of movement4 7a7 ,trailing-edge ,ailerons4--,trailing-edge ailerons should be set inch lower than the trailing edge of the plane to which they are attached4 7b7 ,interplane ,ailerons4--,interplane ailerons should be set so that they are both in the same plane1 when in neutral position4 ,in machines having interplane ailerons1 nose heaviness and tail heaviness may be corrected by setting the trailing edges of the ailerons up or down4 ,the proper amount to raise or lower the trailing edges can be determined only by experimenting with each particular type of machine4 7c7 ,the control wires should be just tight enough to eliminate any lost motion4 #ab4 ,alignment of ,stabilizer4--,support the weight of the tail on the tail skid4 ,the rear edge of the stabilizer should be perfectly straight1 and should be parallel with lateral axis of the machine4 ,stand behind the center of the stabilizer1 and align its rear edge on the leading edge of the upper plane by sighting4 ,tighten wires and safety turnbuckles4 #ac4 ,alignment of ,elevator ,flaps4--,set the elevator control in its mid-position4 ,adjust the elevator control wires until the flaps are in their neutral position and both are in the same plane4 ,the wires should be just tight enough to eliminate any lost motion4 ,safety turnbuckles4 #ad4 ,alignment of ,rudder4--,set the rudder control 7wheel1 foot pedals1 or foot bar7 in its mid-position4 ,adjust the rudder control wires until the rudder is in its neutral position4 ,the control wires should be just tight enough to eliminate any lost motion4 ,safety the turnbuckles4 #ae4 ,general4--,all connections having been made1 carefully go over each shackle1 pin1 and turnbuckle1 and see that all pins are properly in place1 all nuts on bolts tight and all cotter-pinned4 ,try out all controls for action and freedom of movement4 ,see that no brace wires are slack1 yet not so taut that when plucked they 8sing40 #af4 ,overall ,adjustments4--,as a final check1 the following overall measurements should be taken 7see ,fig4 #ci74 ,the straight lines ,,ac and ,,bc should be equal to within in4 ,the point ,c is the center of the propeller1 or in the case of the pusher the center of the nacelle4 ,a and ,b are points on the main spar and must be at the same distance from the butt of the spar4 ,they must not be merely the sockets of the outer struts as these may not be accurately placed4 ,,ac and ,,bc must be taken from both top and bottom spars2 two measurements on each side of the airplane4 ,similarly ,,fd and ,,fe should be equal to within in4 ,f is the center of the fuselage or rudder post4 ,d and ,e are points marked on both top and bottom rear spars just as ,a and ,b were marked on front spars4 ,if these measurements are not correct1 it is probably due to some of the drift or antidrift wires being too tight or too slack4 ,these must then be located and corrected4 ,,wing ,,covering ,,and ,,patching ,the wings are covered with best quality ,irish linen which must have a tensile strength of at least #ej lb4 per inch width1 undoped1 and #gj lb4 when doped4 ,the linen strips are sewed together on a sewing machine in such a way that when folded together they form a sort of bag which just slips over the wing frame4 ,the seams then run diagonally across the wing4 ,the bag is stretched up loosely and tacked temporarily along the leading edge4 ,the edges are folded under a little and sewed together along the leading edge of the wing and the temporary tacks are removed4 ,to hold the covering up to the ribs1 thread is looped through from one side of the panel to the other around the ribs4 ,the rough surfaces made by the thread along the ribs and the edges are covered over with strips of linen pasted on with dope4 ,to make a smooth job1 the edges of these strips are frayed out in4 ,three or more coats of dope are applied and rubbed down after each coating is dry4 ,this is then covered over with one or two coats of varnish to make it more weatherproof and smooth4 ,varnish also prevents the dope from peeling off4 ,dope shrinks the linen and makes it fit up tight to the framework4 ,breaks in the fabric are patched by first removing the dope around the break with dope remover and then sticking on a patch with dope4 ,this is applied with a rag instead of a brush in order to prevent the patch from becoming white4 ,ten to sixteen coats of dope are then applied over the patch1 each coat being allowed to dry before the next is applied4 ,,faults ,,in ,,flight1 ,,due ,,to ,,improper ,,alignment ,,and ,,how ,,to ,,correct ,,them ,an airplane pilot may experience difficulty with the flying qualities of his machine4 ,consequently he should know something about the conditions which are responsible for the various kinds of unsatisfactory flying qualities which are more or less characteristic of airplanes4 ,in the chapter on 8,principles of ,flight0 the reader has been made acquainted with such terms as stability1 instability1 longitudinal stability1 etc4 ,for the purposes of rigging1 however1 it will be well to review these terms again4 ,stability is a condition whereby an object disturbed has a natural tendency to return to its first and normal position4 ,example3 a weight suspended by a cord4 ,instability is a condition whereby an object disturbed has a natural tendency to move as far as possible away from its first position1 with no tendency to return4 ,example3 a stick balanced vertically on your finger4 ,neutral stability is a condition whereby an object disturbed has no tendency to move farther than displaced by the force of the disturbance1 and no tendency to return to its first position4 ,now in order that an airplane may be reasonably controllable1 it is necessary for it to possess some degree of stability longitudinally1 laterally and indirectionally4 ,longitudinal stability is its stability about an axis transverse to the direction of normal horizontal flight1 and without which it would pitch and toss4 ,lateral stability is its stability about its longitudinal axis1 and without which it would roll sideways4 ,directional stability is its stability about its vertical axis1 and without which it would have no tendency to keep its course4 ,whenever an airplane does not fly properly1 aside from conditions arising from engine or propeller trouble1 either its longitudinal1 lateral1 or directional stability is affected4 ,when its longitudinal stability is affected we call this condition longitudinal instability2 likewise1 regarding lateral stability and directional stability1 referring to these conditions respectively as lateral and as directional instability4 ,the effect of alignment errors will be treated under the foregoing respective heads4 ,alignment ,errors1 ,longitudinal4-- #a4 ,the ,stagger ,may ,be ,wrong4--,the top surface or wing may have drifted back a little owing to some of the wires1 probably the incidence wires1 having elongated their loops or having pulled the fittings into the wood4 ,if the top surface is not staggered forward to the correct amount1 then consequently the whole of its lift is too far back1 and it will then have a tendency to lift up the tail of the machine too much4 ,the airplane will then be said to be nose-heavy4 ,a -in4 error in the stagger will make a very considerable difference in the longitudinal stability4 #b4 ,the ,angle at ,which the ,main ,surfaces ,are ,set ,relative to the ,fuselage ,may ,be ,wrong4--,this will have a bad effect especially in the case of an airplane with a lifting tail plane or horizontal stabilizer4 ,if the angle of incidence is too great1 the machine will have a tendency to fly 8tail-high40 ,if the angle is too small the airplane may have a tendency to fly 8tail-down40 #c4 ,the ,fuselage ,may ,have ,become ,warped ,upward or ,downward4--,this would give the tail plane or horizontal stabilizer an incorrect angle of incidence4 ,if it has too much angle1 it will lift too much1 and the airplane will be 8nose-heavy40 ,if it has too little angle1 it will not lift enough and the airplane will be 8tail-heavy40 #d4 ,the ,tail ,plane ,may ,be ,mounted upon the ,fuselage at a ,wrong ,angle of ,incidence4--,if this condition exists1 it must be corrected by making a change at the fittings4 ,if nose-heavy1 the tail plane should be given a smaller angle of incidence4 ,if tail-heavy1 it should be given a greater angle of incidence2 but care should be taken not to give it too great an angle1 because the longitudinal stability entirely depends upon the tail plane being set at a smaller angle of incidence than is the main surface1 and if that difference is decreased too much1 the airplane will become uncontrollable longitudinally4 ,sometimes the tail plane is mounted on the airplane at the same angle as the main surface1 but it actually engages the air at a lesser angle1 owing to the air being deflected downward by the main surfaces4 ,alignment ,errors1 ,lateral4--,the machine manifests a tendency to fly one wing down4 ,the reason for such a condition is a difference in the lifts of the right and left wings1 assuming the motor torque is already taken care of by washout4 ,that may be caused as follows3 #a4 ,the ,angle of ,incidence of ,one ,wing ,may ,be ,wrong4--,if it is too great1 it will produce more lift than on the other side of the airplane2 and if too small1 it will produce less lift than on the other side--with the result1 in either case1 the airplane will try to fly one wing down4 #b4 ,distorted ,surfaces4--,if some part of the surface is distorted1 the lift will not be the same on both sides of the airplane1 which1 of course1 will again cause it to fly one wing down4 #c4 ,the ,ailerons ,may ,be ,set ,slightly ,wrong4--,this may be due to one control cable being longer than the other1 or one of the aileron horns being bent or twisted4 ,this condition can easily be detected by setting the aileron control--in neutral and checking up the position of the ailerons4 ,alignment ,errors1 ,directional4--,if there is more resistance on one side of the airplane than on the other the airplane will1 of course1 tend to turn to the side having the most resistance4 ,this may be caused by the following conditions3 #a4 ,the ,angle of ,incidence of the ,right and ,left ,surfaces ,may ,be ,unequal4--,the greater the angle of incidence1 the greater the resistance4 ,the less the angle1 the less the resistance4 #b4 ,if the ,alignment of the ,fuselage1 ,vertical ,stabilizer1 the ,struts or ,stream-line ,wires ,is ,not ,absolutely ,correct4--,that is to say1 if they are turned a little to the right or left instead of being in line with the direction of flight--then they will act as a rudder and cause the airplane to turn off its course4 #c4 ,if ,any ,part of the ,surface ,is ,disturbed ,it ,will ,cause the ,airplane to ,turn off ,its ,course4--,if1 owing to the leading edge1 spars1 or trailing edge becoming bent1 curvature is spoiled1 that will result in changing the amount of resistance on one side of the airplane1 which will then develop a tendency to turn off its course4 ,additional ,flight ,defects4--,in addition to the foregoing the following conditions may also exist which cause trouble when flying as well as when landing3 ,airplane ,climbs ,badly4--,such a condition1 apart from engine or propeller trouble1 is probably due to excess resistance somewhere4 ,flight ,speed ,poor4--,this condition apart from engine or propeller trouble1 is probably due to 7#a7 distorted surfaces1 7#b7 wrong angle of incidence1 or 7#c7 dirt or mud1 resulting in excessive skin friction and weight4 ,inefficient ,control4--,this is probably due to 7#a7 wrong setting of the control surfaces1 7#b7 distortion of control surfaces1 or 7#c7 control cables being badly tensioned4 ,will ,not ,taxi ,straight4--,if the airplane is uncontrollable on the ground it is probably due to 7#a7 alignment of the undercarriage being wrong1 7#b7 unequal tension of shock absorbers1 7#c7 tires unequally inflated1 7#d7 axle bent1 7#e7 tight wheel and axle1 7#f7 loose spokes causing wheel to wobble4 ,,chapter ,,ix ,,truing ,,up ,,the ,,fuselage ,before an airplane is assembled for the first time after leaving the factory1 and especially after it has made its first few 8breaking-in0 flights1 the fuselage or basic framework should be carefully examined and checked up4 ,this is done in order to determine whether or not the fuselage became distorted from rough usage during shipment 7which is always likely7 or from taking sets due to the flying stresses to which it was subjected for the first time during the 8breaking-in0 flights4 ,it frequently happens that rough landings and 8stunt0 flying cause distortions of the fuselage frame and other parts of the airplane so that it is very necessary to make a careful inspection immediately after to ascertain not only what twists1 bows and stretching of vital parts have resulted1 but also to detect fittings1 wires1 etc41 which may have been pulled loose or broken4 ,the extreme importance of having your airplane adjusted correctly and carefully1 and to know that it is in the proper condition can not be reiterated too often4 ,and1 since the fuselage is the foundation from which1 so to speak1 the entire apparatus is built up1 it is doubly important that it should always be in correct adjustment4 ,when the fuselage is built in the factory it is placed on a long table whose surface is perfectly horizontal and which has metal strips inlaid4 ,this table in reality is a big face plate especially arranged1 as described1 for fuselage truing in the factory4 ,the fuselage1 of course1 has had none of its coverings applied when it is placed on the table1 nor are the accessories such as controls and engine in place4 ,on this table then the builders begin to do the necessary adjusting and this is no simple or quick job4 ,working from a perfectly smooth horizontal surface it is1 of course1 easy to detect warpings1 twists1 etc41 of the framework4 ,these are first remedied by tightening or loosening of cross wires1 etc41 as the case may be4 ,then1 when the fuselage is reasonably square and level1 lengthwise and crosswise1 as determined by the eye1 check measurements are taken by rule1 trams and level and final adjustments made to bring the various parts in final proper relation to one another4 ,for instance1 the rudder post must be perfectly vertical1 as determined by a plumb line1 when the engine bearers or the top longerons are level4 ,the various fittings such as those for horizontal and vertical stabilizers and the engine sections and side panels must all conform accurately to one another so that the airplane as a whole1 when it is assembled1 will not contain any inherent defects such as tail planes with slightly distorted angles of incidence1 left main panels ahead of right or over or under right main panels1 fittings so located that an initial strain must be imposed upon them by forcing them together1 etc4 ,after the fuselage has been lined up in the factory as described briefly above1 it is permitted to set for a week or so and then it is checked up again and such additional slight corrections made which would be necessitated by the sets which had occurred4 ,the additional fittings required are then applied and the fuselage finally covered and sent away to have the engine and instruments applied4 ,when checking and truing a fuselage on the flying field after the airplane has been assembled and flown the process is not quite so simple as when the fuselage is checked up and trued in the factory1 largely owing to the lack of ideal factory facilities and also because so many fittings1 coverings1 etc41 are in the way which one must always be cautious about removing4 ,in general1 the method of procedure may be outlined as follows1 but it must be obvious that one can not in a series of written notes touch upon all the possible queries and combinations of fuselage distortions which may occur and the ways for detecting and correcting them4 ,a certain amount of experience in the field accompanied with some fixed habits of inspection1 and everlasting curiosity about the perfections of your machine1 and a willingness and readiness always to pitch in and help correct the defects found1 will soon develop in you the ability to diagnose easily and quickly and remedy intelligently whatever trouble you may run across4 ,for satisfactory fuselage checking and truing let us say in the field shop1 a certain minimum equipment of tools is necessary4 ,this equipment is3 ,at least two sawhorses about #c to #d ft4 high for mounting the fuselage in flying position4 ,several wooden wedges 7show taper7 for easy adjustment of fuselage for cross and lengthwise level4 ,about #be yd4 of strong linen line for checking center lines4 #b carpenter levels about #b to #c ft4 long4 #d perfectly formed steel cubes about #a to #a in4 in size4 #a plumb bob4 #a small screw jack4 #a pair of wood clamps4 #a straight edge about #ab ft4 long4 ,several small ,crescent adjustable wrenches4 ,several pliers with wire-cutting attachment4 ,pins for manipulating turnbuckles4 #a steel tape4 #a foot rule1 #f ft4 long4 #a small brass hammer4 ,a small work bench equipped with a #c-;in4 or #d-;in4 vise4 ,the fuselage which is to be trued is mounted on the horse with the wedges between the top horse rails and the lower longerons4 ,these horses or trestles should be so arranged that about three-fourths of the fuselage toward the tail sticks out unsupported4 ,in this way it will take1 as near as possible1 its normal flying position4 ,it is always desirable1 in fact quite necessary1 especially when checking a fuselage for the first time1 to have the airplane's specifications as well as a detailed drawing of the fuselage and an assembly of the airplane as a whole available4 ,the reason for this1 of course1 is quite obvious4 ,the engine bearers and the top longerons are the basic parts from which the fuselage as a whole is lined up4 ,consequently the first thing which is done1 when inspecting the fuselage for alignment1 is to test the truth of these parts4 ,this is done by sighting the top longerons lengthwise to see if they are bowed downward1 upward1 inward or outward4 ,as near as possible the fuselage is made level on the trestles4 ,the steel blocks or cubes referred to in the tool list above are placed on the longerons and the straight edge and level placed on these1 first crosswise and then lengthwise4 ,a string is stretched over the top of the fuselage touching the top cross braces and brought as close as possible to the center of these pieces4 ,this string should stretch from the rudder post as far forward as possible4 ,then the cross wires or diagonal brace wires are sighted to see how close their intersections agree with this center-line string4 ,furthermore1 the level is placed on the engine bearers and they are tested for cross level and longitudinal level4 ,if the engine is mounted in place1 but one point on the bearers will be available for this purpose1 but the check should nevertheless be made4 ,it may also be found that the longitudinal level of the engine bearers can be tested from underneath by placing the steel cubes mentioned above on the top of the level and then holding the level up against the bottom of the bearers4 ,as a rule1 if the fuselage is warped it should be possible to detect this with the eye1 but when engine bearers are out of line this can only be detected with certainty by the use of the level4 ,let it be assumed that the fuselage is out of true4 ,the first parts to tackle are1 of course1 the engine bearers4 ,if they should not be in line they must first be brought so1 and afterward kept in this condition4 ,the diagonal wires at the front of the fuselage should be adjusted to make this correction4 ,if the bearers are badly out of line it will1 perhaps1 be wisest to remove the engine1 or at least loosen it up from the bearers before doing any adjusting for the reason that it may become strained by serious pulling on the bearers4 ,after the bearers are in place1 it will be safe to bolt the engine fast again4 ,with the engine bearers temporarily disposed of1 the fuselage proper is tackled4 ,here the first thing to do is to get the top surfaces of the longerons level crosswise4 ,use the spirit level and the two steel cubes mentioned in the tool list for this purpose4 ,start at the front of the fuselage in the cock pit4 ,adjust the internal diagonal wires until the level bubble is in its proper place4 ,then measure these first two sets of diagonal wires1 getting them of equal length4 ,continue this process throughout the length of the fuselage until the rear end is reached1 always working from the front4 ,lastly1 before proceeding to the next operation1 try the engine bearers for level again4 ,if out1 make the proper adjustments4 ,if the centers of the crosswise struts are not marked1 this should first be done before going further4 ,then stretch a string from ,no4 #a strut1 or as far forward as possible to the center of the rudder post4 ,all center points on the cross struts1 if the fuselage is true lengthwise1 should lie exactly on this string4 ,if not1 adjust the horizontal diagonal wires1 top and bottom1 working from the front1 until the center-line points all agree4 ,always check by measuring diagonal wires which are mates4 ,these should be of equal length4 ,if not1 some wire in the series may be overstressed4 ,in order to pull the center points on the cross struts over1 always stop to analyze the situation carefully1 determining which are the long diagonals and which the short ones from the way the fuselage is bowed4 ,then shorten the long ones and ease off on the short ones1 being careful never to overstress any of the wires4 ,the last thing to do is to bring the longerons or the center line of the fuselage into level lengthwise4 ,for this purpose a long straight-edge1 the two cubes1 and a spirit level are of advantage1 although simply stretching a string closely over the top of the longeron may suffice4 ,then as in the case of removing a crosswise bow in the fuselage1 here too1 we manipulate the outside up and down diagonal wires in bringing the top longerons into their proper level position lengthwise1 always working from the front4 ,after all this is done it is well to make some overall checks with steel tape or trams to see how various fittings located according to the drawings1 agree with one another4 ,since there is a right and a left side1 distance between fittings on these sides may be compared4 ,and1 finally1 the engine bearers should be tried again4 ,in short no opportunity should be neglected to prove the truth of the fuselage as a whole and in detail4 ,it might be pointed out that an excellent time to check the fuselage is when engine is being removed or changed4 ,in fact this time in general is a good one to give the airplane as a whole1 a careful inspection4 ,after all the necessary corrections have been made and all the parts of the fuselage brought into correct relation with one another1 the turnbuckles are safety wired and then served with tape to act as a final protection4 ,the linen covering is reapplied if it had previously to be removed and the level1 empennage wires1 panels etc41 are placed in position and aligned as pointed out in the notes on assembly and alignment4 ,,chapter ,x ,,handling ,,of ,,airplanes ,,in ,,the ,,field ,,and ,,at ,,the ,,bases ,,previous ,,to ,,and ,,after ,,flights ,no unimportant part of the operation and maintenance of airplanes is their handling in the field1 and at the various bases previous to1 between1 and after flights4 ,this phase of the entire subject contemplates the transportation of airplanes in knockdown condition either by railway or truck1 their unloading and unpacking1 to a certain extent their assembly1 their storage in hangars and sheds1 their storage and disposition in the open1 their disassembling and packing for transportation1 etc4 ,the ,unloading and ,unpacking of ,airplanes4--,the personnel required to unload an airplane properly boxed and crated from a railway car1 is #ae men and two non-commissioned officers4 ,the tools needed for this purpose are3 #a ax4 #b crowbars4 #f lengths of iron pipe about #b in4 in diameter1 #c ft4 long4 #f lengths of iron pipe about #b in4 in diameter1 #d ft4 long4 #ajj ft4 manila rope1 #a in4 in diameter4 ,a regular flat-bed moving truck or ordinary truck with a flat-bed trailer should be provided for handling the machine from the car to the field erecting shop4 ,airplanes are usually shipped in automobile cars with end doors or gondola cars4 ,after opening doors of cars1 examine and inspect all crates and boxes carefully to see that they are all there in accordance with the bill of loading or shipping memorandum1 as well as to see that they are in good condition4 ,if any boxes are found damaged1 they should not be removed from the car without first reporting the fact to the receiving officer4 ,next1 all cleats and bracing should be removed4 ,the crate containing the fuselage and engine should1 if possible1 be unloaded first4 ,the heavy end where the engine is fixed should be lifted up1 have #b-;in4 pipe rollers put underneath and manipulated into the truck which has been backed up against the car door so that this heavy end1 when finally placed1 will rest on the body of the truck as far forward as possible4 ,next lash the front end of the box securely to the truck4 ,should it happen that the fuselage crate is so located in the car that the light end must of necessity emerge first through the door1 then this end may be run on to a truck and the crate removed from the car with the heavy end adequately supported by sufficient help4 ,another truck is then backed up against the rear of the first one which has been moved into the clear1 and the heavy end of the fuselage crate brought to rest as far forward as possible in the second truck4 ,it is then secured and the first truck released4 ,after the box is properly lashed by means of the manila rope1 a man should be placed on each side of it to watch and see that the lashings do not loosen and the box shift in transit4 ,trucks should be driven slowly1 especially over rough ground1 tracks1 etc4 ,in addition to the fuselage crate it may also be possible to load the panel crates on this same truck1 but as a rule it is better to load these on a second truck4 ,common sense goes a long way in transporting aircrafts by motor trucks4 ,unloading of the crates is done with the use of skids applied to the rear of the truck and secured so as to form a sort of an inclined plane down which to slide the boxes on the pipe rollers to the ground4 ,these skids should be at least #d in4 by #d in4 by #f ft4 and made of strong wood4 ,the rear end of the crate may be brought to the ground1 rested there1 and the truck moved forward slowly until the entire length rests on the ground4 ,care must be used not to jolt or drop this box at any stage whatsoever4 ,when uncrating the fuselage1 remove the top and both ends of the box4 ,fold both sides of box flat down on ground and use same for assembling machine4 ,the wing boxes should have the tops removed and planes lifted out in that manner4 ,next1 the airplane is assembled in accordance with instructions already given4 ,the ,dismantling and ,loading of ,airplanes4--,when airplanes are to be prepared for shipment by motor truck or railway1 they should1 of course1 be taken down and crated similar to the way they were shipped from the factory4 ,the order in which this is done should be as follows3 ,remove propeller4 ,unfasten control wires4 ,unfasten main planes from fuselage and dismantle on ground4 ,remove tail surfaces4 ,unless machine is to be placed in box1 landing gear and tail skid should remain attached to fuselage4 ,if the machine is crated it should be handled when shipped the same as described above4 ,if1 however1 it is to be loaded without being crated1 then the following procedure should be observed4 ,using two planks1 #b in4 by #ab in4 by #ah ft4 long for runway from ground into car1 load machine into car1 engine first4 ,block wheels to prevent machine shifting4 ,secure fuselage1 tail end1 to the floor of the car by means of ropes passed over the fuselage and fastened to the floor with cleats4 ,the wings should be crated against the sides of car and secured by wires1 ropes or canvas strips4 ,all boxes should be marked with name of organization1 destination1 weight1 cubic contents1 hoisting centers1 number of box1 8,this ,side ,up10 etc4 ,a shipping memorandum should always be made out and mailed to destination when shipment goes forth4 ,storing of ,airplanes and ,parts at ,bases and in ,fields4--,airplanes when not in active flying duty are stored in hangars or sheds especially adapted to house them4 ,under certain conditions it is necessary to store them in the open4 ,in each case particular precautions should be observed in order not to subject the machines to unnecessary wear and tear4 ,since moisture is one of the airplanes' worst enemies in that it deteriorates the weatherproofing and the fabric1 distorts and otherwise injures the wooden parts of the machines and worst of all1 rusts the metal parts1 the first consideration for proper storage facilities should be the absence of moisture4 ,next1 extreme heat and cold are a menace to airplanes4 ,the temperature of the air surrounding them while in storage should be regulated as much as possible4 ,under shelter1 especially when the machine is to be out of active service for #dh hr4 or more1 the entire machine should be raised off the ground a few inches so that the wheels are free and the flexible connections released4 ,this is done by the points where the undercarriage struts meet the skids4 ,furthermore1 the wings might well be supported and the weight thus taken off the landing wires1 and hinge connections by placing padded trestles underneath the wing skids4 ,care should be exercised that dirt1 grease1 water1 etc41 does not accumulate in any part of the airplane4 ,furthermore1 all water should be drained from the radiator and gasoline from the gasoline tank4 ,the propeller should be placed in a vertical position and covered with a weatherproof cloth4 ,the engine cockpit and instruments should all be covered and the magneto should be enclosed in a thick layer of felt or cotton waste4 ,if any fluid is apt to freeze1 and oil will freeze in temperatures low enough1 it should be carefully drained4 ,when spare parts such as wings1 struts1 fuselages1 etc41 are stored1 the same general precautions outlined above should be observed4 ,spare planes particularly should be placed in such a manner that their weight is evenly supported4 ,never should planes of any kind be laid flat on the ground4 ,they should always stand edgewise1 with the leading edge down1 supported several inches off the ground on blocks or boards evenly spaced4 ,one plane must not be allowed to lean against another4 ,in fact1 the best way is to suspend planes by means of canvas slings hung from overhead4 ,within the loop of the slings there must be a batten about #b in4 wide4 ,all parts of an airplane subject to attack by rust should be kept well coated with grease or oil4 ,periodically the entire machine should be wiped by means of clean1 dry cheese cloth or selected cotton waste4 ,engines which are in stored planes or which have been set aside for future use should be turned over by hand daily4 ,it will sometimes be impossible for airplane sheds or hangars to be brought up to the front on service1 hence1 airplanes must be prepared to remain in the open4 ,when this is the case they should be placed to the leeward of the highest hedge available1 a clump of trees1 a building1 a bank1 a knoll1 or hill1 etc4 ,they should be sunk as low as possible by digging a trench for the wheels and undercarriage4 ,the nose of the plane should1 of course1 first be run into the wind1 and then the wings and the tail pegged down with ropes1 particularly if there is any chance of a wind starting up4 ,the engine1 propeller1 instruments1 and cockpit should be covered over with a waterproof cloth and great care taken to protect the propeller from the sun1 for it will surely warp if not cared for properly4 ,at night in cold or wet weather the magneto should be packed round with waste and water in the radiator drained4 ,while machines are stored in the open1 the necessity of wiping them to keep them moisture and dirt free is all the more urgent and should be pursued with doubled energy4 ,,chapter ,,xi ,,inspection ,,of ,,airplanes ,mechanics in charge of airplanes1 who are primarily responsible for their safety while in their care1 should constantly think of new methods for insuring greater safety and reliability4 ,they should invariably bring any fresh points they think of to the attention of their ,flight ,commander1 in order that the rest of the ,corps may benefit by them4 ,they should always try to find out the cause of anything wrong1 and inform the officer in charge of the machine of their opinion4 ,they should bear in mind any particular incidents which may have happened to their machine while under their charge during each flight1 and be on the lookout for signs of stresses that may have occurred to the machine in consequence of these incidents4 ,for example1 a steep spiral may cause side strains on the engine bearers2 a flight in bad weather may cause bending stresses on the longitudinal members of the body1 besides stretching the landing and flying wires4 ,no part of a machine can be safely overlooked1 and good mechanics will always be seeking for the possible cause of accidents and bringing them to the notice of the officer in charge of the machines4 ,during all inspections the following matters of detail deserve particular attention3 ,look out for dirt1 dust1 rust1 mud1 oil on fabric4 ,cleanliness is the very first consideration4 ,give the control cables particular attention4 ,these should not be too tight1 otherwise they will rub stiffly in the guides4 ,the hand should be passed over them to detect kinks and broken strands4 ,they should be especially well examined where they run over pulley4 ,don't forget the aileron balance wire on the top plane4 ,see that all wires are well greased and oiled1 and that they are all in the same tension4 ,when examining wires1 be sure to have machine on level ground as otherwise it may get twisted1 throwing some wires into undue tension and slackening others4 ,the best way1 if time is available1 is to jack the airplane up into 8flying position40 ,if a slack wire is found1 do not jump to the conclusion that it must be tensioned4 ,perhaps its opposite wire is too tight1 in which case it should be slackened4 ,carefully examine all wires and their connections near the propeller1 and be sure that they are snaked around with safety wire1 so that the latter may keep them out of the way of the propeller if they come adrift4 ,carefully examine all surfaces1 including the controlling surfaces1 to see whether any distortions have occurred4 ,if distortions can be corrected by adjustment of wires1 well and good1 but if not1 matter should be reported4 ,verify the angles of incidence1 the dihedral angle1 the stagger1 and the overall measurements as often as possible 7at least once a week7 and correct as outlined in notes on assembly and adjustment of airplanes4 ,constantly examine the alignment and fittings of the undercarriage1 the condition of tires1 shock absorbers and the skids4 ,verify the rigging position of the ailerons and elevators4 ,constantly inspect the locking arrangements of the turnbuckles1 bolts1 etc4 ,learn to become an expert at vetting1 which means the ability to judge the alignment of the airplane and its parts by eye4 ,whenever you have the opportunity practice sighting one strut against another to see that they are parallel4 ,standing in front of the machine1 which in such a case should be on level ground1 sight the center section plane against the tail plane and see that the latter is in line4 ,sight the leading edge against the main spars1 the rear spars1 and the trailing edges1 taking into consideration the 8washin0 and 8washout40 ,you will be able to see the shadow of the spars through the fabric4 ,by practising this sort of thing you will1 after a time1 become quite expert1 and will be able to diagnose by eye faults in efficiency1 stability and control4 ,the following order should be observed in the daily and weekly inspections3 ,daily ,inspection4--,all struts and their sockets1 longerons1 skids1 etc4 ,all outside wires and their attachments4 ,all control levers or wheels1 control wires and cable and their attachments4 ,all splices for any signs of their drawing4 ,lift and landing gear cables or wires for any signs of stretching4 ,all fabrics1 whether on wings or other parts of the machine1 for holes1 cuts1 weak or badly doped places1 or signs of being soaked with gasoline1 and to see if properly fastened to wings1 etc4 ,all outside turnbuckles1 to see that they have sufficient threads engaged1 and that they are properly locked4 ,axles1 wheels1 shock absorbers1 and tires1 pumping the latter up to the correct pressure4 ,the seats1 both for passenger and pilot1 seeing that they are fastened correctly4 ,safety belts and their fastenings4 ,this examination should be carried out systematically in the following order3 7a7 ,lower wings1 landing gear complete1 tail planes with all wires attached to these tail skids and all attachments and rudder4 7b7 ,nacelle or fuselage1 bolts of lower plane1 all control levers and wires4 7c7 ,top wings1 wing flaps or ailerons and wires4 ,inspection after ,each ,flight4--,the landing gear1 tail skid and attachments and lift and drag wires for tautness4 ,the wheels1 after a rough landing1 for bent spokes1 uncovering them if necessary4 ,after flying is finished for the day1 wipe all oil off the planes as far as possible with a cloth or cotton waste4 ,weekly ,inspection4--,check over all dimensions1 span1 chord1 gap1 stagger of wings1 angles of incidence or set angle of wings and tail1 dihedral angle1 alignment of fuselage1 rudder1 elevators1 and the general truth of the machine4 ,examine the points of crossing of all wires to see that there are no signs of wear1 and that each wire is properly bound with insulating tape to prevent rubbing4 ,examine all places where wires cross the strut to see if the plates require renewal4 ,examine any control wires which are bound together1 and see that they are correct4 7,insulating tape should be used for this in preference to wires which are bound to slip and cause slack47 ,examine the wheels for bent or loose spokes1 uncovering if necessary4 ,examine all nuts and bolts of cotter-pin applications1 lock washers1 etc4 ,the following directions for inspection are given to the ,u4 ,s4 ,inspectors of ,airplanes3 ,inspection of ,cables4 ,are there any kinks in the cable8 ,are loops properly made8 ,are thimbles used in eyes8 ,are ends wrapped properly 7when wrapped splice is used1 wrap must be at least fifteen times the diameter of wire74 ,no splicing of the cable itself is permitted4 ,has acid struck cable during soldering8 ,are any of the strands broken8 ,are unwrapped ends stream-lined and show the result of skilled workmanship8 ,for ,roebling ,hard ,wire4 ,are there any file cuts or flaws to weaken it8 ,is loop well made8 ,is ferrule put on correctly8 ,are there any sharp bends or kinks8 ,are wires too loose or tight in machine8 ,fittings4 ,is workmanship good8 ,is material good8 ,are holes drilled correctly to develop proper strength8 ,are there any deep file cuts or flaws to weaken it8 ,is rivet or fastening wire put in properly8 ,are thimbles of large enough diameter8 ,turnbuckles4 ,any file cuts1 tool marks1 or flaws in shank or barrel8 ,are there too many threads exposed8 ,is turnbuckle of right strength and size to develop full strength of wire8 ,are shanks bent8 ,are threads on shank or in barrel well made8 ,is barrel cracked8 ,is turnbuckle properly wired8 ,inspection of ,linen4 ,all linen used in airplane construction should be of the following specifications3 ,free from all knots or kinks4 ,without sizing or filling4 ,as near white as possible4 ,weight1 between #c4e and #d4e oz4 per square yard4 ,strength as per ,government ,specifications4 ,inspection of ,wood4 ,all wood should be inspected before varnish is applied4 ,is grain satisfactory8 ,are there any sap or worm holes8 ,are there any knots that look as if they would weaken the member8 ,any brashiness8 ,any holes drilled for bolts or screws that would weaken the member8 ,any splits or checks8 ,are laminations glued properly8 ,are there any plugged holes8 ,any signs of dry rot8 ,inspection of ,metal ,fittings4 ,when fittings are copper plated and japanned the inspection should take place after the copper plating4 ,have fittings been bent in assembling8 ,does fitting show any defects that lessen its strength8 ,are holes drilled properly4 ,do fittings fit8 ,sheet aluminum should be inspected for defects such as cracks1 bad dents1 etc4 ,where openings occur in sheet aluminum the corners should be rounded1 allowing a good-sized radius4 ,directions for ,work4 ,before you start work on rigging you are advised as follows3 #a4 ,do not hurry about the work4 ,no rush jobs can be done in airplane rigging4 #b4 ,you are cautioned against leaving tools of any kind in any part of the airplane4 #c4 ,the bolts and their threads must not be burred in any way2 for this reason1 the use of pliers or pipe wrenches on bolts is very bad form4 #d4 ,start all turnbuckles from both ends every time they are connected up4 #e4 ,full threads must be had in every case to develop the full strength of a bolt and nut1 with turnbuckles at least turn on for a distance equal to three times the thickness of the shank4 #f4 ,lock with safety wires all turnbuckles and pins1 and cotter-pin every nut4 #g4 ,watch for kinking of wires and their rubbing around controls and wherever they may vibrate against one another4 #h4 ,all bolts and pins must have an easy tapping fit only2 do not pound them into position4 ,transcriber's ,notes pg #bb ,changed3 funished with dual control to3 furnished with dual control pg #hc ,changed3 rather than flying off in a straight ine to3 rather than flying off in a straight line pg #hf ,changed3 to get out of an immanent pancake to3 to get out of an imminent pancake