,,the ,,aeroplane ,,speaks ,by ,h4 ,barber 7,captain1 ,royal ,flying ,corps7 ,,dedicated ,,to ,,the ,,subaltern ,,flying ,,officer ,,motive ,the reasons impelling me to write this book1 the maiden effort of my pen1 are1 firstly1 a strong desire to help the ordinary man to understand the ,aeroplane and the joys and troubles of its ,pilot2 and1 secondly1 to produce something of ,,practical assistance to the ,pilot and his invaluable assistant the ,rigger4 ,having had some eight years' experience in designing1 building1 and flying aeroplanes1 ,i have hopes that the practical knowledge ,i have gained may offset the disadvantage of a hand more used to managing the 8joy-stick0 than the dreadful haltings1 the many side-slips1 the irregular speed1 and1 in short1 the altogether disconcerting ways of a pen4 ,the matter contained in the ,prologue appeared in the ,field of ,may #fth1 #acth1 #bjth1 and #bgth1 #aiaf1 and is now reprinted by the kind permission of the editor1 ,sir ,theodore ,cook4 ,i have much pleasure in also acknowledging the kindness of ,mr4 ,c4 ,g4 ,grey1 editor of the ,aeroplane1 to whom ,i am indebted for the valuable illustrations reproduced at the end of this book4 ,,contents ,,prologue ,,part ,i4 ,,the ,,elementary ,,principles ,,air ,,their ,,grievances ,,ii4 ,,the ,,principles1 ,,having ,,settled ,,their ,,differences1 ,,finish ,,the ,,job ,,iii4 ,,the ,,great ,,test ,,iv4 ,,cross ,,country ,,chapter ,i4 ,,flight ,,ii4 ,,stability ,,and ,,control ,,iii4 ,,rigging ,,iv4 ,,propellers ,v4 ,,maintenance ,,types ,,of ,,aeroplanes ,,glossary ,,the ,,aeroplane ,,speaks ,,prologue ,,part ,i4 ,,the ,,elementary ,,principles ,,air ,,their ,,grievances ,the ,lecture ,hall at the ,royal ,flying ,corps ,school for ,officers was deserted4 ,the pupils had dispersed1 and the ,officer ,instructor1 more fagged than any pupil1 was out on the aerodrome watching the test of a new machine4 ,deserted1 did ,i say8 ,but not so4 ,the lecture that day had been upon the ,elementary ,principles of ,flight1 and they lingered yet4 ,upon the ,blackboard was the illustration you see in the frontispiece4 8,i am the side view of a ,surface10 it said1 mimicking the tones of the lecturer4 8,flight is secured by driving me through the air at an angle inclined to the direction of motion40 8,quite right10 said the ,angle4 8,that's me1 and ,i'm the famous ,angle of ,incidence40 8,and10 continued the ,surface1 8my action is to deflect the air downwards1 and also1 by fleeing from the air behind1 to create a semi-vacuum or rarefied area over most of the top of my surface40 8,this is where ,i come in10 a thick1 gruff voice was heard1 and went on3 8,i'm the ,reaction4 ,you can't have action without me4 ,i'm a very considerable force1 and my direction is at right-angles to you10 and he looked heavily at the ,surface4 8,like this10 said he1 picking up the chalk with his ,lift1 and drifting to the ,blackboard4 8,i act in the direction of the arrow ,r1 that is1 more or less1 for the direction varies somewhat with the ,angle of ,incidence and the curvature of the ,surface2 and1 strange but true1 ,i'm stronger on the top of the ,surface than at the bottom of it4 ,the ,wind ,tunnel has proved that by exhaustive research--and don't forget how quickly ,i can grow6 ,as the speed through the air increases my strength increases more rapidly than you might think--approximately1 as the ,square of the ,speed2 so you see that if the ,speed of the ,surface through the air is1 for instance1 doubled1 then ,i am a good deal more than doubled4 ,that's because ,i am the result of not only the mass of air displaced1 but also the result of the ,speed with which the ,surface engages the ,air4 ,i am a product of those two factors1 and at the speeds at which ,aeroplanes fly to-day1 and at the altitudes and consequent density of air they at present experience1 ,i increase at about the ,square of the ,speed4 8,oh1 ,i'm a most complex and interesting personality1 ,i assure you--in fact1 a dual personality1 a sort of aeronautical ,dr4 ,jekyll and ,mr4 ,hyde4 ,there's ,lift1 my vertical part or ,,component1 as those who prefer long words would say2 he always acts vertically upwards1 and hates ,gravity like poison4 ,he's the useful and admirable part of me4 ,then there's ,drift1 my horizontal component1 sometimes1 though rather erroneously1 called ,head ,resistance2 he's a villain of the deepest dye1 and must be overcome before flight can be secured40 8,and ,i10 said the ,propeller1 8,i screw through the air and produce the ,thrust4 ,i thrust the ,aeroplane through the air and overcome the ,drift2 and the ,lift increases with the ,speed and when it equals the ,gravity of ,weight1 then--there you are--,flight6 ,and nothing mysterious about it at all40 8,i hope you'll excuse me interrupting10 said a very beautiful young lady1 8my name is ,efficiency1 and1 while no doubt1 all you have said is quite true1 and that1 as my young man the ,designer says1 ,you can make a tea-tray fly if you slap on ,power enough1' ,i can assure you that ,i'm not to be won quite so easily40 8,well10 eagerly replied the ,lift and the ,thrust1 8let's be friends4 ,do tell us what we can do to help you to overcome ,gravity and ,drift with the least possible ,power4 ,that obviously seems the game to play1 for more ,power means heavier engines1 and that in a way plays into the hands of our enemy1 ,gravity1 besides necessitating a larger ,surface or ,angle to lift the ,weight1 and that increases the ,drift40 8,very well10 from ,efficiency1 8,i'll do my best1 though ,i'm so shy1 and ,i've just had such a bad time at the ,factory1 and ,i'm terribly afraid you'll find it awfully dry40 8,buck up1 old dear60 ,this from several new-comers1 who had just appeared4 8,we'll help you10 and one of them1 so lean and long that he took up the whole height of the lecture room1 introduced himself4 8,i'm the ,high ,aspect ,ratio10 he said1 8and what we have got to do to help this young lady is to improve the proportion of ,lift to ,drift4 ,the more ,lift we can get for a certain area of ,surface1 the greater the ,weight the latter can carry2 and the less the ,drift1 then the less ,thrust and ,power required to overcome it4 ,now it is a fact that1 if the ,surface is shaped to have the greatest possible span1 i4e41 distance from wing-tip to wing-tip1 it then engages more air and produces both a maximum ,reaction and a better proportion of ,lift to ,drift4 8,that being so1 we can then well afford to lose a little ,reaction by reducing the ,angle of ,incidence to a degree giving a still better proportion of ,lift to ,drift than would otherwise be the case2 for you must understand that the ,lift-,drift ,ratio depends very much upon the size of the ,angle of ,incidence1 which should be as small as possible within certain limits4 ,so what ,i say is1 make the surface of ,infinite ,span with no width or chord1 as they call it4 ,that's all ,i require1 ,i assure you1 to make me quite perfect and of infinite service to ,miss ,efficiency40 8,that's not practical politics10 said the ,surface4 8,the way you talk one would think you were drawing ,l#djj a year at ,westminster1 and working up a reputation as an ,aeronautical ,expert4 ,i must have some depth and chord to take my ,spars and ,ribs1 and again1 ,i must have a certain chord to make it possible for my ,camber 7that's curvature7 to be just right for the ,angle of ,incidence4 ,if that's not right the air won't get a nice uniform compression and downward acceleration from my underside1 and the rarefied suction' area over the top of me will not be as even and clean in effect as it might be4 ,that would spoil the ,lift-,drift ,ratio more than you can help it4 ,just thrust that chalk along1 will you8 and the ,blackboard will show you what ,i mean40 8,well10 said the ,aspect ,ratio1 8have it your own way1 though ,i'm sorry to see a pretty young lady like ,efficiency compromised so early in the game40 8,look here10 exclaimed a number of ,struts1 8we have got a brilliant idea for improving the ,aspect ,ratio10 and with that they hopped up on to the ,spars4 8,now10 excitedly1 8place another ,surface on top of us4 ,now do you see8 ,there is double the ,surface1 and that being so1 the proportion of ,weight to ,surface area is halved4 ,that's less burden of work for the ,surface1 and so the ,spars need not be so strong and so deep1 which results in not so thick a ,surface4 ,that means the ,chord can be proportionately decreased without adversely affecting the ,camber4 ,with the ,chord decreased1 the ,span becomes relatively greater1 and so produces a splendid ,aspect ,ratio1 and an excellent proportion of ,lift to ,drift40 8,i don't deny that they have rather got me there10 said the ,drift1 8but all the same1 don't forget my increase due to the drift of the ,struts and their bracing wires40 8,yes1 ,i dare say10 replied the ,surface1 8but remember that my ,spars are less deep than before1 and consequently ,i am not so thick now1 and shall for that reason also be able to go through the air with a less proportion of ,drift to ,lift40 8,remember me also1 please10 croaked the ,angle of ,incidence4 8,since the ,surface has now less weight to carry for its area1 ,i may be set at a still lesser and finer ,angle4 ,that means less ,drift again4 ,we are certainly getting on splendidly6 ,show us how it looks now1 ,blackboard40 ,and the ,blackboard obligingly showed them as follows3 8,well1 what do you think of that80 they all cried to the ,drift4 8,you think you are very clever10 sneered the ,drift4 8,but you are not helping ,efficiency as much as you think4 ,the suction effect on the top of the lower ,surface will give a downward motion to the air above it and the result will be that the bottom of the top ,surface will not secure as good a ,reaction from the air as would otherwise be the case1 and that means loss of ,lift2 and you can't help matters by increasing the gap between the surfaces because that means longer ,struts and ,wires1 and that in itself would help me1 not to speak of increasing the ,weight4 ,you see it's not quite so easy as you thought40 ,at this moment a hiccough was heard1 and a rather fast and rakish-looking chap1 named ,stagger1 spoke up4 8,how d'ye do1 miss10 he said politely to ,efficiency1 with a side glance out of his wicked old eye4 8,i'm a bit of a knut1 and without the slightest trouble ,i can easily minimize the disadvantage that old reprobate ,drift has been frightening you with4 ,i just stagger the top ,surface a bit forward1 and no longer is that suction effect dead under it4 ,at the same time ,i'm sure the top ,surface will kindly extend its ,span for such distance as its ,spars will support it without the aid of ,struts4 ,such extension will be quite useful1 as there will be no ,surface at all underneath it to interfere with the ,reaction above40 ,and the ,stagger leaned forward and picked up the ,chalk1 and this is the picture he drew3 ,said the ,blackboard1 8,that's not half bad6 ,it really begins to look something like the real thing1 eh80 8,the real thing1 is it80 grumbled ,drift4 8,just consider that contraption in the light of any one ,principle1 and ,i warrant you will not find one of them applied to perfection4 ,the whole thing is nothing but a ,compromise40 ,and he glared fixedly at poor ,efficiency4 8,oh1 dear6 ,oh1 dear60 she cried4 8,i'm always getting into trouble4 ,what ,,will the ,designer say80 8,never mind1 my dear10 said the ,lift-,drift ,ratio1 consolingly4 8,you are improving rapidly1 and quite useful enough now to think of doing a job of work40 8,well1 that's good news10 and ,efficiency wiped her eyes with her ,fabric and became almost cheerful4 8,suppose we think about finishing it now8 ,there will have to be an ,engine and ,propeller1 won't there8 ,and a body to fix them in1 and tanks for oil and petrol1 and a tail1 and10 archly1 8one of those dashing young ,pilots1 what80 8,well1 we are getting within sight of those interesting ,factors10 said the ,lift-,drift ,ratio1 8but first of all we had better decide upon the ,area of the ,surfaces1 their ,angle of ,incidence and ,camber4 ,if we are to ascend as quickly as possible the ,aeroplane must be ,,slow in order to secure the best possible ,lift-,drift ,ratio1 for the drift of the struts wires1 body1 etc41 increases approximately as the square of the speed1 but it carries with it no lift as it does in the case of the ,surface4 ,the less speed then1 the less such drift1 and the better the ,aeroplane's proportion of lift to drift2 and1 being slow1 we shall require a ,,large ,,surface in order to secure a large lift relative to the weight to be carried4 ,we shall also require a ,,large ,,angle ,,of ,,incidence relative to the horizontal1 in order to secure a proper inclination of the ,surface to the direction of motion1 for you must remember that1 while we shall fly upon an even keel and with the propeller thrust horizontal 7which is its most efficient attitude71 our flight path1 which is our direction of motion1 will be sloping upwards1 and it will therefore be necessary to fix the ,surface to the ,aeroplane at a very considerable angle relative to the horizontal ,propeller ,thrust in order to secure a proper angle to the upwards direction of motion4 ,apart from that1 we shall require a larger ,angle of ,incidence than in the case of a machine designed purely for speed1 and that means a correspondingly ,,large ,,camber4 8,on the other hand1 if we are thinking merely of ,speed1 then a ,,small ,,surface1 just enough to lift the weight off the ground1 will be best1 also a ,,small ,,angle to cut the ,drift down and that1 of course1 means a relatively ,,small ,,camber4 8,so you see the essentials for ,,climb or quick ascent and for ,,speed are diametrically opposed4 ,now which is it to be80 8,nothing but perfection for me10 said ,efficiency4 8,what ,i want is ,maximum ,climb and ,maximum ,speed for the ,power the ,engine produces40 ,and each ,principle fully agreed with her beautiful sentiments1 but work together they would not4 ,the ,aspect ,ratio wanted infinite ,span1 and hang the ,chord4 ,the ,angle of ,incidence would have two ,angles and two ,cambers in one1 which was manifestly absurd2 the ,surface insisted upon no thickness whatever1 and would not hear of such things as ,spars and ,ribs2 and the ,thrust objected to anything at all likely to produce ,drift1 and very nearly wiped the whole thing off the ,blackboard4 ,there was1 indeed1 the makings of a very pretty quarrel when the ,letter arrived4 ,it was about a mile long1 and began to talk at once4 8,i'm from the ,inventor10 he said1 and hope rose in the heart of each heated ,principle4 8,it's really absurdly simple4 ,all the ,pilot has to do is to touch a button1 and at his will1 ,,vary the area of the ,surface1 the ,angle of ,incidence1 and the ,camber6 ,and there you are--,maximum ,climb or ,maximum ,speed as required6 ,how does that suit you80 8,that suits us very well10 said the ,surface1 8but1 excuse me asking1 how is it done without apparatus increasing the ,drift and the ,weight out of all reason8 ,you won't mind showing us your ,calculations1 ,working ,drawings1 ,stress ,diagrams1 etc41 will you80 ,said the ,letter with dignity1 8,i come from an ,inventor so brilliantly clever as to be far above the unimportant matters you mention4 ,he is no common working man1 sir6 ,he leaves such things to ,mechanics4 ,the point is1 you press a button and----0 8,look here10 said a ,strut1 rather pointedly1 8where do you think you are going1 anyway80 8,well10 from the ,letter1 8as a matter of fact1 ,i'm not addressed yet1 but1 of course1 there's no doubt ,i shall reach the very highest quarters and absolutely revolutionize ,flight when ,i get there40 ,said the ,chalk1 8,i'll address you1 if that's all you want2 now drift along quickly60 ,and off went the ,letter to ,the ,technical ,editor1 8,daily ,mauler10 ,london4 ,and a ,league was formed1 and there were ,directors with ,fees1 and several out-of-service ,tin ,hats1 and the ,man-who-takes-the-credit1 and a fine fat ,guinea-pig1 and all the rest of them4 ,and the ,inventor paid his ,tailor and had a ,hair-,cut1 and is now a recognized ,press ,expert--but he is still waiting for those ,mechanics6 8,i'm afraid10 said the ,slide-rule1 who had been busy making those lightning-like automatic calculations for which he is so famous1 8it's quite impossible to fully satisfy all of you1 and it is perfectly plain to me that we shall have to effect a ,compromise and sacrifice some of the ,lift for ,speed40 ,thud6 ,what was that8 ,efficiency had fainted dead away6 ,the last blow had been too much for her4 ,and the ,principles gathered mournfully round1 but with the aid of the ,propeller ,slip#a and a friendly lift from the ,surface she was at length revived and regained a more normal aspect4 ,said the ,stagger with a raffish air1 8,my dear young lady1 ,i assure you that from the experiences of a varied career1 ,i have learned that perfection is impossible1 and ,i am sure the ,designer will be quite satisfied if you become the ,most ,efficient ,compromise40 8,well1 that sounds so common sense10 sighed ,efficiency1 8,i suppose it must be true1 and if the ,designer is satisfied1 that's all ,i really care about4 ,now do let's get on with the job40 ,so the ,chalk drew a nice long slim body to hold the ,engine and the tanks1 etc41 with room for the ,pilot's and ,passenger's seats1 and placed it exactly in the middle of the ,biplane4 ,and he was careful to make its position such that the ,centre of ,gravity was a little in advance of the ,centre of ,lift1 so that when the ,engine was not running and there was consequently no ,thrust1 the ,aeroplane should be 8nose-heavy0 just to the right degree1 and so take up a natural glide to ,earth--and this was to help the ,pilot and relieve him of work and worry1 should he find himself in a fog or a cloud4 ,and so that this tendency to glide downwards should not be in evidence when the ,engine was running and descent not desired1 the ,thrust was placed a little below the ,centre of ,drift or ,resistance4 ,in this way it would in a measure pull the nose of the ,aeroplane up and counterbalance the 8nose-heavy0 tendency4 ,and the ,engine was so mounted that when the ,propeller-,thrust was horizontal1 which is its most efficient position1 the ,angle of ,incidence and the ,area of the surfaces were just sufficient to give a ,lift a little in excess of the ,weight4 ,and the ,camber was such that1 as far as it was concerned1 the ,lift-,drift ,ratio should be the best possible for that ,angle of ,incidence4 ,and a beautifully simple under-carriage was added1 the outstanding features of which were simplicity1 strength1 light-weight1 and minimum drift4 ,and1 last of all1 there was the ,elevator1 of which you will hear more by-and-by4 ,and this is what it looked like then3 ,and ,efficiency1 smiling1 thought that it was not such a bad compromise after all and that the ,designer might well be satisfied4 8,now10 said she1 8there's just one or two points ,i'm a bit hazy about4 ,it appears that when the ,propeller shaft is horizontal and so working in its most efficient attitude1 ,i shall have a ,lift from the ,surfaces slightly in excess of the ,weight4 ,that means ,i shall ascend slightly1 at the same time making nearly maximum speed for the power and thrust4 ,can't ,i do better than that80 8,yes1 indeed10 spoke up the ,propeller1 8though it means that ,i must assume a most undignified attitude1 for helicopters#b ,i never approved of4 ,in order to ascend more quickly the ,pilot will deflect the ,elevator1 which1 by the way1 you see hinged to the ,tail4 ,by that means he will force the whole ,aeroplane to assume a greater ,angle of ,incidence4 ,and with greater ,angle1 the ,lift will increase1 though ,i'm sorry to say the ,drift will increase also4 ,owing to the greater ,drift1 the ,speed through the air will lessen1 and ,i'm afraid that won't be helpful to the ,lift2 but ,i shall now be pointing upwards1 and besides overcoming the ,drift in a forward direction ,i shall be doing my best to haul the ,aeroplane skywards4 ,at a certain angle known as the ,best ,climbing ,angle1 we shall have our ,maximum ,margin of ,lift1 and ,i'm hoping that may be as much as almost a thousand feet altitude a minute40 8,then1 if the ,pilot is green1 my chance will come10 said the ,maximum ,angle of ,incidence4 8,for if the ,angle is increased over the ,best ,climbing ,angle1 the ,drift will rush up2 and the ,speed1 and with it the ,lift1 will1 when my ,angle is reached1 drop to a point when the latter will be no more than the ,weight4 ,the ,margin of ,lift will have entirely disappeared1 and there we shall be1 staggering along at my tremendous angle1 and only just maintaining horizontal flight40 8,and then with luck ,i'll get my chance10 said the ,drift4 8,if he is a bit worse than green1 he'll perhaps still further increase the ,angle4 ,then the ,drift1 largely increasing1 the ,speed1 and consequently the ,lift1 will become still less1 i4e41 less than the ,weight1 and then--what price pancakes1#c eh80 8,thank you10 from ,efficiency1 8that was all most informing4 ,and now will you tell me1 please1 how the greatest ,speed may be secured80 8,certainly1 now it's my turn10 piped the ,minimum ,angle of ,incidence4 8,by means of the ,elevator1 the ,pilot places the ,aeroplane at my small ,angle1 at which the ,lift only just equals the ,weight1 and1 also1 at which we shall make greater speed with no more ,drift than before4 ,then we get our greatest ,speed1 just maintaining horizontal flight40 8,yes2 though ,i'm out of the horizontal and thrusting downwards10 grumbled the ,propeller1 8and that's not efficient1 though ,i suppose it's the best we can do until that ,inventor fellow finds his ,mechanics40 8,thank you so much10 said ,efficiency4 8,i think ,i have now at any rate an idea of the ,elementary ,principles of ,flight1 and ,i don't know that ,i care to delve much deeper1 for sums always give me a headache2 but isn't there something about ,stability and ,control8 ,don't you think ,i ought to have a glimmering of them too80 8,well1 ,i should smile10 said a spruce ,spar1 who had come all the way from ,america4 8,and that1 as the ,lecturer says1 will be the subject of our next lecture1' so be here again to-morrow1 and you will be glad to hear that it will be distinctly more lively than the subject we have covered to-day40 ,,part ,,ii4 ,,the ,,principles1 ,,having ,,settled ,,their ,,differences1 ,,finish ,,the ,,job ,another day had passed1 and the ,flight ,folk had again gathered together and were awaiting the arrival of ,efficiency who1 as usual1 was rather late in making an appearance4 ,the crowd was larger than ever1 and among the newcomers some of the most important were the three ,stabilities1 named ,directional1 ,longitudinal1 and ,lateral1 with their assistants1 the ,rudder1 ,elevator1 and ,ailerons4 ,there was ,centrifugal ,force1 too1 who would not sit still and created a most unfavourable impression1 and ,keel-,surface1 the ,dihedral ,angle1 and several other lesser fry4 8,well10 said ,centrifugal ,force1 8,i wish this ,efficiency ,i've heard so much about would get a move on4 ,sitting still doesn't agree with me at all4 ,motion ,i believe in4 ,there's nothing like motion--the more the better40 8,we are entirely opposed to that10 objected the three ,stabilities1 all in a breath4 8,unless it's in a perfectly straight line or a perfect circle4 ,nothing but perfectly straight lines or1 upon occasion1 perfect circles satisfy us1 and we are strongly suspicious of your tendencies40 8,well1 we shall see what we shall see10 said the ,force darkly4 8,but who in the name of blue sky is this80 ,and in tripped ,efficiency1 in a beautifully 8doped0 dress of the latest fashionable shade of khaki-coloured fabric1 a perfectly stream-lined bonnet1 and a bewitching little ,morane parasol1#d smiling as usual1 and airily exclaiming1 8,i'm so sorry ,i'm late1 but you see the ,designer's such a funny man4 ,he objects to skin friction1#e and insisted upon me changing my fabric for one of a smoother surface1 and that delayed me4 ,dear me1 there are a lot more of us to-day1 aren't there8 ,i think ,i had better meet one at a time40 ,and turning to ,directional ,stability1 she politely asked him what he preferred to do4 8,my purpose in life1 miss10 said he1 8is to keep the ,aeroplane on its course1 and to achieve that there must be1 in effect1 more ,keel-,surface behind the ,vertical ,turning ,axis than there is in front of it40 ,efficiency looking a little puzzled1 he added3 8,just like a weathercock1 and by ,keel-,surface ,i mean everything you can see when you view the ,aeroplane from the side of it--the sides of the body1 struts1 wires1 etc40 8,oh1 now ,i begin to see light10 said she3 8but just exactly how does it work80 8,i'll answer that10 said ,momentum4 8,when perhaps by a gust of air the ,aeroplane is blown out of its course and points in another direction1 it doesn't immediately fly off on that new course4 ,i'm so strong ,i pull it off the new course to a certain extent1 and towards the direction of the old course4 ,and so it travels1 as long as my strength lasts1 in a more or less sideways position40 8,then10 said the ,keel-,surface1 8,i get a pressure of air all on one side1 and as there is1 in effect1 most of me towards the tail1 the latter gets pressed sideways1 and the ,aeroplane thus tends to assume its first position and course40 8,i see10 said ,efficiency1 and1 daintily holding the ,chalk1 she approached the ,blackboard4 8,is this what you mean80 8,yes1 that's right enough10 said the ,keel-,surface1 8and you might remember1 too1 that ,i always make the ,aeroplane nose into the gusts rather than away from them40 8,if that was not the case10 broke in ,lateral ,stability1 and affecting the fashionable ,flying ,corps stammer1 8it would be a h-h-h-o-r-rible affair6 ,if there were too much ,keel-,surface in front1 then that gust would blow the ,aeroplane round the other way a very considerable distance4 ,and the right-hand ,surface being on the outside of the turn would have more speed1 and consequently more ,lift1 than the ,surface on the other side4 ,that means a greater proportion of the ,lift on that side1 and before you could say ,warp to the ,ailerons over the ,aeroplane would go--probable result a bad side-slip0 8,and what can the ,pilot do to save such a situation as that80 said ,efficiency4 8,well10 replied ,lateral ,stability1 8he will try to turn the ,aeroplane sideways and back to an even keel by means of warping the ,ailerons or little wings which are hinged on to the ,wing-tips1 and about which you will hear more later on2 but if the side-slip is very bad he may not be able to right the ,aeroplane by means of the ,ailerons1 and then the only thing for him to do is to use the ,rudder and to turn the nose of the ,aeroplane down and head-on to the direction of motion4 ,the ,aeroplane will then be meeting the air in the direction it is designed to do so1 and the ,surfaces and also the controls 7the ,rudder1 ,ailerons1 and ,elevator7 will be working efficiently2 but its attitude relative to the earth will probably be more or less upside-down1 for the action of turning the ,aeroplane's nose down results1 as you will see by the illustration ,b1 in the right wing1 which is on the outside of the circle4 travelling through the air with greater speed than the left-hand wing4 ,more ,speed means more ,lift1 so that results in overturning the ,aeroplane still more2 but now it is1 at any rate1 meeting the air as it is designed to meet it1 and everything is working properly4 ,it is then only necessary to warp the ,elevator1 as shown in illustration ,c1 in order to bring the ,aeroplane into a proper attitude relative to the earth40 8,ah60 said the ,rudder1 looking wise1 8it's in a case like that when ,i become the ,elevator and the ,elevator becomes me40 8,that's absurd nonsense10 said the ,blackboard1 8due to looseness of thought and expression40 8,well10 replied the ,rudder1 8when 'the ,aeroplane is in position ,a and ,i am used1 then ,i depress or ,,elevate the nose of the machine2 and1 if the ,elevator is used1 then it turns the ,aeroplane to right or left1 which is normally my function4 ,surely our roles have changed one with the other1 and ,i'm then the ,elevator and the ,elevator is me60 ,said ,lateral ,stability to the ,rudder1 8,that's altogether the wrong way of looking at it1 though ,i admit0--and this rather sarcastically--8that the way you put it sounds rather fine when you are talking of your experiences in the air to those 'interested in aviation' but knowing little about it2 but it won't go down here6 ,you are a ,controlling ,surface designed to turn the ,aeroplane about its vertical axis1 and the ,elevator is a ,controlling ,surface designed to turn the ,aeroplane about its lateral axis4 ,those are your respective jobs1 and you can't possibly change them about4 ,such talk only leads to confusion1 and ,i hope we shall hear no more of it40 8,thanks10 said ,efficiency to ,lateral ,stability4 8,and now1 please1 will you explain your duties80 8,my duty is to keep the ,aeroplane horizontal from ,wing-tip to ,wing-tip4 ,first of all1 ,i sometimes arrange with the ,rigger to wash-out1 that is decrease1 the ,angle of ,incidence on one side of the ,aeroplane1 and to effect the reverse condition1 if it is not too much trouble1 on the other side40 8,but10 objected ,efficiency1 8the ,lift varies with the ,angle of ,incidence1 and surely such a condition will result in one side of the ,aeroplane lifting more than the other side8' 8,that's all right10 said the ,propeller1 8it's meant to off-set the tendency of the ,aeroplane to turn over sideways in the opposite direction to which ,i revolve40 8,that's quite clear1 though rather unexpected2 but how do you counteract the effect of the gusts when they try to overturn the ,aeroplane sideways80 said she1 turning to ,lateral ,stability again4 8,well10 he replied1 rather miserably1 8,i'm not nearly so perfect as the ,longitudinal and ,directional ,stabilities4 ,the ,dihedral ,angle--that is1 the upward inclination of the ,surfaces towards their wing-tips--does what it can for me1 but1 in my opinion1 it's a more or less futile effort4 ,the ,blackboard will show you the argument40 ,and he at once showed them two ,surfaces1 each set at a ,dihedral ,angle like this3 8,please imagine10 said the ,blackboard1 8that the top ,v is the front view of a ,surface flying towards you4 ,now if a gust blows it into the position of the lower ,v you see that the horizontal equivalent of the ,surface on one side becomes larger1 and on the other side it becomes smaller4 ,that results in more ,lift on the lower side and less on the higher side1 and if the ,v is large enough it should produce such a difference in the ,lift of one side to the other as to quickly turn the ,aeroplane back to its former and normal position40 8,yes10 said the ,dihedral ,angle1 8that's what would happen if they would only make me large enough2 but they won't do it because it would too greatly decrease the horizontal equivalent1 and therefore the ,lift1 and incidentally it would1 as ,aeroplanes are built to-day1 produce an excess of ,keel ,surface above the turning axis1 and that in itself would spoil the ,lateral ,stability4 ,the ,keel ,surface should be equally divided above and below the longitudinal turning axis 7upon which the ,aeroplane rolls sideways71 or the side upon which there is an excess will get blown over by the gusts4 ,it strikes me that my future isn't very promising1 and about my only chance is when the ,junior ,draughtsman makes a mistake1 as he did the other day4 ,and just think of it1 they call him a ,designer now that he's got a job at the ,factory6 ,what did he do8 ,why1 he calculated the weights wrong and got the ,centre of ,gravity too high1 and they didn't discover it until the machine was built4 ,then all they could do was to give me a larger ,angle4 ,that dropped the bottom of the ,v lower down1 and as that's the centre of the machine1 where all the ,weight is1 of course that put the ,centre of ,gravity in its right place4 ,but now there is too much ,keel ,surface above1 and the whole thing's a ,bad ,compromise1 not at all like ,our ,efficiency40 ,and ,efficiency1 blushing very prettily at the compliment1 then asked1 8,and how does the ,centre of ,gravity affect matters80 8,that's easy10 said ,grandfather ,gravity4 8,i'm so heavy that if ,i am too low down ,i act like a pendulum and cause the ,aeroplane to roll about sideways1 and if ,i am too high ,i'm like a stick balanced on your finger1 and then if ,i'm disturbed1 over ,i go and the ,aeroplane with me2 and1 in addition to that1 there are the tricks ,i play with the ,aeroplane when it's banked up1#f i4e41 tilted sideways for a turn1 and ,centrifugal ,force sets me going the way ,i'm not wanted to go4 ,no2 ,i get on best with ,lateral ,stability when my ,centre is right on the centre of ,drift1 or1 at any rate1 not much below it40 ,and with that he settled back into the ,lecturer's ,chair and went sound asleep again1 for he was so very1 very old1 in fact the father of all the ,principles4 ,and the ,blackboard had been busy1 and now showed them a picture of the ,aeroplane as far as they knew it1 and you will see that there is a slight ,dihedral ,angle1 and also1 fixed to the tail1 a vertical ,keel ,surface or fin1 as is very often the case in order to ensure the greater effect of such surface being behind the vertical turning axis4 ,but ,efficiency1 growing rather critical with her newly gained knowledge1 cried out3 8,but where's the horizontal ,tail ,surface8 ,it doesn't look right like that60 8,this is when ,i have the pleasure of meeting you1 my dear10 said ,longitudinal ,stability4 8,here's the ,tail ,surface10 he said1 8and in order to help me it must be set ,,in ,,effect at a much less ,angle of ,incidence than the ,main ,surface4 ,to explain we must trouble the ,blackboard again10 and this was his effort3 8,i have tried to make that as clear as possible10 he said4 8,it may appear a bit complicated at first1 but if you will take the trouble to look at it for a minute you will find it quite simple4 ,a is the normal and proper direction of motion of the ,aeroplane1 but1 owing to a gust of air1 it takes up the new nose-down position4 ,owing to ,momentum1 however1 it does not fly straight along in that direction1 but moves more or less in the direction ,b1 which is the resultant of the two forces1 ,momentum and ,thrust4 ,and so you will note that the ,angle of ,incidence1 which is the inclination of the ,surfaces to the ,direction of ,motion1 has decreased1 and of course the ,lift decreases with it4 ,you will also see1 and this is the point1 that the ,tail ,surface has lost a higher proportion of its ,angle1 and consequently its ,lift1 than has the ,main ,surface4 ,then1 such being the case1 the ,tail must fall and the ,aeroplane assume its normal position again1 though probably at a slightly lower altitude40 8,i'm afraid ,i'm very stupid10 said ,efficiency1 8but please tell me why you lay stress upon the words ',,in ,,effect4'0 8,ah6 ,i was wondering if you would spot that10 he replied4 8,and there is a very good reason for it4 ,you see1 in some ,aeroplanes the ,tail ,surface may be actually set at the same ,angle on the machine as the ,main ,surface1 but owing to the air being deflected downwards by the front ,main ,surface it meets the ,tail ,surface at a lesser angle1 and indeed in some cases at no angle at all4 ,the ,tail is then for its surface getting less ,lift than the ,main ,surface1 although set at the same angle on the machine4 ,it may then be said to have ,,in ,,effect a less ,angle of ,incidence4 ,i'll just show you on the ,blackboard40 8,and now10 said ,efficiency1 8,i have only to meet the ,ailerons and the ,rudder1 haven't ,i80 8,here we are10 replied the ,ailerons1 or little wings4 8,please hinge us on to the back of the ,main ,surfaces1 one of us at each ,wing-tip1 and join us up to the ,pilot's joystick by means of the control cables4 ,when the ,pilot wishes to tilt the ,aeroplane sideways1 he will move the stick and depress us upon one side1 thus giving us a larger ,angle of ,incidence and so creating more ,lift on that side of the ,aeroplane2 and1 by means of a cable connecting us with the ,ailerons on the other side of the ,aeroplane1 we shall1 as we are depressed1 pull them up and give them a reverse or negative ,angle of ,incidence1 and that side will then get a reverse ,lift or downward thrust1 and so we are able to tilt the ,aeroplane sideways4 8,and we work best when the ,angle of ,incidence of the ,surface in front of us is very small1 for which reason it is sometimes decreased or washed-out towards the ,wing-tips4 ,the reason of that is that by the time the air reaches us it has been deflected downwards--the greater the ,angle of ,incidence the more it is driven downwards--and in order for us to secure a ,reaction from it1 we have to take such a large ,angle of ,incidence that we produce a poor proportion of ,lift to ,drift2 but the smaller the ,angle of the ,surface in front of us the less the air is deflected downwards1 and consequently the less ,angle is required of us1 and the better our proportion of ,lift to ,drift1 which1 of course1 makes us much more effective ,controls40 8,yes10 said the ,lateral and ,directional ,stabilities in one voice1 8that's so1 and the wash-out helps us also1 for then the ,surfaces towards their ,wing-tips have less ,drift or ',head-,resistance1' and consequently the gusts will affect them and us less2 but such decreased ,angle of ,incidence means decreased ,lift as well as ,drift1 and the ,designer does not always care to pay the price40 8,well10 said the ,ailerons1 8if it's not done it will mean more work for the ,rudder1 and that won't please the ,pilot40 8,whatever do you mean80 asked ,efficiency4 8,what can the ,rudder have to do with you80 8,it's like this10 they replied3 8when we are deflected downwards we gain a larger ,angle of ,incidence and also enter an area of compressed air1 and so produce more ,drift than those of us on the other side of the ,aeroplane1 which are deflected upwards into an area of rarefied air due to the ,,suction effect 7though that term is not academically correct7 on the top of the ,surface4 ,if there is more ,drift1 i4e41 ,resistance1 on one side of the ,aeroplane than on the other side1 then of course it will turn off its course1 and if that difference in ,drift is serious1 as it will very likely be if there is no wash-out1 then it will mean a good deal of work for the ,rudder in keeping the ,aeroplane on its course1 besides creating extra ,drift in doing so40 8,i think1 then10 said ,efficiency1 8,i should prefer to have that wash-out1#g and my friend the ,designer is so clever at producing strength of construction for light weight1 ,i'm pretty sure he won't mind paying the price in ,lift4 ,and now let me see if ,i can sketch the completed ,aeroplane40 8,well1 ,i hope that's all as it should be10 she concluded1 8for to-morrow the ,great ,test in the air is due40 ,,part ,,iii4 ,,the ,,great ,,test ,it is five o'clock of a fine calm morning1 when the ,aeroplane is wheeled out of its shed on to the greensward of the ,military ,aerodrome4 ,there is every promise of a good flying day1 and1 although the sun has not yet risen1 it is light enough to discern the motionless layer of fleecy clouds some five thousand feet high1 and far1 far above that a few filmy mottled streaks of vapour4 ,just the kind of morning beloved of pilots4 ,a brand new1 rakish1 up-to-date machine it is1 of highly polished1 beautifully finished wood1 fabric as tight as a drum1 polished metal1 and every part so perfectly 8streamlined0 to minimize ,drift1 which is the resistance of the air to the passage of the machine1 that to the veriest tyro the remark of the ,pilot is obviously justified4 8,clean looking 'bus1 looks almost alive and impatient to be off4 ,ought to have a turn for speed with those lines40 8,yes10 replies the ,flight-,commander1 8it's the latest of its type and looks a beauty4 ,give it a good test4 ,a special report is required on this machine40 ,the ,a4,m4's#h have now placed the ,aeroplane in position facing the gentle air that is just beginning to make itself evident2 the engine ,fitter1 having made sure of a sufficiency of oil and petrol in the tanks1 is standing by the ,propeller2 the ,rigger1 satisfied with a job well done1 is critically 8vetting0 the machine by eye1 four ,a4,m4's are at their posts1 ready to hold the ,aeroplane from jumping the blocks which have been placed in front of the wheels2 and the ,flight-,sergeant is awaiting the ,pilot's orders4 ,as the ,pilot approaches the ,aeroplane the ,rigger springs to attention and reports1 8,all correct1 sir10 but the ,fitter does not this morning report the condition of the ,engine1 for well he knows that this ,pilot always personally looks after the preliminary engine test4 ,the latter1 in leathern kit1 warm flying boots and goggled1 climbs into his seat1 and now1 even more than before1 has the ,aeroplane an almost living appearance1 as if straining to be off and away4 ,first he moves the ,controls to see that everything is clear1 for sometimes when the ,aeroplane is on the ground the control lever or 8joy-stick0 is lashed fast to prevent the wind from blowing the controlling surfaces about and possibly damaging them4 ,the air of this early dawn is distinctly chilly1 and the ,a4,m4's are beginning to stamp their cold feet upon the dewy grass1 but very careful and circumspect is the ,pilot1 as he mutters to himself1 8,don't worry and flurry1 or you'll die in a hurry40 ,at last he fumbles for his safety belt1 but with a start remembers the ,pilot ,air ,speed ,indicator1 and1 adjusting it to zero1 smiles as he hears the ,pilot-head's gruff voice1 8,well1 ,i should think so1 twenty miles an hour ,i was registering4 ,that's likely to cause a green pilot to stall the ,aeroplane4 ,pancake1 they call it40 ,and the ,pilot1 who is an old hand and has learned a lot of things in the air that mere earth-dwellers know nothing about1 distinctly heard the ,pilot ,tube1 whose mouth is open to the air to receive its pressure1 stammer4 8,oh ,lor6 ,i've got an earwig already--hope to goodness the ,rigger blows me out when ,i come down--and this morning air simply fills me with moisture2 ,i'll never keep the ,liquid steady in the ,gauge4 ,i'm not sure of my rubber connections either40 8,oh1 shut up60 cry all the ,wires in unison1 8haven't we got our troubles too8 ,we're in the most horrible state of tension4 ,it's simply murdering our ,factor of ,safety1 and how we can possibly stand it when we get the ,lift only the ,designer knows40 8,that's all right10 squeak all the little ,wire loops1 8we're that accommodating1 we're sure to elongate a bit and so relieve your tension40 ,for the whole ,aeroplane is braced together with innumerable wires1 many of which are at their ends bent over in the form of loops in order to connect with the metal fittings on the spars and elsewhere--cheap and easy way of making connection4 8,elongate1 you little devils1 would you80 fairly shout the ,angles of ,incidence1 ,dihedral and ,stagger1 amid a chorus of groans from all parts of the ,aeroplane4 8,what's going to happen to us then8 ,how are we going to keep our adjustments upon which good flying depends80 8,butt us and screw us10#i wail the ,wires4 8,butt us and screw us1 and death to the ,loops4 ,that's what we sang to the ,designer1 but he only looked sad and scowled at the ,directors40 8,and who on earth are they80 asked the ,loops1 trembling for their troublesome little lives4 8,oh earth indeed10 sniffed ,efficiency1 who had not spoken before1 having been rendered rather shy by being badly compromised in the ,drawing ,office4 8,i'd like to get some of them up between ,heaven and ,earth1 ,i would4 ,i'd give 'em something to think of besides their ,debits and ,credits--but all the same the ,designer will get his way in the end4 ,i'm his ,best ,girl1 you know1 and if we could only get rid of the ,directors1 the little ,tin god1 and the ,man-who-takes-the-credit1 we should be quite happy40 ,then she abruptly subsides1 feeling that perhaps the less said the better until she has made a reputation in the ,air4 ,the matter of that ,compromise still rankled1 and indeed it does seem hardly fit that a bold bad ,tin god should flirt with ,efficiency4 ,you see there was a little ,tin god1 and he said 8,boom1 ,boom ,,boom6 ,nonsense6 ,it ,,must be done10 and things like that in a very loud voice1 and the ,designer tore his hair and was furious1 but the ,directors1 who were thinking of nothing but ,orders and ,dividends1 had the whip-hand of ,,him1 and so there you are1 and so poor beautiful ,miss ,efficiency was compromised4 ,all this time the ,pilot is carefully buckling his belt and making himself perfectly easy and comfortable1 as all good pilots do4 ,as he straightens himself up from a careful inspection of the ,deviation ,curve#aj of the ,compass and takes command of the ,controls1 the ,throttle and the ,ignition1 the voices grow fainter and fainter until there is nothing but a trembling of the ,lift and ,drift wires to indicate to his understanding eye their state of tension in expectancy of the ,great ,test4 8,petrol on80 shouts the ,fitter to the ,pilot4 8,petrol on10 replies the ,pilot4 8,ignition off80 8,ignition off40 ,round goes the ,propeller1 the ,engine sucking in the ,petrol ,vapour with satisfied gulps4 ,and then-- 8,contact80 from the ,fitter4 8,contact10 says the ,pilot4 ,now one swing of the ,propeller by the ,fitter1 and the ,engine is awake and working4 ,slowly at first though1 and in a weak voice demanding1 8,not too much ,throttle1 please4 ,i'm very cold and mustn't run fast until my ,oil has thinned and is circulating freely4 ,three minutes slowly1 as you love me1 ,pilot40 ,faster and faster turn the ,engine and ,propeller1 and the ,aeroplane1 trembling in all its parts1 strains to jump the blocks and be off4 ,carefully the ,pilot listens to what the ,engine ,revolution ,indicator says4 ,at last1 8,steady at #a1ejj revs4 and ,i'll pick up the rest in the ,air40 ,then does he throttle down the ,engine1 carefully putting the lever back to the last notch to make sure that in such position the ,throttle is still sufficiently open for the ,engine to continue working1 as otherwise it might lead to him 8losing0 his ,engine in the air when throttling down the power for descent4 ,then1 giving the official signal1 he sees the blocks removed from the wheels1 and the ,flight-,sergeant saluting he knows that all is clear to ascend4 ,one more signal1 and all the ,a4,m4's run clear of the ,aeroplane4 ,then gently1 gently mind you1 with none of the 8crashing on0 bad ,pilots think so fine1 he opens the ,throttle and1 the ,propeller ,thrust overcoming its enemy the ,drift1 the ,aeroplane moves forward4 8,ah60 says the ,wind-screen1 8that's ,discipline1 that is4 ,through my little window ,i see most things1 and don't ,i just know that poor discipline always results in poor work in the air1 and don't you forget it40 8,discipline is it80 complains the ,under-carriage1 as its wheels roll swiftly over the rather rough ground4 8,i'm bump getting it2 and bump1 bump1 all ,i want1 bang1 bump1 rattle1 too60 ,but1 as the ,lift increases with the ,speed1 the complaints of the ,under-carriage are stilled1 and then1 the friendly ,lift becoming greater than the ,weight1 the ,aeroplane swiftly and easily takes to the air4 ,below is left the ,earth with all its bumps and troubles4 ,up into the clean clear ,air moves with incredible speed and steadiness this triumph of the ,designer1 the result of how much mental effort1 imagination1 trials and errors1 failures and successes1 and many a life lost in high endeavour4 ,now is the mighty voice of the ,engine heard as he turns the ,propeller nine hundred times a minute4 ,now does the ,thrust fight the ,drift for all it's worth1 and the ,air ,speed ,indicator gasps with delight1 8,one hundred miles an hour60 ,and now does the burden of work fall upon the ,lift and ,drift ,wires1 and they scream to the ,turnbuckles whose business it is to hold them in tension1 8,this is the limit6 the ,limit6 ,,the ,,limit6 ,release us1 if only a quarter turn40 ,but the ,turnbuckles are locked too fast to turn their eyes or utter a word4 ,only the ,locking ,wires thus3 8,ha6 ha6 the ,rigger knew his job4 ,he knew the trick1 and there's no release here40 ,for an expert rigger will always use the locking wire in such a way as to oppose the slightest tendency of the turnbuckle to unscrew4 ,the other kind of rigger will often use the wire in such a way as to allow the turnbuckle1 to the 8eyes0 of which the wires are attached1 to unscrew a quarter of a turn or more1 with the result that the correct adjustment of the wires may be lost2 and upon their fine adjustment much depends4 ,and the ,struts and the ,spars groan in compression and pray to keep straight1 for once 8out of truth0 there is1 in addition to possible collapse1 the certainty that in bending they will throw many wires out of adjustment4 ,and the ,fabric's quite mixed in its mind1 and ejaculates1 8,now1 who would have thought ,i got more ,lift from the top of the ,surface than its bottom80 ,and then truculently to the ,distance ,pieces1 which run from rib to rib1 8,just keep the ,ribs from rolling1 will you8 or you'll see me strip4 ,i'm an ,irishman1 ,i am1 and if my coat comes off---- ,yes1 ,irish1 ,i said4 ,i used to come from ,egypt1 but ,i've got naturalized since the ,war began40 ,then the ,air ,speed ,indicator catches the eye of the ,pilot4 8,good enough10 he says as he gently deflects the ,elevator and points the nose of the ,aeroplane upwards in search of the elusive ,best ,climbing ,angle4 8,ha6 ha60 shouts the ,drift1 growing stronger with the increased ,angle of ,incidence4 8,ha6 ha60 he laughs to the ,thrust4 8,now ,i've got you4 ,now who's ,master80 ,and the ,propeller shrieks hysterically1 8,oh6 look at me4 ,i'm a helicopter4 ,that's not fair4 ,where's ,efficiency80 ,and she can only sadly reply1 8,yes1 indeed1 but you see we're a ,compromise40 ,and the ,drift has hopes of reaching the ,maximum ,angle of ,incidence and vanquishing the ,thrust and the ,lift4 ,and he grows very bold as he strangles the ,thrust2 but the situation is saved by the ,propeller1 who is now bravely helicopting skywards1 somewhat to the chagrin of ,efficiency4 8,much ado about nothing10 quotes the ,aeroplane learnedly4 8,compromise or not1 ,i'm climbing a thousand feet a minute4 ,ask the ,altimeter4 ,he'll confirm it40 ,and so indeed it was4 ,the vacuum box of the ,altimeter was steadily expanding under the decreased pressure of the rarefied air1 and by means of its little levers and its wonderful chain no larger than a hair it was moving the needle round the gauge and indicating the ascent at the rate of a thousand feet a minute4 ,and lo6 the ,aeroplane has almost reached the clouds6 ,but what's this8 ,a sudden gust1 and down sinks one wing and up goes the other4 8,oh1 my ,horizontal ,equivalent60 despairingly call the ,planes3 8it's eloping with the ,lift1 and what in the name of ,gravity will happen8 ,surely there was enough scandal in the ,factory without this1 too60 ,for the lift varies with the horizontal equivalent of the planes1 so that if the aeroplane tilts sideways beyond a certain angle1 the lift becomes less than the weight of the machine1 which must then fall4 ,a fall in such a position is known as a 8side-slip40 ,but the ever-watchful ,pilot instantly depresses one aileron1 elevating the other1 with just a touch of the rudder to keep on the course1 and the ,planes welcome back their precious ,lift as the ,aeroplane flicks back to its normal position4 8,bit bumpy here under these clouds10 is all the ,pilot says as he heads for a gap between them1 and the next minute the ,aeroplane shoots up into a new world of space4 8,my eye60 ejaculates the ,wind-screen1 8talk about a view60 ,and indeed mere words will always fail to express the wonder of it4 ,six thousand feet up now1 and look6 ,the sun is rising quicker than ever mortal on earth witnessed its ascent4 ,far below is ,mother ,earth1 wrapt in mists and deep blue shadows1 and far above are those light1 filmy1 ethereal clouds now faintly tinged with pink ,and all about great mountains of cloud1 lazily floating in space4 ,the sun rises and they take on all colours1 blending one with the other1 from dazzling white to crimson and deep violet-blue4 ,lakes and rivers here and there in the enormous expanse of country below refract the level rays of the sun and1 like so many immense diamonds1 send dazzling shafts of light far upwards4 ,the tops of the hills now laugh to the light of the sun1 but the valleys are still mysterious dark blue caverns1 clowned with white filmy lace-like streaks of vapour4 ,and withal the increasing sense with altitude of vast1 clean1 silent solitudes of space4 ,lives there the man who can adequately describe this ,wonder8 8,never10 says the ,pilot1 who has seen it many times1 but to whom it is ever new and more wonderful4 ,up1 up1 up1 and still up1 unfalteringly speeds the ,pilot and his mount4 ,sweet the drone of the ,engine and steady the ,thrust as the ,propeller exultingly battles with the ,drift4 ,and look6 ,what is that bright silver streak all along the horizon8 ,it puzzled the ,pilot when first he saw it1 but now he knows it for the ,sea1 full fifty miles away6 ,and on his right is the brightness of the ,morn and the smiling ,earth unveiling itself to the ardent rays of the ,sun2 and on his left1 so high is he1 there is yet black ,night1 hiding innumerable ,cities1 ,towns1 ,villages and all those places where soon teeming multitudes of men shall awake1 and by their unceasing toil and the spirit within them produce marvels of which the ,aeroplane is but the harbinger4 ,and the ,pilot's soul is refreshed1 and his vision1 now exalted1 sees the ,earth a very garden1 even as it appears at that height1 with discord banished and a happy time come1 when the ,designer shall have at last captured ,efficiency1 and the ,man-who-takes-the-credit is he who has earned it1 and when kisses are the only things that go by favour4 ,now the ,pilot anxiously scans the ,barograph1 which is an instrument much the same as the ,altimeter2 but in this case the expansion of the vacuum box causes a pen to trace a line upon a roll of paper4 ,this paper is made by clockwork to pass over the point of the pen1 and so a curved line is made which accurately registers the speed of the ascent in feet per minute4 ,no longer is the ascent at the rate of a thousand feet a minute1 and the ,propeller complains to the ,engine1 8,i'm losing my ,revs4 and the ,thrust4 ,buck up with the ,power1 for the ,lift is decreasing1 though the ,weight remains much the same40 ,quoth the ,engine3 8,i strangle for ,air4 ,a certain proportion1 and that of right density1 ,i must have to one part of ,petrol1 in order to give me full power and compression1 and here at an altitude of ten thousand feet the ,air is only two-thirds as dense as at sea-level4 ,oh1 where is he who will invent a contrivance to keep me supplied with ,air of right density and quality8 ,it should not be impossible within certain limits40 8,we fully agree10 said the dying ,power and ,thrust4 8,only maintain ,us and you shall be surprised at the result4 ,for our enemy ,drift decreases in respect of distance with the increase of altitude and rarity of air1 and there is no limit to the speed through space if only our strength remains4 ,and with oxygen for ,pilot and ,passengers and a steeper pitch#aa for the ,propeller we may then circle the ,earth in a day60 ,ah1 ,reader1 smile not unbelievingly1 as you smiled but a few years past4 ,there may be greater wonders yet4 ,consider that as the speed increases1 so does the momentum or stored-up force in the mass of the aeroplane become terrific4 ,and1 bearing that in mind1 remember that with altitude gravity decreases4 ,there may yet be literally other worlds to conquer4#ab ,now at fifteen thousand feet the conditions are chilly and rare1 and the ,pilot1 with thoughts of breakfast far below1 exclaims1 8,high enough6 ,i had better get on with the ,test40 ,and then1 as he depresses the ,elevator1 the ,aeroplane with relief assumes its normal horizontal position4 ,then1 almost closing the ,throttle1 the ,thrust dies away4 ,now1 the nose of the ,aeroplane should sink of its own volition1 and the craft glide downward at flying speed1 which is in this case a hundred miles an hour4 ,that is what should happen if the ,designer has carefully calculated the weight of every part and arranged for the centre of gravity to be just the right distance in front of the centre of lift4 ,thus is the ,aeroplane 8nose-heavy0 as a glider1 and just so to a degree ensuring a speed of glide equal to its flying speed4 ,and the ,air ,speed ,indicator is steady at one hundred miles an hour1 and 8,that's all right60 exclaims the ,pilot4 8,and very useful1 too1 in a fog or a cloud10 he reflects1 for then he can safely leave the angle of the glide to itself1 and give all his attention1 and he will need it all1 to keeping the ,aeroplane horizontal from wing-tip to wing-tip1 and to keeping it straight on its course4 ,the latter he will manage with the rudder1 controlled by his feet1 and the ,compass will tell him whether a straight course is kept4 ,the former he will control by the ,ailerons1 or little wings hinged to the tips of the planes1 and the bubble in the ,inclinometer in front of him must be kept in the middle4 ,a ,pilot1 being only human1 may be able to do two things at once1 but three is a tall order1 so was this ,pilot relieved to find the ,design not at fault and his craft a 8natural glider40 ,to correct this nose-heavy tendency when the ,engine is running1 and descent not required1 the centre of ,thrust is arranged to be a little below the centre of ,drift or ,resistance1 and thus acts as a counter-balance4 ,but what is this stream of bad language from the ,exhaust ,pipe1 accompanied by gouts of smoke and vapour8 ,the ,engine1 now revolving at no more than one-tenth its normal speed1 has upset the proportion of petrol to air1 and combustion is taking place intermittently or in the ,exhaust ,pipe1 where it has no business to be4 8,crash1 ,bang1 ,rattle----6----6----60 and worse than that1 yells the ,exhaust1 and the ,aeroplane1 who is a gentleman and not a box kite1#ac remonstrates with the severity of a ,senior ,officer4 8,see the ,medical ,officer1 you young ,hun4 ,go and see a doctor4 ,vocal diarrhoea1 that's your complaint1 and a very nasty one too4 ,bad form1 bad for discipline1 and a nuisance in the ,mess4 ,what's your ,regiment8 ,special ,reserve1 you say8 ,humph6 ,sounds like ,secondhand ,bicycle ,trade to me60 ,now the ,pilot decides to change the straight gliding descent to a spiral one1 and1 obedient to the ,rudder1 the ,aeroplane turns to the left4 ,but the ,momentum 7two tons at #ajj miles per hour is no small affair7 heavily resents this change of direction1 and tries its level best to prevent it and to pull the machine sideways and outwards from its spiral course--that is1 to make it 8side-skid0 outwards4 ,but the ,pilot deflects the ,ailerons and 8banks0 up the planes to the correct angle1 and1 the ,aeroplane skidding sideways and outwards1 the lowest surfaces of the planes press up against the air until the pressure equals the centrifugal force of the ,momentum1 and the ,aeroplane spirals steadily downwards4 ,down1 down1 down1 and the air grows denser1 and the ,pilot gulps largely1 filling his lungs with the heavier air to counteract the increasing pressure from without4 ,down through a gap in the clouds1 and the ,aerodrome springs into view1 appearing no larger than a saucer1 and the ,pilot1 having by now got the 8feel0 of the ,controls1 proceeds to put the ,aeroplane through its paces4 ,first at its ,maximum ,angle1 staggering along tail-down and just maintaining horizontal flight2 then a dive at far over flying speed1 finishing with a perfect loop2 then sharp turns with attendant vertical 8banks0 and then a wonderful switchback flight1 speeding down at a hundred and fifty miles an hour with short1 exhilarating ascents at the rate of two thousand feet a minute6 ,all the parts are now working well together4 ,such wires as were before in undue tension have secured relief by slightly elongating their loops1 and each one is now doing its bit1 and all are sharing the burden of work together4 ,the ,struts and the ,spars1 which felt so awkward at first1 have bedded themselves in their sockets1 and are taking the compression stresses uncomplainingly4 ,the ,control ,cables of twisted wire1 a bit tight before1 have slightly lengthened by perhaps the eighth of an inch1 and1 the ,controls instantly responding to the delicate touch of the ,pilot1 the ,aeroplane1 at the will of its ,master1 darts this way and that way1 dives1 loops1 spirals1 and at last1 in one long1 magnificent glide1 lands gently in front of its shed4 8,well1 what result80 calls the ,flight-,commander to the ,pilot4 8,a hundred miles an hour and a thousand feet a minute10 he briefly replies4 8,and a very good result too10 says the ,aeroplane1 complacently1 as he is carefully wheeled into his shed4 ,that is the way ,aeroplanes speak to those who love them and understand them4 ,lots of ,pilots know all about it1 and can spin you wonderful yarns1 much better than this one1 if you catch them in a confidential mood--on leave1 for instance1 and after a good dinner4 ,,part ,,iv4 ',,cross ,,country ,the ,aeroplane had been designed and built1 and tested in the air1 and now stood on the ,aerodrome ready for its first 'cross-country flight4 ,it had run the gauntlet of pseudo-designers1 crank inventors1 press 8experts10 and politicians2 of manufacturers keen on cheap work and large profits2 of poor pilots who had funked it1 and good pilots who had expected too much of it4 ,thousands of pounds had been wasted on it1 many had gone bankrupt over it1 and others it had provided with safe fat jobs4 ,somehow1 and despite every conceivable obstacle1 it had managed to muddle through1 and now it was ready for its work4 ,it was not perfect1 for there were fifty different ways in which it might be improved1 some of them shamefully obvious4 ,but it was fairly sound mechanically1 had a little inherent stability1 was easily controlled1 could climb a thousand feet a minute1 and its speed was a hundred miles an hour4 ,in short1 quite a creditable machine1 though of course the right man had not got the credit4 ,it is rough1 unsettled weather with a thirty mile an hour wind on the ground1 and that means fifty more or less aloft4 ,lots of clouds at different altitudes to bother the ,pilot1 and the air none to clear for the observation of landmarks4 ,as the ,pilot and ,observer approach the ,aeroplane the former is clearly not in the best of tempers4 8,it's rotten luck10 he is saying1 8a blank shame that ,i should have to take this blessed 'bus and join ,x ,reserve ,squadron1 stationed a hundred and fifty miles from anywhere2 and just as ,i have licked my ,flight into shape4 ,now some slack blighter will1 ,i suppose1 command it and get the credit of all my work60 8,shut up1 you grouser10 said the ,observer4 8,do you think you're the only one with troubles8 ,haven't ,i been through it too8 ,oh6 ,i know all about it6 ,you're from the ,special ,reserve and your ,c4,o4 doesn't like your style of beauty1 and you won't lick his boots1 and you were a bit of a technical knut in civil life1 but now you've jolly well got to know less than those senior to you4 ,well6 ,it's a jolly good experience for most of us4 ,perhaps conceit won't be at quite such a premium after this war4 ,and what's the use of grousing8 ,that never helped anyone4 ,so buck up1 old chap4 ,your day will come yet4 ,here's our machine1 and ,i must say it looks a beauty60 ,and1 as the ,pilot approaches the ,aeroplane1 his face brightens and he soon forgets his troubles as he critically inspects the craft which is to transport him and the ,observer over the hills and far away4 ,turning to the ,flight-,sergeant he inquires1 8,tank full of petrol and oil80 8,yes1 sir10 he replies1 8and everything else all correct4 ,propeller1 engine1 and body covers on board1 sir2 tool kit checked over and in the locker2 engine and ,aeroplane logbooks written up1 signed1 and under your seat2 engine revs4 up to mark1 and all the control cables in perfect condition and tension40 8,very good10 said the ,pilot2 and then turning to the ,observer1 8,before we start you had better have a look at the course ,i have mapped out4 8,a is where we stand and we have to reach ,b1 a hundred and fifty miles due ,north4 ,i judge that1 at the altitude we shall fly1 there will be an ,east wind1 for although it is not quite ,east on the ground it is probably about twenty degrees different aloft1 the wind usually moving round clockways to about that extent4 ,i think that it is blowing at the rate of about fifty miles an hour1 and ,i therefore take a line on the map to ,c1 fifty miles due ,west of ,a4 ,the ,aeroplane's speed is a hundred miles an hour1 and so ,i take a line of one hundred miles from ,c to ,d4 ,our compass course will then be in the direction ,a--,e1 which is always a line parallel to ,c--,d4 ,that is1 to be exact1 it will be fourteen degrees off the ,c--,d course1 as1 in this part of the globe1 there is that much difference between the ,north and ,south lines on the map and the magnetic ,north to which the compass needle points4 ,if the compass has an error1 as it may have of a few degrees1 that1 too1 must be taken into account1 and the deviation or error curve on the dashboard will indicate it4 8,the ,aeroplane will then always be pointing in a direction parallel to ,a--,e1 but1 owing to the side wind1 it will be actually travelling over the course ,a--,b1 though in a rather sideways attitude to that course4 8,the distance we shall travel over the ,a--,b course in one hour is ,a--,d4 ,that is nearly eighty-seven miles1 so we ought to accomplish our journey of a hundred and fifty miles in about one and three-quarter hours4 8,i hope that's quite clear to you4 ,it's a very simple way of calculating the compass course1 and ,i always do it like that40 8,yes1 that's plain enough4 ,you have drafted what engineers call 'a parallelogram of forces'2 but suppose you have miscalculated the velocity of the wind1 or that it should change in velocity or direction80 8,well1 that of course will more or less alter matters10 replies the ,pilot4 8,but there are any number of good landmarks such as lakes1 rivers1 towns1 and railway lines4 ,they will help to keep us on the right course1 and the compass will1 at any rate1 prevent us from going far astray when between them40 8,well1 we'd better be off1 old chap4 ,hop aboard40 ,this from the ,observer as he climbs into the front seat from which he will command a good view over the lower plane2 and the ,pilot takes his place in the rear seat1 and1 after making himself perfectly comfortable1 fixing his safety belt1 and moving the control levers to make sure that they are working freely1 he gives the signal to the ,engine ,fitter to turn the propeller and so start the engine4 ,round buzzes the ,propeller1 and the ,pilot1 giving the official signal1 the ,aeroplane is released and rolls swiftly over the ground in the teeth of the gusty wind4 ,in less than fifty yards it takes to the air and begins to climb rapidly upwards1 but how different are the conditions to the calm morning of yesterday6 ,if the air were visible it would be seen to be acting in the most extraordinary manner2 crazily swirling1 lifting and dropping1 gusts viciously colliding--a mad phantasmagoria of forces6 ,wickedly it seizes and shakes the ,aeroplane2 then tries to turn it over sideways2 then instantly changes its mind and in a second drops it into a hole a hundred feet deep1 and if it were not for his safety belt the ,pilot might find his seat sinking away from beneath him4 ,gusts strike the front of the craft like so many slaps in the face2 and others1 with the motion of mountainous waves1 sometimes lift it hundreds of feet in a few seconds1 hoping to see it plunge over the summit in a death-dive--and so it goes on1 but the ,pilot1 perfectly at one with his mount and instantly alert to its slightest motion1 is skilfully and naturally making perhaps fifty movements a minute of hand and feet2 the former lightly grasping the 8joy-stick0 which controls the ,elevator hinged to the tail1 and also the ,ailerons or little wings hinged to the wing-tips2 and the latter moving the ,rudder control-bar4 ,a strain on the ,pilot8 ,not a bit of it1 for this is his ,work which he loves and excels in2 and given a cool head1 alert eye1 and a sensitive touch for the controls1 what sport can compare with these ever-changing battles of the air8 ,the ,aeroplane has all this time been climbing in great wide circles1 and is now some three thousand feet above the ,aerodrome which from such height looks absurdly small4 ,the buildings below now seem quite squat2 the hills appear to have sunk away into the ground1 and the whole country below1 cut up into diminutive fields1 has the appearance of having been lately tidied and thoroughly spring-cleaned6 ,a doll's country it looks1 with tiny horses and cows ornamenting the fields and little model motor-cars and carts stuck on the roads1 the latter stretching away across the country like ribbons accidentally dropped4 ,at three thousand feet altitude the ,pilot is satisfied that he is now sufficiently high to secure1 in the event of engine failure1 a long enough glide to earth to enable him to choose and reach a good landing-place2 and1 being furthermore content with the steady running of the engine1 he decides to climb no more but to follow the course he has mapped out4 ,consulting the compass1 he places the ,aeroplane on the ,a--,e course and1 using the ,elevator1 he gives his craft its minimum angle of incidence at which it will just maintain horizontal flight and secure its maximum speed4 ,swiftly he speeds away1 and few thoughts he has now for the changing panorama of country1 cloud1 and colour4 ,ever present in his mind are the three great 'cross-country queries4 8,am ,i on my right course8 ,can ,i see a good landing-ground within gliding distance80 ,and 8,how is the ,engine running80 ,keenly both he and the ,observer compare their maps with the country below4 ,the roads1 khaki-coloured ribbons1 are easily seen but are not of much use1 for there are so many of them and they all look alike from such an altitude4 ,now where can that lake be which the map shows so plainly8 ,he feels that surely he should see it by now1 and has an uncomfortable feeling that he is flying too far ,west4 ,what pilot is there indeed who has not many times experienced such unpleasant sensation8 ,few things in the air can create greater anxiety4 ,wisely1 however1 he sticks to his compass course1 and the next minute he is rewarded by the sight of the lake1 though indeed he now sees that the direction of his travel will not take him over it1 as should be the case if he were flying over the shortest route to his destination4 ,he must have slightly miscalculated the velocity or direction of the side-wind4 8,about ten degrees off10 he mutters1 and1 using the ,rudder1 corrects his course accordingly4 ,now he feels happier and that he is well on his way4 ,the gusts1 too1 have ceased to trouble him as1 at this altitude1 they are not nearly so bad as they were near the ground the broken surface of which does much to produce them2 and sometimes for miles he makes but a movement or two of the controls4 ,the clouds just above race by with dizzy and uniform speed2 the country below slowly unrolls1 and the steady drone of the ,engine is almost hypnotic in effect4 8,sleep1 sleep1 sleep10 it insidiously suggests4 8,listen to me and watch the clouds2 there's nothing else to do4 ,dream1 dream1 dream of speeding through space for ever1 and ever1 and ever2 and rest1 rest1 rest to the sound of my rhythmical hum4 ,droning on and on1 nothing whatever matters4 ,all things now are merged into speed through space and a sleepy monotonous d-d-r-r-o-o-n-n-e - - - - -40 ,but the ,pilot pulls himself together with a start and peers far ahead in search of the next landmark4 ,this time it is a little country town1 red-roofed his map tells him1 and roughly of cruciform shape2 and1 sure enough1 there in the right direction are the broken outlines of a few red roofs peeping out from between the trees4 ,another minute and he can see this little town1 a fairy town it appears1 nestling down between the hills with its red roofs and picturesque shape1 a glowing and lovely contrast with the dark green of the surrounding moors4 ,so extraordinarily clean and tidy it looks from such a height1 and laid out in such orderly fashion with perfectly defined squares1 parks1 avenues1 and public buildings1 it indeed appears hardly real1 but rather as if it has this very day materialized from some delightful children's book6 ,every city and town you must know has its distinct individuality to the ,pilot's eye4 ,some are not fairy places at all1 but great dark ugly blots upon the fair countryside1 and with tall shafts belching forth murky columns of smoke to defile clean space4 ,others1 melancholy-looking masses of grey1 slate-roofed houses1 are always sad and dispirited2 never welcoming the glad sunshine1 but ever calling for leaden skies and a weeping ,heaven4 ,others again1 little coquettes with village green1 white palings everywhere1 bright gravel roads1 and an irrepressible air of brightness and gaiety4 ,then there are the rivers1 silvery streaks peacefully winding far1 far away to the distant horizon2 they and the lakes the finest landmarks the ,pilot can have4 ,and the forests4 ,how can ,i describe them8 ,the trees cannot be seen separately1 but merge altogether into enormous irregular dark green masses sprawling over the country1 and sometimes with great ungainly arms half encircling some town or village2 and the wind passing over the foliage at times gives the forest an almost living appearance1 as of some great dragon of olden times rousing itself from slumber to devour the peaceful villages which its arms encircle4 ,and the ,pilot and ,observer fly on and on1 seeing these things and many others which baffle my poor skill to describe--things1 dear ,reader1 that you shall see1 and poets sing of1 and great artists paint in the days to come when the ,designer has captured ,efficiency4 ,then1 and the time is near1 shall you see this beautiful world as you have never seen it before1 the garden it is1 the peace it breathes1 and the wonder of it4 ,the ,pilot1 flying on1 is now anxiously looking for the railway line which midway on his journey should point the course4 ,ah6 ,there it is at last1 but suddenly 7and the map at fault7 it plunges into the earth6 ,well the writer remembers when that happened to him on a long 'cross-country flight in the early days of aviation4 ,anxiously he wondered 8,are tunnels always straight80 and with what relief1 keeping on a straight course1 he picked up the line again some three miles farther on6 ,now at last the ,pilot sees the sea1 just a streak on the north-eastern horizon1 and he knows that his flight is two-thirds over4 ,indeed1 he should have seen it before1 but the air is none too clear1 and he is not yet able to discern the river which soon should cross his path4 ,as he swiftly speeds on the air becomes denser and denser with what he fears must be the beginning of a sea-fog1 perhaps drifting inland along the course of the river4 ,now does he feel real anxiety1 for it is the ,,duty of a ,pilot to fear fog1 his deadliest enemy4 ,fog not only hides the landmarks by which he keeps his course1 but makes the control of the ,aeroplane a matter of the greatest difficulty4 ,he may not realize it1 but1 in keeping his machine on an even keel1 he is unconsciously balancing it against the horizon1 and with the horizon gone he is lost indeed4 ,not only that1 but it also prevents him from choosing his landing-place1 and the chances are that1 landing in a fog1 he will smash into a tree1 hedge1 or building1 with disastrous results4 ,the best and boldest pilot 'wares a fog1 and so this one1 finding the conditions becoming worse and yet worse1 and being forced to descend lower and lower in order to keep the earth within view1 wisely decides to choose a landing-place while there is yet time to do so4 ,throttling down the power of the engine he spirals downwards1 keenly observing the country below4 ,there are plenty of green fields to lure him1 and his great object is to avoid one in which the grass is long1 for that would bring his machine to a stop so suddenly as to turn it over2 or one of rough surface likely to break the under-carriage4 ,now is perfect eyesight and a cool head indispensable4 ,he sees and decides upon a field and1 knowing his job1 he sticks to that field with no change of mind to confuse him4 ,it is none too large1 and gliding just over the trees and head on to the wind he skilfully 8stalls0 his machine2 that is1 the speed having decreased sufficiently to avoid such a manoeuvre resulting in ascent1 he1 by means of the ,elevator1 gives the ,aeroplane as large an angle of incidence as possible1 and the undersides of the planes meeting the air at such a large angle act as an air-brake1 and the ,aeroplane1 skimming over the ground1 lessens its speed and finally stops just at the farther end of the field4 ,then1 after driving the ,aeroplane up to and under the lee of the hedge1 he stops the engine1 and quickly lashing the joy-stick fast in order to prevent the wind from blowing the controlling surfaces about and possibly damaging them1 he hurriedly alights4 ,now running to the tail he lifts it up on to his shoulder1 for the wind has become rough indeed and there is danger of the ,aeroplane becoming unmanageable4 ,by this action he decreases the angle at which the planes are inclined to the wind and so minimizes the latter's effect upon them4 ,then to the ,observer1 8,hurry up1 old fellow1 and try to find some rope1 wire1 or anything with which to picket the machine4 ,the wind is rising and ,i shan't be able to hold the 'bus steady for long4 ,don't forget the wire-cutters4 ,they're in the tool kit40 ,and the ,observer rushes off in frantic haste1 before long triumphantly returning with a long length of wire from a neighbouring fence4 ,blocking up the tail with some debris at hand1 they soon succeed1 with the aid of the wire1 in stoutly picketing the ,aeroplane to the roots of the high hedge in front of it2 done with much care1 too1 so that the wire shall not fray the fabric or set up dangerous bending-stresses in the woodwork4 ,their work is not done yet1 for the ,observer remarking1 8,i don't like the look of this thick weather and rather fear a heavy rain-storm10 the ,pilot replies1 8,well1 it's a fearful bore1 but the first rule of our game is never to take an unnecessary risk1 so out with the engine and body covers40 ,working with a will they soon have the engine and the open part of the body which contains the seats1 controls1 and instruments snugly housed with their waterproof covers1 and the ,aeroplane is ready to weather the possible storm4 ,says the ,observer1 8,i'm remarkably peckish1 and methinks ,i spy the towers of one of ,england's stately homes showing themselves just beyond that wood1 less than a quarter of a mile away4 ,what ho6 for a raid4 ,what do you say80 8,all right1 you cut along and ,i'll stop here1 for the ,aeroplane must not be left alone4 ,get back as quickly as possible40 ,and the ,observer trots off1 leaving the ,pilot filling his pipe and anxiously scrutinizing the weather conditions4 ,very thick it is now1 but the day is yet young1 and he has hopes of the fog lifting sufficiently to enable the flight to be resumed4 ,a little impatiently he awaits the return of his comrade1 but with never a doubt of the result1 for the hospitality of the country house is proverbial among pilots6 ,what old hand among them is there who cannot instance many a forced landing made pleasant by such hospitality8 ,never too late or too early to help with food1 petrol1 oil1 tools1 and assistants4 ,many a grateful thought has the writer for such kind help given in the days before the war 7how long ago they seem671 when aeroplanes were still more imperfect than they are now1 and involuntary descents often a part of 'cross-country flying4 ,ah6 those early days6 ,how fresh and inspiring they were6 ,as one started off on one's first 'cross-country flight1 on a machine the first of its design1 and with everything yet to learn1 and the wonders of the air yet to explore2 then the joy of accomplishment1 the dreams of ,efficiency1 the hard work and long hours better than leisure2 and what a field of endeavour--the realms of space to conquer6 ,and the battle still goes on with ever-increasing success4 ,who is bold enough to say what its limits shall be8 ,so ruminates this ,pilot-,designer1 as he puffs at his pipe1 until his reverie is abruptly disturbed by the return of the ,observer4 8,wake up1 you ,,airman10 the latter shouts4 8,here's the very thing the doctor ordered6 ,a basket of first-class grub and something to keep the fog out1 too40 8,well1 that's splendid1 but don't call me newspaper names or you'll spoil my appetite60 ,then1 with hunger such as only flying can produce1 they appreciatively discuss their lunch1 and with many a grateful thought for the donors--and they talk shop4 ,they can't help it1 and even golf is a poor second to flight talk4 ,says the ,pilot1 who must have his grievance1 8,just observe where ,i managed to stop the machine4 ,not twenty feet from this hedge6 ,a little more and we should have been through it and into ,kingdom ,come6 ,i stalled as well as one could1 but the tail touched the ground and so ,i could not give the ,aeroplane any larger angle of incidence4 ,could ,i have given it a larger angle1 then the planes would have become a much more effective air-brake1 and we should have come to rest in a much shorter distance4 ,it's all the fault of the tail4 ,there's hardly a type of ,aeroplane in existence in which the tail could not be raised several feet1 and that would make all the difference4 ,high tails mean a large angle of incidence when the machine touches ground and1 with enough angle1 ,i'll guarantee to safely land the fastest machine in a five-acre field4 ,you can1 ,i am sure1 imagine what a difference that would make where forced landings are concerned60 ,then rapidly sketching in his notebook1 he shows the ,observer the following illustration3 8,that's very pretty10 said the ,observer1 8but how about ,mechanical ,difficulties1 and ,efficiency in respect of ,flight8 ,and1 anyway1 why hasn't such an obvious thing been done already80 8,as regards the first part of your question ,i assure you that there's nothing in it1 and ,i'll prove it to you as follows----0 8,oh6 ,that's all right1 old chap4 ,i'll take your word for it10 hurriedly replies the ,observer1 whose soul isn't tuned to a technical key4 8,as regards the latter part of your inquiry10 went on the ,pilot1 a little nettled at having such a poor listener1 8it's very simple4 ,aeroplanes have 'just growed' like ,topsy1 and they consequently contain this and many another relic of early day design when ,aeroplanes were more or less thrown together and anything was good enough that could get off the ground40 8,by ,jove10 interrupts the ,observer1 8,i do believe the fog is lifting4 ,hadn't we better get the engine and body covers off1 just in case it's really so80 8,i believe you're right4 ,i am sure those hills over there could not be seen a few minutes ago1 and look--there's sunshine over there4 ,we'd better hurry up40 ,ten minutes' hard work and the covers are off1 neatly folded and stowed aboard2 the picketing wires are cast adrift1 and the ,pilot is once more in his seat4 ,the ,aeroplane has been turned to face the other end of the field1 and1 the ,observer swinging round the propeller1 the engine is awake again and slowly ticking over4 ,quickly the ,observer climbs into his seat in front of the ,pilot1 and1 the latter slightly opening the throttle1 the ,aeroplane leisurely rolls over the ground towards the other end of the field1 from which the ascent will be made4 ,arriving there the ,pilot turns the ,aeroplane in order to face the wind and thus secure a quick 8get-off40 ,then he opens the throttle fully and the mighty voice of the ,engine roars out 8,now see me clear that hedge60 and the ,aeroplane races forward at its minimum angle of incidence4 ,tail up1 and with ever-increasing speed1 it rushes towards the hedge under the lee of which it has lately been at rest2 and then1 just as the ,observer involuntarily pulls back an imaginary 8joy-stick10 the ,pilot moves the real one and places the machine at its best climbing angle4 ,like a living thing it responds1 and instantly leaves the ground1 clearing the hedge like a--well1 like an ,aeroplane with an excellent margin of lift4 ,upwards it climbs with even and powerful lift1 and the familiar scenes below again gladden the eyes of the ,pilot4 ,smaller and more and more squat grow the houses and hills2 more and more doll-like appear the fields which are clearly outlined by the hedges2 and soon the country below is easily identified with the map4 ,now they can see the river before them and a bay of the sea which must be crossed or skirted4 ,the fog still lingers along the course of the river and between the hills1 but is fast rolling away in grey1 ghost-like masses4 ,out to sea it obscures the horizon1 making it difficult to be sure where water ends and fog begins1 and creating a strange1 rather weird effect by which ships at a certain distance appear to be floating in space4 ,now the ,aeroplane is almost over the river1 and the next instant it suddenly drops into a 8hole in the air40 ,with great suddenness it happens1 and for some two hundred feet it drops nose-down and tilted over sideways2 but the ,pilot is prepared and has put his craft on an even keel in less time than it takes to tell you about it2 for well he knows that he must expect such conditions when passing over a shore or1 indeed1 any well-defined change in the composition of the earth's surface4 ,especially is this so on a hot and sunny day1 for then the warm surface of the earth creates columns of ascending air1 the speed of the ascent depending upon the composition of the surface4 ,sandy soil1 for instance1 such as borders this river produces a quickly ascending column of air1 whereas water and forests have not such a marked effect4 ,thus1 when our ,aeroplane passed over the shore of the river1 it suddenly lost the lift due to the ascending air produced by the warm sandy soil1 and it consequently dropped just as if it had fallen into a hole4 ,now the ,aeroplane is over the bay and1 the sea being calm1 the ,pilot looks down1 down through the water1 and clearly sees the bottom1 hundreds of feet below the surface4 ,down through the reflection of the blue sky and clouds1 and one might think that is all1 but it isn't4 ,only those who fly know the beauties of the sea as viewed from above2 its dappled pearly tints2 its soft dark blue shadows2 the beautiful contrasts of unusual shades of colour which are always differing and shifting with the changing sunshine and the ever moving position of the aerial observer4 ,ah6 for some better pen than mine to describe these things6 ,one with glowing words and a magic rhythm to express the wonders of the air and the beauty of the garden beneath--the immensity of the sea--the sense of space and of one's littleness there--the realization of the ,power moving the multitudes below--the exaltation of spirit altitude produces--the joy of speed4 ,a new world of sensation6 ,now the bay is almost crossed and the ,aerodrome at ,b can be distinguished4 ,on the ,aerodrome is a little crowd waiting and watching for the arrival of the ,aeroplane1 for it is of a new and improved type and its first 'cross-country performance is of keen interest to these men2 men who really know something about flight4 ,there is the ,squadron ,commander who has done some real flying in his time2 several well-seasoned ,flight-,commanders2 a dozen or more ,flight-,lieutenants2 a knowledgeable ,flight-,sergeant2 a number of ,air ,mechanics1 and1 a little on one side and almost unnoticed1 the ,designer4 8,i hope they are all right10 said someone1 8and that they haven't had difficulties with the fog4 ,it rolled up very quickly1 you know40 8,never fear10 remarked a ,flight-,commander4 8,i know the ,pilot well and he's a good 'un2 far too good to carry on into a fog40 8,they say the machine is really something out of the ordinary10 said another1 8and that1 for once1 the ,designer has been allowed full play2 that he hasn't been forced to unduly standardize ribs1 spars1 struts1 etc41 and has more or less had his own way4 ,i wonder who he is4 ,it seems strange we hear so little of him40 8,ah6 my boy4 ,you do a bit more flying and you'll discover that things are not always as they appear from a distance60 8,there she is1 sir60 cries the ,flight-,sergeant4 8,just a speck over the silvery corner of that cloud40 ,a tiny speck it looks1 some six miles distant and three thousand feet high2 but1 racing along1 it rapidly appears larger and soon its outlines can be traced and the sunlight be seen playing upon the whirling propeller4 ,now the distant drone of the engine can be heard1 but not for long1 for suddenly it ceases and1 the nose of the ,aeroplane sinking1 the craft commences gliding downwards4 8,surely too far away10 says a subaltern4 8,it will be a wonderful machine if1 from that distance and height1 it can glide into the ,aerodrome40 ,and more than one express the opinion that it cannot be done2 but the ,designer smiles to himself1 yet with a little anxiety1 for his reputation is at stake1 and ,efficiency1 the main reward he desires1 is perhaps1 or perhaps not1 at last within his grasp6 ,swiftly the machine glides downwards towards them1 and it can now be seen how surprisingly little it is affected by the rough weather and gusts2 so much so that a little chorus of approval is heard4 8,jolly good gliding angle10 says someone2 and another1 8,beautifully quick controls1 what80 and from yet another1 8,by ,jove6 ,the ,pilot must be sure of the machine4 ,look1 he's stopped the engine entirely40 ,then the ,aeroplane with noiseless engine glides over the boundary of the ,aerodrome1 and1 with just a soft soughing sound from the air it cleaves1 lands gently not fifty yards from the onlookers4 8,glad to see you10 says the ,squadron ,commander to the ,pilot4 8,how do you like the machine80 ,and the ,pilot replies3 8,i never want a better one1 sir4 ,it almost flies itself60 ,and the ,designer turns his face homewards and towards his beloved drawing-office2 well satisfied1 but still dreaming dreams of the future and444 looking far ahead whom should he see but ,efficiency at last coming towards him6 ,and to him she is all things4 ,in her hair is the morning sunshine2 her eyes hold the blue of the sky1 and on her cheeks is the pearly tint of the clouds as seen from above4 ,the passion of speed1 the lure of space1 the sense of power1 and the wonder of the future444 all these things she holds for him4 8,ah60 he cries4 8,you'll never leave me now1 when at last there is no one between us80 ,and ,efficiency1 smiling and blushing1 but practical as ever1 says3 8,and you will never throw those ,compromises in my face80 8,my dear1 ,i love you for them6 ,haven't they been my life ever since ,i began striving for you ten long years ago80 ,and so they walked off very happily1 arm-in-arm together2 and if this hasn't bored you and you'd like some more of the same sort of thing1 ,i'd just love to tell you some day of the wonderful things they accomplish together1 and of what they dream the future holds in store4 ,and that's the end of the ,prologue4 ,,chapter ,i4 ,,flight ,air has weight 7about #ac cubic feet #a lb471 inertia1 and momentum4 ,it therefore obeys ,newton's laws#ad and resists movement4 ,it is that resistance or reaction which makes flight possible4 ,flight is secured by driving through the air a surface#ae inclined upwards and towards the direction of motion4 ,s ,side view of surface4 ,m ,direction of motion4 ,,chord4--,the ,chord is1 for practical purposes1 taken to be a straight line from the leading edge of the surface to its trailing edge4 ,n ,a line through the surface starting from its trailing edge4 ,the position of this line1 which ,i call the ,neutral ,lift ,line1 is found by means of wind-tunnel research1 and it varies with differences in the camber 7curvature7 of surfaces4 ,in order to secure flight1 the inclination of the surface must be such that the neutral lift line makes an angle with and ,,above the line of motion4 ,if it is coincident with ,m1 there is no lift4 ,if it makes an angle with ,m and ,,below it1 then there is a pressure tending to force the surface down4 ,i ,angle of ,incidence4 ,this angle is generally defined as the angle the chord makes with the direction of motion1 but that is a bad definition1 as it leads to misconception4 ,the angle of incidence is best described as the angle the neutral lift line makes with the direction of motion relative to the air4 ,you will1 however1 find that in nearly all rigging specifications the angle of incidence is taken to mean the angle the chord makes with a line parallel to the propeller thrust4 ,this is necessary from the point of view of the practical mechanic who has to rig the aeroplane1 for he could not find the neutral lift line1 whereas he can easily find the chord4 ,again1 he would certainly be in doubt as to 8the direction of motion relative to the air10 whereas he can easily find a line parallel to the propeller thrust4 ,it is a pity1 however1 that these practical considerations have resulted in a bad definition of the angle of incidence becoming prevalent1 a consequence of which has been the widespread fallacy that flight may be secured with a negative inclination of the surface4 ,flight may conceivably be secured with a negative angle of chord1 but never with a negative inclination of the surface4 ,all this is only applicable to cambered surfaces4 ,in the case of flat surfaces the neutral lift line coincides with the chord and the definition ,i have criticised adversely is then applicable4 ,flat lifting surfaces are1 however1 never used4 ,the surface acts upon the air in the following manner3 ,as the bottom of the surface meets the air1 it compresses it and accelerates it ,,downwards4 ,as a result of this definite action there is1 of course1 an equal and opposite reaction ,,upwards4 ,the top surface1 in moving forward1 tends to leave the air behind it1 thus creating a semi-vacuum or rarefied area over the top of the surface4 ,consequently the pressure of air on the top of the surface is decreased1 thus assisting the reaction below to lift the surface ,,upwards4 ,the reaction increases approximately as the square of the velocity4 ,it is the result of 7#a7 the mass of air engaged1 and 7#b7 the velocity and consequent force with which the surface engages the air4 ,if the reaction was produced by only one of those factors it would increase in direct proportion to the velocity1 but1 since it is the product of both factors1 it increases as ,v7#b,s74 ,approximately three-fifths of the reaction is due to the decrease of density 7and consequent decrease of downward pressure7 on the top of the surface2 and only some two-fifths is due to the upward reaction secured by the action of the bottom surface upon the air4 ,a practical point in respect of this is that1 in the event of the fabric covering the surface getting into bad condition1 it is more likely to strip off the top than off the bottom4 ,the direction of the reaction is approximately at right-angles to the chord of the surface1 as illustrated above2 and it is1 in considering flight1 convenient to divide it into two component parts or values1 thus3 #a4 ,the vertical component of the reaction1 i4e41 ,lift1 which is opposed to ,gravity1 i4e41 the weight of the aeroplane4 #b4 ,the horizontal component1 i4e41 ,drift 7sometimes called ,resistance71 to which is opposed the thrust of the propeller4 ,the direction of the reaction is1 of course1 the resultant of the forces ,lift and ,drift4 ,the ,lift is the useful part of the reaction1 for it lifts the weight of the aeroplane4 ,the ,drift is the villain of the piece1 and must be overcome by the ,thrust in order to secure the necessary velocity to produce the requisite ,lift for flight4 ,,drift4--,the drift of the whole aeroplane 7we have considered only the lifting surface heretofore7 may be conveniently divided into three parts1 as follows3 ,active ,drift1 which is the drift produced by the lifting surfaces4 ,passive ,drift1 which is the drift produced by all the rest of the aeroplane--the struts1 wires1 fuselage1 under-carriage1 etc41 all of which is known as 8detrimental surface40 ,skin ,friction1 which is the drift produced by the friction of the air with roughnesses of surface4 ,the latter is practically negligible having regard to the smooth surface of the modern aeroplane1 and its comparatively slow velocity compared with1 for instance1 the velocity of a propeller blade4 ,,lift-,,drift ,,ratio4--,the proportion of lift to drift is known as the lift-drift ratio1 and is of paramount importance1 for it expresses the efficiency of the aeroplane 7as distinct from engine and propeller74 ,a knowledge of the factors governing the lift-drift ratio is1 as will be seen later1 an absolute necessity to anyone responsible for the rigging of an aeroplane1 and the maintenance of it in an efficient and safe condition4 ,those factors are as follows3 #a4 ,velocity4--,the greater the velocity the greater the proportion of drift to lift1 and consequently the less the efficiency4 ,considering the lifting surfaces alone1 both the lift and the 7active7 drift1 being component parts of the reaction1 increase as the square of the velocity1 and the efficiency remains the same at all speeds4 ,but1 considering the whole aeroplane1 we must remember the passive drift4 ,it also increases as the square of the velocity 7with no attendant lift71 and1 adding itself to the active drift1 results in increasing the proportion of total drift 7active passive7 to lift4 ,but for the increase in passive drift the efficiency of the aeroplane would not fall with increasing velocity1 and it would be possible1 by doubling the thrust1 to approximately double the speed or lift--a happy state of affairs which can never be1 but which we may1 in a measure1 approach by doing everything possible to diminish the passive drift4 ,every effort is then made to decrease it by 8stream-lining10 i4e41 by giving all 8detrimental0 parts of the aeroplane a form by which they will pass through the air with the least possible drift4 ,even the wires bracing the aeroplane together are1 in many cases1 stream-lined1 and with a markedly good effect upon the lift-drift ratio4 ,in the case of a certain well-known type of aeroplane the replacing of the ordinary wires by stream-lined wires added over five miles an hour to the flight speed4 ,head-resistance is a term often applied to passive drift1 but it is apt to convey a wrong impression1 as the drift is not nearly so much the result of the head or forward part of struts1 wires1 etc41 as it is of the rarefied area behind4 ,above is illustrated the flow of air round two objects moving in the direction of the arrow ,m4 ,in the case of ,a1 you will note that the rarefied area ,,dd is of very considerable extent2 whereas in the case of ,b1 the air flows round it in such a way as to meet very closely to the rear of the object1 thus ,,decreasing ,,dd4 ,the greater the rarefied area ,,dd4 then1 the less the density1 and1 consequently1 the less the pressure of air upon the rear of the object4 ,the less such pressure1 then1 the better is head-resistance ,d able to get its work in1 and the more thrust will be required to overcome it4 ,the 8fineness0 of the stream-line shape1 i4e41 the proportion of length to width1 is determined by the velocity--the greater the velocity1 the greater the fineness4 ,the best degree of fineness for any given velocity is found by means of wind-tunnel research4 ,the practical application of all this is1 from a rigging point of view1 the importance of adjusting all stream-line parts to be dead-on in the line of flight1 but more of that later on4 #b4 ,angle of ,incidence4--,the most efficient angle of incidence varies with the thrust at the disposal of the designer1 the weight to be carried1 and the climb-velocity ratio desired4 ,the best angles of incidence for these varying factors are found by means of wind-tunnel research and practical trial and error4 ,generally speaking1 the greater the velocity the smaller should be the angle of incidence1 in order to preserve a clean1 stream-line shape of rarefied area and freedom from eddies4 ,should the angle be too great for the velocity1 then the rarefied area becomes of irregular shape with attendant turbulent eddies4 ,such eddies possess no lift value1 and since it has taken power to produce them1 they represent drift and adversely affect the lift-drift ratio4 ,from a rigging point of view1 one must presume that every standard aeroplane has its lifting surface set at the most efficient angle1 and the practical application of all this is in taking the greatest possible care to rig the surface at the correct angle and to maintain it at such angle4 ,any deviation will adversely affect the lift-drift ratio1 i4e41 the efficiency4 #c4 ,camber4--7,refer to the second illustration in this chapter47 ,the lifting surfaces are cambered1 i4e41 curved1 in order to decrease the horizontal component of the reaction1 i4e41 the drift4 ,the bottom camber3 ,if the bottom of the surface was flat1 every particle of air meeting it would do so with a shock1 and such shock would produce a very considerable horizontal reaction or drift4 ,by curving it such shock is diminished1 and the curve should be such as to produce a uniform 7not necessarily constant7 acceleration and compression of the air from the leading edge to the trailing edge4 ,any unevenness in the acceleration and compression of the air produces drift4 ,the top camber3 ,if this was flat it would produce a rarefied area of irregular shape4 ,i have already explained the bad effect this has upon the lift-drift ratio4 ,the top surface is then curved to produce a rarefied area the shape of which shall be as stream-line and free from attendant eddies as possible4 ,the camber varies with the angle of incidence1 the velocity1 and the thickness of the surface4 ,generally speaking1 the greater the velocity1 the less the camber and angle of incidence4 ,with infinite velocity the surface would be set at no angle of incidence 7the neutral lift line coincident with the direction of motion relative to the air71 and would be1 top and bottom1 of pure streamline form--i4e41 of infinite fineness4 ,this is1 of course1 carrying theory to absurdity as the surface would then cease to exist4 ,the best cambers for varying velocities1 angles of incidence1 and thicknesses of surface1 are found by means of wind-tunnel research4 ,the practical application of all this is in taking the greatest care to prevent the surface from becoming distorted and thus spoiling the camber and consequently the lift-drift ratio4 #d4 ,aspect ,ratio4--,this is the proportion of span to chord4 ,thus1 if the span is1 for instance1 #ej feet and the chord #e feet1 the surface would be said to have an aspect ratio of #aj to #a4 ,for ,a ,,given ,,velocity and ,a ,,given ,,area of surface1 the greater the aspect ratio1 the greater the reaction4 ,it is obvious1 ,i think1 that the greater the span1 the greater the mass of air engaged1 and1 as already explained1 the reaction is partly the result of the mass of air engaged4 ,not only that1 but1 ,,provided the chord is not decreased to an extent making it impossible to secure the best camber owing to the thickness of the surface1 the greater the aspect ratio1 the better the lift-drift ratio4 ,the reason of this is rather obscure4 ,it is sometimes advanced that it is owing to the 8spill0 of air from under the wing-tips4 ,with a high aspect ratio the chord is less than would otherwise be the case4 ,less chord results in smaller wing-tips and consequently less 8spill40 ,this1 however1 appears to be a rather inadequate reason for the high aspect ratio producing the high lift-drift ratio4 ,other reasons are also advanced1 but they are of such a contentious nature ,i do not think it well to go into them here4 ,they are of interest to designers1 but this is written for the practical pilot and rigger4 #e4 ,stagger4--,this is the advancement of the top surface relative to the bottom surface1 and is not1 of course1 applicable to a single surface1 i4e41 a monoplane4 ,in the case of a biplane having no stagger1 there will be 8interference0 and consequent loss of ,efficiency unless the gap between the top and bottom surfaces is equal to not less than #a #a_/b times the chord4 ,if less than that1 the air engaged by the bottom of the top surface will have a tendency to be drawn into the rarefied area over the top of the bottom surface1 with the result that the surfaces will not secure as good a reaction as would otherwise be the case4 ,it is not practicable to have a gap of much more than a distance equal to the chord1 owing to the drift produced by the great length of struts and wires such a large gap would necessitate4 ,by staggering the top surface forward1 however1 it is removed from the action of the lower surface and engages undisturbed air1 with the result that the efficiency can in this way be increased by about #e per cent4 ,theoretically the top plane should be staggered forward for a distance equal to about #cj per cent4 of the chord1 the exact distance depending upon the velocity and angle of incidence2 but this is not always possible to arrange in designing an aeroplane1 owing to difficulties of balance1 desired position1 and view of pilot1 observer1 etc4 #f4 ,horizontal ,equivalent4--,the vertical component of the reaction1 i4e41 lift1 varies as the horizontal equivalent 7,h4,e47 of the surface1 but the drift remains the same4 ,then it follows that if ,h4,e4 grows less1 the ratio of lift to drift must do the same4 ,a1 ,b1 and ,c are front views of three surfaces4 ,a has its full ,h4,e41 and therefore1 from the point of view from which we are at the moment considering efficiency1 it has its best lift-drift ratio4 ,b and ,c both possess the same surface as ,a1 but one is inclined upwards from its centre and the other is straight but tilted4 ,for these reasons their ,h4,e4's are1 as illustrated1 less than in the case of ,a4 ,that means less vertical lift1 and1 the drift remaining the same 7for there is the same amount of surface as in ,a to produce it71 the lift-drift ratio falls4 ,,the ,,margin ,,of ,,power is the power available above that necessary to maintain horizontal flight4 ,,the ,,margin ,,of ,,lift is the height an aeroplane can gain in a given time and starting from a given altitude4 ,as an example1 thus3 #a1jjj feet the first minute1 and starting from an altitude of #ejj feet above sea-level4 ,the margin of lift decreases with altitude1 owing to the decrease in the density of the air1 which adversely affects the engine4 ,provided the engine maintained its impulse with altitude1 then1 if we ignore the problem of the propeller1 which ,i will go into later on1 the margin of lift would not disappear4 ,moreover1 greater velocity for a given power would be secured at a greater altitude1 owing to the decreased density of air to be overcome4 ,after reading that1 you may like to light your pipe and indulge in dreams of the wonderful possibilities which may become realities if some brilliant genius shows us some day how to secure a constant power with increasing altitude4 ,i am afraid1 however1 that will always remain impossible2 but it is probable that some very interesting steps may be taken in that direction4 ,,the ,,minimum ,,angle ,,of ,,incidence is the smallest angle at which1 for a given power1 surface 7including detrimental surface71 and weight1 horizontal flight can be maintained4 ,,the ,,maximum ,,angle ,,of ,,incidence is the greatest angle at which1 for a given power1 surface 7including detrimental surface71 and weight1 horizontal flight can be maintained4 ,,the ,,optimum ,,angle ,,of ,,incidence is the angle at which the lift-drift ratio is highest4 ,in modern aeroplanes it is that angle of incidence possessed by the surface when the axis of the propeller is horizontal4 ,,the ,,best ,,climbing ,,angle is approximately half-way between the maximum and the optimum angles4 ,all present-day aeroplanes are a compromise between ,climb and horizontal ,velocity4 ,we will compare the essentials for two aeroplanes1 one designed for maximum climb1 and the other for maximum velocity4 ,,essentials ,,for ,,maximum ,,climb3 #a4 ,low velocity1 in order to secure the best lift-drift ratio4 #b4 ,having a low velocity1 a large surface will be necessary in order to engage the necessary mass of air to secure the requisite lift4 #c4 ,since 7#a7 such a climbing machine will move along an upward sloping path1 and 7#b7 will climb with its propeller thrust horizontal1 then a large angle relative to the direction of the thrust will be necessary in order to secure the requisite angle relative to the direction of motion4 ,the propeller thrust should be always horizontal1 because the most efficient flying-machine 7having regard to climb ,,or velocity7 has1 so far1 been found to be an arrangement of an inclined surface driven by a ,,horizontal thrust--the surface lifting the weight1 and the thrust overcoming the drift4 ,this is1 in practice1 a far more efficient arrangement than the helicopter1 i4e41 the air-screw revolving about a vertical axis and producing a thrust opposed to gravity4 ,if1 when climbing1 the propeller thrust is at such an angle as to tend to haul the aeroplane upwards1 then it is1 in a measure1 acting as a helicopter1 and that means inefficiency4 ,the reason of a helicopter being inefficient in practice is due to the fact that1 owing to mechanical difficulties1 it is impossible to construct within a reasonable weight an air-screw of the requisite dimensions4 ,that being so1 it would be necessary1 in order to absorb the power of the engine1 to revolve the comparatively small-surfaced air screw at an immensely greater velocity than that of the aeroplane's surface4 ,as already explained1 the lift-drift ratio falls with velocity on account of the increase in passive drift4 ,this applies to a blade of a propeller or air-screw1 which is nothing but a revolving surface set at angle of incidence1 and which it is impossible to construct without a good deal of detrimental surface near the central boss4 #d4 ,the velocity being low1 then it follows that for that reason also the angle of incidence should be comparatively large4 #e4 ,camber4--,since such an aeroplane would be of low velocity1 and therefore possess a large angle of incidence1 a large camber would be necessary4 ,let us now consider the essentials for an aeroplane of maximum velocity for its power1 and possessing merely enough lift to get off the ground1 but no margin of lift4 #a4 ,comparatively ,,high ,,velocity4 #b4 ,a comparatively ,,small ,,surface1 because1 being of greater velocity than the maximum climber1 a greater mass of air will be engaged for a given surface and time1 and therefore a smaller surface will be sufficient to secure the requisit lift4 #c4 ,a small angle relative to the propeller thrust1 since the latter coincides with the direction of motion4 #d4 ,a comparatively small angle of incidence by reason of the high velocity4 #e4 ,a comparatively small camber follows as a result of the small angle of incidence4 ,,summary4 ,essentials for ,maximum ,essentials for ,maximum ,climb4 ,velocity #a4 ,low velocity4 ,high velocity4 #b4 ,large surface4 ,small surface4 #c4 ,large angle relative to ,small angle relative to propeller thrust4 propeller thrust4 #d4 ,large angle relative to ,small angle relative to direction direction of motion4 of motion4 #e4 ,large camber4 ,small camber4 ,it is mechanically impossible to construct an aeroplane of reasonable weight of which it would be possible to very the above opposing essentials4 ,therefore1 all aeroplanes are designed as a compromise between ,climb and ,velocity4 ,as a rule aeroplanes are designed to have at low altitude a slight margin of lift when the propeller thrust is horizontal4 ,,angles ,,of ,,incidence 7,,indicated ,,approximately7 ,,of ,,an ,,aeroplane ,,designed ,,as ,a ,,compromise ,,between ,,velocity ,,and ,,climb1 ,,and ,,possessing ,a ,,slight ,,margin ,,of ,,lift ,,at ,a ,,low ,,altitude ,,and ,,when ,,the ,,thrust ,,is ,,horizontal ,,minimum ,,angle4 ,this gives the greatest velocity during horizontal flight at a low altitude4 ,greater velocity would be secured if the surface1 angle1 and camber were smaller and designed to just maintain horizontal flight with a horizontal thrust4 ,also1 in such case1 the propeller would not be thrusting downwards1 but along a horizontal line which is obviously a more efficient arrangement if we regard the aeroplane merely from one point of view1 i4e41 either with reference to velocity ,,or climb4 ,,optimum ,,angle 7,thrust horizontal7 ,the velocity is less than at the smaller minimum angle1 and1 as aeroplanes are designed to-day1 the area and angle of incidence of the surface is such as to secure a slight ascent at a low altitude4 ,the camber of the surface is designed for this angle of incidence and velocity4 ,the lift-drift ratio is best at this angle4 ,,best ,,climbing ,,angle ,the velocity is now still less by reason of the increased angle producing increase of drift4 ,less velocity at ,a ,,given ,,angle produces less lift1 but the increased angle more or less offsets the loss of lift due to the decreased velocity1 and in addition1 the thrust is now hauling the aeroplane upwards4 ,,maximum ,,angle ,the greater angle has now produced so much drift as to lessen the velocity to a point where the combined lifts from the surface and from the thrust are only just able to maintain horizontal flight4 ,any greater angle will result in a still lower lift-drift ratio4 ,the lift will then become less than the weight and the aeroplane will consequently fall4 ,such a fall is known as 8stalling0 or 8pancaking40 ,,note4--,the golden rule for beginners3 ,never exceed the ,best ,climbing ,angle4 ,always maintain the flying speed of the aeroplane4 ,by this means1 when the altitude is reached where the margin of lift disappears 7on account of loss of engine power71 and which is1 consequently1 the altitude where it is just possible to maintain horizontal flight1 the aeroplane is flying with its thrust horizontal and with maximum efficiency 7as distinct from engine and propeller efficiency74 ,the margin of lift at low altitude1 and when the thrust is horizontal1 should then be such that the higher altitude at which the margin of lift is lost is that altitude at which most of the aeroplane's horizontal flight work is done4 ,that ensures maximum velocity when most required4 ,unfortunately1 where aeroplanes designed for fighting are concerned1 the altitude where most of the work is done is that at which both maximum velocity and maximum margin of lift for power are required4 ,perhaps some day a brilliant inventor will design an aeroplane of reasonable weight and drift of which it will be possible for the pilot to vary at will the above-mentioned opposing essentials4 ,then we shall get maximum velocity1 or maximum margin of lift1 for power as required4 ,until then the design of the aeroplane must remain a compromise between ,velocity and ,climb4 ,,chapter ,,ii4 ,,stability ,,and ,,control ,,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 upon your finger4 ,,neutral ,,instability 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 ,in order that an aeroplane may be reasonably controllable1 it is necessary for it to possess some degree of stability longitudinally1 laterally1 and directionally4 ,,longitudinal ,,stability in an aeroplane 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 ,for such directional stability to exist there must be1 in effect1#af more 8keel-surface0 behind the vertical axis than there is in front of it4 ,by keel-surface ,i mean every-thing to be seen when looking at an aeroplane from the side of it--the sides of the body1 undercarriage1 struts1 wires1 etc4 ,the same thing applies to a weathercock4 ,you know what would happen if there was insufficient keel-surface behind the vertical axis upon which it is pivoted4 ,it would turn off its proper course1 which is opposite to the direction of the wind4 ,it is very much the same in the case of an aeroplane4 ,the above illustration represents an aeroplane 7directionally stable7 flying along the course ,b4 ,a gust striking it as indicated acts upon the greater proportion of keel-surface behind the turning axis and throws it into the new course4 ,it does not1 however1 travel along the new course1 owing to its momentum in the direction ,b4 ,it travels1 as long as such momentum lasts1 in a direction which is the resultant of the two forces ,thrust and ,momentum4 ,but the centre line of the aeroplane is pointing in the direction of the new course4 ,therefore its attitude1 relative to the direction of motion1 is more or less sideways1 and it consequently receives an air pressure in the direction ,c4 ,such pressure1 acting upon the keel-surface1 presses the tail back towards its first position in which the aeroplane is upon its course ,b4 ,what ,i have described is continually going on during flight1 but in a well-designed aeroplane such stabilizing movements are1 most of the time1 so slight as to be imperceptible to the pilot4 ,if an aeroplane was not stabilized in this way1 it would not only be continually trying to leave its course1 but it would also possess a dangerous tendency to 8nose away0 from the direction of the side gusts4 ,in such case the gust shown in the above illustration would turn the aeroplane round the opposite way a very considerable distance2 and the right wing1 being on the outside of the turn1 would travel with greater velocity than the left wing4 ,increased velocity means increased lift2 and so1 the right wing lifting1 the aeroplane would turn over sideways very quickly4 ,,longitudinal ,,stability4--,flat surfaces are longitudinally stable owing to the fact that with decreasing angles of incidence the centre line of pressure 7,c4,p47 moves forward4 ,the ,c4,p4 is a line taken across the surface1 transverse to the direction of motion1 and about which all the air forces may be said to balance1 or through which they may be said to act4 ,imagine ,a to be a flat surface1 attitude vertical1 travelling through the air in the direction of motion ,m4 ,its ,c4,p4 is then obviously along the exact centre line of the surface as illustrated4 ,in ,b1 ,c1 and ,d the surfaces are shown with angles of incidence decreasing to nothing1 and you will note that the ,c4,p4 moves forward with the decreasing angle4 ,now1 should some gust or eddy tend to make the surface decrease the angle1 i4e41 dive1 then the ,c4,p4 moves forward and pushes the front of the surface up4 ,should the surface tend to assume too large an angle1 then the reverse happens--the ,c4,p4 moves back and pushes the rear of the surface up4 ,flat surfaces are1 then1 theoretically stable longitudinally4 ,they are not1 however1 used1 on account of their poor lift-drift ratio4 ,as already explained1 cambered surfaces are used1 and these are longitudinally unstable at those angles of incidence producing a reasonable lift-drift ratio1 i4e41 at angles below3 about #ab degrees4 ,a is a cambered surface1 attitude approximately vertical1 moving through the air in the direction ,m4 ,obviously the ,c4 ,p4 coincides with the transverse centre line of the surface4 ,with decreasing angles1 down to angles of about #cj degrees1 the ,c4,p4 moves forward as in the case of flat surfaces 7see ,b71 but angles above #cj degrees do not interest us1 since they produce a very low ratio of lift to drift4 ,below angles of about #cj degrees 7see ,c7 the dipping front part of the surface assumes a negative angle of incidence resulting in the ,,downward air pressure ,d1 and the more the angle of incidence is decreased1 the greater such negative angle and its resultant pressure ,d4 ,since the ,c4,p4 is the resultant of all the air forces1 its position is naturally affected by ,d1 which causes it to move backwards4 ,now1 should some gust or eddy tend to make the surface decrease its angle of incidence1 i4e41 dive1 then the ,c4,p4 moves backwards1 and1 pushing up the rear of the surface1 causes it to dive the more4 ,should the surface tend to assume too large an angle1 then the reverse happens2 the pressure ,d decreases1 with the result that ,c4,p4 moves forward and pushes up the front of the surface1 thus increasing the angle still further1 the final result being a 8tail-slide40 ,it is therefore necessary to find a means of stabilizing the naturally unstable cambered surface4 ,this is usually secured by means of a stabilizing surface fixed some distance in the rear of the main surface1 and it is a necessary condition that the neutral lift lines of the two surfaces1 when projected to meet each other1 make a dihedral angle4 ,in other words1 the rear stabilizing surface must have a lesser angle of incidence than the main surface--certainly not more than one-third of that of the main surface4 ,this is known as the longitudinal dihedral4 ,i may add that the tail-plane is sometimes mounted upon the aeroplane at the same angle as the main surface1 but1 in such cases1 it attacks air which has received a downward deflection from the main surface1 thus3 ,the angle at which the tail surface attacks the air 7the angle of incidence7 is therefore less than the angle of incidence of the main surface4 ,i will now1 by means of the following illustration1 try to explain how the longitudinal dihedral secures stability3 ,first1 imagine the aeroplane travelling in the direction of motion1 which coincides with the direction of thrust ,t4 ,the weight is1 of course1 balanced about a ,c4,p41 the resultant of the ,c4,p4 of the main surface and the ,c4,p4 of the stabilizing surface4 ,for the sake of illustration1 the stabilizing surface has been given an angle of incidence1 and therefore has a lift and ,c4,p4 ,in practice the stabilizer is often set at no angle of incidence4 ,in such case the proposition remains the same1 but it is1 perhaps1 a little easier to illustrate it as above4 ,now1 we will suppose that a gust or eddy throws the machine into the lower position4 ,it no longer travels in the direction of ,t1 since the momentum in the old direction pulls it off that course4 ,m is now the resultant of the ,thrust and the ,momentum1 and you will note that this results in a decrease in the angle our old friend the neutral lift line makes with ,m1 i4e41 a decrease in the angle of incidence and therefore a decrease in lift4 ,we will suppose that this decrease is #b degrees4 ,such decrease applies to both main surface and stabilizer1 since both are fixed rigidly to the aeroplane4 ,the main surface1 which had #ab degrees angle1 has now only #aj degrees1 i4e41 a loss of ,,one-,,sixth4 ,the stabilizer1 which had #d degrees angle1 has now only #b degrees1 i4e41 a loss of ,,one-,,half4 ,the latter has therefore lost a greater ,,proportion of its angle of incidence1 and consequently its lift1 than has the main surface4 ,it must then fall relative to the main surface4 ,the tail falling1 the aeroplane then assumes its first position1 though at a slightly less altitude4 ,should a gust throw the nose of the aeroplane up1 then the reverse happens4 ,both main surface and stabilizer increase their angles of incidence in the same amount1 but the angle1 and therefore the lift1 of the stabilizer increases in greater proportion than does the lift of the main surface1 with the result that it lifts the tail4 ,the aeroplane then assumes its first position1 though at a slightly greater altitude4 ,do not fall into the widespread error that the angle of incidence varies as the angle of the aeroplane to the horizontal4 ,it varies with such angle1 but not as anything approaching it4 ,remember that the stabilizing effect of the longitudinal dihedral lasts only as long as there is momentum in the direction of the first course4 ,these stabilizing movements are taking place all the time1 even though imperceptible to the pilot4 ,aeroplanes have1 in the past1 been built with a stabilizing surface in front of the main surface instead of at the rear of it4 ,in such design the main surface 7which is then the tail surface as well as the principal lifting surface7 must be set at a less angle than the forward stabilizing surface1 in order to secure a longitudinal dihedral4 ,the defect of such design lies in the fact that the main surface must have a certain angle to lift the weight--say #e degrees4 ,then1 in order to secure a sufficiency of longitudinal stability1 it is necessary to set the forward stabilizer at about #ae degrees4 ,such a large angle of incidence results in a very poor lift-drift ratio 7and consequently great loss of efficiency71 except at very low velocities compared with the speed of modern aeroplanes4 ,at the time such aeroplanes were built velocities were comparatively low1 and this defect was2 for that reason1 not sufficiently appreciated4 ,in the end it killed the 8canard0 or 8tail-first0 design4 ,aeroplanes of the ,dunne and similar types possess no stabilizing surface distinct from the main surface1 but they have a longitudinal dihedral which renders them stable4 ,the main surface towards the wing-tips is given a decreasing angle of incidence and corresponding camber4 ,the wing-tips then act as longitudinal stabilizers4 ,this design of aeroplane1 while very interesting1 has not proved very practicable1 owing to the following disadvantages3 7#a7 ,the plan design is not1 from a mechanical point of view1 so sound as that of the ordinary aeroplane surface1 which is1 in plan1 a parallelogram4 ,it is1 then1 necessary to make the strength of construction greater than would otherwise be the case4 ,that means extra weight4 7#b7 ,the plan of the surface area is such that the aspect ratio is not so high as if the surface was arranged with its leading edges at right angles to the direction of motion4 ,the lower the aspect ratio1 then1 the less the lift4 ,this design1 then1 produces less lift for weight of surface than would the same surface if arranged as a parallelogram4 7#c7 ,in order to secure the longitudinal dihedral1 the angle of incidence has to be very much decreased towards the wing-tips4 ,then1 in order that the lift-drift ratio may be preserved1 there must be a corresponding decrease in the camber4 ,that calls for surface ribs of varying cambers1 and results in an expensive and lengthy job for the builder4 7#d7 ,in order to secure directional stability1 the surface is1 in the centre1 arranged to dip down in the form of a ,v1 pointing towards the direction of motion4 ,should the aeroplane turn off its course1 then its momentum in the direction of its first course causes it to move in a direction the resultant of the thrust and the momentum4 ,it then moves in a more or less sideways attitude1 which results in an air pressure upon one side of the ,v1 and which tends to turn the aeroplane back to its first course4 ,this arrangement of the surface results in a bad drift4 ,vertical surfaces at the wing-tips may also be set at an angle producing the same stabilizing effect1 but they also increase the drift4 ,the gyroscopic action of a rotary engine will affect the longitudinal stability when an aeroplane is turned to right or left4 ,in the case of a ,gnome engine1 such gyroscopic action will tend to depress the nose of the aeroplane when it is turned to the left1 and to elevate it when it is turned to the right4 ,in modern aeroplanes this tendency is not sufficiently important to bother about4 ,in the old days of crudely designed and under-powered aeroplanes this gyroscopic action was very marked1 and led the majority of pilots to dislike turning an aeroplane to the right1 since1 in doing so1 there was some danger of 8stalling40 ,,lateral ,,stability is far more difficult for the designer to secure than is longitudinal or directional stability4 ,some degree of lateral stability may be secured by means of the 8lateral dihedral10 i4e41 the upward inclination of the surface towards its wing-tips thus3 ,imagine the top ,v1 illustrated opposite1 to be the front view of a surface flying towards you4 ,the horizontal equivalent 7,h4,e47 of the left wing is the same as that of the right wing4 ,therefore1 the lift of one wing is equal to the lift of the other1 and the weight1 being situated always in the centre1 is balanced4 ,if some movement of the air causes the surface to tilt sideways1 as in the lower illustration1 then you will note that the ,h4,e4 of the left wing increases1 and the ,h4,e4 of the right wing decreases4 ,the left wing then1 having the greatest lift1 rises2 and the surface assumes its first and normal position4 ,unfortunately however1 the righting effect is not proportional to the difference between the right and left ,h4,e4's4 ,in the case of ,a1 the resultant direction of the reaction of both wings is opposed to the direction of gravity or weight4 ,the two forces ,r ,r and gravity are then evenly balanced1 and the surface is in a state of equilibrium4 ,in the case of ,b1 you will note that the ,r ,r is not directly opposed to gravity4 ,this results in the appearance of ,m1 and so the resultant direction of motion of the aeroplane is no longer directly forward1 but is along a line the resultant of the thrust and ,m4 ,in other words1 it is1 while flying forward1 at the same time moving sideways in the direction ,m4 ,in moving sideways1 the keel-surface receives1 of course1 a pressure from the air equal and opposite to ,m4 ,since such surface is greatest in effect towards the tail1 then the latter must be pushed sideways4 ,that causes the aeroplane to turn2 and1 the highest wing being on the outside of the turn1 it has a greater velocity than the lower wing4 ,that produces greater lift1 and tends to tilt the aeroplane over still more4 ,such tilting tendency is1 however1 opposed by the difference in the ,h4,e4's of the two wings4 ,it then follows that1 for the lateral dihedral angle to be effective1 such angle must be large enough to produce1 when the aeroplane tilts1 a difference in the ,h4,e4's of the two wings1 which difference must be sufficient to not only oppose the tilting tendency due to the aeroplane turning1 but sufficient to also force the aeroplane back to its original position of equilibrium4 ,it is now1 ,i hope1 clear to the reader that the lateral dihedral is not quite so effective as would appear at first sight4 ,some designers1 indeed1 prefer not to use it1 since its effect is not very great1 and since it must be paid for in loss of ,h4,e4 and consequently loss of lift1 thus decreasing the lift-drift ratio1 i4e41 the efficiency4 ,also1 it is sometimes advanced that the lateral dihedral increases the 8spill0 of air from the wing-tips and that this adversely affects the lift-drift ratio4 ,the disposition of the keel-surface affects the lateral stability4 ,it should be1 in effect1 equally divided by the longitudinal turning axis of the aeroplane4 ,if there is an excess of keel-surface above or below such axis1 then a side gust striking it will tend to turn the aeroplane over sideways4 ,the position of the centre of gravity affects lateral stability4 ,if too low1 it produces a pendulum effect and causes the aeroplane to roll sideways4 ,if too high1 it acts as a stick balanced vertically would act4 ,if disturbed1 it tends to travel to a position as far as possible from its original position4 ,it would then tend1 when moved1 to turn the aeroplane over sideways and into an upside-down position4 ,from the point of view of lateral stability1 the best position for the centre of gravity is one a little below the centre of drift4 ,propeller torque affects lateral stability4 ,an aeroplane tends to turn over sideways in the opposite direction to which the propeller revolves4 ,this tendency is offset by increasing the angle of incidence 7and consequently the lift7 of the side tending to fall2 and it is always advisable1 if practical considerations allow it1 to also decrease the angle upon the other side4 ,in that way it is not necessary to depart so far from the normal angle of incidence at which the lift-drift ratio is highest4 ,wash-in is the term applied to the increased angle4 ,wash-out is the term applied to the decreased angle4 ,both lateral and directional stability may be improved by washing out the angle of incidence on both sides of the surface1 thus3 ,the decreased angle decreases the drift and therefore the effect of gusts upon the wing-tips which is just where they have the most effect upon the aeroplane1 owing to the distance from the turning axis4 ,the wash-out also renders the ailerons 7lateral controlling services7 more effective1 as1 in order to operate them1 it is not then necessary to give them such a large angle of incidence as would otherwise be required4 ,the less the angle of incidence of the ailerons1 the better their lift-drift ratio1 i4e41 their efficiency4 ,you will note that1 while the aileron attached to the surface with washed-out angle is operated to the same extent as the aileron illustrated above it1 its angle of incidence is considerably less4 ,its efficiency is therefore greater4 ,the advantages of the wash-in must1 of course be paid for in some loss of lift1 as the lift decreases with the decreased angle4 ,in order to secure all the above described advantages1 a combination is sometimes effected1 thus3 ,,banking4--,an aeroplane turned off its course to right or left does not at once proceed along its new course4 ,its momentum in the direction of its first course causes it to travel along a line the resultant of such momentum and the thrust4 ,in other words1 it more or less skids sideways and away from the centre of the turn4 ,its lifting surfaces do not then meet the air in their correct attitude1 and the lift may fall to such an extent as to become less than the weight1 in which case the aeroplane must fall4 ,this bad effect is minimized by 8banking10 i4e41 tilting the aeroplane sideways4 ,the bottom of the lifting surface is in that way opposed to the air through which it is moving in the direction of the momentum and receives an opposite air pressure4 ,the rarefied area over the top of the surface is rendered still more rare1 and this1 of course1 assists the air pressure in opposing the momentum4 ,the velocity of the 8skid10 or sideways movement1 is then only such as is necessary to secure an air pressure equal and opposite to the centrifugal force of the turn4 ,the sharper the turn1 the greater the effect of the centrifugal force1 and therefore the steeper should be the 8bank40 ,experentia docet4 ,the position of the centre of gravity affects banking4 ,a low ,c4,g4 will tend to swing outward from the centre of the turn1 and will cause the aeroplane to bank--perhaps too much1 in which case the pilot must remedy matters by operating the ailerons4 ,a high ,c4,g4 also tends to swing outward from the centre of the turn4 ,it will tend to make the aeroplane bank the wrong way1 and such effect must be remedied by means of the ailerons4 ,the pleasantest machine from a banking point of view is one in which the ,c4,g4 is a little below the centre of drift4 ,it tends to bank the aeroplane the right way for the turn1 and the pilot can1 if necessary1 perfect the bank by means of the ailerons4 ,the disposition of the keel-surface affects banking4 ,it should be1 in effect1 evenly divided by the longitudinal axis4 ,an excess of keel-surface above the longitudinal axis will1 when banking1 receive an air pressure causing the aeroplane to bank1 perhaps too much4 ,an excess of keel-surface below the axis has the reverse effect4 ,,side-,,slipping4--,this usually occurs as a result of over-banking4 ,it is always the result of the aeroplane tilting sideways and thus decreasing the horizontal equivalent1 and therefore the lift1 of the surface4 ,an excessive 8bank10 or sideways tilt1 results in the ,h4,e41 and therefore the lift1 becoming less than the weight1 when1 of course1 the aeroplane must fall1 i4e41 side-slip4 ,when making a very sharp turn it is necessary to bank very steeply indeed4 ,if1 at the same time1 the longitudinal axis of the aeroplane remains approximately horizontal1 then there must be a fall1 and the direction of motion will be the resultant of the thrust and the fall as illustrated above in sketch ,a4 ,the lifting surfaces and the controlling surfaces are not then meeting the air in the correct attitude1 with the result that1 in addition to falling1 the aeroplane will probably become quite unmanageable4 ,the ,pilot1 however1 prevents such a state of affairs from happening by 8nosing-down10 i4e41 by operating the rudder to turn the nose of the aeroplane downward and towards the direction of motion as illustrated in sketch ,b4 ,this results in the higher wing1 which is on the outside of the turn1 travelling with greater velocity1 and therefore securing a greater reaction than the lower wing1 thus tending to tilt the aeroplane over still more4 ,the aeroplane is now almost upside-down1 but its attitude relative to the direction of motion is correct and the controlling surfaces are all of them working efficiently4 ,the recovery of a normal attitude relative to the ,earth is then made as illustrated in sketch ,c4 ,the ,pilot must then learn to know just the angle of bank at which the margin of lift is lost1 and1 if a sharp turn necessitates banking beyond that angle1 he must 8nose-down40 ,in this matter of banking and nosing-down1 and1 indeed1 regarding stability and control generally1 the golden rule for all but very experienced pilots should be3 ,keep the aeroplane in such an attitude that the air pressure is always directly in the pilot's face4 ,the aeroplane is then always engaging the air as designed to do so1 and both lifting and controlling surfaces are acting efficiently4 ,the only exception to this rule is a vertical dive1 and ,i think that is obviously not an attitude for any but very experienced pilots to hanker after4 ,,spinning4--,this is the worst of all predicaments the pilot can find himself in4 ,fortunately it rarely happens4 ,it is due to the combination of 7#a7 a very steep spiral descent of small radius1 and 7#b7 insufficiency of keel-surface behind the vertical axis1 or the jamming of the rudder end or elevator into a position by which the aeroplane is forced into an increasingly steep and small spiral4 ,owing to the small radius of such a spiral1 the mass of the aeroplane may gain a rotary momentum greater1 in effect1 than the air pressure of the keel-surface or controlling surfaces opposed to it2 and1 when once such a condition occurs1 it is difficult to see what can be done by the pilot to remedy it4 ,the sensible pilot will not go beyond reasonable limits of steepness and radius when executing spiral descents4 ,,gliding ,,descent ,,without ,,propeller ,,thrust4--,all aeroplanes are1 or should be1 designed to assume their gliding angle when the power and thrust is cut off4 ,this relieves the pilot of work1 worry1 and danger should he find himself in a fog or cloud4 ,the ,pilot1 although he may not realize it1 maintains the correct attitude of the aeroplane by observing its position relative to the horizon4 ,flying into a fog or cloud the horizon is lost to view1 and he must then rely upon his instruments--7#a7 the compass for direction2 7#b7 an inclinometer 7arched spirit-level7 mounted transversely to the longitudinal axis1 for lateral stability2 and 7#c7 an inclinometer mounted parallel to the longitudinal axis1 or the airspeed indicator1 which will indicate a nose-down position by increase in air speed1 and a tail-down position by decrease in air speed4 ,the pilot is then under the necessity of watching three instruments and manipulating his three controls to keep the instruments indicating longitudinal1 lateral1 and directional stability4 ,that is a feat beyond the capacity of the ordinary man4 ,if1 however1 by the simple movement of throttling down the power and thrust1 he can be relieved of looking after the longitudinal stability1 he then has only two instruments to watch4 ,that is no small job in itself1 but it is1 at any rate1 fairly practicable4 ,aeroplanes are1 then1 designed1 or should be1 so that the centre of gravity is slightly forward of centre of lift4 ,the aeroplane is then1 as a glider1 nose-heavy--and the distance the ,c4,g4 is placed in advance of the ,c4,l4 should be such as to ensure a gliding angle producing a velocity the same as the normal flying speed 7for which the strength of construction has been designed74 ,in order that this nose-heavy tendency should not exist when the thrust is working and descent not required1 the centre of thrust is placed a little below the centre of drift or resistance1 and thus tends to pull up the nose of the aeroplane4 ,the distance the centre of thrust is placed below the centre of drift should be such as to produce a force equal and opposite to that due to the ,c4,g4 being forward of the ,c4,l4 ,,looping ,,and ,,upside ,,down ,,flying4--,if a loop is desired1 it is best to throttle the engine down at point ,a4 ,the ,c4,g4 being forward of the ,c4,p41 then causes the aeroplane to nose-down1 and assists the pilot in making a reasonably small loop along the course ,c and in securing a quick recovery4 ,if the engine is not throttled down1 then the aeroplane may be expected to follow the course ,d1 which results in a longer nose dive than in the case of the course ,c4 ,a steady1 gentle movement of the elevator is necessary4 ,a jerky movement may change the direction of motion so suddenly as to produce dangerous air stresses upon the surfaces1 in which case there is a possibility of collapse4 ,if an upside-down flight is desired1 the engine may1 or may not1 be throttled down at point ,a4 ,if not throttled down1 then the elevator must be operated to secure a course approximately in the direction ,b4 ,if it is throttled down1 then the course must be one of a steeper angle than ,b1 or there will be danger of stalling4 ,diagram p4 #hh4--,this is not set at quite the correct angle4 ,path ,b should slope slightly downwards from ,position ,a4 ,,chapter ,,iii4 ,,rigging ,in order to rig an aeroplane intelligently1 and to maintain it in an efficient and safe condition1 it is necessary to possess a knowledge of the stresses it is called upon to endure1 and the strains likely to appear4 ,,stress is the load or burden a body is called upon to bear4 ,it is usually expressed by the result found by dividing the load by the number of superficial square inches contained in the cross-sectional area of the body4 ,thus1 if1 for instance1 the object illustrated above contains #d square inches of cross-sectional area1 and the total load it is called upon to endure is #aj tons1 the stress would be expressed as #b #a_/b tons4 ,,strain is the deformation produced by stress4 ,,the ,,factor ,,of ,,safety is usually expressed by the result found by dividing the stress at which it is known the body will collapse1 by the maximum stress it will be called upon to endure4 ,for instance1 if a control wire be called upon to endure a maximum stress of #b cwts41 and the known stress at which it will collapse is #aj cwts41 the factor of safety is then #e4 cwts4 centerweights #ajj pound units as in cent century4 ,interestingly enough1 this word only exists today in abbreviation form1 probably of centreweights1 but the dictionary entries1 even from a hundred years ago do not list this as a word1 but do list c4 or ,c4 as the previous popular abbreviation as in ,roman ,numerals ,the word listed is 8hundredweight4 ,michael ,s4 ,hart1 #aiig ,,compression4--,the simple stress of compression tends to produce a crushing strain4 ,example3 the interplane and fuselage struts4 ,,tension4--,the simple stress of tension tends to produce the strain of elongation4 ,example3 all the wires4 ,,bending4--,the compound stress of bending is a combination of compression and tension4 ,the above sketch illustrates a straight piece of wood of which the top1 centre1 and bottom lines are of equal length4 ,we will now imagine it bent to form a circle1 thus3 ,the centre line is still the same length as before being bent2 but the top line1 being farther from the centre of the circle1 is now longer than the centre line4 ,that can be due only to the strain of elongation produced by the stress of tension4 ,the wood between the centre line and the top line is then in tension2 and the farther from the centre1 the greater the strain1 and consequently the greater the tension4 ,the bottom line1 being nearest to the centre of the circle1 is now shorter than the centre line4 ,that can be due only to the strain of crushing produced by the stress of compression4 ,the wood between the centre and bottom lines is then in compression2 and the nearer the centre of the circle1 the greater the strain1 and consequently the greater the compression4 ,it then follows that there is neither tension nor compression1 i4e41 no stress1 at the centre line1 and that the wood immediately surrounding it is under considerably less stress than the wood farther away4 ,this being so1 the wood in the centre may be hollowed out without unduly weakening struts and spars4 ,in this way #be to #cc per cent4 is saved in the weight of wood in an aeroplane4 ,the strength of wood is in its fibres1 which should1 as far as possible1 run without break from one end of a strut or spar to the other end4 ,a point to remember is that the outside fibres1 being farthest removed from the centre line1 are doing by far the greatest work4 ,,shear ,,stress ,,is such that1 when material collapses under it1 one part slides over the other4 ,example3 all the locking pins4 ,some of the bolts are also in shear or 8sideways0 stress1 owing to lugs under their heads and from which wires are taken4 ,such a wire1 exerting a sideways pull upon a bolt1 tries to break it in such a way as to make one piece of the bolt slide over the other piece4 ,,torsion4--,this is a twisting stress compounded of compression1 tension1 and shear stresses4 ,example3 the propeller shaft4 ,,nature ,,of ,,wood ,,under ,,stress4--,wood1 for its weight1 takes the stress of compression far better than any other stress4 ,for instance3 a walking-stick of less than #a lb4 in weight will1 if kept perfectly straight1 probably stand up to a compression stress of a ton or more before crushing2 whereas1 if the same stick is put under a bending stress1 it will probably collapse to a stress of not more than about #ej lb4 ,that is a very great difference1 and1 since weight is of the greatest importance1 the design of an aeroplane is always such as to1 as far as possible1 keep the various wooden parts of its construction in direct compression4 ,weight being of such vital importance1 and designers all trying to outdo each other in saving weight1 it follows that the factor of safety is rather low in an aeroplane4 ,the parts in direct compression will1 however1 take the stresses safely provided the following conditions are carefully observed4 ,,conditions ,,to ,,be ,,observed3 #a4 ,all the spars and struts must be perfectly straight4 ,the above sketch illustrates a section through an interplane strut4 ,if the strut is to be kept straight1 i4e41 prevented from bending1 then the stress of compression must be equally disposed about the centre of strength4 ,if it is not straight1 then there will be more compression on one side of the centre of strength than on the other side4 ,that is a step towards getting compression on one side and tension on the other side1 in which case it may be forced to take a bending stress for which it is not designed4 ,even if it does not collapse it will1 in effect1 become shorter1 and thus throw out of adjustment the gap and all the wires attached to the top and bottom of the strut1 with the result that the flight efficiency of the aeroplane will be spoiled4 ,the only exception to the above condition is what is known as the ,arch4 ,for instance1 in the case of the ,maurice ,farman1 the spars of the centre-section plane1 which have to take the weight of the nacelle1 are arched upwards4 ,if this was not done1 it is possible that rough landings might result in the weight causing the spars to become slightly distorted downwards4 ,that would produce a dangerous bending stress1 but1 as long as the wood is arched1 or1 at any rate1 kept from bending downwards1 it will remain in direct compression and no danger can result4 #b4 ,struts and spars must be symmetrical4 ,by that ,i mean that the cross-sectional dimensions must be correct1 as otherwise there will be bulging places on the outside1 with the result that the stress will not be evenly disposed about the centre of strength1 and a bending stress may be produced4 #c4 ,struts1 spars1 etc41 must be undamaged4 ,remember that1 from what ,i have already explained about bending stresses1 the outside fibres of the wood are doing by far the most work4 ,if these get bruised or scored1 then the strut or spar suffers in strength much more than one might think at first sight2 and1 if it ever gets a tendency to bend1 it is likely to collapse at that point4 #d4 ,the wood must have a good1 clear grain with no cross-grain1 knots1 or shakes4 ,such blemishes produce weak places and1 if a tendency to bend appears1 then it may collapse at such a point4 #e4 ,the struts1 spars1 etc41 must be properly bedded into their sockets or fittings4 ,to begin with1 they must be of good pushing or gentle tapping fit4 ,they must never be driven in with a heavy hammer4 ,then again1 a strut must bed well down all over its cross-sectional area as illustrated above2 otherwise the stress of compression will not be evenly disposed about the centre of strength1 and that may produce a bending stress4 ,the bottom of the strut or spar should be covered with some sort of paint1 bedded into the socket or fitting1 and then withdrawn to see if the paint has stuck all over the bed4 #f4 ,the atmosphere is sometimes much damper than at other times1 and this causes wood to expand and contract appreciably4 ,this would not matter but for the fact that it does not expand and contract uniformly1 but becomes unsymmetrical1 i4e41 distorted4 ,i have already explained the danger of that in condition #b4 ,this should be minimized by ,,well ,,varnishing ,,the ,,wood to keep the moisture out of it4 ,,function ,,of ,,interplane ,,struts4--,these struts have to keep the lifting surfaces or 8planes0 apart1 but this is only part of their work4 ,they must keep the planes apart1 so that the latter are in their correct attitude4 ,that is only so when the spars of the bottom plane are parallel with those of the top plane4 ,also1 the chord of the top plane must be parallel with the chord of the bottom plane4 ,if that is not so1 then one plane will not have the same angle of incidence as the other one4 ,at first sight one might think that all that is necessary is to cut all the struts to be the same length1 but that is not the case4 ,sometimes1 as illustrated above1 the rear spar is not so thick as the main spar1 and it is then necessary to make up for that difference by making the rear struts correspondingly longer4 ,if that is not done1 then the top and bottom chords will not be parallel1 and the top and bottom planes will have different angles of incidence4 ,also1 the sockets or fittings1 or even the spars upon which they are placed1 sometimes vary in thickness owing to faulty manufacture4 ,this must be offset by altering the length of the struts4 ,the best way to proceed is to measure the distance between the top and bottom spars by the side of each strut1 and if that distance1 or 8gap0 as it is called1 is not as stated in the aeroplane's specifications1 then make it correct by changing the length of the strut4 ,this applies to both front and rear interplane struts4 ,when measuring the gap1 always be careful to measure from the centre of the spar1 as it may be set at an angle1 and the rear of it may be considerably lower than its front4 ,,boring ,,holes ,,in ,,wood4--,it should be a strict rule that no spar be used which has an unnecessary hole in it4 ,before boring a hole1 its position should be confirmed by whoever is in charge of the workshop4 ,a bolt-hole should be of a size to enable the bolt to be pushed in1 or1 at any rate1 not more than gently tapped in4 ,bolts should not be hammered in1 as that may split the spar4 ,on the other hand1 a bolt should not be slack in its hole1 as1 in such a case1 it may work sideways and split the spar1 not to speak of throwing out of adjustment the wires leading from the lug or socket under the bolt-head4 ,,washers4--,under the bolt-head1 and also under the nut1 a washer must be placed--a very large washer compared with the size which would be used in all-metal construction4 ,this is to disperse the stress over a large area2 otherwise the washer may be pulled into the wood and weaken it1 besides possibly throwing out of adjustment the wires attached to the bolt or the fitting it is holding to the spar4 ,,locking4--,now as regards locking the bolts4 ,if split pins are used1 be sure to see that they are used in such a way that the nut cannot possibly unscrew at all4 ,the split pin should be passed through the bolt as near as possible to the nut4 ,it should not be passed through both nut and bolt4 ,if it is locked by burring over the edge of the bolt1 do not use a heavy hammer and try to spread the whole head of the bolt4 ,that might damage the woodwork inside the fabric-covered surface4 ,use a small1 light hammer1 and gently tap round the edge of the bolt until it is burred over4 ,,turnbuckles4--,a turnbuckle is composed of a central barrel into each end of which is screwed an eye-bolt4 ,wires are taken from the eyes of the eye-bolt1 and so1 by turning the barrel1 they can be adjusted to their proper tension4 ,eye-bolts must be a good fit in the barrel2 that is to say1 not slack and not very tight4 ,theoretically it is not necessary to screw the eye-bolt into the barrel for a distance greater than the diameter of the bolt1 but1 in practice1 it is better to screw it in for a considerably greater distance than that if a reasonable degree of safety is to be secured4 ,now about turning the barrel to secure the right adjustment4 ,the barrel looks solid1 but1 as a matter of fact1 it is hollow and much more frail than it appears4 ,for that reason it should not be turned by seizing it with pliers1 as that may distort it and spoil the bore within it4 ,the best method is to pass a piece of wire through the hole in its centre1 and to use that as a lever4 ,when the correct adjustment has been secured1 the turnbuckle must be locked to prevent it from unscrewing4 ,it is quite possible to lock it in such a way as to allow it to unscrew a quarter or a half turn1 and that would throw the wires out of the very fine adjustment necessary4 ,the proper way is to use the locking wire so that its direction is such as to oppose the tendency of the barrel to unscrew1 thus3 ,,wires4--,the following points should be carefully observed where wire is concerned3 #a4 ,quality4--,it must not be too hard or too soft4 ,an easy practical way of learning to know the approximate quality of wire is as follows3 ,take three pieces1 all of the same gauge1 and each about a foot in length4 ,one piece should be too soft1 another too hard1 and the third piece of the right quality4 ,fix them in a vice1 about an inch apart and in a vertical position1 and with the light from a window shining upon them4 ,burnish them if necessary1 and you will see a band of light reflected from each wire4 ,now bend the wires over as far as possible and away from the light4 ,where the soft wire is concerned1 it will squash out at the bend1 and this will be indicated by the band of light1 which will broaden at that point4 ,in the case of the wire which is too hard1 the band of light will broaden very little at the turn1 but1 if you look carefully1 you will see some little roughnesses of surface4 ,in the case of the wire of the right quality1 the band of light may broaden a very little at the turn1 but there will be no roughnesses of surface4 ,by making this experiment two or three times one can soon learn to know really bad wire from good1 and also learn to know the strength of hand necessary to bend the right quality4 #b4 ,it must not be damaged4 ,that is to say1 it must be unkinked1 rustless1 and unscored4 #c4 ,now as regards keeping wire in good condition4 ,where outside wires are concerned1 they should be kept ,,well ,,greased ,,or ,,oiled1 especially where bent over at the ends4 ,internal bracing wires cannot be reached for the purpose of regreasing them1 as they are inside fabric-covered surfaces4 ,they should be prevented from rusting by being painted with an anti-rust mixture4 ,great care should be taken to see that the wire is perfectly clean and dry before being painted4 ,a greasy finger-mark is sufficient to stop the paint from sticking to the wire4 ,in such a case there will be a little space between the paint and the wire4 ,air may enter there and cause the wire to rust4 #d4 ,tension of ,wires4--,the tension to which the wires are adjusted is of the greatest importance4 ,all the wires should be of the same tension when the aeroplane is supported in such a way as to throw no stress upon them4 ,if some wires are in greater tension than others1 the aeroplane will quickly become distorted and lose its efficiency4 ,in order to secure the same tension of all wires1 the aeroplane1 when being rigged1 should be supported by packing underneath the lower surfaces as well as by packing underneath the fuselage or nacelle4 ,in this way the anti-lift wires are relieved of the weight1 and there is no stress upon any of the wires4 ,as a general rule the wires of an aeroplane are tensioned too much4 ,the tension should be sufficient to keep the framework rigid4 ,anything more than that lowers the factor of safety1 throws various parts of the framework into undue compression1 pulls the fittings into the wood1 and will1 in the end1 distort the whole framework of the aeroplane4 ,only experience will teach the rigger what tension to employ4 ,much may be done by learning the construction of the various types of aeroplanes1 the work the various parts do1 and in cultivating a touch for tensioning wires by constantly handling them4 #e4 ,wires with no ,opposition ,wires4--,in some few cases wires will be found which have no opposition wires pulling in the opposite direction4 ,for instance1 an auxiliary lift wire may run from the bottom of a strut to a spar in the top plane at a point between struts4 ,in such a case great care should be taken not to tighten the wire beyond barely taking up the slack4 ,such a wire must be a little slack1 or1 as illustrated above1 it will distort the framework4 ,that1 in the example given1 will spoil the camber 7curvature7 of the surface1 and result in changing both the lift and the drift at that part of the surface4 ,such a condition will cause the aeroplane to lose its directional stability and also to fly one wing down4 ,i cannot impress this matter of tension upon the reader too strongly4 ,it is of the utmost importance4 ,when this1 and also accuracy in securing the various adjustments1 has been learned1 one is on the way to becoming a good rigger4 #f4 ,wire ,loops4--,wire is often bent over at its end in the form of a loop1 in order to connect with a turnbuckle or fitting4 ,these loops1 even when made as perfectly as possible1 have a tendency to elongate1 thus spoiling the adjustment of the wires ,great care should be taken to minimize this as far as possible4 ,the rules to be observed are as follows3 7a7 ,the size of the loop should be as small as possible within reason4 ,by that ,i mean it should not be so small as to create the possibility of the wire breaking4 7b7 ,the shape of the loop should be symmetrical4 7c7 ,it should have well-defined shoulders in order to prevent the ferrule from slipping up4 ,at the same time1 a shoulder should not have an angular place4 7d7 ,when the loop is finished it should be undamaged1 and it should not be1 as is often the case1 badly scored4 #g4 ,stranded ,wire ,cable4--,no splice should be served with twine until it has been inspected by whoever is in charge of the workshop4 ,the serving may cover bad work4 ,should a strand become broken1 then the cable should be replaced at once by another one4 ,control cables have a way of wearing out and fraying wherever they pass round pulleys4 ,every time an aeroplane comes down from flight the rigger should carefully examine the cables1 especially where they pass round pulleys4 ,if he finds a strand broken1 he should replace the cable4 ,the ailerons' balance cable on the top of the top plane is often forgotten1 since it is necessary to fetch a high pair of steps in order to examine it4 ,don't slack this1 or some gusty day the pilot may unexpectedly find himself minus the aileron control4 ,,controlling ,,surfaces4--,the greatest care should be exercised in rigging the aileron1 rudder1 and elevator properly1 for the pilot entirely depends upon them in managing the aeroplane4 ,the ailerons and elevator should be rigged so that1 when the aeroplane is in flight1 they are in a fair true line with the surface in front and to which they are hinged4 ,if the surface to which they are hinged is not a lifting surface1 then they should be rigged to be in a fair true line with it as illustrated above4 ,if the controlling surface is1 as illustrated1 hinged to the back of a lifting surface1 then it should be rigged a little below the position it would occupy if in a fair true line with the surface in front4 ,this is because1 in such a case1 it is set at an angle of incidence4 ,this angle will1 during flight1 cause it to lift a little above the position in which it has been rigged4 ,it is able to lift owing to a certain amount of slack in the control wire holding it--and one cannot adjust the control wire to have no slack1 because that would cause it to bind against the pulleys and make the operation of it too hard for the pilot4 ,it is therefore necessary to rig it a little below the position it would occupy if it was rigged in a fair true line with the surface in front4 ,remember that this only applies when it is hinged to a lifting surface4 ,the greater the angle of incidence 7and therefore the lift7 of the surface in front1 then the more the controlling surface will have to be rigged down4 ,as a general rule it is safe to rig it down so that its trailing edge is #a_/b to #c_/d inch below the position it would occupy if in a fair line with the surface in front2 or about #a_/b inch down for every #ah inches of chord of the controlling surface4 ,when making these adjustments the pilot's control levers should be in their neutral positions4 ,it is not sufficient to lash them4 ,they should be rigidly blocked into position with wood packing4 ,the surfaces must not be distorted in any way4 ,if they are held true by bracing wires1 then such wires must be carefully adjusted4 ,if they are distorted and there are no bracing wires with which to true them1 then some of the internal framework will probably have to be replaced4 ,the controlling surfaces should never be adjusted with a view to altering the stability of the aeroplane4 ,nothing can be accomplished in that way4 ,the only result will be to spoil the control of the aeroplane4 ,,fabric-,,covered ,,surfaces4--,first of all make sure that there is no distortion of spars or ribs1 and that they are perfectly sound4 ,then adjust the internal bracing wires so that the ribs are parallel to the direction of flight4 ,the ribs usually cause the fabric to make a ridge where they occur1 and1 if such ridge is not parallel to the direction of flight1 it will produce excessive drift4 ,as a rule the ribs are at right angles to both main and rear spars4 ,the tension of the internal bracing wires should be just sufficient to give rigidity to the framework4 ,they should not be tensioned above that unless the wires are1 at their ends1 bent to form loops4 ,in that case a little extra tension may be given to offset the probable elongation of the loops4 ,the turnbuckles must now be generously greased1 and served round with adhesive tape4 ,the wires must be rendered perfectly dry and clean1 and then painted with an anti-rust mixture4 ,the woodwork must be well varnished4 ,if it is necessary to bore holes in the spars for the purpose of receiving1 for instance1 socket bolts1 then their places should be marked before being bored and their positions confirmed by whoever is in charge of the workshop4 ,all is now ready for the sail-maker to cover the surface with fabric4 ,,adjustment ,,of ,,control ,,cables4--,the adjustment of the control cables is quite an art1 and upon it will depend to a large degree the quick and easy control of the aeroplane by the pilot4 ,the method is as follows3 ,after having rigged the controlling surfaces1 and as far as possible secured the correct adjustment of the control cables1 then remove the packing which has kept the control levers rigid4 ,then1 sitting in the pilot's seat1 move the control levers ,,smartly4 ,tension the control cables so that when the levers are smartly moved there is no perceptible snatch or lag4 ,be careful not to tension the cables more than necessary to take out the snatch4 ,if tensioned too much they will 7#a7 bind round the pulleys and result in hard work for the pilot2 7#b7 throw dangerous stresses upon the controlling surfaces1 which are of rather flimsy construction2 and 7#c7 cause the cables to fray round the pulleys quicker than would otherwise be the case4 ,now1 after having tensioned the cables sufficiently to take out the snatch1 place the levers in their neutral positions1 and move them to and fro about #a_/h inch either side of such positions4 ,if the adjustment is correct1 it should be possible to see the controlling surfaces move4 ,if they do not move1 then the control cables are too slack4 ,,flying ,,position4--,before rigging an aeroplane or making any adjustments it is necessary to place it in what is known as its 8flying position40 ,i may add that it would be better termed its 8rigging position40 ,in the case of an aeroplane fitted with a stationary engine this is secured by packing up the machine so that the engine foundations are perfectly horizontal both longitudinally and laterally4 ,this position is found by placing a straight-edge and a spirit-level across the engine foundations 7both longitudinally and laterally71 and great care should be taken to see that the bubble is exactly in the centre of the level4 ,the slightest error will assume magnitude towards the extremities of the aeroplane4 ,great care should be taken to block up the aeroplane rigidly4 ,in case it gets accidentally disturbed while the work is going on1 it is well to constantly verify the flying position by running the straight-edge and spirit-level over the engine foundations4 ,the straight-edge should be carefully tested before being used1 as1 being generally made of wood1 it will not remain true long4 ,place it lightly in a vice1 and in such a position that a spirit-level on top shows the bubble exactly in the centre4 ,now slowly move the level along the straight-edge1 and the bubble should remain exactly in the centre4 ,if it does not do so1 then the straight-edge is not true and must be corrected4 ,,this ,,should ,,never ,,be ,,omitted4 ,in the case of aeroplanes fitted with engines of the rotary type1 the 8flying position0 is some special attitude laid down in the aeroplane's specifications1 and great care should be taken to secure accuracy4 ,,angle ,,of ,,incidence4--,one method of finding the angle of incidence is as follows3 ,first place the aeroplane in its flying position4 ,the corner of the straight-edge must be placed underneath and against the ,,centre of the rear spar1 and held in a horizontal position parallel to the ribs4 ,this is secured by using a spirit-level4 ,the set measurement will then be from the top of the straight-edge to the centre of the bottom surface of the main spar1 or it may be from the top of the straight-edge to the lowest part of the leading edge4 ,care should be taken to measure from the centre of the spar and to see that the bubble is exactly in the centre of the level4 ,remember that all this will be useless if the aeroplane has not been placed accurately in its flying position4 ,this method of finding the angle of incidence must be used under every part of the lower surface where struts occur4 ,it should not be used between the struts1 because1 in such places1 the spars may have taken a slight permanent set up or down2 not1 perhaps1 sufficiently bad to make any material difference to the flying of the machine1 but quite bad enough to throw out the angle of incidence1 which cannot be corrected at such a place4 ,if the angle is wrong1 it should then be corrected as follows3 ,if it is too great1 then the rear spar must be warped up until it is right1 and this is done by slackening ,,all the wires going to the top of the strut1 and then tightening ,,all the wires going to the bottom of the strut4 ,if the angle is too small1 then slacken ,,all the wires going to the bottom of the strut1 and tighten ,,all the wires going to the top of the strut1 until the correct adjustment is secured4 ,never attempt to adjust the angle by warping the main spar4 ,the set measurement1 which is of course stated in the aeroplane's specifications1 should be accurate to #a_/af inch4 ,,lateral ,,dihedral ,,angle4--,one method of securing this is as follows1 and this method will1 at the same time1 secure the correct angle of incidence3 ,the strings1 drawn very tight1 must be taken over both the main and rear spars of the top surface4 ,they must run between points on the spars just inside the outer struts4 ,the set measurement 7which should be accurate to #a_/af inch or less7 is then from the strings down to four points on the main and rear spars of the centre-section surface4 ,these points should be just inside the four centre-section struts2 that is to say1 as far as possible away from the centre of the centre-section4 ,do not attempt to take the set measurement near the centre of the centre-section4 ,the strings should be as tight as possible1 and1 if it can be arranged1 the best way to accomplish that is as shown in the above illustration1 i4e41 by weighting the strings down to the spars by means of weights and tying each end of the strings to a strut4 ,this will give a tight and motionless string4 ,however carefully the above adjustment is made1 there is sure to be some slight error4 ,this is of no great importance1 provided it is divided equally between the left- and right-hand wings4 ,in order to make sure of this1 certain check measurements should be taken as follows3 ,each bay must be diagonally measured1 and such measurements must be the same to within #a_/af inch on each side of the aeroplane4 ,as a rule such diagonal measurements are taken from the bottom socket of one strut to the top socket of another strut1 but this is bad practice1 because of possible inaccuracies due to faulty manufacture4 ,the points between which the diagonal measurements are taken should be at fixed distances from the butts of the spars1 such distances being the same on each side of the aeroplane1 thus3 ,it would be better to use the centre line of the aeroplane rather than the butts of the spars4 ,it is not practicable to do so1 however1 as the centre line probably runs through the petrol tanks1 etc4 ,,the ,,dihedral ,,board4--,another method of securing the dihedral angle1 and also the angle of incidence1 is by means of the dihedral board4 ,it is a light handy thing to use1 but leads to many errors1 and should not be used unless necessary4 ,the reasons are as follows3 ,the dihedral board is probably not true4 ,if it must be used1 then it should be very carefully tested for truth before-hand4 ,another reason against its use is that it has to be placed on the spars in a position between the struts1 and that is just where the spars may have a little permanent set up or down1 or some inaccuracy of surface which will1 of course1 throw out the accuracy of the adjustment4 ,the method of using it is as follows3 ,the board is cut to the same angle as that specified for the upward inclination of the surface towards its wing-tips4 ,it is placed on the spar as indicated above1 and it is provided with two short legs to raise it above the flanges of the ribs 7which cross over the spars71 as they may vary in depth4 ,a spirit-level is then placed on the board1 and the wires must be adjusted to give the surface such an inclination as to result in the bubble being in the centre of the level4 ,this operation must be performed in respect of each bay both front and rear4 ,the bays must then be diagonally measured as already explained4 ,,yet ,,another ,,method of finding the dihedral angle1 and at the same time the angle of incidence1 is as follows3 ,a horizontal line is taken from underneath the butt of each spar1 and the set measurement is either the angle it makes with the spar1 or a fixed measurement from the line to the spar taken at a specified distance from the butt4 ,this operation must be performed in respect of both main and rear spars1 and all the bays must be measured diagonally afterwards4 ,whichever method is used1 be sure that after the job is done the spars are perfectly straight4 ,,stagger4--,the stagger is the distance the top surface is in advance of the bottom surface when the aeroplane is in flying position4 ,the set measurement is obtained as follows3 ,plumb-lines must be dropped over the leading edge of the top surface wherever struts occur1 and also near the fuselage4 ,the set measurement is taken from the front of the lower leading edge to the plumb-lines4 ,it makes a difference whether the measurement is taken along a horizontal line 7which can be found by using a straight-edge and a spirit-level7 or along a projection of the chord4 ,the line along which the measurement should be taken is laid down in the aeroplane's specifications4 ,if a mistake is made and the measurement taken along the wrong line1 it may result in a difference of perhaps #a_/d will1 in flight1 be nose-heavy or tail-heavy4 ,after the adjustments of the angles of incidence1 dihedral1 and stagger have been secured1 it is as well to confirm all of them1 as1 in making the last adjustment1 the first one may have been spoiled4 ,,over-,,all ,,adjustments4--,the following over-all check measurements should now be taken4 ,the straight lines ,,ac and ,,bc should be equal to within #a_/h inch4 ,the point ,c is the centre of the propeller1 or1 in the case of a 8pusher0 aeroplane1 the centre of the nacelle4 ,the points ,a and ,b are marked on the main spar1 and must in each case be the same distance from the butt of the spar4 ,the rigger should not attempt to make ,a and ,b merely the sockets of the outer struts1 as they may not have been placed quite accurately by the manufacturer4 ,the lines ,,ac and ,,bc must be taken from both top and bottom spars--two measurements on each side of the aeroplane4 ,the two measurements ,,fd and ,,fe should be equal to within #a_/h inch4 ,f is the centre of the fuselage or rudder-post4 ,d and ,e are points marked on both top and bottom rear spars1 and each must be the same fixed distance from the butt of the spar4 ,two measurements on each side of the aeroplane4 ,if these over-all measurements are not correct1 then it is probably due to some of the drift or anti-drift wires being too tight or too slack4 ,it may possibly be due to the fuselage being out of truth1 but of course the rigger should have made quite sure that the fuselage was true before rigging the rest of the machine4 ,again1 it may be due to the internal bracing wires within the lifting surfaces not being accurately adjusted1 but of course this should have been seen to before covering the surfaces with fabric4 ,,fuselage4--,the method of truing the fuselage is laid down in the aeroplane's specifications4 ,after it has been adjusted according to the specified directions1 it should then be arranged on trestles in such a way as to make about three-quarters of it towards the tail stick out unsupported4 ,in this way it will assume a condition as near as possible to flying conditions1 and when it is in this position the set measurements should be confirmed4 ,if this is not done it may be out of truth1 but perhaps appear all right when supported by trestles at both ends1 as1 in such case1 its weight may keep it true as long as it is resting upon the trestles4 ,,the ,,tail-,,plane 7,,empennage74--,the exact angle of incidence of the tail-plane is laid down in the aeroplane's specifications4 ,it is necessary to make sure that the spars are horizontal when the aeroplane is in flying position and the tail unsupported as explained above under the heading of ,fuselage4 ,if the spars are tapered1 then make sure that their centre lines are horizontal4 ,,undercarriage4--,the undercarriage must be very carefully aligned as laid down in the specifications4 #a4 ,the aeroplane must be placed in its flying position and sufficiently high to ensure the wheels being off the ground when rigged4 ,when in this position the axle must be horizontal and the bracing wires adjusted to secure the various set measurements stated in the specifications4 #b4 ,make sure that the struts bed well down into their sockets4 #c4 ,make sure that the shock absorbers are of equal tension4 ,in the case of rubber shock absorbers1 both the number of turns and the lengths must be equal4 ,,how ,,to ,,diagnose ,,faults ,,in ,,flight1 ,,stability1 ,,and ,,control4 ,,directional ,,stability will be badly affected if there is more drift 7i4e41 resistance7 on one side of the aeroplane than there is on the other side4 ,the aeroplane will tend to turn towards the side having the most drift4 ,this may be caused as follows3 #a4 ,the angle of incidence of the main surface or the tail surface may be wrong4 ,the greater the angle of incidence1 the greater the drift4 ,the less the angle1 the less the drift4 #b4 ,if the alignment of the fuselage1 fin in front of the rudder1 the struts or stream-line wires1 or1 in the case of the ,maurice ,farman1 the front outriggers1 are not absolutely correct--that is to say1 if they are turned a little to the left or to the right instead of being in line with the direction of flight--then they will act as a rudder and cause the aeroplane to turn off its course4 #c4 ,if any part of the surface is distorted1 it will cause the aeroplane to turn off its course4 ,the surface is cambered1 i4e41 curved1 to pass through the air with the least possible drift4 ,if1 owing perhaps to the leading edge1 spars1 or trailing edge becoming bent1 the curvature is spoiled1 that will result in changing the amount of drift on one side of the aeroplane1 which will then have a tendency to turn off its course4 ,,lateral ,,instability 7,,flying ,,one ,,wing ,,down74--,the only possible reason for such a condition is a difference in the lifts of right and left wings4 ,that may be caused as follows3 #a4 ,the angle of incidence may be wrong4 ,if it is too great1 it will produce more lift than on the other side of the aeroplane2 and if too small1 it will produce less lift than on the other side--the result being that1 in either case1 the aeroplane will try to fly one wing down4 #b4 ,distorted ,surfaces4--,if some part of the surface is distorted1 then its camber is spoiled1 and the lift will not be the same on both sides of the aeroplane1 and that1 of course1 will cause it to fly one wing down4 ,,longitudinal ,,instability may be due to the following reasons3 #a4 ,the stagger may be wrong4 ,the top surface 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 degree1 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 aeroplane would then be said to be 8nose-heavy40 ,a #a_/d-;inch area in the stagger will make a very considerable difference to the longitudinal stability4 #b4 ,if the angle of incidence of the main surface is not right1 it will have a bad effect1 especially in the case of an aeroplane with a lifting tail-plane4 ,if the angle is too great1 it will produce an excess of lift1 and that may lift up the nose of the aeroplane and result in a tendency to fly 8tail-down40 ,if the angle is too small1 it will produce a decreased lift1 and the aeroplane may have a tendency to fly 8nose-down40 #c4 ,the fuselage may have become warped upward or downward1 thus giving the tail-plane an incorrect angle of incidence4 ,if it has too much angle1 it will lift too much1 and the aeroplane will be 8nose-heavy40 ,if it has too little angle1 then it will not lift enough1 and the aeroplane will be 8tail-heavy40 #d4 7,the least likely reason47 ,the tail-plane may be mounted upon the fuselage at a wrong angle of incidence1 in which case it must be corrected4 ,if nose-heavy1 it should be given a smaller angle of incidence4 ,if tail-heavy1 it should be given a larger angle2 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 much smaller angle of incidence than is the main surface1 and if that difference is decreased too much1 the aeroplane will become uncontrollable longitudinally4 ,sometimes the tail-plane is mounted on the aeroplane at the same angle as the main surface1 but it actually engages the air at a lesser angle1 owing to the air being deflected downwards by the main surface4 ,there is then1 in effect1 a longitudinal dihedral as explained and illustrated in ,chapter ,i4 ,,climbs ,,badly4--,such a condition is1 apart from engine or propeller trouble1 probably due to 7#a7 distorted surfaces1 or 7#b7 too small an angle of incidence4 ,,flight ,,speed ,,poor4--,such a condition is1 apart from engine or propeller trouble1 probably due to 7#a7 distorted surfaces1 7#b7 too great an angle of incidence1 or 7#c7 dirt or mud1 and consequently excessive skin-friction4 ,,inefficient ,,control is probably due to 7#a7 wrong setting of control surfaces1 7#b7 distortion of control surfaces1 or 7#c7 control cables being badly tensioned4 ,,will ,,not ,,taxi ,,straight4--,if the aeroplane is uncontrollable on the ground1 it is probably due to 7#a7 alignment of undercarriage being wrong1 or 7#b7 unequal tension of shock absorbers4 ,,chapter ,,iv4 ,,the ,,propeller1 ,,or 8,,air-,,screw0 ,the sole object of the propeller is to translate the power of the engine into thrust4 ,the propeller screws through the air1 and its blades1 being set at an angle inclined to the direction of motion1 secure a reaction1 as in the case of the aeroplane's lifting surface4 ,this reaction may be conveniently divided into two component parts or values1 namely1 ,thrust and ,drift4 ,the ,thrust is opposed to the ,drift of the aeroplane1 and must be equal and opposite to it at flying speed4 ,if it falls off in power1 then the flying speed must decrease to a velocity1 at which the aeroplane drift equals the decreased thrust4 ,the ,drift of the propeller may be conveniently divided into the following component values3 ,active ,drift1 produced by the useful thrusting part of the propeller4 ,passive ,drift1 produced by all the rest of the propeller1 i4e41 by its detrimental surface4 ,skin ,friction1 produced by the friction of the air with roughnesses of surface4 ,eddies attending the movement of the air caused by the action of the propeller4 ,cavitation 7very marked at excessive speed of revolution74 ,a tendency of the propeller to produce a cavity or semi-vacuum in which it revolves1 the thrust decreasing with increase of speed and cavitation4 ,,thrust-,,drift ,,ratio4--,the proportion of thrust to drift is of paramount importance1 for it expresses the efficiency of the propeller4 ,it is affected by the following factors3 ,speed of ,revolution4--,the greater the speed1 the greater the proportion of drift to thrust4 ,this is due to the increase with speed of the passive drift1 which carries with it no increase in thrust4 ,for this reason propellers are often geared down to revolve at a lower speed than that of the engine4 ,angle of ,incidence4--,the same reasons as in the case of the aeroplane surface4 ,surface ,area4--,ditto4 ,aspect ,ratio4--,ditto4 ,camber4--,ditto4 ,in addition to the above factors there are1 when it comes to actually designing a propeller1 mechanical difficulties to consider4 ,for instance1 the blades must be of a certain strength and consequent thickness4 ,that1 in itself1 limits the aspect ratio1 for it will necessitate a chord long enough in proportion to the thickness to make a good camber possible4 ,again1 the diameter of the propeller must be limited1 having regard to the fact that greater diameters than those used to-day would not only result in excessive weight of construction1 but would also necessitate a very high undercarriage to keep the propeller off the ground1 and such undercarriage would not only produce excessive drift1 but would also tend to make the aeroplane stand on its nose when alighting4 ,the latter difficulty cannot be overcome by mounting the propeller higher1 as the centre of its thrust must be approximately coincident with the centre of aeroplane drift4 ,,maintenance ,,of ,,efficiency4 ,the following conditions must be observed3 #a4 ,,pitch ,,angle4--,the angle1 at any given point on the propeller1 at which the blade is set is known as the pitch angle1 and it must be correct to half a degree if reasonable efficiency is to be maintained4 ,this angle secures the 8pitch10 which is the distance the propeller advances during one revolution1 supposing the air to be solid4 ,the air1 as a matter of fact1 gives back to the thrust of the blades just as the pebbles slip back as one ascends a shingle beach4 ,such 8give-back0 is known as ,slip4 ,if a propeller has a pitch of1 say1 #aj feet1 but actually advances1 say1 only #h feet owing to slip1 then it will be said to possess #bj per cent4 slip4 ,thus1 the pitch must equal the flying speed of the aeroplane plus the slip of the propeller4 ,for example1 let us find the pitch of a propeller1 given the following conditions3 ,flying speed44444444444444 #gj miles per hour4 ,propeller revolutions44444 #a1bjj per minute4 ,slip4444444444444444444444 #ae per cent4 ,first find the distance in feet the aeroplane will travel forward in one minute4 ,that is-- #cfi1fjj feet 7#gj miles7 ------------------------ #f1afj feet per minute4 #fj 8 7minutes7 ,now divide the feet per minute by the propeller revolutions per minute1 add #ae per cent4 for the slip1 and the result will be the propeller pitch3 #f1afj ----- #ae per cent4 #e feet #a #c_/e inches4 #a1bjj ,in order to secure a constant pitch from root to tip of blade1 the pitch angle decreases towards the tip4 ,this is necessary1 since the end of the blade travels faster than its root1 and yet must advance forward at the same speed as the rest of the propeller4 ,for example1 two men ascending a hill4 ,one prefers to walk fast and the other slowly1 but they wish to arrive at the top of the hill simultaneously4 ,then the fast walker must travel a farther distance than the slow one1 and his angle of path 7pitch angle7 must be smaller than the angle of path taken by the slow walker4 ,their pitch angles are different1 but their pitch 7in this case altitude reached in a given time7 is the same4 ,in order to test the pitch angle1 the propeller must be mounted upon a shaft at right angles to a beam the face of which must be perfectly level1 thus3 ,first select a point on the blade at some distance 7say about #b feet7 from the centre of the propeller4 ,at that point find1 by means of a protractor1 the angle a projection of the chord makes with the face of the beam4 ,that angle is the pitch angle of the blade at that point4 ,now lay out the angle on paper1 thus3 ,the line above and parallel to the circumference line must be placed in a position making the distance between the two lines equal to the specified pitch1 which is1 or should be1 marked upon the boss of the propeller4 ,now find the circumference of the propeller where the pitch angle is being tested4 ,for example1 if that place is #b feet radius from the centre1 then the circumference will be #b feet ,x #b #d feet diameter1 which1 if multiplied by #c4adaf #ae4ef feet circumference4 ,now mark off the circumference distance1 which is represented above by ,a-,b1 and reduce it in scale for convenience4 ,the distance a vertical line makes between ,b and the chord dine is the pitch at the point where the angle is being tested1 and it should coincide with the specified pitch4 ,you will note1 from the above illustration1 that the actual pitch line should meet the junction of the chord line and top line4 ,the propeller should be tested at several points1 about a foot apart1 on each blade2 and the diagram1 provided the propeller is not faulty1 will then look like this3 ,at each point tested the actual pitch coincides with the specified pitch3 a satisfactory condition4 ,a faulty propeller will produce a diagram something like this3 ,at every point tested the pitch angle is wrong1 for nowhere does the actual pitch coincide with the specified pitch4 ,angles ,a1 ,c1 and ,d1 are too large1 and ,b is too small4 ,the angle should be correct to half a degree if reasonable efficiency is to be maintained4 ,a fault in the pitch angle may be due to 7#a7 faulty manufacture1 7#b7 distortion1 or 7#c7 the shaft hole through the boss being out of position4 #b4 ,,straightness4--,to test for straightness the propeller must be mounted upon a shaft4 ,now bring the tip of one blade round to graze some fixed object4 ,mark the point it grazes4 ,now bring the other tip round1 and it should come within #a_/h inch of the mark4 ,if it does not do so1 it is due to 7#a7 faulty manufacture1 7#b7 distortion1 or 7#c7 to the hole through the boss being out of position4 #c4 ,,length4--,the blades should be of equal length to inch4 #d4 ,,balance4--,the usual method of testing a propeller for balance is as follows3 ,mount it upon a shaft1 which must be on ball-bearings4 ,place the propeller in a horizontal position1 and it should remain in that position4 ,if a weight of a trifle over an ounce placed in a bolt-hole on one side of the boss fails to disturb the balance1 then the propeller is usually regarded as unfit for use4 ,the above method is rather futile1 as it does not test for the balance of centrifugal force1 which comes into play as soon as the propeller revolves4 ,it can be tested as follows3 ,the propeller must be in a horizontal position1 and then weighed at fixed points1 such as ,a1 ,b1 ,c1 ,d1 ,e1 and ,f1 and the weights noted4 ,the points ,a1 ,b1 and ,c must1 of course1 be at the same fixed distances from the centre of the propeller as the points ,d1 ,e1 and ,f4 ,now reverse the propeller and weigh at each point again4 ,note the results4 ,the first series of weights should correspond to the second series1 thus3 ,weight ,a should equal weight ,f4 8 ,b 8 8 8 ,e4 8 ,c 8 8 8 ,d4 ,there is no standard practice as to the degree of error permissible1 but if there are any appreciable differences the propeller is unfit for use4 #e4 ,,surface ,,area4--,the surface area of the blades should be equal4 ,test with callipers thus3 ,the points between which the distances are taken must1 of course1 be at the same distance from the centre in the case of each blade4 ,there is no standard practice as to the degree of error permissible4 ,if1 however1 there is an error of over #a_/h inch1 the propeller is really unfit for use4 #f4 ,,camber4--,the camber 7curvature7 of the blades should be 7#a7 equal1 7#b7 decrease evenly towards the tips of the blades1 and 7#c7 the greatest depth of the curve should1 at any point of the blade1 be approximately at the same percentage of the chord from the leading edge as at other points4 ,it is difficult to test the top camber without a set of templates1 but a fairly accurate idea of the concave camber can be secured by slowly passing a straight-edge along the blade1 thus3 ,the camber can now be easily seen1 and as the straight-edge is passed along the blade1 the observer should look for any irregularities of the curvature1 which should gradually and evenly decrease towards the tip of the blade4 #g4 ,,the ,,joints4--,the usual method for testing the glued joints is by revolving the propeller at greater speed than it will be called upon to make during flight1 and then carefully examining the joints to see if they have opened4 ,it is not likely1 however1 that the reader will have the opportunity of making this test4 ,he should1 however1 examine all the joints very carefully1 trying by hand to see if they are quite sound4 ,suspect a propeller of which the joints appear to hold any thickness of glue4 ,sometimes the joints in the boss open a little1 but this is not dangerous unless they extend to the blades1 as the bolts will hold the laminations together4 #h4 ,,condition ,,of ,,surface4--,the surface should be very smooth1 especially towards the tips of the blades4 ,some propeller tips have a speed of over #cj1jjj feet a minute1 and any roughness will produce a bad drift or resistance and lower the efficiency4 #i4 ,,mounting4--,great care should be taken to see that the propeller is mounted quite straight on its shaft4 ,test in the same way as for straightness4 ,if it is not straight1 it is possibly due to some of the propeller bolts being too slack or to others having been pulled up too tightly4 ,,flutter4--,propeller 8flutter10 or vibration1 may be due to faulty pitch angle1 balance1 camber1 or surface area4 ,it causes a condition sometimes mistaken for engine trouble1 and one which may easily lead to the collapse of the propeller4 ,,care ,,of ,,propellers4--,the care of propellers is of the greatest importance1 as they become distorted very easily4 #a4 ,do not store them in a very damp or a very dry place4 #b4 ,do not store them where the sun will shine upon them4 #c4 ,never leave them long in a horizontal position or leaning up against a wall4 #d4 ,they should be hung on horizontal pegs1 and the position of the propellers should be vertical4 ,if the points ,i have impressed upon you in these notes are not attended to1 you may be sure of the following results3 #a4 ,lack of efficiency1 resulting in less aeroplane speed and climb than would otherwise be the case4 #b4 ,propeller 8flutter0 and possible collapse4 #c4 ,a bad stress upon the propeller shaft and its bearings4 ,,tractor4--,a propeller mounted in front of the main surface4 ,,pusher4--,a propeller mounted behind the main surface4 ,,four-,,bladed ,,propellers4--,four-bladed propellers are suitable only when the pitch is comparatively large4 ,for a given pitch1 and having regard to 8interference10 they are not so efficient as two-bladed propellers4 ,the smaller the pitch1 the less the 8gap10 i4e41 the distance1 measured in the direction of the thrust1 between the spiral courses of the blades4 ,if the gap is too small1 then the following blade will engage air which the preceding blade has put into motion1 with the result that the following blade will not secure as good a reaction as would otherwise be the case4 ,it is very much the same as in the case of the aeroplane gap4 ,for a given pitch1 the gap of a four-bladed propeller is only half that of a two-bladed one4 ,therefore the four-bladed propeller is only suitable for large pitch1 as such pitch produces spirals with a large gap1 thus offsetting the decrease in gap caused by the numerous blades4 ,the greater the speed of rotation1 the less the pitch for a given aeroplane speed4 ,then1 in order to secure a large pitch and consequently a good gap1 the four-bladed propeller is usually geared to rotate at a lower speed than would be the case if directly attached to the engine crank-shaft4 ,,chapter ,v4 ,,maintenance ,,cleanliness4--,the fabric must be kept clean and free from oil1 as that will rot it4 ,to take out dirt or oily patches1 try acetone4 ,if that will not remedy matters1 then try petrol1 but use it sparingly1 as otherwise it will take off an unnecessary amount of dope4 ,if that will not remove the dirt1 then hot water and soap will do so1 but1 in that case1 be sure to use soap having no alkali in it1 as otherwise it may injure the fabric4 ,use the water sparingly1 or it may get inside the planes and rust the internal bracing wires1 or cause some of the wooden framework to swell4 ,the wheels of the undercarriage have a way of throwing up mud on to the lower surface4 ,this should1 if possible1 be taken off while wet4 ,it should never be scraped off when dry1 as that may injure the fabric4 ,if dry1 then it should be moistened before being removed4 ,measures should be taken to prevent dirt from collecting upon any part of the aeroplane1 as1 otherwise1 excessive skin-friction will be produced with resultant loss of flight speed4 ,the wires1 being greasy1 collect dirt very easily4 ,,control ,,cables4--,after every flight the rigger should pass his hand over the control cables and carefully examine them near pulleys4 ,removal of grease may be necessary to make a close inspection possible4 ,if only one strand is broken the wire should be replaced4 ,do not forget the aileron balance wire on the top surface4 ,once a day try the tension of the control cables by smartly moving the control levers about as explained elsewhere4 ,,wires4--,all the wires should be kept well greased or oiled1 and in the correct tension4 ,when examining the wires1 it is necessary to place the aeroplane on level ground1 as otherwise it may be twisted1 thus throwing some wires into undue tension and slackening others4 ,the best way1 if there is time1 is to pack the machine up into its 8flying position40 ,if you see a slack wire1 do not jump to the conclusion that it must be tensioned4 ,perhaps its opposition wire is too tight1 in which case slacken it1 and possibly you will find that will tighten the slack wire4 ,carefully examine all wires and their connections near the propeller1 and be sure that they are snaked round with safety wire1 so that the latter may keep them out of the way of the propeller if they come adrift4 ,the wires inside the fuselage should be cleaned and regreased about once a fortnight4 ,,struts ,,and ,,sockets4--,these should be carefully examined to see if any splitting has occurred4 ,,distortion4--,carefully examine all surfaces1 including the controlling surfaces1 to see whether any distortion has occurred4 ,if distortion can be corrected by the adjustment of wires1 well and good2 but if not1 then some of the internal framework probably requires replacement4 ,,adjustments4--,verify the angles of incidence2 dihedral1 and stagger1 and the rigging position of the controlling-surfaces1 as often as possible4 ,,undercarriage4--,constantly examine the alignment and fittings of the undercarriage1 and the condition of tyres and shock absorbers4 ,the latter1 when made of rubber1 wear quickest underneath4 ,inspect axles and skids to see if there are any signs of them becoming bent4 ,the wheels should be taken off occasionally and greased4 ,,locking ,,arrangements4--,constantly inspect the locking arrangements of turnbuckles1 bolts1 etc4 ,pay particular attention to the control cable connections1 and to all moving parts in respect of the controls4 ,,lubrication4--,keep all moving parts1 such as pulleys1 control levers1 and hinges of controlling surfaces1 well greased4 ,,special ,,inspection4--,apart from constantly examining the aeroplane with reference to the above points ,i have made1 ,i think that1 in the case of an aeroplane in constant use it is an excellent thing to make a special inspection of every part1 say once a week4 ,this will take from two to three hours1 according to the type of aeroplane4 ,in order to carry it out methodically1 the rigger should have a list of every part down to the smallest split-pin4 ,he can then check the parts as he examines them1 and nothing will be passed over4 ,this1 ,i know from experience1 greatly increases the confidence of the pilot1 and tends to produce good work in the air4 ,,windy ,,weather4--,the aeroplane1 when on the ground1 should face the wind2 and it is advisable to lash the control lever fast1 so that the controlling surfaces may not be blown about and possibly damaged4 8,,vetting0 ,,by ,,eye4--,this should be practiced at every opportunity1 and1 if persevered in1 it is possible to become quite expert in diagnosing by eye faults in flight efficiency1 stability and control4 ,the aeroplane should be standing upon level ground1 or1 better than that1 packed up into its 8flying position40 ,now stand in front of it and line up the leading edge with the main spar1 rear spar1 and trailing edge4 ,their shadows can usually be seen through the fabric4 ,allowance must1 of course1 be made for wash-in and wash-out2 otherwise1 the parts ,i have specified should be parallel with each other4 ,now line up the centre part of the main-plane with the tail-plane4 ,the latter should be horizontal4 ,next1 sight each interplane front strut with its rear strut4 ,they should be parallel4 ,then1 standing on one side of the aeroplane1 sight all the front struts4 ,the one nearest to you should cover all the others4 ,this applies to the rear struts also4 ,look for distortion of leading edges1 main and rear spars1 trailing edges1 tail-plane and controlling surfaces4 ,this sort of thing1 if practiced constantly1 will not only develop an expert eye for diagnosis of faults1 but will also greatly assist in impressing upon the memory the characteristics and possible troubles of the various types of aeroplanes4 ,,mishandling ,,of ,,the ,,ground4--,this is the cause of a lot of unnecessary damage4 ,the golden rule to observe is3 ,,produce ,,no ,,bending ,,stresses4 ,nearly all the wood in an aeroplane is designed to take merely the stress of direct compression1 and it cannot be bent safely4 ,therefore1 in packing an aeroplane up from the ground1 or in pulling or pushing it about1 be careful to stress it in such a way as to produce1 as far as possible1 only direct compression stresses4 ,for instance1 if it is necessary to support the lifting surface1 then the packing should be arranged to come directly under the struts so that they may take the stress in the form of compression for which they are designed4 ,such supports should be covered with soft packing in order to prevent the fabric from becoming damaged4 ,when pulling an aeroplane along1 if possible1 pull from the top of the undercarriage struts4 ,if necessary to pull from elsewhere1 then do so by grasping the interplane struts as low down as possible4 ,never lay fabric-covered parts upon a concrete floor4 ,any slight movement will cause the fabric to scrape over the floor with resultant damage4 ,struts1 spars1 etc41 should never be left about the floor1 as in such position they are likely to become scored4 ,i have already explained the importance of protecting the outside fibres of the wood4 ,remember also that wood becomes distorted easily4 ,this particularly applies to interplane struts4 ,if there are no proper racks to stand them in1 then the best plan is to lean them up against the wall in as near a vertical position as possible4 ,,time4--,learn to know the time necessary to complete any of the various rigging jobs4 ,this is really important4 ,ignorance of this will lead to bitter disappointments in civil life2 and1 where ,service flying is concerned1 it will1 to say the least of it1 earn unpopularity with senior officers1 and fail to develop respect and good work where men are concerned4 ,,the ,,aeroplane ,,shed4--,this should be kept as clean and orderly as possible4 ,a clean1 smart shed produces briskness1 energy1 and pride of work4 ,a dirty1 disorderly shed nearly always produces slackness and poor quality of work1 lost tools and mislaid material4 ,,glossary ,aeronautics--,the science of aerial navigation4 ,aerofoil--,a rigid structure1 of large superficial area relative to its thickness1 designed to obtain1 when driven through the air at an angle inclined to the direction of motion1 a reaction from the air approximately at right angles to its surface4 ,always cambered when intended to secure a reaction in one direction only4 ,as the term 8aerofoil0 is hardly ever used in practical aeronautics1 ,i have1 throughout this book1 used the term ,,surface1 which1 while academically incorrect1 since it does not indicate thickness1 is a term usually used to describe the cambered lifting surfaces1 i4e41 the 8planes0 or 8wings10 and the stabilizers and the controlling aerofoils4 ,aerodrome--,the name usually applied to a ground used for the practice of aviation4 ,it really means 8flying machine10 but is never used in that sense nowadays4 ,aeroplane--,a power-driven aerofoil with stabilizing and controlling surfaces4 ,acceleration--,the rate of change of velocity4 ,angle of ,incidence--,the angle at which the 8neutral lift line0 of a surface attacks the air4 ,angle of ,incidence1 ,rigger's--,the angle the chord of a surface makes with a line parallel to the axis of the propeller4 ,angle of ,incidence1 ,maximum--,the greatest angle of incidence at which1 for a given power1 surface 7including detrimental surface71 and weight1 horizontal flight can be maintained4 ,angle of ,incidence1 ,minimum--,the smallest angle of incidence at which1 for a given power1 surface 7including detrimental surface71 and weight1 horizontal flight can be maintained4 ,angle of ,incidence1 ,best ,climbing--,that angle of incidence at which an aeroplane ascends quickest4 ,an angle approximately halfway between the maximum and optimum angles4 ,angle of ,incidence1 ,optimum--,the angle of incidence at which the lift-drift ratio is the highest4 ,angle1 ,gliding--,the angle between the horizontal and the path along which an aeroplane at normal flying speed1 but not under engine power1 descends in still air4 ,angle1 ,dihedral--,the angle between two planes4 ,angle1 ,lateral ,dihedral--,the lifting surface of an aeroplane is said to be at a lateral dihedral angle when it is inclined upward towards its wing-tips4 ,angle1 ,longitudinal ,dihedral--,the main surface and tail surface are said to be at a longitudinal dihedral angle when the projections of their neutral lift lines meet and produce an angle above them4 ,angle1 ,rigger's ,longitudinal ,dihedral--,ditto1 but substituting 8chords0 for 8neutral life lines40 ,angle1 ,pitch--,the angle at any given point of a propeller1 at which the blade is inclined to the direction of motion when the propeller is revolving but the aeroplane stationary4 ,altimeter--,an instrument used for measuring height4 ,air-,speed ,indicator--,an instrument used for measuring air pressures or velocities4 ,it consequently indicates whether the surface is securing the requisite reaction for flight4 ,usually calibrated in miles per hour1 in which case it indicates the correct number of miles per hour at only one altitude4 ,this is owing to the density of the air decreasing with increase of altitude and necessitating a greater speed through space to secure the same air pressure as would be secured by less speed at a lower altitude4 ,it would be more correct to calibrate it in units of air pressure4 ,air ,pocket--,a local movement or condition of the air causing an aeroplane to drop or lose its correct attitude4 ,aspect-,ratio--,the proportion of span to chord of a surface4 ,air-,screw 7,propeller7--,a surface so shaped that its rotation about an axis produces a force 7thrust7 in the direction of its axis4 ,aileron--,a controlling surface1 usually situated at the wing-tip1 the operation of which turns an aeroplane about its longitudinal axis2 causes an aeroplane to tilt sideways4 ,aviation--,the art of driving an aeroplane4 ,aviator--,the driver of an aeroplane4 ,barograph--,a recording barometer1 the charts of which can be calibrated for showing air density or height4 ,barometer--,an instrument used for indicating the density of air4 ,bank1 to--,to turn an aeroplane about its longitudinal axis 7to tilt sideways7 when turning to left or right4 ,biplane--,an aeroplane of which the main lifting surface consists of a surface or pair of wings mounted above another surface or pair of wings4 ,bay--,the space enclosed by two struts and whatever they are fixed to4 ,boom--,a term usually applied to the long spars joining the tail of a 8pusher0 aeroplane to its main lifting surface4 ,bracing--,a system of struts and tie wires to transfer a force from one point to another4 ,canard--,literally 8duck40 ,the name which was given to a type of aeroplane of which the longitudinal stabilizing surface 7empennage7 was mounted in front of the main lifting surface4 ,sometimes termed 8tail-first0 aeroplanes1 but such term is erroneous1 as in such a design the main lifting surface acts as1 and is1 the empennage4 ,cabre--,to fly or glide at an excessive angle of incidence2 tail down4 ,camber--,curvature4 ,chord--,usually taken to be a straight line between the trailing and leading edges of a surface4 ,cell--,the whole of the lower surface1 that part of the upper surface directly over it1 together with the struts and wires holding them together4 ,centre 7,line7 of ,pressure--,a line running from wing-tip to wing-tip1 and through which all the air forces acting upon the surface may be said to act1 or about which they may be said to balance4 ,centre 7,line7 of ,pressure1 ,resultant--,a line transverse to the longitudinal axis1 and the position of which is the resultant of the centres of pressure of two or more surfaces4 ,centre of ,gravity--,the centre of weight4 ,cabane--,a combination of two pylons1 situated over the fuselage1 and from which anti-lift wires are suspended4 ,cloche--,literally 8bell40 ,is applied to the bell-shaped construction which forms the lower part of the pilot's control lever in a ,bleriot monoplane1 and to which the control cables are attached4 ,centrifugal ,force--,every body which moves in a curved path is urged outwards from the centre of the curve by a force termed 8centrifugal40 ,control ,lever--,a lever by means of which the controlling surfaces are operated4 ,it usually operates the ailerons and elevator4 ,the 8joy-stick04 ,cavitation1 ,propeller--,the tendency to produce a cavity in the air4 ,distance ,piece--,a long1 thin piece of wood 7sometimes tape7 passing through and attached to all the ribs in order to prevent them from rolling over sideways4 ,displacement--,change of position4 ,drift 7of an aeroplane as distinct from the propeller7--,the horizontal component of the reaction produced by the action of driving through the air a surface inclined upwards and towards its direction of motion ,,plus the horizontal component of the reaction produced by the 8detrimental0 surface ,,plus resistance due to 8skin-friction40 ,sometimes termed 8head-resistance40 ,drift1 ,active--,drift produced by the lifting surface4 ,drift1 ,passive--,drift produced by the detrimental surface4 ,drift 7of a propeller7--,analogous to the drift of an aeroplane4 ,it is convenient to include 8cavitation0 within this term4 ,drift1 to--,to be carried by a current of air2 to make leeway4 ,dive1 to--,to descend so steeply as to produce a speed greater than the normal flying speed4 ,dope1 to--,to paint a fabric with a special fluid for the purpose of tightening and protecting it4 ,density--,mass of unit volume1 for instance1 pounds per cubic foot4 ,efficiency--,output ,input ,efficiency 7of an aeroplane as distinct from engine and propeller7-- ,lift and ,velocity ,thrust 7 aeroplane drift7 ,efficiency1 ,engine--,brake horse-power ,indicated horse-power ,efficiency1 ,propeller-- ,thrust horse-power ,horse-power received from engine 7 propeller drift7 ,,note4--,the above terms can1 of course1 be expressed in foot-pounds4 ,it is then only necessary to divide the upper term by the lower one to find the measure of efficiency4 ,elevator--,a controlling surface1 usually hinged to the rear of the tail-plane1 the operation of which turns an aeroplane about an axis which is transverse to the direction of normal horizontal flight4 ,empennage--,see 8,tail-plane40 ,energy--,stored work4 ,for instance1 a given weight of coal or petroleum stores a given quantity of energy which may be expressed in foot-pounds4 ,extension--,that part of the upper surface extending beyond the span of the lower surface4 ,edge1 ,leading--,the front edge of a surface relative to its normal direction of motion4 ,edge1 ,trailing--,the rear edge of a surface relative to its normal direction of motion4 ,factor of ,safety--,usually taken to mean the result found by dividing the stress at which a body will collapse by the maximum stress it will be called upon to bear4 ,fineness 7of stream-line7--,the proportion of length to maximum width4 ,flying ,position--,a special position in which an aeroplane must be placed when rigging it or making adjustments4 ,it varies with different types of aeroplanes4 ,would be more correctly described as 8rigging position40 ,fuselage--,that part of an aeroplane containing the pilot1 and to which is fixed the tail-plane4 ,fin--,additional keel-surface1 usually mounted at the rear of an aeroplane4 ,flange 7of a rib7--,that horizontal part of a rib which prevents it from bending sideways4 ,flight--,the sustenance of a body heavier than air by means of its action upon the air4 ,foot-pound--,a measure of work representing the weight of #a lb4 raised #a foot4 ,fairing--,usually made of thin sheet aluminum1 wood1 or a light construction of wood and fabric2 and bent round detrimental surface in order to give it a 8fair0 or 8stream-like0 shape4 ,gravity--,is the force of the ,earth's attraction upon a body4 ,it decreases with increase of distance from the ,earth4 ,see 8,weight40 ,gravity1 ,specific--,density of substance ,density of water4 ,thus1 if the density of water is #aj lb4 per unit volume1 the same unit volume of petrol1 if weighing #g lb41 would be said to have a specific gravity of #g_/aj1 i4e41 #j4g4 ,gap 7of an aeroplane7--,the distance between the upper and lower surfaces of a biplane4 ,in a triplane or multiplane1 the distance between a surface and the one first above it4 ,gap1 ,propeller--,the distance1 measured in the direction of the thrust1 between the spiral courses of the blades4 ,girder--,a structure designed to resist bending1 and to combine lightness and strength4 ,gyroscope--,a heavy circular wheel revolving at high speed1 the effect of which is a tendency to maintain its plane of rotation against disturbing forces4 ,hangar--,an aeroplane shed4 ,head-,resistance--,drift4 ,the resistance of the air to the passage of a body4 ,helicopter--,an air-screw revolving about a vertical axis1 the direction of its thrust being opposed to gravity4 ,horizontal ,equivalent--,the plan view of a body whatever its attitude may be4 ,impulse--,a force causing a body to gain or lose momentum4 ,inclinometer--,a curved form of spirit-level used for indicating the attitude of a body relative to the horizontal4 ,instability--,an inherent tendency of a body1 which1 if the body is disturbed1 causes it to move into a position as far as possible away from its first position4 ,instability1 ,neutral--,an inherent tendency of a body to remain in the position given it by the force of a disturbance1 with no tendency to move farther or to return to its first position4 ,inertia--,the inherent resistance to displacement of a body as distinct from resistance the result of an external force4 ,joy-,stick--,see 8,control ,lever40 ,keel-,surface--,everything to be seen when viewing an aeroplane from the side of it4 ,king-,post--,a bracing strut2 in an aeroplane1 usually passing through a surface and attached to the main spar1 and from the end or ends of which wires are taken to spar1 surface1 or other part of the construction in order to prevent distortion4 ,when used in connection with a controlling surface1 it usually performs the additional function of a lever1 control cables connecting its ends with the pilot's control lever4 ,lift--,the vertical component of the reaction produced by the action of driving through the air a surface inclined upwards and towards its direction of motion4 ,lift1 ,margin of--,the height an aeroplane can gain in a given time and starting from a given altitude4 ,lift-,drift ,ratio--,the proportion of lift to drift4 ,loading--,the weight carried by an aerofoil4 ,usually expressed in pounds per square foot of superficial area4 ,longeron--,the term usually applied to any long spar running length-ways of a fuselage4 ,mass--,the mass of a body is a measure of the quantity of material in it4 ,momentum--,the product of the mass and velocity of a body is known as 8momentum40 ,monoplane--,an aeroplane of which the main lifting surface consists of one surface or one pair of wings4 ,multiplane--,an aeroplane of which the main lifting surface consists of numerous surfaces or pairs of wings mounted one above the other4 ,montant--,fuselage strut4 ,nacelle--,that part of an aeroplane containing the engine and pilot and passenger1 and to which the tail plane is not fixed4 ,neutral ,lift ,line--,a line taken through a surface in a forward direction relative to its direction of motion1 and starting from its trailing edge4 ,if the attitude of the surface is such as to make the said line coincident with the direction of motion1 it results in no lift1 the reaction then consisting solely of drift4 ,the position of the neutral lift line1 i4e41 the angle it makes with the chord1 varies with differences of camber1 and it is found by means of wind-tunnel research4 ,newton's ,laws of ,motion--#a4 ,if a body be at rest1 it will remain at rest2 or1 if in motion1 it will move uniformly in a straight line until acted upon by some force4 #b4 ,the rate of change of the quantity of motion 7momentum7 is proportional to the force which causes it1 and takes place in the direction of the straight line in which the force acts4 ,if a body be acted upon by several forces1 it will obey each as though the others did not exist1 and this whether the body be at rest or in motion4 #c4 ,to every action there is opposed an equal and opposite reaction4 ,ornithopter 7or ,orthopter7--,a flapping wing design of aircraft intended to imitate the flight of a bird4 ,outrigger--,this term is usually applied to the framework connecting the main surface with an elevator placed in advance of it4 ,sometimes applied to the 8tail-boom0 framework connecting the tail-plane with the main lifting surface4 ,pancake1 to--,to 8stall 0 ,plane--,this term is often applied to a lifting surface4 ,such application is not quite correct1 since 8plane0 indicates a flat surface1 and the lifting surfaces are always cambered4 ,propeller--,see 8,air-,screw40 ,propeller1 ,tractor--,an air-screw mounted in front of the main lifting surface4 ,propeller1 ,pusher--,an air-screw mounted behind the main lifting surface4 ,pusher--,an aeroplane of which the propeller is mounted behind the main lifting surface4 ,pylon--,any ,v-shaped construction from the point of which wires are taken4 ,power--,rate of working4 ,power1 ,horse--,one horse-power represents a force sufficient to raise #cc1jjj lbs4 #a foot in a minute4 ,power1 ,indicated ,horse--,the ,i4,h4,p4 of an engine is a measure of the rate at which work is done by the pressure upon the piston or pistons1 as distinct from the rate at which the engine does work4 ,the latter is usually termed 8brake horse-power10 since it may be measured by an absorption brake4 ,power1 ,margin of--,the available quantity of power above that necessary to maintain horizontal flight at the optimum angle4 ,pitot ,tube--,a form of air-speed indicator consisting of a tube with open end facing the wind1 which1 combined with a static pressure or suction tube1 is used in conjunction with a gauge for measuring air pressures or velocities4 7,no4 #a in diagram47 ,pitch1 ,propeller--,the distance a propeller advances during one revolution supposing the air to be solid4 ,pitch1 to--,to plunge nose-down4 ,reaction--,a force1 equal and opposite to the force of the action producing it4 ,rudder--,a controlling surface1 usually hinged to the tail1 the operation of which turns an aeroplane about an axis which is vertical in normal horizontal flight2 causes an aeroplane to turn to left or right of the pilot4 ,roll1 to--,to turn about the longitudinal axis4 ,rib1 ,ordinary--,a light curved wooden part mounted in a fore and aft direction within a surface4 ,the ordinary ribs give the surface its camber1 carry the fabric1 and transfer the lift from the fabric to the spars4 ,rib1 ,compression--,acts as an ordinary rib1 besides bearing the stress of compression produced by the tension of the internal bracing wires4 ,rib1 ,false--,a subsidiary rib1 usually used to improve the camber of the front part of the surface4 ,right and ,left ,hand--,always used relative to the position of the pilot4 ,when observing an aeroplane from the front of it1 the right hand side of it is then on the left hand of the observer4 ,remou--,a local movement or condition of the air which may cause displacement of an aeroplane4 ,rudder-,bar--,a control lever moved by the pilot's feet1 and operating the rudder4 ,surface--,see 8,aerofoil40 ,surface1 ,detrimental--,all exterior parts of an aeroplane including the propeller1 but excluding the 7aeroplane7 lifting and 7propeller7 thrusting surfaces4 ,surface1 ,controlling--,a surface the operation of which turns an aeroplane about one of its axes4 ,skin-,friction--,the friction of the air with roughness of surface4 ,a form of drift4 ,span---,the distance from wing-tip to wing-tip4 ,stagger--,the distance the upper surface is forward of the lower surface when the axis of the propeller is horizontal4 ,stability--,the inherent tendency of a body1 when disturbed1 to return to its normal position4 ,stability1 ,directional--,the stability about an axis which is vertical during normal horizontal flight1 and without which an aeroplane has no natural tendency to remain upon its course4 ,stability1 ,longitudinal--,the stability of an aeroplane about an axis transverse to the direction of normal horizontal flight1 and without which it has no tendency to oppose pitching and tossing4 ,stability1 ,lateral--,the stability of an aeroplane about its longitudinal axis1 and without which it has no tendency to oppose sideways rolling4 ,stabilizer--,a surface1 such as fin or tail-plane1 designed to give an aeroplane inherent stability4 ,stall1 to--,to give or allow an aeroplane an angle of incidence greater than the 8maximum0 angle1 the result being a fall in the lift-drift ratio1 the lift consequently becoming less than the weight of the aeroplane1 which must then fall1 i4e41 8stall0 or 8pancake40 ,stress--,burden or load4 ,strain--,deformation produced by stress4 ,side-,slip1 to--,to fall as a result of an excessive 8bank0 or 8roll40 ,skid1 to--,to be carried sideways by centrifugal force when turning to left or right4 ,skid1 ,undercarriage--,a spar1 mounted in a fore and aft direction1 and to which the wheels of the undercarriage are sometimes attached4 ,should a wheel give way the skid is then supposed to act like the runner of a sleigh and to support the aeroplane4 ,skid1 ,tail--,a piece of wood or other material1 orientable1 and fitted with shock absorbers1 situated under the tail of an aeroplane in order to support it upon the ground and to absorb the shock of alighting4 ,section--,any separate part of the top surface1 that part of the bottom surface immediately underneath it1 with their struts and wires4 ,spar--,any long piece of wood or other material4 ,spar1 ,main--,a spar within a surface and to which all the ribs are attached1 such spar being the one situated nearest to the centre of pressure4 ,it transfers more than half the lift from the ribs to the bracing4 ,spar1 ,rear--,a spar within a surface1 and to which all the ribs are attached1 such spar being situated at the rear of the centre of pressure and at a greater distance from it than is the main spar4 ,it transfers less than half of the lift from the ribs to the bracing4 ,strut--,any wooden member intended to take merely the stress of direct compression4 ,strut1 ,interplane--,a strut holding the top and bottom surfaces apart4 ,strut1 ,fuselage--,a strut holding the fuselage longerons apart4 ,it should be stated whether top1 bottom1 or side4 ,if side1 then it should be stated whether right or left hand4 ,montant4 ,strut1 ,extension--,a strut supporting an 8extension0 when not in flight4 ,it may also prevent the extension from collapsing upwards during flight4 ,strut1 ,undercarriage-- ,strut1 ,dope--,a strut within a surface1 so placed as to prevent the tension of the doped fabric from distorting the framework4 ,serving--,to bind round with wire1 cord1 or similar material4 ,usually used in connection with wood joints and wire cable splices4 ,slip1 ,propeller--,the pitch less the distance the propeller advances during one revolution4 ,stream-,line--,a form or shape of detrimental surface designed to produce minimum drift4 ,toss1 to--,to plunge tail-down4 ,torque1 ,propeller--,the tendency of a propeller to turn an aeroplane about its longitudinal axis in a direction opposite to that in which the propeller revolves4 ,tail-,slide--,a fall whereby the tail of an aeroplane leads4 ,tractor--,an aeroplane of which the propeller is mounted in front of the main lifting surface4 ,triplane--,an aeroplane of which the main lifting surface consists of three surfaces or pairs of wings mounted one above the other4 ,tail-,plane--,a horizontal stabilizing surface mounted at some distance behind the main lifting surface4 ,empennage4 ,turnbuckle--,a form of wire-tightener1 consisting of a barrel into each end of which is screwed an eyebolt4 ,wires are attached to the eyebolts and the required degree of tension is secured by means of rotating the barrel4 ,thrust1 ,propeller--,see 8,air-,screw40 ,undercarriage--,that part of an aeroplane beneath the fuselage or nacelle1 and intended to support the aeroplane when at rest1 and to absorb the shock of alighting4 ,velocity--,rate of displacement2 speed4 ,volplane--,a gliding descent4 ,weight--,is a measure of the force of the ,earth's attraction 7gravity7 upon a body4 ,the standard unit of weight in this country is #a lb41 and is the force of the ,earth's attraction on a piece of platinum called the standard pound1 deposited with the ,board of ,trade in ,london4 ,at the centre of the ,earth a body will be attracted with equal force in every direction4 ,it will therefore have no weight1 though its mass is unchanged4 ,gravity1 of which weight is a measure1 decreases with increase of altitude4 ,web 7of a rib7--,that vertical part of a rib which prevents it from bending upwards4 ,warp1 to--,to distort a surface in order to vary its angle of incidence4 ,to vary the angle of incidence of a controlling surface4 ,wash--,the disturbance of air produced by the flight of an aeroplane4 ,wash-in--,an increasing angle of incidence of a surface towards its wing-tip4 ,wash-out--,a decreasing angle of incidence of a surface towards its wing-tip4 ,wing-tip--,the right- or left-hand extremity of a surface4 ,wire--,a wire is1 in ,aeronautics1 always known by the name of its function4 ,wire1 ,lift or ,flying--,a wire opposed to the direction of lift1 and used to prevent a surface from collapsing upward during flight4 ,wire1 ,anti-lift or ,landing--,a wire opposed to the direction of gravity1 and used to sustain a surface when it is at rest4 ,wire1 ,drift--,a wire opposed to the direction of drift1 and used to prevent a surface from collapsing backwards during flight4 ,wire1 ,anti-drift--,a wire opposed to the tension of a drift wire1 and used to prevent such tension from distorting the framework4 ,wire1 ,incidence--,a wire running from the top of an interplane strut to the bottom of the interplane strut in front of or behind it4 ,it maintains the 8stagger0 and assists in maintaining the angle of incidence4 ,sometimes termed 8stagger wire40 ,wire1 ,bracing--,any wire holding together the framework of any part of an aeroplane4 ,it is not1 however1 usually applied to the wires described above unless the function performed includes a function additional to those described above4 ,thus1 a lift wire1 while strictly speaking a bracing wire1 is not usually described as one unless it performs the additional function of bracing some well-defined part such as the undercarriage4 ,it will then be said to be an 8undercarriage bracing lift wire40 ,it might1 perhaps1 be acting as a drift wire also1 in which case it will then be de-scribed as an 8undercarriage bracing lift-drift wire40 ,it should always be stated whether a bracing wire is 7#a7 top1 7#b7 bottom1 7#c7 cross1 or 7#d7 side4 ,if a 8side bracing wire10 then it should be stated whether right- or left-hand4 ,wire1 ,internal ,bracing--,a bracing wire 7usually drift or anti-drift7 within a surface4 ,wire1 ,top ,bracing--,a bracing wire1 approximately horizontal and situated between the top longerons of fuselate1 between top tail booms1 or at the top of similar construction4 ,wire1 ,bottom ,bracing--,ditto1 substituting 8bottom0 for 8top40 ,wire1 ,side ,bracing--,a bracing wire crossing diagonally a side bay of fuselage1 tail boom bay1 undercarriage side bay or centre-section side bay4 ,this term is not usually used with reference to incidence wires1 although they cross diagonally the side bays of the cell4 ,it should be stated whether right- or left-hand4 ,wire1 ,cross ,bracing--,a bracing wire1 the position of which is diagonal from right to left when viewing it from the front of an aeroplane4 ,wire1 ,control ,bracing--,a wire preventing distortion of a controlling surface4 ,wire1 ,control--,a wire connecting a controlling surface with the pilot's control lever1 wheel1 or rudder-bar4 ,wire1 ,aileron ,gap--,a wire connecting top and bottom ailerons4 ,wire1 ,aileron ,balance--,a wire connecting the right- and left-hand top ailerons4 ,sometimes termed the 8aileron compensating wire40 ,wire1 ,snaking--,a wire1 usually of soft metal1 wound spirally or tied round another wire1 and attached at each end to the framework4 ,used to prevent the wire round which it is 8snaked0 from becoming1 in the event of its displacement1 entangled with the propeller4 ,wire1 ,locking--,a wire used to prevent a turnbuckle barrel or other fitting from losing its adjustment4 ,wing--,strictly speaking1 a wing is one of the surfaces of an ornithopter4 ,the term is1 however1 often applied to the lifting surface of an aeroplane when such surface is divided into two parts1 one being the left-hand 8wing10 and the other the right-hand 8wing40 ,wind-,tunnel--,a large tube used for experimenting with surfaces and models1 and through which a current of air is made to flow by artificial means4 ,work--,force ,x displacement4 ,wind-,screen--,a small transparent screen mounted in front of the pilot to protect his face from the air pressure4 ,,footnotes3 #a ,propeller ,slip3 ,as the propeller screws through the air1 the latter to a certain extent gives back to the thrust of the propellor blades1 just as the shingle on the beach slips back as you ascend it4 ,such 8give-back0 is known as 8slip10 and anyone behind the propellor will feel the slip as a strong draught of air4 #b ,helicopter4 ,an air-screw revolving upon a vertical axis4 ,if driven with sufficient power1 it will lift vertically1 but having regard to the mechanical difficulties of such construction1 it is a most inefficient way of securing lift compared with the arrangement of an inclined surface driven by a propeller revolving about a horizontal axis4 #c ,pancakes3 ,pilot's slang for stalling an aeroplane and dropping like a pancake4 #d ,morane parasol3 ,a type of ,morane monoplane in which the lifting surfaces are raised above the pilot in order to afford him a good view of the earth4 #e ,skin friction is that part of the drift due to the friction of the air with roughnesses upon the surface of the aeroplane4 #f ,banking3 ,when an aeroplane is turned to the left or the right the centrifugal force of its momentum causes it to skid sideways and outwards away from the centre of the turn4 ,to minimize such action the pilot banks1 i4e41 tilts1 the aeroplane sideways in order to oppose the underside of the planes to the air4 ,the aeroplane will not then skid outwards beyond the slight skid necessary to secure a sufficient pressure of air to balance the centrifugal force4 #g ,an explanation of the way in which the wash-out is combined with a wash-in to offset propellor torque will be found on p4 #hb4 #h ,a4,m4's3 ,air ,mechanics4 #i ,butt means to thicken at the end4 ,screw means to machine a thread on the butt-end of the wire1 and in this way the wire can make connection with the desired place by being screwed into a metal fitting1 thus eliminating the disadvantage of the unsatisfactory loop4 #aj ,deviation curve3 ,a curved line indicating any errors in the compass4 #aa ,a propeller screws through the air1 and the distance it advances during one revolution1 supposing the air to be solid1 is known as the pitch4 ,the pitch1 which depends upon the angle of the propeller blades1 must be equal to the speed of the aeroplane1 plus the slip1 and if1 on account of the rarity of the air the speed of the aeroplane increases1 then the angle and pitch should be correspondingly increased4 ,propellers with a pitch capable of being varied by the pilot are the dream of propeller designers4 ,for explanation of 8slip0 see ,chapter ,,iv4 on propellers4 #ab ,getting out of my depth8 ,invading the realms of fancy8 ,well1 perhaps so1 but at any rate it is possible that extraordinary speed through space may be secured if means are found to maintain the impulse of the engine and the thrust-drift efficiency of the propeller at great altitude4 #ac ,box-kite4 ,the first crude form of biplane4 #ad ,see ,newton's laws in the ,glossary at the end of the book4 #ae ,see 8,aerofoil0 in the ,glossary4 #af 8,in effect0 because1 although there may be actually the greatest proportion of keel-surface ,in front of the vertical axis1 such surface may be much nearer to the axis than is the keel-surface towards the tail4 ,the latter may then be actually less than the surface in front1 but1 being farther from the axis1 it has a greater leverage1 and consequently is greater in effect than the surface in front4