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diff --git a/818-h/818-h.htm b/818-h/818-h.htm new file mode 100644 index 0000000..17b29d6 --- /dev/null +++ b/818-h/818-h.htm @@ -0,0 +1,6233 @@ +<?xml version="1.0" encoding="utf-8"?> + +<!DOCTYPE html + PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" + "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd" > + +<html xmlns="http://www.w3.org/1999/xhtml" lang="en"> + <head> + <title> + The Aeroplane Speaks, by H. Barber + </title> + <style type="text/css" xml:space="preserve"> + + body { margin:5%; background:#faebd0; text-align:justify} + P { text-indent: 1em; margin-top: .25em; margin-bottom: .25em; } + H1,H2,H3,H4,H5,H6 { text-align: center; margin-left: 15%; margin-right: 15%; } + hr { width: 50%; text-align: center;} + .foot { margin-left: 20%; margin-right: 20%; text-align: justify; text-indent: -3em; font-size: 90%; } + blockquote {font-size: 97%; font-style: italic; margin-left: 10%; margin-right: 10%;} + .mynote {background-color: #DDE; color: #000; padding: .5em; margin-left: 10%; margin-right: 10%; font-family: sans-serif; font-size: 95%;} + .toc { margin-left: 10%; margin-bottom: .75em;} + .toc2 { margin-left: 20%;} + div.fig { display:block; margin:0 auto; text-align:center; } + div.middle { margin-left: 20%; margin-right: 20%; text-align: justify; } + .figleft {float: left; margin-left: 0%; margin-right: 1%;} + .figright {float: right; margin-right: 0%; margin-left: 1%;} + .pagenum {display:inline; font-size: 70%; font-style:normal; + margin: 0; padding: 0; position: absolute; right: 1%; + text-align: right;} + pre { font-style: italic; font-size: 90%; margin-left: 10%;} + +</style> + </head> + <body> +<pre xml:space="preserve"> + +The Project Gutenberg EBook of The Aeroplane Speaks, by H. Barber + +This eBook is for the use of anyone anywhere at no cost and with +almost no restrictions whatsoever. You may copy it, give it away or +re-use it under the terms of the Project Gutenberg License included +with this eBook or online at www.gutenberg.org + + +Title: The Aeroplane Speaks + +Author: H. Barber + +Release Date: July 21, 2008 [EBook #818] +Last Updated: March 15, 2018 + +Language: English + +Character set encoding: UTF-8 + +*** START OF THIS PROJECT GUTENBERG EBOOK THE AEROPLANE SPEAKS *** + + + + +Produced by Charles Keller, and David Widger + + + + + +</pre> + <p> + <br /><br /> + </p> + <h1> + THE AEROPLANE SPEAKS + </h1> + <p> + <br /> + </p> + <h2> + By H. Barber + </h2> + <p> + <br /> + </p> + <h3> + (Captain, Royal Flying Corps) + </h3> + <p> + <br /> <br /> + </p> + <h3> + DEDICATED TO THE SUBALTERN FLYING OFFICER + </h3> + <p> + <br /> <br /> + </p> + <hr /> + <p> + <br /> <br /> <a name="link2H_4_0001" id="link2H_4_0001"> + <!-- H2 anchor --> </a> + </p> + <div style="height: 4em;"> + <br /><br /><br /><br /> + </div> + <h2> + MOTIVE + </h2> + <p> + The reasons impelling me to write this book, the maiden effort of my pen, + are, firstly, a strong desire to help the ordinary man to understand the + Aeroplane and the joys and troubles of its Pilot; and, secondly, to + produce something of PRACTICAL assistance to the Pilot and his invaluable + assistant the Rigger. Having had some eight years' experience in + designing, building, and flying aeroplanes, I have hopes that the + practical knowledge I have gained may offset the disadvantage of a hand + more used to managing the “joy-stick” than the dreadful haltings, the many + side-slips, the irregular speed, and, in short, the altogether + disconcerting ways of a pen. + </p> + <p> + The matter contained in the Prologue appeared in the Field of May 6th, + 13th, 20th, and 27th, 1916, and is now reprinted by the kind permission of + the editor, Sir Theodore Cook. + </p> + <p> + I have much pleasure in also acknowledging the kindness of Mr. C. G. Grey, + editor of the Aeroplane, to whom I am indebted for the valuable + illustrations reproduced at the end of this book. + </p> + <p> + <br /> <br /> + </p> + <hr /> + <p> + <br /> <br /> + </p> + <blockquote> + <p class="toc"> + <big><b>CONTENTS</b></big> + </p> + <p> + <br /> + </p> + <p class="toc"> + <a href="#link2H_4_0001"> MOTIVE </a> + </p> + <p class="toc"> + <a href="#link2H_4_0002"> <b>THE AEROPLANE SPEAKS</b> </a> + </p> + <p> + <br /> + </p> + <p class="toc"> + <a href="#link2H_PROL"> PROLOGUE </a> + </p> + <p> + <br /> + </p> + <p class="toc"> + <a href="#link2H_PART1"> PART I. THE ELEMENTARY PRINCIPLES AIR THEIR + GRIEVANCES </a> + </p> + <p class="toc"> + <a href="#link2H_PART2"> PART II. THE PRINCIPLES, HAVING SETTLED THEIR + DIFFERENCES, FINISH THE </a> + </p> + <p class="toc"> + <a href="#link2H_PART3"> PART III. THE GREAT TEST </a> + </p> + <p class="toc"> + <a href="#link2H_PART4"> PART IV. 'CROSS COUNTRY </a> + </p> + <p> + <br /> + </p> + <p class="toc"> + <a href="#link2HCH0001"> CHAPTER I. FLIGHT </a> + </p> + <p class="toc"> + <a href="#link2HCH0002"> CHAPTER II. STABILITY AND CONTROL </a> + </p> + <p class="toc"> + <a href="#link2HCH0003"> CHAPTER III. RIGGING </a> + </p> + <p class="toc"> + <a href="#link2HCH0004"> CHAPTER IV. THE PROPELLER, OR “AIR-SCREW” </a> + </p> + <p class="toc"> + <a href="#link2HCH0005"> CHAPTER V. MAINTENANCE </a> + </p> + <p> + <br /> + </p> + <p class="toc"> + <a href="#link2H_GLOS"> GLOSSARY </a> + </p> + <p class="toc"> + <a href="#link2H_FOOT"> FOOTNOTES </a> + </p> + </blockquote> + <p> + <br /> <br /> + </p> + <hr /> + <p> + <br /> <br /> <a name="link2H_4_0002" id="link2H_4_0002"> + <!-- H2 anchor --> </a> + </p> + <div style="height: 4em;"> + <br /><br /><br /><br /> + </div> + <h1> + THE AEROPLANE SPEAKS + </h1> + <p> + <a name="link2H_PROL" id="link2H_PROL"> + <!-- H2 anchor --> </a> + </p> + <div style="height: 4em;"> + <br /><br /><br /><br /> + </div> + <h2> + PROLOGUE + </h2> + <p> + <a name="link2H_PART1" id="link2H_PART1"> + <!-- H2 anchor --> </a> + </p> + <div style="height: 4em;"> + <br /><br /><br /><br /> + </div> + <h2> + PART I. THE ELEMENTARY PRINCIPLES AIR THEIR GRIEVANCES + </h2> + <p> + The Lecture Hall at the Royal Flying Corps School for Officers was + deserted. The pupils had dispersed, and the Officer Instructor, more + fagged than any pupil, was out on the aerodrome watching the test of a new + machine. + </p> + <p> + Deserted, did I say? But not so. The lecture that day had been upon the + Elementary Principles of Flight, and they lingered yet. Upon the + Blackboard was the illustration you see in the frontispiece. + </p> + <p> + “I am the side view of a Surface,” it said, mimicking the tones of the + lecturer. “Flight is secured by driving me through the air at an angle + inclined to the direction of motion.” + </p> + <p> + “Quite right,” said the Angle. “That's me, and I'm the famous Angle of + Incidence.” + </p> + <p> + “And,” continued the Surface, “my action is to deflect the air downwards, + and also, by fleeing from the air behind, to create a semi-vacuum or + rarefied area over most of the top of my surface.” + </p> + <p> + “This is where I come in,” a thick, gruff voice was heard, and went on: + “I'm the Reaction. You can't have action without me. I'm a very + considerable force, and my direction is at right-angles to you,” and he + looked heavily at the Surface. “Like this,” said he, picking up the chalk + with his Lift, and drifting to the Blackboard. + </p> + <p> + “I act in the direction of the arrow R, that is, more or less, for the + direction varies somewhat with the Angle of Incidence and the curvature of + the Surface; and, strange but true, I'm stronger on the top of the Surface + than at the bottom of it. The Wind Tunnel has proved that by exhaustive + research—and don't forget how quickly I can grow! As the speed + through the air increases my strength increases more rapidly than you + might think—approximately, as the Square of the Speed; so you see + that if the Speed of the Surface through the air is, for instance, + doubled, then I am a good deal more than doubled. That's because I am the + result of not only the mass of air displaced, but also the result of the + Speed with which the Surface engages the Air. I am a product of those two + factors, and at the speeds at which Aeroplanes fly to-day, and at the + altitudes and consequent density of air they at present experience, I + increase at about the Square of the Speed. + </p> + <p> + “Oh, I'm a most complex and interesting personality, I assure you—in + fact, a dual personality, a sort of aeronautical Dr. Jekyll and Mr. Hyde. + There's Lift, my vertical part or COMPONENT, as those who prefer long + words would say; he always acts vertically upwards, and hates Gravity like + poison. He's the useful and admirable part of me. Then there's Drift, my + horizontal component, sometimes, though rather erroneously, called Head + Resistance; he's a villain of the deepest dye, and must be overcome before + flight can be secured.” + </p> + <p> + “And I,” said the Propeller, “I screw through the air and produce the + Thrust. I thrust the Aeroplane through the air and overcome the Drift; and + the Lift increases with the Speed and when it equals the Gravity of + Weight, then—there you are—Flight! And nothing mysterious + about it at all.” + </p> + <p> + “I hope you'll excuse me interrupting,” said a very beautiful young lady, + “my name is Efficiency, and, while no doubt, all you have said is quite + true, and that, as my young man the Designer says, `You can make a + tea-tray fly if you slap on Power enough,' I can assure you that I'm not + to be won quite so easily.” + </p> + <p> + “Well,” eagerly replied the Lift and the Thrust, “let's be friends. Do + tell us what we can do to help you to overcome Gravity and Drift with the + least possible Power. That obviously seems the game to play, for more + Power means heavier engines, and that in a way plays into the hands of our + enemy, Gravity, besides necessitating a larger Surface or Angle to lift + the Weight, and that increases the Drift.” + </p> + <p> + “Very well,” from Efficiency, “I'll do my best, though I'm so shy, and + I've just had such a bad time at the Factory, and I'm terribly afraid + you'll find it awfully dry.” + </p> + <p> + “Buck up, old dear!” This from several new-comers, who had just appeared. + “We'll help you,” and one of them, so lean and long that he took up the + whole height of the lecture room, introduced himself. + </p> + <p> + “I'm the High Aspect Ratio,” he said, “and what we have got to do to help + this young lady is to improve the proportion of Lift to Drift. The more + Lift we can get for a certain area of Surface, the greater the Weight the + latter can carry; and the less the Drift, then the less Thrust and Power + required to overcome it. Now it is a fact that, if the Surface is shaped + to have the greatest possible span, i.e., distance from wing-tip to + wing-tip, it then engages more air and produces both a maximum Reaction + and a better proportion of Lift to Drift. + </p> + <p> + “That being so, 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 case; for you must + understand that the Lift-Drift Ratio depends very much upon the size of + the Angle of Incidence, which should be as small as possible within + certain limits. So what I say is, make the surface of Infinite Span with + no width or chord, as they call it. That's all I require, I assure you, to + make me quite perfect and of infinite service to Miss Efficiency.” + </p> + <p> + “That's not practical politics,” said the Surface. “The way you talk one + would think you were drawing L400 a year at Westminster, and working up a + reputation as an Aeronautical Expert. I must have some depth and chord to + take my Spars and Ribs, and again, I must have a certain chord to make it + possible for my Camber (that's curvature) to be just right for the Angle + of Incidence. If that's not right the air won't get a nice uniform + compression and downward acceleration from my underside, and the rarefied + `suction' area over the top of me will not be as even and clean in effect + as it might be. That would spoil the Lift-Drift Ratio more than you can + help it. Just thrust that chalk along, will you? and the Blackboard will + show you what I mean.” + </p> + <p> + “Well,” said the Aspect Ratio, “have it your own way, though I'm sorry to + see a pretty young lady like Efficiency compromised so early in the game.” + </p> + <p> + “Look here,” exclaimed a number of Struts, “we have got a brilliant idea + for improving the Aspect Ratio,” and with that they hopped up on to the + Spars. “Now,” excitedly, “place another Surface on top of us. Now do you + see? There is double the Surface, and that being so, the proportion of + Weight to Surface area is halved. That's less burden of work for the + Surface, and so the Spars need not be so strong and so deep, which results + in not so thick a Surface. That means the Chord can be proportionately + decreased without adversely affecting the Camber. With the Chord + decreased, the Span becomes relatively greater, and so produces a splendid + Aspect Ratio, and an excellent proportion of Lift to Drift.” + </p> + <p> + “I don't deny that they have rather got me there,” said the Drift, “but + all the same, don't forget my increase due to the drift of the Struts and + their bracing wires.” + </p> + <p> + “Yes, I dare say,” replied the Surface, “but remember that my Spars are + less deep than before, and consequently I am not so thick now, and shall + for that reason also be able to go through the air with a less proportion + of Drift to Lift.” + </p> + <p> + “Remember me also, please,” croaked the Angle of Incidence. “Since the + Surface has now less weight to carry for its area, I may be set at a still + lesser and finer Angle. That means less Drift again. We are certainly + getting on splendidly! Show us how it looks now, Blackboard.” And the + Blackboard obligingly showed them as follows: + </p> + <p> + “Well, what do you think of that?” they all cried to the Drift. + </p> + <p> + “You think you are very clever,” sneered the Drift. “But you are not + helping Efficiency as much as you think. 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 case, and that means + loss of Lift; and you can't help matters by increasing the gap between the + surfaces because that means longer Struts and Wires, and that in itself + would help me, not to speak of increasing the Weight. You see it's not + quite so easy as you thought.” + </p> + <p> + At this moment a hiccough was heard, and a rather fast and rakish-looking + chap, named Stagger, spoke up. “How d'ye do, miss,” he said politely to + Efficiency, with a side glance out of his wicked old eye. “I'm a bit of a + knut, and without the slightest trouble I can easily minimize the + disadvantage that old reprobate Drift has been frightening you with. I + just stagger the top Surface a bit forward, and no longer is that suction + effect dead under it. 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 Struts. Such extension will be quite useful, as there + will be no Surface at all underneath it to interfere with the Reaction + above.” And the Stagger leaned forward and picked up the Chalk, and this + is the picture he drew: + </p> + <p> + Said the Blackboard, “That's not half bad! It really begins to look + something like the real thing, eh?” + </p> + <p> + “The real thing, is it?” grumbled Drift. “Just consider that contraption + in the light of any one Principle, and I warrant you will not find one of + them applied to perfection. The whole thing is nothing but a Compromise.” + And he glared fixedly at poor Efficiency. + </p> + <p> + “Oh, dear! Oh, dear!” she cried. “I'm always getting into trouble. What + WILL the Designer say?” + </p> + <p> + “Never mind, my dear,” said the Lift-Drift Ratio, consolingly. “You are + improving rapidly, and quite useful enough now to think of doing a job of + work.” + </p> + <p> + “Well, that's good news,” and Efficiency wiped her eyes with her Fabric + and became almost cheerful. “Suppose we think about finishing it now? + There will have to be an Engine and Propeller, won't there? And a body to + fix them in, and tanks for oil and petrol, and a tail, and,” archly, “one + of those dashing young Pilots, what?” + </p> + <p> + “Well, we are getting within sight of those interesting Factors,” said the + Lift-Drift Ratio, “but first of all we had better decide upon the Area of + the Surfaces, their Angle of Incidence and Camber. If we are to ascend as + quickly as possible the Aeroplane must be SLOW in order to secure the best + possible Lift-Drift Ratio, for the drift of the struts wires, body, etc., + increases approximately as the square of the speed, but it carries with it + no lift as it does in the case of the Surface. The less speed then, the + less such drift, and the better the Aeroplane's proportion of lift to + drift; and, being slow, we shall require a LARGE SURFACE in order to + secure a large lift relative to the weight to be carried. We shall also + require a LARGE ANGLE OF INCIDENCE relative to the horizontal, in order to + secure a proper inclination of the Surface to the direction of motion, for + you must remember that, while we shall fly upon an even keel and with the + propeller thrust horizontal (which is its most efficient attitude), our + flight path, which is our direction of motion, will be sloping upwards, + 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 motion. Apart + from that, we shall require a larger Angle of Incidence than in the case + of a machine designed purely for speed, and that means a correspondingly + LARGE CAMBER. + </p> + <p> + “On the other hand, if we are thinking merely of Speed, then a SMALL + SURFACE, just enough to lift the weight off the ground, will be best, also + a SMALL ANGLE to cut the Drift down and that, of course, means a + relatively SMALL CAMBER. + </p> + <p> + “So you see the essentials for CLIMB or quick ascent and for SPEED are + diametrically opposed. Now which is it to be?” + </p> + <p> + “Nothing but perfection for me,” said Efficiency. “What I want is Maximum + Climb and Maximum Speed for the Power the Engine produces.” + </p> + <p> + And each Principle fully agreed with her beautiful sentiments, but work + together they would not. + </p> + <p> + The Aspect Ratio wanted infinite Span, and hang the Chord. + </p> + <p> + The Angle of Incidence would have two Angles and two Cambers in one, which + was manifestly absurd; the Surface insisted upon no thickness whatever, + and would not hear of such things as Spars and Ribs; and the Thrust + objected to anything at all likely to produce Drift, and very nearly wiped + the whole thing off the Blackboard. + </p> + <p> + There was, indeed, the makings of a very pretty quarrel when the Letter + arrived. It was about a mile long, and began to talk at once. + </p> + <p> + “I'm from the Inventor,” he said, and hope rose in the heart of each + heated Principle. “It's really absurdly simple. All the Pilot has to do is + to touch a button, and at his will, VARY the area of the Surface, the + Angle of Incidence, and the Camber! And there you are—Maximum Climb + or Maximum Speed as required! How does that suit you?” + </p> + <p> + “That suits us very well,” said the Surface, “but, excuse me asking, how + is it done without apparatus increasing the Drift and the Weight out of + all reason? You won't mind showing us your Calculations, Working Drawings, + Stress Diagrams, etc., will you?” + </p> + <p> + Said the Letter with dignity, “I come from an Inventor so brilliantly + clever as to be far above the unimportant matters you mention. He is no + common working man, sir! He leaves such things to Mechanics. The point is, + you press a button and——” + </p> + <p> + “Look here,” said a Strut, rather pointedly, “where do you think you are + going, anyway?” + </p> + <p> + “Well,” from the Letter, “as a matter of fact, I'm not addressed yet, but, + of course, there's no doubt I shall reach the very highest quarters and + absolutely revolutionize Flight when I get there.” + </p> + <p> + Said the Chalk, “I'll address you, if that's all you want; now drift along + quickly!” And off went the Letter to The Technical Editor, “Daily Mauler,” + London. + </p> + <p> + And a League was formed, and there were Directors with Fees, and several + out-of-service Tin Hats, and the Man-who-takes-the-credit, and a fine fat + Guinea-pig, and all the rest of them. And the Inventor paid his Tailor and + had a Hair-Cut, and is now a recognized Press Expert—but he is still + waiting for those Mechanics! + </p> + <p> + “I'm afraid,” said the Slide-rule, who had been busy making those + lightning-like automatic calculations for which he is so famous, “it's + quite impossible to fully satisfy all of you, and it is perfectly plain to + me that we shall have to effect a Compromise and sacrifice some of the + Lift for Speed.” + </p> + <p> + Thud! What was that? + </p> + <p> + Efficiency had fainted dead away! The last blow had been too much for her. + And the Principles gathered mournfully round, but with the aid of the + Propeller Slip<a href="#linknote-1" name="linknoteref-1" id="linknoteref-1"><small>1</small></a> + and a friendly lift from the Surface she was at length revived and + regained a more normal aspect. + </p> + <p> + Said the Stagger with a raffish air, “My dear young lady, I assure you + that from the experiences of a varied career, I have learned that + perfection is impossible, and I am sure the Designer will be quite + satisfied if you become the Most Efficient Compromise.” + </p> + <p> + “Well, that sounds so common sense,” sighed Efficiency, “I suppose it must + be true, and if the Designer is satisfied, that's all I really care about. + Now do let's get on with the job.” + </p> + <p> + So the Chalk drew a nice long slim body to hold the Engine and the tanks, + etc., with room for the Pilot's and Passenger's seats, and placed it + exactly in the middle of the Biplane. And he was careful to make its + position such that the Centre of Gravity was a little in advance of the + Centre of Lift, so that when the Engine was not running and there was + consequently no Thrust, the Aeroplane should be “nose-heavy” just to the + right degree, and so take up a natural glide to Earth—and this was + to help the Pilot and relieve him of work and worry, should he find + himself in a fog or a cloud. And so that this tendency to glide downwards + should not be in evidence when the Engine was running and descent not + desired, the Thrust was placed a little below the Centre of Drift or + Resistance. In this way it would in a measure pull the nose of the + Aeroplane up and counterbalance the “nose-heavy” tendency. + </p> + <p> + And the Engine was so mounted that when the Propeller-Thrust was + horizontal, which is its most efficient position, the Angle of Incidence + and the Area of the surfaces were just sufficient to give a Lift a little + in excess of the Weight. And the Camber was such that, as far as it was + concerned, the Lift-Drift Ratio should be the best possible for that Angle + of Incidence. And a beautifully simple under-carriage was added, the + outstanding features of which were simplicity, strength, light-weight, and + minimum drift. And, last of all, there was the Elevator, of which you will + hear more by-and-by. And this is what it looked like then: + </p> + <p> + And Efficiency, smiling, thought that it was not such a bad compromise + after all and that the Designer might well be satisfied. + </p> + <p> + “Now,” said she, “there's just one or two points I'm a bit hazy about. It + appears that when the Propeller shaft is horizontal and so working in its + most efficient attitude, I shall have a Lift from the Surfaces slightly in + excess of the Weight. That means I shall ascend slightly, at the same time + making nearly maximum speed for the power and thrust. Can't I do better + than that?” + </p> + <p> + “Yes, indeed,” spoke up the Propeller, “though it means that I must assume + a most undignified attitude, for helicopters<a href="#linknote-2" + name="linknoteref-2" id="linknoteref-2"><small>2</small></a> I never + approved of. In order to ascend more quickly the Pilot will deflect the + Elevator, which, by the way, you see hinged to the Tail. By that means he + will force the whole Aeroplane to assume a greater Angle of Incidence. And + with greater Angle, the Lift will increase, though I'm sorry to say the + Drift will increase also. Owing to the greater Drift, the Speed through + the air will lessen, and I'm afraid that won't be helpful to the Lift; but + I shall now be pointing upwards, and besides overcoming the Drift in a + forward direction I shall be doing my best to haul the Aeroplane skywards. + At a certain angle known as the Best Climbing Angle, we shall have our + Maximum Margin of Lift, and I'm hoping that may be as much as almost a + thousand feet altitude a minute.” + </p> + <p> + “Then, if the Pilot is green, my chance will come,” said the Maximum Angle + of Incidence. “For if the Angle is increased over the Best Climbing Angle, + the Drift will rush up; and the Speed, and with it the Lift, will, when my + Angle is reached, drop to a point when the latter will be no more than the + Weight. The Margin of Lift will have entirely disappeared, and there we + shall be, staggering along at my tremendous angle, and only just + maintaining horizontal flight.” + </p> + <p> + “And then with luck I'll get my chance,” said the Drift. “If he is a bit + worse than green, he'll perhaps still further increase the Angle. Then the + Drift, largely increasing, the Speed, and consequently the Lift, will + become still less, i.e., less than the Weight, and then—what price + pancakes,<a href="#linknote-3" name="linknoteref-3" id="linknoteref-3"><small>3</small></a> + eh?” + </p> + <p> + “Thank you,” from Efficiency, “that was all most informing. And now will + you tell me, please, how the greatest Speed may be secured?” + </p> + <p> + “Certainly, now it's my turn,” piped the Minimum Angle of Incidence. “By + means of the Elevator, the Pilot places the Aeroplane at my small Angle, + at which the Lift only just equals the Weight, and, also, at which we + shall make greater speed with no more Drift than before. Then we get our + greatest Speed, just maintaining horizontal flight.” + </p> + <p> + “Yes; though I'm out of the horizontal and thrusting downwards,” grumbled + the Propeller, “and that's not efficient, though I suppose it's the best + we can do until that Inventor fellow finds his Mechanics.” + </p> + <p> + “Thank you so much,” said Efficiency. “I think I have now at any rate an + idea of the Elementary Principles of Flight, and I don't know that I care + to delve much deeper, for sums always give me a headache; but isn't there + something about Stability and Control? Don't you think I ought to have a + glimmering of them too?” + </p> + <p> + “Well, I should smile,” said a spruce Spar, who had come all the way from + America. “And that, as the Lecturer says, `will be the subject of our next + lecture,' so be here again to-morrow, and you will be glad to hear that it + will be distinctly more lively than the subject we have covered to-day.” + </p> + <p> + <a name="link2H_PART2" id="link2H_PART2"> + <!-- H2 anchor --> </a> + </p> + <div style="height: 4em;"> + <br /><br /><br /><br /> + </div> + <h2> + PART II. THE PRINCIPLES, HAVING SETTLED THEIR DIFFERENCES, FINISH THE + </h2> + <p> + JOB + </p> + <p> + Another day had passed, and the Flight Folk had again gathered together + and were awaiting the arrival of Efficiency who, as usual, was rather late + in making an appearance. + </p> + <p> + The crowd was larger than ever, and among the newcomers some of the most + important were the three Stabilities, named Directional, Longitudinal, and + Lateral, with their assistants, the Rudder, Elevator, and Ailerons. There + was Centrifugal Force, too, who would not sit still and created a most + unfavourable impression, and Keel-Surface, the Dihedral Angle, and several + other lesser fry. + </p> + <p> + “Well,” said Centrifugal Force, “I wish this Efficiency I've heard so much + about would get a move on. Sitting still doesn't agree with me at all. + Motion I believe in. There's nothing like motion—the more the + better.” + </p> + <p> + “We are entirely opposed to that,” objected the three Stabilities, all in + a breath. “Unless it's in a perfectly straight line or a perfect circle. + Nothing but perfectly straight lines or, upon occasion, perfect circles + satisfy us, and we are strongly suspicious of your tendencies.” + </p> + <p> + “Well, we shall see what we shall see,” said the Force darkly. “But who in + the name of blue sky is this?” + </p> + <p> + And in tripped Efficiency, in a beautifully “doped” dress of the latest + fashionable shade of khaki-coloured fabric, a perfectly stream-lined + bonnet, and a bewitching little Morane parasol,<a href="#linknote-4" + name="linknoteref-4" id="linknoteref-4"><small>4</small></a> smiling as + usual, and airily exclaiming, “I'm so sorry I'm late, but you see the + Designer's such a funny man. He objects to skin friction,<a + href="#linknote-5" name="linknoteref-5" id="linknoteref-5"><small>5</small></a> + and insisted upon me changing my fabric for one of a smoother surface, and + that delayed me. Dear me, there are a lot more of us to-day, aren't there? + I think I had better meet one at a time.” And turning to Directional + Stability, she politely asked him what he preferred to do. + </p> + <p> + “My purpose in life, miss,” said he, “is to keep the Aeroplane on its + course, and to achieve that there must be, in effect, more Keel-Surface + behind the Vertical Turning Axis than there is in front of it.” + </p> + <p> + Efficiency looking a little puzzled, he added: “Just like a weathercock, + and by Keel-Surface I mean everything you can see when you view the + Aeroplane from the side of it—the sides of the body, struts, wires, + etc.” + </p> + <p> + “Oh, now I begin to see light,” said she: “but just exactly how does it + work?” + </p> + <p> + “I'll answer that,” said Momentum. “When perhaps by a gust of air the + Aeroplane is blown out of its course and points in another direction, it + doesn't immediately fly off on that new course. I'm so strong I pull it + off the new course to a certain extent, and towards the direction of the + old course. And so it travels, as long as my strength lasts, in a more or + less sideways position.” + </p> + <p> + “Then,” said the Keel-Surface, “I get a pressure of air all on one side, + and as there is, in effect, most of me towards the tail, the latter gets + pressed sideways, and the Aeroplane thus tends to assume its first + position and course.” + </p> + <p> + “I see,” said Efficiency, and, daintily holding the Chalk, she approached + the Blackboard. “Is this what you mean?” + </p> + <p> + “Yes, that's right enough,” said the Keel-Surface, “and you might + remember, too, that I always make the Aeroplane nose into the gusts rather + than away from them.” + </p> + <p> + “If that was not the case,” broke in Lateral Stability, and affecting the + fashionable Flying Corps stammer, “it would be a h-h-h-o-r-rible affair! + If there were too much Keel-Surface in front, then that gust would blow + the Aeroplane round the other way a very considerable distance. And the + right-hand Surface being on the outside of the turn would have more speed, + and consequently more Lift, than the Surface on the other side. That means + a greater proportion of the Lift on that side, and before you could say + Warp to the Ailerons over the Aeroplane would go—probable result a + bad side-slip” + </p> + <p> + “And what can the Pilot do to save such a situation as that?” said + Efficiency. + </p> + <p> + “Well,” replied Lateral Stability, “he 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-tips, and about which you + will hear more later on; but if the side-slip is very bad he may not be + able to right the Aeroplane by means of the Ailerons, 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 motion. The Aeroplane will + then be meeting the air in the direction it is designed to do so, and the + Surfaces and also the controls (the Rudder, Ailerons, and Elevator) will + be working efficiently; but its attitude relative to the earth will + probably be more or less upside-down, for the action of turning the + Aeroplane's nose down results, as you will see by the illustration B, in + the right wing, which is on the outside of the circle. travelling through + the air with greater speed than the left-hand wing. More Speed means more + Lift, so that results in overturning the Aeroplane still more; but now it + is, at any rate, meeting the air as it is designed to meet it, and + everything is working properly. It is then only necessary to warp the + Elevator, as shown in illustration C, in order to bring the Aeroplane into + a proper attitude relative to the earth.” + </p> + <p> + “Ah!” said the Rudder, looking wise, “it's in a case like that when I + become the Elevator and the Elevator becomes me.” + </p> + <p> + “That's absurd nonsense,” said the Blackboard, “due to looseness of + thought and expression.” + </p> + <p> + “Well,” replied the Rudder, “when 'the Aeroplane is in position A and I am + used, then I depress or ELEVATE the nose of the machine; and, if the + Elevator is used, then it turns the Aeroplane to right or left, which is + normally my function. Surely our roles have changed one with the other, + and I'm then the Elevator and the Elevator is me!” + </p> + <p> + Said Lateral Stability to the Rudder, “That's altogether the wrong way of + looking at it, though I admit”—and this rather sarcastically—“that + 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 it; but it won't go down here! You are a Controlling Surface + designed to turn the Aeroplane about its vertical axis, and the Elevator + is a Controlling Surface designed to turn the Aeroplane about its lateral + axis. Those are your respective jobs, and you can't possibly change them + about. Such talk only leads to confusion, and I hope we shall hear no more + of it.” + </p> + <p> + “Thanks,” said Efficiency to Lateral Stability. “And now, please, will you + explain your duties?” + </p> + <p> + “My duty is to keep the Aeroplane horizontal from Wing-tip to Wing-tip. + First of all, I sometimes arrange with the Rigger to wash-out, that is + decrease, the Angle of Incidence on one side of the Aeroplane, and to + effect the reverse condition, if it is not too much trouble, on the other + side.” + </p> + <p> + “But,” objected Efficiency, “the Lift varies with the Angle of Incidence, + and surely such a condition will result in one side of the Aeroplane + lifting more than the other side?' + </p> + <p> + “That's all right,” said the Propeller, “it's meant to off-set the + tendency of the Aeroplane to turn over sideways in the opposite direction + to which I revolve.” + </p> + <p> + “That's quite clear, though rather unexpected; but how do you counteract + the effect of the gusts when they try to overturn the Aeroplane sideways?” + said she, turning to Lateral Stability again. + </p> + <p> + “Well,” he replied, rather miserably, “I'm not nearly so perfect as the + Longitudinal and Directional Stabilities. The Dihedral Angle—that + is, the upward inclination of the Surfaces towards their wing-tips—does + what it can for me, but, in my opinion, it's a more or less futile effort. + The Blackboard will show you the argument.” And he at once showed them two + Surfaces, each set at a Dihedral Angle like this: + </p> + <p> + “Please imagine,” said the Blackboard, “that the top V is the front view + of a Surface flying towards you. 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 larger, and on the other side it becomes smaller. That + results in more Lift on the lower side and less on the higher side, 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 position.” + </p> + <p> + “Yes,” said the Dihedral Angle, “that's what would happen if they would + only make me large enough; but they won't do it because it would too + greatly decrease the horizontal equivalent, and therefore the Lift, and + incidentally it would, as Aeroplanes are built to-day, produce an excess + of Keel Surface above the turning axis, and that in itself would spoil the + Lateral Stability. The Keel Surface should be equally divided above and + below the longitudinal turning axis (upon which the Aeroplane rolls + sideways), or the side upon which there is an excess will get blown over + by the gusts. It strikes me that my future isn't very promising, and about + my only chance is when the Junior Draughtsman makes a mistake, as he did + the other day. And just think of it, they call him a Designer now that + he's got a job at the Factory! What did he do? Why, he calculated the + weights wrong and got the Centre of Gravity too high, and they didn't + discover it until the machine was built. Then all they could do was to + give me a larger Angle. That dropped the bottom of the V lower down, and + as that's the centre of the machine, where all the Weight is, of course + that put the Centre of Gravity in its right place. But now there is too + much Keel Surface above, and the whole thing's a Bad Compromise, not at + all like Our Efficiency.” + </p> + <p> + And Efficiency, blushing very prettily at the compliment, then asked, “And + how does the Centre of Gravity affect matters?” + </p> + <p> + “That's easy,” said Grandfather Gravity. “I'm so heavy that if I am too + low down I act like a pendulum and cause the Aeroplane to roll about + sideways, and if I am too high I'm like a stick balanced on your finger, + and then if I'm disturbed, over I go and the Aeroplane with me; and, in + addition to that, there are the tricks I play with the Aeroplane when it's + banked up,<a href="#linknote-6" name="linknoteref-6" id="linknoteref-6"><small>6</small></a> + i.e., tilted sideways for a turn, and Centrifugal Force sets me going the + way I'm not wanted to go. No; I get on best with Lateral Stability when my + Centre is right on the centre of Drift, or, at any rate, not much below + it.” And with that he settled back into the Lecturer's Chair and went + sound asleep again, for he was so very, very old, in fact the father of + all the Principles. + </p> + <p> + And the Blackboard had been busy, and now showed them a picture of the + Aeroplane as far as they knew it, and you will see that there is a slight + Dihedral Angle, and also, fixed to the tail, a vertical Keel Surface or + fin, as is very often the case in order to ensure the greater effect of + such surface being behind the vertical turning axis. + </p> + <p> + But Efficiency, growing rather critical with her newly gained knowledge, + cried out: “But where's the horizontal Tail Surface? It doesn't look right + like that!” + </p> + <p> + “This is when I have the pleasure of meeting you, my dear,” said + Longitudinal Stability. “Here's the Tail Surface,” he said, “and in order + to help me it must be set IN EFFECT at a much less Angle of Incidence than + the Main Surface. To explain we must trouble the Blackboard again,” and + this was his effort: + </p> + <p> + “I have tried to make that as clear as possible,” he said. “It may appear + a bit complicated at first, but if you will take the trouble to look at it + for a minute you will find it quite simple. A is the normal and proper + direction of motion of the Aeroplane, but, owing to a gust of air, it + takes up the new nose-down position. Owing to Momentum, however, it does + not fly straight along in that direction, but moves more or less in the + direction B, which is the resultant of the two forces, Momentum and + Thrust. And so you will note that the Angle of Incidence, which is the + inclination of the Surfaces to the Direction of Motion, has decreased, and + of course the Lift decreases with it. You will also see, and this is the + point, that the Tail Surface has lost a higher proportion of its Angle, + and consequently its Lift, than has the Main Surface. Then, such being the + case, the Tail must fall and the Aeroplane assume its normal position + again, though probably at a slightly lower altitude.” + </p> + <p> + “I'm afraid I'm very stupid,” said Efficiency, “but please tell me why you + lay stress upon the words 'IN EFFECT.'” + </p> + <p> + “Ah! I was wondering if you would spot that,” he replied. “And there is a + very good reason for it. You see, in some Aeroplanes the Tail Surface may + be actually set at the same Angle on the machine as the Main Surface, but + owing to the air being deflected downwards by the front Main Surface it + meets the Tail Surface at a lesser angle, and indeed in some cases at no + angle at all. The Tail is then for its surface getting less Lift than the + Main Surface, although set at the same angle on the machine. It may then + be said to have IN EFFECT a less Angle of Incidence. I'll just show you on + the Blackboard.” + </p> + <p> + “And now,” said Efficiency, “I have only to meet the Ailerons and the + Rudder, haven't I?” + </p> + <p> + “Here we are,” replied the Ailerons, or little wings. “Please hinge us on + to the back of the Main Surfaces, one of us at each Wing-tip, and join us + up to the Pilot's joystick by means of the control cables. When the Pilot + wishes to tilt the Aeroplane sideways, he will move the stick and depress + us upon one side, thus giving us a larger Angle of Incidence and so + creating more Lift on that side of the Aeroplane; and, by means of a cable + connecting us with the Ailerons on the other side of the Aeroplane, we + shall, as we are depressed, pull them up and give them a reverse or + negative Angle of Incidence, and that side will then get a reverse Lift or + downward thrust, and so we are able to tilt the Aeroplane sideways. + </p> + <p> + “And we work best when the Angle of Incidence of the Surface in front of + us is very small, for which reason it is sometimes decreased or washed-out + towards the Wing-tips. 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 it, we have to take such a large Angle of Incidence + that we produce a poor proportion of Lift to Drift; but the smaller the + Angle of the Surface in front of us the less the air is deflected + downwards, and consequently the less Angle is required of us, and the + better our proportion of Lift to Drift, which, of course, makes us much + more effective Controls.” + </p> + <p> + “Yes,” said the Lateral and Directional Stabilities in one voice, “that's + so, and the wash-out helps us also, for then the Surfaces towards their + Wing-tips have less Drift or 'Head-Resistance,' and consequently the gusts + will affect them and us less; but such decreased Angle of Incidence means + decreased Lift as well as Drift, and the Designer does not always care to + pay the price.” + </p> + <p> + “Well,” said the Ailerons, “if it's not done it will mean more work for + the Rudder, and that won't please the Pilot.” + </p> + <p> + “Whatever do you mean?” asked Efficiency. “What can the Rudder have to do + with you?” + </p> + <p> + “It's like this,” they replied: “when we are deflected downwards we gain a + larger Angle of Incidence and also enter an area of compressed air, and so + produce more Drift than those of us on the other side of the Aeroplane, + which are deflected upwards into an area of rarefied air due to the + SUCTION effect (though that term is not academically correct) on the top + of the Surface. If there is more Drift, i.e., Resistance, on one side of + the Aeroplane than on the other side, then of course it will turn off its + course, and if that difference in Drift is serious, as it will very likely + be if there is no wash-out, then it will mean a good deal of work for the + Rudder in keeping the Aeroplane on its course, besides creating extra + Drift in doing so.” + </p> + <p> + “I think, then,” said Efficiency, “I should prefer to have that wash-out,<a + href="#linknote-7" name="linknoteref-7" id="linknoteref-7"><small>7</small></a> + and my friend the Designer is so clever at producing strength of + construction for light weight, I'm pretty sure he won't mind paying the + price in Lift. And now let me see if I can sketch the completed + Aeroplane.” + </p> + <p> + “Well, I hope that's all as it should be,” she concluded, “for to-morrow + the Great Test in the air is due.” + </p> + <p> + <a name="link2H_PART3" id="link2H_PART3"> + <!-- H2 anchor --> </a> + </p> + <div style="height: 4em;"> + <br /><br /><br /><br /> + </div> + <h2> + PART III. THE GREAT TEST + </h2> + <p> + It is five o'clock of a fine calm morning, when the Aeroplane is wheeled + out of its shed on to the greensward of the Military Aerodrome. There is + every promise of a good flying day, and, although the sun has not yet + risen, it is light enough to discern the motionless layer of fleecy clouds + some five thousand feet high, and far, far above that a few filmy mottled + streaks of vapour. Just the kind of morning beloved of pilots. + </p> + <p> + A brand new, rakish, up-to-date machine it is, of highly polished, + beautifully finished wood, fabric as tight as a drum, polished metal, and + every part so perfectly “streamlined” to minimize Drift, which is the + resistance of the air to the passage of the machine, that to the veriest + tyro the remark of the Pilot is obviously justified. + </p> + <p> + “Clean looking 'bus, looks almost alive and impatient to be off. Ought to + have a turn for speed with those lines.” + </p> + <p> + “Yes,” replies the Flight-Commander, “it's the latest of its type and + looks a beauty. Give it a good test. A special report is required on this + machine.” + </p> + <p> + The A.M.'s<a href="#linknote-8" name="linknoteref-8" id="linknoteref-8"><small>8</small></a> + have now placed the Aeroplane in position facing the gentle air that is + just beginning to make itself evident; the engine Fitter, having made sure + of a sufficiency of oil and petrol in the tanks, is standing by the + Propeller; the Rigger, satisfied with a job well done, is critically + “vetting” the machine by eye, four A.M.'s are at their posts, ready to + hold the Aeroplane from jumping the blocks which have been placed in front + of the wheels; and the Flight-Sergeant is awaiting the Pilot's orders. + </p> + <p> + As the Pilot approaches the Aeroplane the Rigger springs to attention and + reports, “All correct, sir,” but the Fitter does not this morning report + the condition of the Engine, for well he knows that this Pilot always + personally looks after the preliminary engine test. The latter, in + leathern kit, warm flying boots and goggled, climbs into his seat, and + now, even more than before, has the Aeroplane an almost living appearance, + as if straining to be off and away. First he moves the Controls to see + that everything is clear, for sometimes when the Aeroplane is on the + ground the control lever or “joy-stick” is lashed fast to prevent the wind + from blowing the controlling surfaces about and possibly damaging them. + </p> + <p> + The air of this early dawn is distinctly chilly, and the A.M.'s are + beginning to stamp their cold feet upon the dewy grass, but very careful + and circumspect is the Pilot, as he mutters to himself, “Don't worry and + flurry, or you'll die in a hurry.” + </p> + <p> + At last he fumbles for his safety belt, but with a start remembers the + Pilot Air Speed Indicator, and, adjusting it to zero, smiles as he hears + the Pilot-head's gruff voice, “Well, I should think so, twenty miles an + hour I was registering. That's likely to cause a green pilot to stall the + Aeroplane. Pancake, they call it.” And the Pilot, who is an old hand and + has learned a lot of things in the air that mere earth-dwellers know + nothing about, distinctly heard the Pilot Tube, whose mouth is open to the + air to receive its pressure, stammer. “Oh Lor! 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 moisture; I'll never keep the Liquid + steady in the Gauge. I'm not sure of my rubber connections either.” + </p> + <p> + “Oh, shut up!” cry all the Wires in unison, “haven't we got our troubles + too? We're in the most horrible state of tension. It's simply murdering + our Factor of Safety, and how we can possibly stand it when we get the + Lift only the Designer knows.” + </p> + <p> + “That's all right,” squeak all the little Wire loops, “we're that + accommodating, we're sure to elongate a bit and so relieve your tension.” + For the whole Aeroplane is braced together with innumerable wires, 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 connection. + </p> + <p> + “Elongate, you little devils, would you?” fairly shout the Angles of + Incidence, Dihedral and Stagger, amid a chorus of groans from all parts of + the Aeroplane. “What's going to happen to us then? How are we going to + keep our adjustments upon which good flying depends?” + </p> + <p> + “Butt us and screw us,"<a href="#linknote-9" name="linknoteref-9" + id="linknoteref-9"><small>9</small></a> wail the Wires. “Butt us and screw + us, and death to the Loops. That's what we sang to the Designer, but he + only looked sad and scowled at the Directors.” + </p> + <p> + “And who on earth are they?” asked the Loops, trembling for their + troublesome little lives. + </p> + <p> + “Oh earth indeed,” sniffed Efficiency, who had not spoken before, having + been rendered rather shy by being badly compromised in the Drawing Office. + “I'd like to get some of them up between Heaven and Earth, I would. 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 end. I'm his Best Girl, + you know, and if we could only get rid of the Directors, the little Tin + god, and the Man-who-takes-the-credit, we should be quite happy.” Then she + abruptly subsides, feeling that perhaps the less said the better until she + has made a reputation in the Air. The matter of that Compromise still + rankled, and indeed it does seem hardly fit that a bold bad Tin god should + flirt with Efficiency. You see there was a little Tin god, and he said + “Boom, Boom BOOM! Nonsense! It MUST be done,” and things like that in a + very loud voice, and the Designer tore his hair and was furious, but the + Directors, who were thinking of nothing but Orders and Dividends, had the + whip-hand of HIM, and so there you are, and so poor beautiful Miss + Efficiency was compromised. + </p> + <p> + All this time the Pilot is carefully buckling his belt and making himself + perfectly easy and comfortable, as all good pilots do. As he straightens + himself up from a careful inspection of the Deviation Curve<a + href="#linknote-10" name="linknoteref-10" id="linknoteref-10"><small>10</small></a> + of the Compass and takes command of the Controls, the Throttle and the + Ignition, 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 Test. + </p> + <p> + “Petrol on?” shouts the Fitter to the Pilot. + </p> + <p> + “Petrol on,” replies the Pilot. + </p> + <p> + “Ignition off?” + </p> + <p> + “Ignition off.” + </p> + <p> + Round goes the Propeller, the Engine sucking in the Petrol Vapour with + satisfied gulps. And then— + </p> + <p> + “Contact?” from the Fitter. + </p> + <p> + “Contact,” says the Pilot. + </p> + <p> + Now one swing of the Propeller by the Fitter, and the Engine is awake and + working. Slowly at first though, and in a weak voice demanding, “Not too + much Throttle, please. I'm very cold and mustn't run fast until my Oil has + thinned and is circulating freely. Three minutes slowly, as you love me, + Pilot.” + </p> + <p> + Faster and faster turn the Engine and Propeller, and the Aeroplane, + trembling in all its parts, strains to jump the blocks and be off. + Carefully the Pilot listens to what the Engine Revolution Indicator says. + At last, “Steady at 1,500 revs. and I'll pick up the rest in the Air.” + Then does he throttle down the Engine, 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 working, as otherwise it + might lead to him “losing” his Engine in the air when throttling down the + power for descent. Then, giving the official signal, he sees the blocks + removed from the wheels, and the Flight-Sergeant saluting he knows that + all is clear to ascend. One more signal, and all the A.M.'s run clear of + the Aeroplane. + </p> + <p> + Then gently, gently mind you, with none of the “crashing on” bad Pilots + think so fine, he opens the Throttle and, the Propeller Thrust overcoming + its enemy the Drift, the Aeroplane moves forward. + </p> + <p> + “Ah!” says the Wind-screen, “that's Discipline, that is. Through my little + window I see most things, and don't I just know that poor discipline + always results in poor work in the air, and don't you forget it.” + </p> + <p> + “Discipline is it?” complains the Under-carriage, as its wheels roll + swiftly over the rather rough ground. “I'm bump getting it; and bump, + bump, all I want, bang, bump, rattle, too!” But, as the Lift increases + with the Speed, the complaints of the Under-carriage are stilled, and + then, the friendly Lift becoming greater than the Weight, the Aeroplane + swiftly and easily takes to the air. + </p> + <p> + Below is left the Earth with all its bumps and troubles. Up into the clean + clear Air moves with incredible speed and steadiness this triumph of the + Designer, the result of how much mental effort, imagination, trials and + errors, failures and successes, and many a life lost in high endeavour. + </p> + <p> + Now is the mighty voice of the Engine heard as he turns the Propeller nine + hundred times a minute. Now does the Thrust fight the Drift for all it's + worth, and the Air Speed Indicator gasps with delight, “One hundred miles + an hour!” + </p> + <p> + And now does the burden of work fall upon the Lift and Drift Wires, and + they scream to the Turnbuckles whose business it is to hold them in + tension, “This is the limit! the Limit! THE LIMIT! Release us, if only a + quarter turn.” But the Turnbuckles are locked too fast to turn their eyes + or utter a word. Only the Locking Wires thus: “Ha! ha! the Rigger knew his + job. He knew the trick, and there's no release here.” For an expert rigger + will always use the locking wire in such a way as to oppose the slightest + tendency of the turnbuckle to unscrew. The other kind of rigger will often + use the wire in such a way as to allow the turnbuckle, to the “eyes” of + which the wires are attached, to unscrew a quarter of a turn or more, with + the result that the correct adjustment of the wires may be lost; and upon + their fine adjustment much depends. + </p> + <p> + And the Struts and the Spars groan in compression and pray to keep + straight, for once “out of truth” there is, in addition to possible + collapse, the certainty that in bending they will throw many wires out of + adjustment. + </p> + <p> + And the Fabric's quite mixed in its mind, and ejaculates, “Now, who would + have thought I got more Lift from the top of the Surface than its bottom?” + And then truculently to the Distance Pieces, which run from rib to rib, + “Just keep the Ribs from rolling, will you? or you'll see me strip. I'm an + Irishman, I am, and if my coat comes off—— Yes, Irish, I said. + I used to come from Egypt, but I've got naturalized since the War began.” + </p> + <p> + Then the Air Speed Indicator catches the eye of the Pilot. “Good enough,” + he says as he gently deflects the Elevator and points the nose of the + Aeroplane upwards in search of the elusive Best Climbing Angle. + </p> + <p> + “Ha! ha!” shouts the Drift, growing stronger with the increased Angle of + Incidence. “Ha! ha!” he laughs to the Thrust. “Now I've got you. Now who's + Master?” + </p> + <p> + And the Propeller shrieks hysterically, “Oh! look at me. I'm a helicopter. + That's not fair. Where's Efficiency?” And she can only sadly reply, “Yes, + indeed, but you see we're a Compromise.” + </p> + <p> + And the Drift has hopes of reaching the Maximum Angle of Incidence and + vanquishing the Thrust and the Lift. And he grows very bold as he + strangles the Thrust; but the situation is saved by the Propeller, who is + now bravely helicopting skywards, somewhat to the chagrin of Efficiency. + </p> + <p> + “Much ado about nothing,” quotes the Aeroplane learnedly. “Compromise or + not, I'm climbing a thousand feet a minute. Ask the Altimeter. He'll + confirm it.” + </p> + <p> + And so indeed it was. The vacuum box of the Altimeter was steadily + expanding under the decreased pressure of the rarefied air, 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 minute. + </p> + <p> + And lo! the Aeroplane has almost reached the clouds! But what's this? A + sudden gust, and down sinks one wing and up goes the other. “Oh, my + Horizontal Equivalent!” despairingly call the Planes: “it's eloping with + the Lift, and what in the name of Gravity will happen? Surely there was + enough scandal in the Factory without this, too!” For the lift varies with + the horizontal equivalent of the planes, so that if the aeroplane tilts + sideways beyond a certain angle, the lift becomes less than the weight of + the machine, which must then fall. A fall in such a position is known as a + “side-slip.” + </p> + <p> + But the ever-watchful Pilot instantly depresses one aileron, elevating the + other, with just a touch of the rudder to keep on the course, and the + Planes welcome back their precious Lift as the Aeroplane flicks back to + its normal position. + </p> + <p> + “Bit bumpy here under these clouds,” is all the Pilot says as he heads for + a gap between them, and the next minute the Aeroplane shoots up into a new + world of space. + </p> + <p> + “My eye!” ejaculates the Wind-screen, “talk about a view!” And indeed mere + words will always fail to express the wonder of it. Six thousand feet up + now, and look! The sun is rising quicker than ever mortal on earth + witnessed its ascent. Far below is Mother Earth, wrapt in mists and deep + blue shadows, and far above are those light, filmy, ethereal clouds now + faintly tinged with pink And all about great mountains of cloud, lazily + floating in space. The sun rises and they take on all colours, blending + one with the other, from dazzling white to crimson and deep violet-blue. + Lakes and rivers here and there in the enormous expanse of country below + refract the level rays of the sun and, like so many immense diamonds, send + dazzling shafts of light far upwards. The tops of the hills now laugh to + the light of the sun, but the valleys are still mysterious dark blue + caverns, clowned with white filmy lace-like streaks of vapour. And withal + the increasing sense with altitude of vast, clean, silent solitudes of + space. + </p> + <p> + Lives there the man who can adequately describe this Wonder? “Never,” says + the Pilot, who has seen it many times, but to whom it is ever new and more + wonderful. + </p> + <p> + Up, up, up, and still up, unfalteringly speeds the Pilot and his mount. + Sweet the drone of the Engine and steady the Thrust as the Propeller + exultingly battles with the Drift. + </p> + <p> + And look! What is that bright silver streak all along the horizon? It + puzzled the Pilot when first he saw it, but now he knows it for the Sea, + full fifty miles away! + </p> + <p> + And on his right is the brightness of the Morn and the smiling Earth + unveiling itself to the ardent rays of the Sun; and on his left, so high + is he, there is yet black Night, hiding innumerable Cities, Towns, + Villages and all those places where soon teeming multitudes of men shall + awake, and by their unceasing toil and the spirit within them produce + marvels of which the Aeroplane is but the harbinger. + </p> + <p> + And the Pilot's soul is refreshed, and his vision, now exalted, sees the + Earth a very garden, even as it appears at that height, with discord + banished and a happy time come, when the Designer shall have at last + captured Efficiency, and the Man-who-takes-the-credit is he who has earned + it, and when kisses are the only things that go by favour. + </p> + <p> + Now the Pilot anxiously scans the Barograph, which is an instrument much + the same as the Altimeter; but in this case the expansion of the vacuum + box causes a pen to trace a line upon a roll of paper. This paper is made + by clockwork to pass over the point of the pen, and so a curved line is + made which accurately registers the speed of the ascent in feet per + minute. No longer is the ascent at the rate of a thousand feet a minute, + and the Propeller complains to the Engine, “I'm losing my Revs. and the + Thrust. Buck up with the Power, for the Lift is decreasing, though the + Weight remains much the same.” + </p> + <p> + Quoth the Engine: “I strangle for Air. A certain proportion, and that of + right density, I must have to one part of Petrol, in order to give me full + power and compression, and here at an altitude of ten thousand feet the + Air is only two-thirds as dense as at sea-level. Oh, where is he who will + invent a contrivance to keep me supplied with Air of right density and + quality? It should not be impossible within certain limits.” + </p> + <p> + “We fully agree,” said the dying Power and Thrust. “Only maintain Us and + you shall be surprised at the result. For our enemy Drift decreases in + respect of distance with the increase of altitude and rarity of air, and + there is no limit to the speed through space if only our strength remains. + And with oxygen for Pilot and Passengers and a steeper pitch<a + href="#linknote-11" name="linknoteref-11" id="linknoteref-11"><small>11</small></a> + for the Propeller we may then circle the Earth in a day!” + </p> + <p> + Ah, Reader, smile not unbelievingly, as you smiled but a few years past. + There may be greater wonders yet. Consider that as the speed increases, so + does the momentum or stored-up force in the mass of the aeroplane become + terrific. And, bearing that in mind, remember that with altitude gravity + decreases. There may yet be literally other worlds to conquer.<a + href="#linknote-12" name="linknoteref-12" id="linknoteref-12"><small>12</small></a> + </p> + <p> + Now at fifteen thousand feet the conditions are chilly and rare, and the + Pilot, with thoughts of breakfast far below, exclaims, “High enough! I had + better get on with the Test.” And then, as he depresses the Elevator, the + Aeroplane with relief assumes its normal horizontal position. Then, almost + closing the Throttle, the Thrust dies away. Now, the nose of the Aeroplane + should sink of its own volition, and the craft glide downward at flying + speed, which is in this case a hundred miles an hour. 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 lift. Thus is the Aeroplane “nose-heavy” as a + glider, and just so to a degree ensuring a speed of glide equal to its + flying speed. And the Air Speed Indicator is steady at one hundred miles + an hour, and “That's all right!” exclaims the Pilot. “And very useful, + too, in a fog or a cloud,” he reflects, for then he can safely leave the + angle of the glide to itself, and give all his attention, and he will need + it all, to keeping the Aeroplane horizontal from wing-tip to wing-tip, and + to keeping it straight on its course. The latter he will manage with the + rudder, controlled by his feet, and the Compass will tell him whether a + straight course is kept. The former he will control by the Ailerons, or + little wings hinged to the tips of the planes, and the bubble in the + Inclinometer in front of him must be kept in the middle. + </p> + <p> + A Pilot, being only human, may be able to do two things at once, but three + is a tall order, so was this Pilot relieved to find the Design not at + fault and his craft a “natural glider.” To correct this nose-heavy + tendency when the Engine is running, and descent not required, the centre + of Thrust is arranged to be a little below the centre of Drift or + Resistance, and thus acts as a counter-balance. + </p> + <p> + But what is this stream of bad language from the Exhaust Pipe, accompanied + by gouts of smoke and vapour? The Engine, now revolving at no more than + one-tenth its normal speed, has upset the proportion of petrol to air, and + combustion is taking place intermittently or in the Exhaust Pipe, where it + has no business to be. + </p> + <p> + “Crash, Bang, Rattle——!——!——!” and + worse than that, yells the Exhaust, and the Aeroplane, who is a gentleman + and not a box kite,<a href="#linknote-13" name="linknoteref-13" + id="linknoteref-13"><small>13</small></a> remonstrates with the severity + of a Senior Officer. “See the Medical Officer, you young Hun. Go and see a + doctor. Vocal diarrhoea, that's your complaint, and a very nasty one too. + Bad form, bad for discipline, and a nuisance in the Mess. What's your + Regiment? Special Reserve, you say? Humph! Sounds like Secondhand Bicycle + Trade to me!” + </p> + <p> + Now the Pilot decides to change the straight gliding descent to a spiral + one, and, obedient to the Rudder, the Aeroplane turns to the left. But the + Momentum (two tons at 100 miles per hour is no small affair) heavily + resents this change of direction, and tries its level best to prevent it + and to pull the machine sideways and outwards from its spiral course—that + is, to make it “side-skid” outwards. But the Pilot deflects the Ailerons + and “banks” up the planes to the correct angle, and, the Aeroplane + skidding sideways and outwards, the lowest surfaces of the planes press up + against the air until the pressure equals the centrifugal force of the + Momentum, and the Aeroplane spirals steadily downwards. + </p> + <p> + Down, down, down, and the air grows denser, and the Pilot gulps largely, + filling his lungs with the heavier air to counteract the increasing + pressure from without. Down through a gap in the clouds, and the Aerodrome + springs into view, appearing no larger than a saucer, and the Pilot, + having by now got the “feel” of the Controls, proceeds to put the + Aeroplane through its paces. First at its Maximum Angle, staggering along + tail-down and just maintaining horizontal flight; then a dive at far over + flying speed, finishing with a perfect loop; then sharp turns with + attendant vertical “banks” and then a wonderful switchback flight, + speeding down at a hundred and fifty miles an hour with short, + exhilarating ascents at the rate of two thousand feet a minute! + </p> + <p> + All the parts are now working well together. Such wires as were before in + undue tension have secured relief by slightly elongating their loops, and + each one is now doing its bit, and all are sharing the burden of work + together. + </p> + <p> + The Struts and the Spars, which felt so awkward at first, have bedded + themselves in their sockets, and are taking the compression stresses + uncomplainingly. + </p> + <p> + The Control Cables of twisted wire, a bit tight before, have slightly + lengthened by perhaps the eighth of an inch, and, the Controls instantly + responding to the delicate touch of the Pilot, the Aeroplane, at the will + of its Master, darts this way and that way, dives, loops, spirals, and at + last, in one long, magnificent glide, lands gently in front of its shed. + </p> + <p> + “Well, what result?” calls the Flight-Commander to the Pilot. + </p> + <p> + “A hundred miles an hour and a thousand feet a minute,” he briefly + replies. + </p> + <p> + “And a very good result too,” says the Aeroplane, complacently, as he is + carefully wheeled into his shed. + </p> + <p> + That is the way Aeroplanes speak to those who love them and understand + them. Lots of Pilots know all about it, and can spin you wonderful yarns, + much better than this one, if you catch them in a confidential mood—on + leave, for instance, and after a good dinner. + </p> + <p> + <a name="link2H_PART4" id="link2H_PART4"> + <!-- H2 anchor --> </a> + </p> + <div style="height: 4em;"> + <br /><br /><br /><br /> + </div> + <h2> + PART IV. 'CROSS COUNTRY + </h2> + <p> + The Aeroplane had been designed and built, and tested in the air, and now + stood on the Aerodrome ready for its first 'cross-country flight. + </p> + <p> + It had run the gauntlet of pseudo-designers, crank inventors, press + “experts,” and politicians; of manufacturers keen on cheap work and large + profits; of poor pilots who had funked it, and good pilots who had + expected too much of it. Thousands of pounds had been wasted on it, many + had gone bankrupt over it, and others it had provided with safe fat jobs. + </p> + <p> + Somehow, and despite every conceivable obstacle, it had managed to muddle + through, and now it was ready for its work. It was not perfect, for there + were fifty different ways in which it might be improved, some of them + shamefully obvious. But it was fairly sound mechanically, had a little + inherent stability, was easily controlled, could climb a thousand feet a + minute, and its speed was a hundred miles an hour. In short, quite a + creditable machine, though of course the right man had not got the credit. + </p> + <p> + It is rough, unsettled weather with a thirty mile an hour wind on the + ground, and that means fifty more or less aloft. Lots of clouds at + different altitudes to bother the Pilot, and the air none to clear for the + observation of landmarks. + </p> + <p> + As the Pilot and Observer approach the Aeroplane the former is clearly not + in the best of tempers. “It's rotten luck,” he is saying, “a blank shame + that I should have to take this blessed 'bus and join X Reserve Squadron, + stationed a hundred and fifty miles from anywhere; and just as I have + licked my Flight into shape. Now some slack blighter will, I suppose, + command it and get the credit of all my work!” + </p> + <p> + “Shut up, you grouser,” said the Observer. “Do you think you're the only + one with troubles? Haven't I been through it too? Oh! I know all about it! + You're from the Special Reserve and your C.O. doesn't like your style of + beauty, and you won't lick his boots, and you were a bit of a technical + knut in civil life, but now you've jolly well got to know less than those + senior to you. Well! It's a jolly good experience for most of us. Perhaps + conceit won't be at quite such a premium after this war. And what's the + use of grousing? That never helped anyone. So buck up, old chap. Your day + will come yet. Here's our machine, and I must say it looks a beauty!” + </p> + <p> + And, as the Pilot approaches the Aeroplane, 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 away. Turning to the + Flight-Sergeant he inquires, “Tank full of petrol and oil?” + </p> + <p> + “Yes, sir,” he replies, “and everything else all correct. Propeller, + engine, and body covers on board, sir; tool kit checked over and in the + locker; engine and Aeroplane logbooks written up, signed, and under your + seat; engine revs. up to mark, and all the control cables in perfect + condition and tension.” + </p> + <p> + “Very good,” said the Pilot; and then turning to the Observer, “Before we + start you had better have a look at the course I have mapped out. + </p> + <p> + “A is where we stand and we have to reach B, a hundred and fifty miles due + North. I judge that, at the altitude we shall fly, there will be an East + wind, for although it is not quite East on the ground it is probably about + twenty degrees different aloft, the wind usually moving round clockways to + about that extent. I think that it is blowing at the rate of about fifty + miles an hour, and I therefore take a line on the map to C, fifty miles + due West of A. The Aeroplane's speed is a hundred miles an hour, and so I + take a line of one hundred miles from C to D. Our compass course will then + be in the direction A—E, which is always a line parallel to C—D. + That is, to be exact, it will be fourteen degrees off the C—D + course, as, in this part of the globe, there is that much difference + between the North and South lines on the map and the magnetic North to + which the compass needle points. If the compass has an error, as it may + have of a few degrees, that, too, must be taken into account, and the + deviation or error curve on the dashboard will indicate it. + </p> + <p> + “The Aeroplane will then always be pointing in a direction parallel to A—E, + but, owing to the side wind, it will be actually travelling over the + course A—B, though in a rather sideways attitude to that course. + </p> + <p> + “The distance we shall travel over the A—B course in one hour is A—D. + That is nearly eighty-seven miles, so we ought to accomplish our journey + of a hundred and fifty miles in about one and three-quarter hours. + </p> + <p> + “I hope that's quite clear to you. It's a very simple way of calculating + the compass course, and I always do it like that.” + </p> + <p> + “Yes, that's plain enough. You have drafted what engineers call 'a + parallelogram of forces'; but suppose you have miscalculated the velocity + of the wind, or that it should change in velocity or direction?” + </p> + <p> + “Well, that of course will more or less alter matters,” replies the Pilot. + “But there are any number of good landmarks such as lakes, rivers, towns, + and railway lines. They will help to keep us on the right course, and the + compass will, at any rate, prevent us from going far astray when between + them.” + </p> + <p> + “Well, we'd better be off, old chap. Hop aboard.” This from the Observer + as he climbs into the front seat from which he will command a good view + over the lower plane; and the Pilot takes his place in the rear seat, and, + after making himself perfectly comfortable, fixing his safety belt, and + moving the control levers to make sure that they are working freely, he + gives the signal to the Engine Fitter to turn the propeller and so start + the engine. + </p> + <p> + Round buzzes the Propeller, and the Pilot, giving the official signal, the + Aeroplane is released and rolls swiftly over the ground in the teeth of + the gusty wind. + </p> + <p> + In less than fifty yards it takes to the air and begins to climb rapidly + upwards, but how different are the conditions to the calm morning of + yesterday! If the air were visible it would be seen to be acting in the + most extraordinary manner; crazily swirling, lifting and dropping, gusts + viciously colliding—a mad phantasmagoria of forces! + </p> + <p> + Wickedly it seizes and shakes the Aeroplane; then tries to turn it over + sideways; then instantly changes its mind and in a second drops it into a + hole a hundred feet deep, and if it were not for his safety belt the Pilot + might find his seat sinking away from beneath him. + </p> + <p> + Gusts strike the front of the craft like so many slaps in the face; and + others, with the motion of mountainous waves, sometimes lift it hundreds + of feet in a few seconds, hoping to see it plunge over the summit in a + death-dive—and so it goes on, but the Pilot, perfectly at one with + his mount and instantly alert to its slightest motion, is skilfully and + naturally making perhaps fifty movements a minute of hand and feet; the + former lightly grasping the “joy-stick” which controls the Elevator hinged + to the tail, and also the Ailerons or little wings hinged to the + wing-tips; and the latter moving the Rudder control-bar. + </p> + <p> + A strain on the Pilot? Not a bit of it, for this is his Work which he + loves and excels in; and given a cool head, alert eye, and a sensitive + touch for the controls, what sport can compare with these ever-changing + battles of the air? + </p> + <p> + The Aeroplane has all this time been climbing in great wide circles, and + is now some three thousand feet above the Aerodrome which from such height + looks absurdly small. The buildings below now seem quite squat; the hills + appear to have sunk away into the ground, and the whole country below, cut + up into diminutive fields, has the appearance of having been lately tidied + and thoroughly spring-cleaned! A doll's country it looks, with tiny horses + and cows ornamenting the fields and little model motor-cars and carts + stuck on the roads, the latter stretching away across the country like + ribbons accidentally dropped. + </p> + <p> + At three thousand feet altitude the Pilot is satisfied that he is now + sufficiently high to secure, in the event of engine failure, a long enough + glide to earth to enable him to choose and reach a good landing-place; + and, being furthermore content with the steady running of the engine, he + decides to climb no more but to follow the course he has mapped out. + Consulting the compass, he places the Aeroplane on the A—E course + and, using the Elevator, he gives his craft its minimum angle of incidence + at which it will just maintain horizontal flight and secure its maximum + speed. + </p> + <p> + Swiftly he speeds away, and few thoughts he has now for the changing + panorama of country, cloud, and colour. Ever present in his mind are the + three great 'cross-country queries. “Am I on my right course? Can I see a + good landing-ground within gliding distance?” And “How is the Engine + running?” + </p> + <p> + Keenly both he and the Observer compare their maps with the country below. + The roads, khaki-coloured ribbons, are easily seen but are not of much + use, for there are so many of them and they all look alike from such an + altitude. + </p> + <p> + Now where can that lake be which the map shows so plainly? He feels that + surely he should see it by now, and has an uncomfortable feeling that he + is flying too far West. What pilot is there indeed who has not many times + experienced such unpleasant sensation? Few things in the air can create + greater anxiety. Wisely, however, he sticks to his compass course, and the + next minute he is rewarded by the sight of the lake, though indeed he now + sees that the direction of his travel will not take him over it, as should + be the case if he were flying over the shortest route to his destination. + He must have slightly miscalculated the velocity or direction of the + side-wind. + </p> + <p> + “About ten degrees off,” he mutters, and, using the Rudder, corrects his + course accordingly. + </p> + <p> + Now he feels happier and that he is well on his way. The gusts, too, have + ceased to trouble him as, at this altitude, they are not nearly so bad as + they were near the ground the broken surface of which does much to produce + them; and sometimes for miles he makes but a movement or two of the + controls. + </p> + <p> + The clouds just above race by with dizzy and uniform speed; the country + below slowly unrolls, and the steady drone of the Engine is almost + hypnotic in effect. “Sleep, sleep, sleep,” it insidiously suggests. + “Listen to me and watch the clouds; there's nothing else to do. Dream, + dream, dream of speeding through space for ever, and ever, and ever; and + rest, rest, rest to the sound of my rhythmical hum. Droning on and on, + nothing whatever matters. All things now are merged into speed through + space and a sleepy monotonous d-d-r-r-o-o-n-n-e - - - - -.” But the Pilot + pulls himself together with a start and peers far ahead in search of the + next landmark. This time it is a little country town, red-roofed his map + tells him, and roughly of cruciform shape; and, sure enough, there in the + right direction are the broken outlines of a few red roofs peeping out + from between the trees. + </p> + <p> + Another minute and he can see this little town, a fairy town it appears, + nestling down between the hills with its red roofs and picturesque shape, + a glowing and lovely contrast with the dark green of the surrounding + moors. + </p> + <p> + So extraordinarily clean and tidy it looks from such a height, and laid + out in such orderly fashion with perfectly defined squares, parks, + avenues, and public buildings, it indeed appears hardly real, but rather + as if it has this very day materialized from some delightful children's + book! + </p> + <p> + Every city and town you must know has its distinct individuality to the + Pilot's eye. Some are not fairy places at all, but great dark ugly blots + upon the fair countryside, and with tall shafts belching forth murky + columns of smoke to defile clean space. Others, melancholy-looking masses + of grey, slate-roofed houses, are always sad and dispirited; never + welcoming the glad sunshine, but ever calling for leaden skies and a + weeping Heaven. Others again, little coquettes with village green, white + palings everywhere, bright gravel roads, and an irrepressible air of + brightness and gaiety. + </p> + <p> + Then there are the rivers, silvery streaks peacefully winding far, far + away to the distant horizon; they and the lakes the finest landmarks the + Pilot can have. And the forests. How can I describe them? The trees cannot + be seen separately, but merge altogether into enormous irregular dark + green masses sprawling over the country, and sometimes with great ungainly + arms half encircling some town or village; and the wind passing over the + foliage at times gives the forest an almost living appearance, as of some + great dragon of olden times rousing itself from slumber to devour the + peaceful villages which its arms encircle. + </p> + <p> + And the Pilot and Observer fly on and on, seeing these things and many + others which baffle my poor skill to describe—things, dear Reader, + that you shall see, and poets sing of, and great artists paint in the days + to come when the Designer has captured Efficiency. Then, and the time is + near, shall you see this beautiful world as you have never seen it before, + the garden it is, the peace it breathes, and the wonder of it. + </p> + <p> + The Pilot, flying on, is now anxiously looking for the railway line which + midway on his journey should point the course. Ah! There it is at last, + but suddenly (and the map at fault) it plunges into the earth! Well the + writer remembers when that happened to him on a long 'cross-country flight + in the early days of aviation. Anxiously he wondered “Are tunnels always + straight?” and with what relief, keeping on a straight course, he picked + up the line again some three miles farther on! + </p> + <p> + Now at last the Pilot sees the sea, just a streak on the north-eastern + horizon, and he knows that his flight is two-thirds over. Indeed, he + should have seen it before, but the air is none too clear, and he is not + yet able to discern the river which soon should cross his path. As he + swiftly speeds on the air becomes denser and denser with what he fears + must be the beginning of a sea-fog, perhaps drifting inland along the + course of the river. Now does he feel real anxiety, for it is the DUTY of + a Pilot to fear fog, his deadliest enemy. Fog not only hides the landmarks + by which he keeps his course, but makes the control of the Aeroplane a + matter of the greatest difficulty. He may not realize it, but, in keeping + his machine on an even keel, he is unconsciously balancing it against the + horizon, and with the horizon gone he is lost indeed. Not only that, but + it also prevents him from choosing his landing-place, and the chances are + that, landing in a fog, he will smash into a tree, hedge, or building, + with disastrous results. The best and boldest pilot 'wares a fog, and so + this one, finding the conditions becoming worse and yet worse, and being + forced to descend lower and lower in order to keep the earth within view, + wisely decides to choose a landing-place while there is yet time to do so. + </p> + <p> + Throttling down the power of the engine he spirals downwards, keenly + observing the country below. There are plenty of green fields to lure him, + and his great object is to avoid one in which the grass is long, for that + would bring his machine to a stop so suddenly as to turn it over; or one + of rough surface likely to break the under-carriage. Now is perfect + eyesight and a cool head indispensable. He sees and decides upon a field + and, knowing his job, he sticks to that field with no change of mind to + confuse him. It is none too large, and gliding just over the trees and + head on to the wind he skilfully “stalls” his machine; that is, the speed + having decreased sufficiently to avoid such a manoeuvre resulting in + ascent, he, by means of the Elevator, gives the Aeroplane as large an + angle of incidence as possible, and the undersides of the planes meeting + the air at such a large angle act as an air-brake, and the Aeroplane, + skimming over the ground, lessens its speed and finally stops just at the + farther end of the field. + </p> + <p> + Then, after driving the Aeroplane up to and under the lee of the hedge, he + stops the engine, and quickly lashing the joy-stick fast in order to + prevent the wind from blowing the controlling surfaces about and possibly + damaging them, he hurriedly alights. Now running to the tail he lifts it + up on to his shoulder, for the wind has become rough indeed and there is + danger of the Aeroplane becoming unmanageable. By this action he decreases + the angle at which the planes are inclined to the wind and so minimizes + the latter's effect upon them. Then to the Observer, “Hurry up, old + fellow, and try to find some rope, wire, or anything with which to picket + the machine. The wind is rising and I shan't be able to hold the 'bus + steady for long. Don't forget the wire-cutters. They're in the tool kit.” + And the Observer rushes off in frantic haste, before long triumphantly + returning with a long length of wire from a neighbouring fence. Blocking + up the tail with some debris at hand, they soon succeed, with the aid of + the wire, in stoutly picketing the Aeroplane to the roots of the high + hedge in front of it; done with much care, too, so that the wire shall not + fray the fabric or set up dangerous bending-stresses in the woodwork. + Their work is not done yet, for the Observer remarking, “I don't like the + look of this thick weather and rather fear a heavy rain-storm,” the Pilot + replies, “Well, it's a fearful bore, but the first rule of our game is + never to take an unnecessary risk, so out with the engine and body + covers.” + </p> + <p> + Working with a will they soon have the engine and the open part of the + body which contains the seats, controls, and instruments snugly housed + with their waterproof covers, and the Aeroplane is ready to weather the + possible storm. + </p> + <p> + Says the Observer, “I'm remarkably peckish, and methinks I spy the towers + of one of England's stately homes showing themselves just beyond that + wood, less than a quarter of a mile away. What ho! for a raid. What do you + say?” + </p> + <p> + “All right, you cut along and I'll stop here, for the Aeroplane must not + be left alone. Get back as quickly as possible.” + </p> + <p> + And the Observer trots off, leaving the Pilot filling his pipe and + anxiously scrutinizing the weather conditions. Very thick it is now, but + the day is yet young, and he has hopes of the fog lifting sufficiently to + enable the flight to be resumed. A little impatiently he awaits the return + of his comrade, but with never a doubt of the result, for the hospitality + of the country house is proverbial among pilots! What old hand among them + is there who cannot instance many a forced landing made pleasant by such + hospitality? Never too late or too early to help with food, petrol, oil, + tools, and assistants. Many a grateful thought has the writer for such + kind help given in the days before the war (how long ago they seem!), when + aeroplanes were still more imperfect than they are now, and involuntary + descents often a part of 'cross-country flying. + </p> + <p> + Ah! those early days! How fresh and inspiring they were! As one started + off on one's first 'cross-country flight, on a machine the first of its + design, and with everything yet to learn, and the wonders of the air yet + to explore; then the joy of accomplishment, the dreams of Efficiency, the + hard work and long hours better than leisure; and what a field of + endeavour—the realms of space to conquer! And the battle still goes + on with ever-increasing success. Who is bold enough to say what its limits + shall be? + </p> + <p> + So ruminates this Pilot-Designer, as he puffs at his pipe, until his + reverie is abruptly disturbed by the return of the Observer. + </p> + <p> + “Wake up, you AIRMAN,” the latter shouts. “Here's the very thing the + doctor ordered! A basket of first-class grub and something to keep the fog + out, too.” + </p> + <p> + “Well, that's splendid, but don't call me newspaper names or you'll spoil + my appetite!” + </p> + <p> + Then, with hunger such as only flying can produce, they appreciatively + discuss their lunch, and with many a grateful thought for the donors—and + they talk shop. They can't help it, and even golf is a poor second to + flight talk. Says the Pilot, who must have his grievance, “Just observe + where I managed to stop the machine. Not twenty feet from this hedge! A + little more and we should have been through it and into Kingdom Come! I + stalled as well as one could, but the tail touched the ground and so I + could not give the Aeroplane any larger angle of incidence. Could I have + given it a larger angle, then the planes would have become a much more + effective air-brake, and we should have come to rest in a much shorter + distance. It's all the fault of the tail. There's hardly a type of + Aeroplane in existence in which the tail could not be raised several feet, + and that would make all the difference. High tails mean a large angle of + incidence when the machine touches ground and, with enough angle, I'll + guarantee to safely land the fastest machine in a five-acre field. You + can, I am sure, imagine what a difference that would make where forced + landings are concerned!” Then rapidly sketching in his notebook, he shows + the Observer the following illustration: + </p> + <p> + “That's very pretty,” said the Observer, “but how about Mechanical + Difficulties, and Efficiency in respect of Flight? And, anyway, why hasn't + such an obvious thing been done already?” + </p> + <p> + “As regards the first part of your question I assure you that there's + nothing in it, and I'll prove it to you as follows——” + </p> + <p> + “Oh! That's all right, old chap. I'll take your word for it,” hurriedly + replies the Observer, whose soul isn't tuned to a technical key. + </p> + <p> + “As regards the latter part of your inquiry,” went on the Pilot, a little + nettled at having such a poor listener, “it's very simple. Aeroplanes have + 'just growed' like Topsy, 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 ground.” + </p> + <p> + “By Jove,” interrupts the Observer, “I do believe the fog is lifting. + Hadn't we better get the engine and body covers off, just in case it's + really so?” + </p> + <p> + “I believe you're right. I am sure those hills over there could not be + seen a few minutes ago, and look—there's sunshine over there. We'd + better hurry up.” + </p> + <p> + Ten minutes' hard work and the covers are off, neatly folded and stowed + aboard; the picketing wires are cast adrift, and the Pilot is once more in + his seat. The Aeroplane has been turned to face the other end of the + field, and, the Observer swinging round the propeller, the engine is awake + again and slowly ticking over. Quickly the Observer climbs into his seat + in front of the Pilot, and, the latter slightly opening the throttle, the + Aeroplane leisurely rolls over the ground towards the other end of the + field, from which the ascent will be made. + </p> + <p> + Arriving there the Pilot turns the Aeroplane in order to face the wind and + thus secure a quick “get-off.” Then he opens the throttle fully and the + mighty voice of the Engine roars out “Now see me clear that hedge!” and + the Aeroplane races forward at its minimum angle of incidence. Tail up, + and with ever-increasing speed, it rushes towards the hedge under the lee + of which it has lately been at rest; and then, just as the Observer + involuntarily pulls back an imaginary “joy-stick,” the Pilot moves the + real one and places the machine at its best climbing angle. Like a living + thing it responds, and instantly leaves the ground, clearing the hedge + like a—well, like an Aeroplane with an excellent margin of lift. + Upwards it climbs with even and powerful lift, and the familiar scenes + below again gladden the eyes of the Pilot. Smaller and more and more squat + grow the houses and hills; more and more doll-like appear the fields which + are clearly outlined by the hedges; and soon the country below is easily + identified with the map. Now they can see the river before them and a bay + of the sea which must be crossed or skirted. The fog still lingers along + the course of the river and between the hills, but is fast rolling away in + grey, ghost-like masses. Out to sea it obscures the horizon, making it + difficult to be sure where water ends and fog begins, and creating a + strange, rather weird effect by which ships at a certain distance appear + to be floating in space. + </p> + <p> + Now the Aeroplane is almost over the river, and the next instant it + suddenly drops into a “hole in the air.” With great suddenness it happens, + and for some two hundred feet it drops nose-down and tilted over sideways; + but the Pilot is prepared and has put his craft on an even keel in less + time than it takes to tell you about it; for well he knows that he must + expect such conditions when passing over a shore or, indeed, any + well-defined change in the composition of the earth's surface. Especially + is this so on a hot and sunny day, for then the warm surface of the earth + creates columns of ascending air, the speed of the ascent depending upon + the composition of the surface. Sandy soil, for instance, such as borders + this river produces a quickly ascending column of air, whereas water and + forests have not such a marked effect. Thus, when our Aeroplane passed + over the shore of the river, it suddenly lost the lift due to the + ascending air produced by the warm sandy soil, and it consequently dropped + just as if it had fallen into a hole. + </p> + <p> + Now the Aeroplane is over the bay and, the sea being calm, the Pilot looks + down, down through the water, and clearly sees the bottom, hundreds of + feet below the surface. Down through the reflection of the blue sky and + clouds, and one might think that is all, but it isn't. Only those who fly + know the beauties of the sea as viewed from above; its dappled pearly + tints; its soft dark blue shadows; 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 observer. Ah! for some + better pen than mine to describe these things! 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 speed. A new world of sensation! + </p> + <p> + Now the bay is almost crossed and the Aerodrome at B can be distinguished. + </p> + <p> + On the Aerodrome is a little crowd waiting and watching for the arrival of + the Aeroplane, for it is of a new and improved type and its first + 'cross-country performance is of keen interest to these men; men who + really know something about flight. + </p> + <p> + There is the Squadron Commander who has done some real flying in his time; + several well-seasoned Flight-Commanders; a dozen or more + Flight-Lieutenants; a knowledgeable Flight-Sergeant; a number of Air + Mechanics, and, a little on one side and almost unnoticed, the Designer. + </p> + <p> + “I hope they are all right,” said someone, “and that they haven't had + difficulties with the fog. It rolled up very quickly, you know.” + </p> + <p> + “Never fear,” remarked a Flight-Commander. “I know the Pilot well and he's + a good 'un; far too good to carry on into a fog.” + </p> + <p> + “They say the machine is really something out of the ordinary,” said + another, “and that, for once, the Designer has been allowed full play; + that he hasn't been forced to unduly standardize ribs, spars, struts, + etc., and has more or less had his own way. I wonder who he is. It seems + strange we hear so little of him.” + </p> + <p> + “Ah! my boy. You do a bit more flying and you'll discover that things are + not always as they appear from a distance!” + </p> + <p> + “There she is, sir!” cries the Flight-Sergeant. “Just a speck over the + silvery corner of that cloud.” + </p> + <p> + A tiny speck it looks, some six miles distant and three thousand feet + high; but, racing along, it rapidly appears larger and soon its outlines + can be traced and the sunlight be seen playing upon the whirling + propeller. + </p> + <p> + Now the distant drone of the engine can be heard, but not for long, for + suddenly it ceases and, the nose of the Aeroplane sinking, the craft + commences gliding downwards. + </p> + <p> + “Surely too far away,” says a subaltern. “It will be a wonderful machine + if, from that distance and height, it can glide into the Aerodrome.” And + more than one express the opinion that it cannot be done; but the Designer + smiles to himself, yet with a little anxiety, for his reputation is at + stake, and Efficiency, the main reward he desires, is perhaps, or perhaps + not, at last within his grasp! + </p> + <p> + Swiftly the machine glides downwards towards them, and it can now be seen + how surprisingly little it is affected by the rough weather and gusts; so + much so that a little chorus of approval is heard. + </p> + <p> + “Jolly good gliding angle,” says someone; and another, “Beautifully quick + controls, what?” and from yet another, “By Jove! The Pilot must be sure of + the machine. Look, he's stopped the engine entirely.” + </p> + <p> + Then the Aeroplane with noiseless engine glides over the boundary of the + Aerodrome, and, with just a soft soughing sound from the air it cleaves, + lands gently not fifty yards from the onlookers. + </p> + <p> + “Glad to see you,” says the Squadron Commander to the Pilot. “How do you + like the machine?” And the Pilot replies: + </p> + <p> + “I never want a better one, sir. It almost flies itself!” + </p> + <p> + And the Designer turns his face homewards and towards his beloved + drawing-office; well satisfied, but still dreaming dreams of the future + and... looking far ahead whom should he see but Efficiency at last coming + towards him! And to him she is all things. In her hair is the morning + sunshine; her eyes hold the blue of the sky, and on her cheeks is the + pearly tint of the clouds as seen from above. The passion of speed, the + lure of space, the sense of power, and the wonder of the future... all + these things she holds for him. + </p> + <p> + “Ah!” he cries. “You'll never leave me now, when at last there is no one + between us?” + </p> + <p> + And Efficiency, smiling and blushing, but practical as ever, says: + </p> + <p> + “And you will never throw those Compromises in my face?” + </p> + <p> + “My dear, I love you for them! Haven't they been my life ever since I + began striving for you ten long years ago?” + </p> + <p> + And so they walked off very happily, arm-in-arm together; and if this + hasn't bored you and you'd like some more of the same sort of thing, I'd + just love to tell you some day of the wonderful things they accomplish + together, and of what they dream the future holds in store. + </p> + <p> + And that's the end of the Prologue. + </p> + <p> + <a name="link2HCH0001" id="link2HCH0001"> + <!-- H2 anchor --> </a> + </p> + <div style="height: 4em;"> + <br /><br /><br /><br /> + </div> + <h2> + CHAPTER I. FLIGHT + </h2> + <p> + Air has weight (about 13 cubic feet = 1 lb.), inertia, and momentum. It + therefore obeys Newton's laws<a href="#linknote-14" name="linknoteref-14" + id="linknoteref-14"><small>14</small></a> and resists movement. It is that + resistance or reaction which makes flight possible. + </p> + <p> + Flight is secured by driving through the air a surface<a + href="#linknote-15" name="linknoteref-15" id="linknoteref-15"><small>15</small></a> + inclined upwards and towards the direction of motion. + </p> + <p> + S = Side view of surface. + </p> + <p> + M = Direction of motion. + </p> + <p> + CHORD.—The Chord is, for practical purposes, taken to be a straight + line from the leading edge of the surface to its trailing edge. + </p> + <p> + N = A line through the surface starting from its trailing edge. The + position of this line, which I call the Neutral Lift Line, is found by + means of wind-tunnel research, and it varies with differences in the + camber (curvature) of surfaces. In order to secure flight, the inclination + of the surface must be such that the neutral lift line makes an angle with + and ABOVE the line of motion. If it is coincident with M, there is no + lift. If it makes an angle with M and BELOW it, then there is a pressure + tending to force the surface down. + </p> + <p> + I = Angle of Incidence. This angle is generally defined as the angle the + chord makes with the direction of motion, but that is a bad definition, as + it leads to misconception. The angle of incidence is best described as the + angle the neutral lift line makes with the direction of motion relative to + the air. You will, however, 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 thrust. This is necessary from the point of + view of the practical mechanic who has to rig the aeroplane, for he could + not find the neutral lift line, whereas he can easily find the chord. + Again, he would certainly be in doubt as to “the direction of motion + relative to the air,” whereas he can easily find a line parallel to the + propeller thrust. It is a pity, however, that these practical + considerations have resulted in a bad definition of the angle of incidence + becoming prevalent, a consequence of which has been the widespread fallacy + that flight may be secured with a negative inclination of the surface. + Flight may conceivably be secured with a negative angle of chord, but + never with a negative inclination of the surface. All this is only + applicable to cambered surfaces. In the case of flat surfaces the neutral + lift line coincides with the chord and the definition I have criticised + adversely is then applicable. Flat lifting surfaces are, however, never + used. + </p> + <p> + The surface acts upon the air in the following manner: + </p> + <p> + As the bottom of the surface meets the air, it compresses it and + accelerates it DOWNWARDS. As a result of this definite action there is, of + course, an equal and opposite reaction UPWARDS. + </p> + <p> + The top surface, in moving forward, tends to leave the air behind it, thus + creating a semi-vacuum or rarefied area over the top of the surface. + Consequently the pressure of air on the top of the surface is decreased, + thus assisting the reaction below to lift the surface UPWARDS. + </p> + <p> + The reaction increases approximately as the square of the velocity. It is + the result of (1) the mass of air engaged, and (2) the velocity and + consequent force with which the surface engages the air. If the reaction + was produced by only one of those factors it would increase in direct + proportion to the velocity, but, since it is the product of both factors, + it increases as V(2S). + </p> + <p> + Approximately three-fifths of the reaction is due to the decrease of + density (and consequent decrease of downward pressure) on the top of the + surface; and only some two-fifths is due to the upward reaction secured by + the action of the bottom surface upon the air. A practical point in + respect of this is that, in the event of the fabric covering the surface + getting into bad condition, it is more likely to strip off the top than + off the bottom. + </p> + <p> + The direction of the reaction is approximately at right-angles to the + chord of the surface, as illustrated above; and it is, in considering + flight, convenient to divide it into two component parts or values, thus: + </p> + <p> + 1. The vertical component of the reaction, i.e., Lift, which is opposed to + Gravity, i.e., the weight of the aeroplane. + </p> + <p> + 2. The horizontal component, i.e., Drift (sometimes called Resistance), to + which is opposed the thrust of the propeller. + </p> + <p> + The direction of the reaction is, of course, the resultant of the forces + Lift and Drift. + </p> + <p> + The Lift is the useful part of the reaction, for it lifts the weight of + the aeroplane. + </p> + <p> + The Drift is the villain of the piece, and must be overcome by the Thrust + in order to secure the necessary velocity to produce the requisite Lift + for flight. + </p> + <p> + DRIFT.—The drift of the whole aeroplane (we have considered only the + lifting surface heretofore) may be conveniently divided into three parts, + as follows: + </p> + <p> + Active Drift, which is the drift produced by the lifting surfaces. + </p> + <p> + Passive Drift, which is the drift produced by all the rest of the + aeroplane—the struts, wires, fuselage, under-carriage, etc., all of + which is known as “detrimental surface.” + </p> + <p> + Skin Friction, which is the drift produced by the friction of the air with + roughnesses of surface. The latter is practically negligible having regard + to the smooth surface of the modern aeroplane, and its comparatively slow + velocity compared with, for instance, the velocity of a propeller blade. + </p> + <p> + LIFT-DRIFT RATIO.—The proportion of lift to drift is known as the + lift-drift ratio, and is of paramount importance, for it expresses the + efficiency of the aeroplane (as distinct from engine and propeller). A + knowledge of the factors governing the lift-drift ratio is, as will be + seen later, an absolute necessity to anyone responsible for the rigging of + an aeroplane, and the maintenance of it in an efficient and safe + condition. + </p> + <p> + Those factors are as follows: + </p> + <p> + 1. Velocity.—The greater the velocity the greater the proportion of + drift to lift, and consequently the less the efficiency. Considering the + lifting surfaces alone, both the lift and the (active) drift, being + component parts of the reaction, increase as the square of the velocity, + and the efficiency remains the same at all speeds. But, considering the + whole aeroplane, we must remember the passive drift. It also increases as + the square of the velocity (with no attendant lift), and, adding itself to + the active drift, results in increasing the proportion of total drift + (active + passive) to lift. + </p> + <p> + But for the increase in passive drift the efficiency of the aeroplane + would not fall with increasing velocity, and it would be possible, by + doubling the thrust, to approximately double the speed or lift—a + happy state of affairs which can never be, but which we may, in a measure, + approach by doing everything possible to diminish the passive drift. + </p> + <p> + Every effort is then made to decrease it by “stream-lining,” i.e., by + giving all “detrimental” parts of the aeroplane a form by which they will + pass through the air with the least possible drift. Even the wires bracing + the aeroplane together are, in many cases, stream-lined, and with a + markedly good effect upon the lift-drift ratio. 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 speed. + </p> + <p> + Head-resistance is a term often applied to passive drift, but it is apt to + convey a wrong impression, as the drift is not nearly so much the result + of the head or forward part of struts, wires, etc., as it is of the + rarefied area behind. + </p> + <p> + Above is illustrated the flow of air round two objects moving in the + direction of the arrow M. + </p> + <p> + In the case of A, you will note that the rarefied area DD is of very + considerable extent; whereas in the case of B, the air flows round it in + such a way as to meet very closely to the rear of the object, thus + DECREASING DD. + </p> + <p> + The greater the rarefied area DD. then, the less the density, and, + consequently, the less the pressure of air upon the rear of the object. + The less such pressure, then, the better is head-resistance D able to get + its work in, and the more thrust will be required to overcome it. + </p> + <p> + The “fineness” of the stream-line shape, i.e., the proportion of length to + width, is determined by the velocity—the greater the velocity, the + greater the fineness. The best degree of fineness for any given velocity + is found by means of wind-tunnel research. + </p> + <p> + The practical application of all this is, from a rigging point of view, + the importance of adjusting all stream-line parts to be dead-on in the + line of flight, but more of that later on. + </p> + <p> + 2. Angle of Incidence.—The most efficient angle of incidence varies + with the thrust at the disposal of the designer, the weight to be carried, + and the climb-velocity ratio desired. + </p> + <p> + The best angles of incidence for these varying factors are found by means + of wind-tunnel research and practical trial and error. Generally speaking, + the greater the velocity the smaller should be the angle of incidence, in + order to preserve a clean, stream-line shape of rarefied area and freedom + from eddies. Should the angle be too great for the velocity, then the + rarefied area becomes of irregular shape with attendant turbulent eddies. + Such eddies possess no lift value, and since it has taken power to produce + them, they represent drift and adversely affect the lift-drift ratio. + </p> + <p> + From a rigging point of view, one must presume that every standard + aeroplane has its lifting surface set at the most efficient angle, 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 angle. + Any deviation will adversely affect the lift-drift ratio, i.e., the + efficiency. + </p> + <p> + 3. Camber.—(Refer to the second illustration in this chapter.) The + lifting surfaces are cambered, i.e., curved, in order to decrease the + horizontal component of the reaction, i.e., the drift. + </p> + <p> + The bottom camber: If the bottom of the surface was flat, every particle + of air meeting it would do so with a shock, and such shock would produce a + very considerable horizontal reaction or drift. By curving it such shock + is diminished, and the curve should be such as to produce a uniform (not + necessarily constant) acceleration and compression of the air from the + leading edge to the trailing edge. Any unevenness in the acceleration and + compression of the air produces drift. + </p> + <p> + The top camber: If this was flat it would produce a rarefied area of + irregular shape. I have already explained the bad effect this has upon the + lift-drift ratio. 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 possible. + </p> + <p> + The camber varies with the angle of incidence, the velocity, and the + thickness of the surface. Generally speaking, the greater the velocity, + the less the camber and angle of incidence. With infinite velocity the + surface would be set at no angle of incidence (the neutral lift line + coincident with the direction of motion relative to the air), and would + be, top and bottom, of pure streamline form—i.e., of infinite + fineness. This is, of course, carrying theory to absurdity as the surface + would then cease to exist. + </p> + <p> + The best cambers for varying velocities, angles of incidence, and + thicknesses of surface, are found by means of wind-tunnel research. 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 ratio. + </p> + <p> + 4. Aspect Ratio.—This is the proportion of span to chord. Thus, if + the span is, for instance, 50 feet and the chord 5 feet, the surface would + be said to have an aspect ratio of 10 to 1. + </p> + <p> + For A GIVEN VELOCITY and A GIVEN AREA of surface, the greater the aspect + ratio, the greater the reaction. It is obvious, I think, that the greater + the span, the greater the mass of air engaged, and, as already explained, + the reaction is partly the result of the mass of air engaged. + </p> + <p> + Not only that, but, PROVIDED the chord is not decreased to an extent + making it impossible to secure the best camber owing to the thickness of + the surface, the greater the aspect ratio, the better the lift-drift + ratio. The reason of this is rather obscure. It is sometimes advanced that + it is owing to the “spill” of air from under the wing-tips. With a high + aspect ratio the chord is less than would otherwise be the case. Less + chord results in smaller wing-tips and consequently less “spill.” This, + however, appears to be a rather inadequate reason for the high aspect + ratio producing the high lift-drift ratio. Other reasons are also + advanced, but they are of such a contentious nature I do not think it well + to go into them here. They are of interest to designers, but this is + written for the practical pilot and rigger. + </p> + <p> + 5. Stagger.—This is the advancement of the top surface relative to + the bottom surface, and is not, of course, applicable to a single surface, + i.e., a monoplane. In the case of a biplane having no stagger, there will + be “interference” and consequent loss of Efficiency unless the gap between + the top and bottom surfaces is equal to not less than 1 1/2 times the + chord. If less than that, 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 surface, with the result that the surfaces will not secure as + good a reaction as would otherwise be the case. + </p> + <p> + It is not practicable to have a gap of much more than a distance equal to + the chord, owing to the drift produced by the great length of struts and + wires such a large gap would necessitate. By staggering the top surface + forward, however, it is removed from the action of the lower surface and + engages undisturbed air, with the result that the efficiency can in this + way be increased by about 5 per cent. Theoretically the top plane should + be staggered forward for a distance equal to about 30 per cent. of the + chord, the exact distance depending upon the velocity and angle of + incidence; but this is not always possible to arrange in designing an + aeroplane, owing to difficulties of balance, desired position, and view of + pilot, observer, etc. + </p> + <p> + 6. Horizontal Equivalent.—The vertical component of the reaction, + i.e., lift, varies as the horizontal equivalent (H.E.) of the surface, but + the drift remains the same. Then it follows that if H.E. grows less, the + ratio of lift to drift must do the same. + </p> + <p> + A, B, and C are front views of three surfaces. + </p> + <p> + A has its full H.E., and therefore, from the point of view from which we + are at the moment considering efficiency, it has its best lift-drift + ratio. + </p> + <p> + B and C both possess the same surface as A, but one is inclined upwards + from its centre and the other is straight but tilted. For these reasons + their H.E.'s are, as illustrated, less than in the case of A. That means + less vertical lift, and, the drift remaining the same (for there is the + same amount of surface as in A to produce it), the lift-drift ratio falls. + </p> + <p> + THE MARGIN OF POWER is the power available above that necessary to + maintain horizontal flight. + </p> + <p> + THE MARGIN OF LIFT is the height an aeroplane can gain in a given time and + starting from a given altitude. As an example, thus: 1,000 feet the first + minute, and starting from an altitude of 500 feet above sea-level. + </p> + <p> + The margin of lift decreases with altitude, owing to the decrease in the + density of the air, which adversely affects the engine. Provided the + engine maintained its impulse with altitude, then, if we ignore the + problem of the propeller, which I will go into later on, the margin of + lift would not disappear. Moreover, greater velocity for a given power + would be secured at a greater altitude, owing to the decreased density of + air to be overcome. After reading that, 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 altitude. I am afraid, however, that will + always remain impossible; but it is probable that some very interesting + steps may be taken in that direction. + </p> + <p> + THE MINIMUM ANGLE OF INCIDENCE is the smallest angle at which, for a given + power, surface (including detrimental surface), and weight, horizontal + flight can be maintained. + </p> + <p> + THE MAXIMUM ANGLE OF INCIDENCE is the greatest angle at which, for a given + power, surface (including detrimental surface), and weight, horizontal + flight can be maintained. + </p> + <p> + THE OPTIMUM ANGLE OF INCIDENCE is the angle at which the lift-drift ratio + is highest. In modern aeroplanes it is that angle of incidence possessed + by the surface when the axis of the propeller is horizontal. + </p> + <p> + THE BEST CLIMBING ANGLE is approximately half-way between the maximum and + the optimum angles. + </p> + <p> + All present-day aeroplanes are a compromise between Climb and horizontal + Velocity. We will compare the essentials for two aeroplanes, one designed + for maximum climb, and the other for maximum velocity. + </p> + <p> + ESSENTIALS FOR MAXIMUM CLIMB: + </p> + <p> + 1. Low velocity, in order to secure the best lift-drift ratio. + </p> + <p> + 2. Having a low velocity, a large surface will be necessary in order to + engage the necessary mass of air to secure the requisite lift. + </p> + <p> + 3. Since (1) such a climbing machine will move along an upward sloping + path, and (2) will climb with its propeller thrust horizontal, 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 motion. + </p> + <p> + The propeller thrust should be always horizontal, because the most + efficient flying-machine (having regard to climb OR velocity) has, so far, + been found to be an arrangement of an inclined surface driven by a + HORIZONTAL thrust—the surface lifting the weight, and the thrust + overcoming the drift. This is, in practice, a far more efficient + arrangement than the helicopter, i.e., the air-screw revolving about a + vertical axis and producing a thrust opposed to gravity. If, when + climbing, the propeller thrust is at such an angle as to tend to haul the + aeroplane upwards, then it is, in a measure, acting as a helicopter, and + that means inefficiency. The reason of a helicopter being inefficient in + practice is due to the fact that, owing to mechanical difficulties, it is + impossible to construct within a reasonable weight an air-screw of the + requisite dimensions. That being so, it would be necessary, in order to + absorb the power of the engine, to revolve the comparatively + small-surfaced air screw at an immensely greater velocity than that of the + aeroplane's surface. As already explained, the lift-drift ratio falls with + velocity on account of the increase in passive drift. This applies to a + blade of a propeller or air-screw, which is nothing but a revolving + surface set at angle of incidence, and which it is impossible to construct + without a good deal of detrimental surface near the central boss. + </p> + <p> + 4. The velocity being low, then it follows that for that reason also the + angle of incidence should be comparatively large. + </p> + <p> + 5. Camber.—Since such an aeroplane would be of low velocity, and + therefore possess a large angle of incidence, a large camber would be + necessary. + </p> + <p> + Let us now consider the essentials for an aeroplane of maximum velocity + for its power, and possessing merely enough lift to get off the ground, + but no margin of lift. + </p> + <p> + 1. Comparatively HIGH VELOCITY. + </p> + <p> + 2. A comparatively SMALL SURFACE, because, being of greater velocity than + the maximum climber, a greater mass of air will be engaged for a given + surface and time, and therefore a smaller surface will be sufficient to + secure the requisit lift. + </p> + <p> + 3. A small angle relative to the propeller thrust, since the latter + coincides with the direction of motion. + </p> + <p> + 4. A comparatively small angle of incidence by reason of the high + velocity. + </p> + <p> + 5. A comparatively small camber follows as a result of the small angle of + incidence. + </p> + <p> + <br /> + </p> + <h3> + SUMMARY. + </h3> +<pre xml:space="preserve"> + Essentials for Maximum Essentials for Maximum + Climb. Velocity + + 1. Low velocity. High velocity. + 2. Large surface. Small surface. + 3. Large angle relative to Small angle relative to + propeller thrust. propeller thrust. + 4. Large angle relative to Small angle relative to direction + direction of motion. of motion. + 5. Large camber. Small camber. +</pre> + <p> + It is mechanically impossible to construct an aeroplane of reasonable + weight of which it would be possible to very the above opposing + essentials. Therefore, all aeroplanes are designed as a compromise between + Climb and Velocity. + </p> + <p> + As a rule aeroplanes are designed to have at low altitude a slight margin + of lift when the propeller thrust is horizontal. + </p> + <p> + ANGLES OF INCIDENCE (INDICATED APPROXIMATELY) OF AN AEROPLANE DESIGNED AS + A COMPROMISE BETWEEN VELOCITY AND CLIMB, AND POSSESSING A SLIGHT MARGIN OF + LIFT AT A LOW ALTITUDE AND WHEN THE THRUST IS HORIZONTAL + </p> + <p> + MINIMUM ANGLE. + </p> + <p> + This gives the greatest velocity during horizontal flight at a low + altitude. Greater velocity would be secured if the surface, angle, and + camber were smaller and designed to just maintain horizontal flight with a + horizontal thrust. Also, in such case, the propeller would not be + thrusting downwards, but along a horizontal line which is obviously a more + efficient arrangement if we regard the aeroplane merely from one point of + view, i.e., either with reference to velocity OR climb. + </p> + <p> + OPTIMUM ANGLE (Thrust horizontal) + </p> + <p> + The velocity is less than at the smaller minimum angle, and, as aeroplanes + are designed to-day, the area and angle of incidence of the surface is + such as to secure a slight ascent at a low altitude. The camber of the + surface is designed for this angle of incidence and velocity. The + lift-drift ratio is best at this angle. + </p> + <p> + BEST CLIMBING ANGLE + </p> + <p> + The velocity is now still less by reason of the increased angle producing + increase of drift. Less velocity at A GIVEN ANGLE produces less lift, but + the increased angle more or less offsets the loss of lift due to the + decreased velocity, and in addition, the thrust is now hauling the + aeroplane upwards. + </p> + <p> + MAXIMUM ANGLE + </p> + <p> + 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 flight. Any greater angle will + result in a still lower lift-drift ratio. The lift will then become less + than the weight and the aeroplane will consequently fall. Such a fall is + known as “stalling” or “pancaking.” + </p> + <p> + NOTE.—The golden rule for beginners: Never exceed the Best Climbing + Angle. Always maintain the flying speed of the aeroplane. + </p> + <p> + By this means, when the altitude is reached where the margin of lift + disappears (on account of loss of engine power), and which is, + consequently, the altitude where it is just possible to maintain + horizontal flight, the aeroplane is flying with its thrust horizontal and + with maximum efficiency (as distinct from engine and propeller + efficiency). + </p> + <p> + The margin of lift at low altitude, and when the thrust is horizontal, + 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 done. That ensures maximum velocity when most required. + </p> + <p> + Unfortunately, where aeroplanes designed for fighting are concerned, the + altitude where most of the work is done is that at which both maximum + velocity and maximum margin of lift for power are required. + </p> + <p> + 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 essentials. Then we shall get + maximum velocity, or maximum margin of lift, for power as required. Until + then the design of the aeroplane must remain a compromise between Velocity + and Climb. + </p> + <p> + <a name="link2HCH0002" id="link2HCH0002"> + <!-- H2 anchor --> </a> + </p> + <div style="height: 4em;"> + <br /><br /><br /><br /> + </div> + <h2> + CHAPTER II. STABILITY AND CONTROL + </h2> + <p> + STABILITY is a condition whereby an object disturbed has a natural + tendency to return to its first and normal position. Example: a weight + suspended by a cord. + </p> + <p> + INSTABILITY is a condition whereby an object disturbed has a natural + tendency to move as far as possible away from its first position, with no + tendency to return. Example: a stick balanced vertically upon your finger. + </p> + <p> + NEUTRAL INSTABILITY is a condition whereby an object disturbed has no + tendency to move farther than displaced by the force of the disturbance, + and no tendency to return to its first position. + </p> + <p> + In order that an aeroplane may be reasonably controllable, it is necessary + for it to possess some degree of stability longitudinally, laterally, and + directionally. + </p> + <p> + LONGITUDINAL STABILITY in an aeroplane is its stability about an axis + transverse to the direction of normal horizontal flight, and without which + it would pitch and toss. + </p> + <p> + LATERAL STABILITY is its stability about its longitudinal axis, and + without which it would roll sideways. + </p> + <p> + DIRECTIONAL STABILITY is its stability about its vertical axis, and + without which it would have no tendency to keep its course. + </p> + <p> + For such directional stability to exist there must be, in effect,<a + href="#linknote-16" name="linknoteref-16" id="linknoteref-16"><small>16</small></a> + more “keel-surface” behind the vertical axis than there is in front of it. + By keel-surface I mean every-thing to be seen when looking at an aeroplane + from the side of it—the sides of the body, undercarriage, struts, + wires, etc. The same thing applies to a weathercock. You know what would + happen if there was insufficient keel-surface behind the vertical axis + upon which it is pivoted. It would turn off its proper course, which is + opposite to the direction of the wind. It is very much the same in the + case of an aeroplane. + </p> + <p> + The above illustration represents an aeroplane (directionally stable) + flying along the course B. A gust striking it as indicated acts upon the + greater proportion of keel-surface behind the turning axis and throws it + into the new course. It does not, however, travel along the new course, + owing to its momentum in the direction B. It travels, as long as such + momentum lasts, in a direction which is the resultant of the two forces + Thrust and Momentum. But the centre line of the aeroplane is pointing in + the direction of the new course. Therefore its attitude, relative to the + direction of motion, is more or less sideways, and it consequently + receives an air pressure in the direction C. Such pressure, acting upon + the keel-surface, presses the tail back towards its first position in + which the aeroplane is upon its course B. + </p> + <p> + What I have described is continually going on during flight, but in a + well-designed aeroplane such stabilizing movements are, most of the time, + so slight as to be imperceptible to the pilot. + </p> + <p> + If an aeroplane was not stabilized in this way, it would not only be + continually trying to leave its course, but it would also possess a + dangerous tendency to “nose away” from the direction of the side gusts. In + such case the gust shown in the above illustration would turn the + aeroplane round the opposite way a very considerable distance; and the + right wing, being on the outside of the turn, would travel with greater + velocity than the left wing. Increased velocity means increased lift; and + so, the right wing lifting, the aeroplane would turn over sideways very + quickly. + </p> + <p> + LONGITUDINAL STABILITY.—Flat surfaces are longitudinally stable + owing to the fact that with decreasing angles of incidence the centre line + of pressure (C.P.) moves forward. + </p> + <p> + The C.P. is a line taken across the surface, transverse to the direction + of motion, and about which all the air forces may be said to balance, or + through which they may be said to act. + </p> + <p> + Imagine A to be a flat surface, attitude vertical, travelling through the + air in the direction of motion M. Its C.P. is then obviously along the + exact centre line of the surface as illustrated. + </p> + <p> + In B, C, and D the surfaces are shown with angles of incidence decreasing + to nothing, and you will note that the C.P. moves forward with the + decreasing angle. + </p> + <p> + Now, should some gust or eddy tend to make the surface decrease the angle, + i.e., dive, then the C.P. moves forward and pushes the front of the + surface up. Should the surface tend to assume too large an angle, then the + reverse happens—the C.P. moves back and pushes the rear of the + surface up. + </p> + <p> + Flat surfaces are, then, theoretically stable longitudinally. They are + not, however, used, on account of their poor lift-drift ratio. + </p> + <p> + As already explained, cambered surfaces are used, and these are + longitudinally unstable at those angles of incidence producing a + reasonable lift-drift ratio, i.e., at angles below: about 12 degrees. + </p> + <p> + A is a cambered surface, attitude approximately vertical, moving through + the air in the direction M. Obviously the C. P. coincides with the + transverse centre line of the surface. + </p> + <p> + With decreasing angles, down to angles of about 30 degrees, the C.P. moves + forward as in the case of flat surfaces (see B), but angles above 30 + degrees do not interest us, since they produce a very low ratio of lift to + drift. + </p> + <p> + Below angles of about 30 degrees (see C) the dipping front part of the + surface assumes a negative angle of incidence resulting in the DOWNWARD + air pressure D, and the more the angle of incidence is decreased, the + greater such negative angle and its resultant pressure D. Since the C.P. + is the resultant of all the air forces, its position is naturally affected + by D, which causes it to move backwards. Now, should some gust or eddy + tend to make the surface decrease its angle of incidence, i.e., dive, then + the C.P. moves backwards, and, pushing up the rear of the surface, causes + it to dive the more. Should the surface tend to assume too large an angle, + then the reverse happens; the pressure D decreases, with the result that + C.P. moves forward and pushes up the front of the surface, thus increasing + the angle still further, the final result being a “tail-slide.” + </p> + <p> + It is therefore necessary to find a means of stabilizing the naturally + unstable cambered surface. This is usually secured by means of a + stabilizing surface fixed some distance in the rear of the main surface, + and it is a necessary condition that the neutral lift lines of the two + surfaces, when projected to meet each other, make a dihedral angle. In + other words, 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 surface. This is known as the longitudinal dihedral. + </p> + <p> + I may add that the tail-plane is sometimes mounted upon the aeroplane at + the same angle as the main surface, but, in such cases, it attacks air + which has received a downward deflection from the main surface, thus: + </p> + <p> + The angle at which the tail surface attacks the air (the angle of + incidence) is therefore less than the angle of incidence of the main + surface. + </p> + <p> + I will now, by means of the following illustration, try to explain how the + longitudinal dihedral secures stability: + </p> + <p> + First, imagine the aeroplane travelling in the direction of motion, which + coincides with the direction of thrust T. The weight is, of course, + balanced about a C.P., the resultant of the C.P. of the main surface and + the C.P. of the stabilizing surface. For the sake of illustration, the + stabilizing surface has been given an angle of incidence, and therefore + has a lift and C.P. In practice the stabilizer is often set at no angle of + incidence. In such case the proposition remains the same, but it is, + perhaps, a little easier to illustrate it as above. + </p> + <p> + Now, we will suppose that a gust or eddy throws the machine into the lower + position. It no longer travels in the direction of T, since the momentum + in the old direction pulls it off that course. M is now the resultant of + the Thrust and the Momentum, and you will note that this results in a + decrease in the angle our old friend the neutral lift line makes with M, + i.e., a decrease in the angle of incidence and therefore a decrease in + lift. + </p> + <p> + We will suppose that this decrease is 2 degrees. Such decrease applies to + both main surface and stabilizer, since both are fixed rigidly to the + aeroplane. + </p> + <p> + The main surface, which had 12 degrees angle, has now only 10 degrees, + i.e., a loss of ONE-SIXTH. + </p> + <p> + The stabilizer, which had 4 degrees angle, has now only 2 degrees, i.e., a + loss of ONE-HALF. + </p> + <p> + The latter has therefore lost a greater PROPORTION of its angle of + incidence, and consequently its lift, than has the main surface. It must + then fall relative to the main surface. The tail falling, the aeroplane + then assumes its first position, though at a slightly less altitude. + </p> + <p> + Should a gust throw the nose of the aeroplane up, then the reverse + happens. Both main surface and stabilizer increase their angles of + incidence in the same amount, but the angle, and therefore the lift, of + the stabilizer increases in greater proportion than does the lift of the + main surface, with the result that it lifts the tail. The aeroplane then + assumes its first position, though at a slightly greater altitude. + </p> + <p> + Do not fall into the widespread error that the angle of incidence varies + as the angle of the aeroplane to the horizontal. It varies with such + angle, but not as anything approaching it. Remember that the stabilizing + effect of the longitudinal dihedral lasts only as long as there is + momentum in the direction of the first course. + </p> + <p> + These stabilizing movements are taking place all the time, even though + imperceptible to the pilot. + </p> + <p> + Aeroplanes have, in the past, been built with a stabilizing surface in + front of the main surface instead of at the rear of it. In such design the + main surface (which is then the tail surface as well as the principal + lifting surface) must be set at a less angle than the forward stabilizing + surface, in order to secure a longitudinal dihedral. The defect of such + design lies in the fact that the main surface must have a certain angle to + lift the weight—say 5 degrees. Then, in order to secure a + sufficiency of longitudinal stability, it is necessary to set the forward + stabilizer at about 15 degrees. Such a large angle of incidence results in + a very poor lift-drift ratio (and consequently great loss of efficiency), + except at very low velocities compared with the speed of modern + aeroplanes. At the time such aeroplanes were built velocities were + comparatively low, and this defect was; for that reason, not sufficiently + appreciated. In the end it killed the “canard” or “tail-first” design. + </p> + <p> + Aeroplanes of the Dunne and similar types possess no stabilizing surface + distinct from the main surface, but they have a longitudinal dihedral + which renders them stable. + </p> + <p> + The main surface towards the wing-tips is given a decreasing angle of + incidence and corresponding camber. The wing-tips then act as longitudinal + stabilizers. + </p> + <p> + This design of aeroplane, while very interesting, has not proved very + practicable, owing to the following disadvantages: (1) The plan design is + not, from a mechanical point of view, so sound as that of the ordinary + aeroplane surface, which is, in plan, a parallelogram. It is, then, + necessary to make the strength of construction greater than would + otherwise be the case. That means extra weight. (2) 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 motion. The lower the aspect ratio, then, the less the lift. + This design, then, produces less lift for weight of surface than would the + same surface if arranged as a parallelogram. (3) In order to secure the + longitudinal dihedral, the angle of incidence has to be very much + decreased towards the wing-tips. Then, in order that the lift-drift ratio + may be preserved, there must be a corresponding decrease in the camber. + That calls for surface ribs of varying cambers, and results in an + expensive and lengthy job for the builder. (4) In order to secure + directional stability, the surface is, in the centre, arranged to dip down + in the form of a V, pointing towards the direction of motion. Should the + aeroplane turn off its course, then its momentum in the direction of its + first course causes it to move in a direction the resultant of the thrust + and the momentum. It then moves in a more or less sideways attitude, which + results in an air pressure upon one side of the V, and which tends to turn + the aeroplane back to its first course. This arrangement of the surface + results in a bad drift. Vertical surfaces at the wing-tips may also be set + at an angle producing the same stabilizing effect, but they also increase + the drift. + </p> + <p> + The gyroscopic action of a rotary engine will affect the longitudinal + stability when an aeroplane is turned to right or left. In the case of a + Gnome engine, such gyroscopic action will tend to depress the nose of the + aeroplane when it is turned to the left, and to elevate it when it is + turned to the right. In modern aeroplanes this tendency is not + sufficiently important to bother about. In the old days of crudely + designed and under-powered aeroplanes this gyroscopic action was very + marked, and led the majority of pilots to dislike turning an aeroplane to + the right, since, in doing so, there was some danger of “stalling.” + </p> + <p> + LATERAL STABILITY is far more difficult for the designer to secure than is + longitudinal or directional stability. Some degree of lateral stability + may be secured by means of the “lateral dihedral,” i.e., the upward + inclination of the surface towards its wing-tips thus: + </p> + <p> + Imagine the top V, illustrated opposite, to be the front view of a surface + flying towards you. The horizontal equivalent (H.E.) of the left wing is + the same as that of the right wing. Therefore, the lift of one wing is + equal to the lift of the other, and the weight, being situated always in + the centre, is balanced. + </p> + <p> + If some movement of the air causes the surface to tilt sideways, as in the + lower illustration, then you will note that the H.E. of the left wing + increases, and the H.E. of the right wing decreases. The left wing then, + having the greatest lift, rises; and the surface assumes its first and + normal position. + </p> + <p> + Unfortunately however, the righting effect is not proportional to the + difference between the right and left H.E.'s. + </p> + <p> + In the case of A, the resultant direction of the reaction of both wings is + opposed to the direction of gravity or weight. The two forces R R and + gravity are then evenly balanced, and the surface is in a state of + equilibrium. + </p> + <p> + In the case of B, you will note that the R R is not directly opposed to + gravity. This results in the appearance of M, and so the resultant + direction of motion of the aeroplane is no longer directly forward, but is + along a line the resultant of the thrust and M. In other words, it is, + while flying forward, at the same time moving sideways in the direction M. + </p> + <p> + In moving sideways, the keel-surface receives, of course, a pressure from + the air equal and opposite to M. Since such surface is greatest in effect + towards the tail, then the latter must be pushed sideways. That causes the + aeroplane to turn; and, the highest wing being on the outside of the turn, + it has a greater velocity than the lower wing. That produces greater lift, + and tends to tilt the aeroplane over still more. Such tilting tendency is, + however, opposed by the difference in the H.E.'s of the two wings. + </p> + <p> + It then follows that, for the lateral dihedral angle to be effective, such + angle must be large enough to produce, when the aeroplane tilts, a + difference in the H.E.'s of the two wings, which difference must be + sufficient to not only oppose the tilting tendency due to the aeroplane + turning, but sufficient to also force the aeroplane back to its original + position of equilibrium. + </p> + <p> + It is now, I hope, clear to the reader that the lateral dihedral is not + quite so effective as would appear at first sight. Some designers, indeed, + prefer not to use it, since its effect is not very great, and since it + must be paid for in loss of H.E. and consequently loss of lift, thus + decreasing the lift-drift ratio, i.e., the efficiency. Also, it is + sometimes advanced that the lateral dihedral increases the “spill” of air + from the wing-tips and that this adversely affects the lift-drift ratio. + </p> + <p> + The disposition of the keel-surface affects the lateral stability. It + should be, in effect, equally divided by the longitudinal turning axis of + the aeroplane. If there is an excess of keel-surface above or below such + axis, then a side gust striking it will tend to turn the aeroplane over + sideways. + </p> + <p> + The position of the centre of gravity affects lateral stability. If too + low, it produces a pendulum effect and causes the aeroplane to roll + sideways. + </p> + <p> + If too high, it acts as a stick balanced vertically would act. If + disturbed, it tends to travel to a position as far as possible from its + original position. It would then tend, when moved, to turn the aeroplane + over sideways and into an upside-down position. + </p> + <p> + From the point of view of lateral stability, the best position for the + centre of gravity is one a little below the centre of drift. + </p> + <p> + Propeller torque affects lateral stability. An aeroplane tends to turn + over sideways in the opposite direction to which the propeller revolves. + </p> + <p> + This tendency is offset by increasing the angle of incidence (and + consequently the lift) of the side tending to fall; and it is always + advisable, if practical considerations allow it, to also decrease the + angle upon the other side. In that way it is not necessary to depart so + far from the normal angle of incidence at which the lift-drift ratio is + highest. + </p> + <p> + Wash-in is the term applied to the increased angle. + </p> + <p> + Wash-out is the term applied to the decreased angle. + </p> + <p> + Both lateral and directional stability may be improved by washing out the + angle of incidence on both sides of the surface, thus: + </p> + <p> + 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 + aeroplane, owing to the distance from the turning axis. + </p> + <p> + The wash-out also renders the ailerons (lateral controlling services) more + effective, as, in order to operate them, it is not then necessary to give + them such a large angle of incidence as would otherwise be required. + </p> + <p> + The less the angle of incidence of the ailerons, the better their + lift-drift ratio, i.e., their efficiency. You will note that, while the + aileron attached to the surface with washed-out angle is operated to the + same extent as the aileron illustrated above it, its angle of incidence is + considerably less. Its efficiency is therefore greater. + </p> + <p> + The advantages of the wash-in must, of course be paid for in some loss of + lift, as the lift decreases with the decreased angle. + </p> + <p> + In order to secure all the above described advantages, a combination is + sometimes effected, thus: + </p> + <p> + BANKING.—An aeroplane turned off its course to right or left does + not at once proceed along its new course. Its momentum in the direction of + its first course causes it to travel along a line the resultant of such + momentum and the thrust. In other words, it more or less skids sideways + and away from the centre of the turn. Its lifting surfaces do not then + meet the air in their correct attitude, and the lift may fall to such an + extent as to become less than the weight, in which case the aeroplane must + fall. This bad effect is minimized by “banking,” i.e., tilting the + aeroplane sideways. 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 pressure. The rarefied area over the + top of the surface is rendered still more rare, and this, of course, + assists the air pressure in opposing the momentum. + </p> + <p> + The velocity of the “skid,” or sideways movement, is then only such as is + necessary to secure an air pressure equal and opposite to the centrifugal + force of the turn. + </p> + <p> + The sharper the turn, the greater the effect of the centrifugal force, and + therefore the steeper should be the “bank.” Experentia docet. + </p> + <p> + The position of the centre of gravity affects banking. A low C.G. will + tend to swing outward from the centre of the turn, and will cause the + aeroplane to bank—perhaps too much, in which case the pilot must + remedy matters by operating the ailerons. + </p> + <p> + A high C.G. also tends to swing outward from the centre of the turn. It + will tend to make the aeroplane bank the wrong way, and such effect must + be remedied by means of the ailerons. + </p> + <p> + The pleasantest machine from a banking point of view is one in which the + C.G. is a little below the centre of drift. It tends to bank the aeroplane + the right way for the turn, and the pilot can, if necessary, perfect the + bank by means of the ailerons. + </p> + <p> + The disposition of the keel-surface affects banking. It should be, in + effect, evenly divided by the longitudinal axis. An excess of keel-surface + above the longitudinal axis will, when banking, receive an air pressure + causing the aeroplane to bank, perhaps too much. An excess of keel-surface + below the axis has the reverse effect. + </p> + <p> + SIDE-SLIPPING.—This usually occurs as a result of over-banking. It + is always the result of the aeroplane tilting sideways and thus decreasing + the horizontal equivalent, and therefore the lift, of the surface. An + excessive “bank,” or sideways tilt, results in the H.E., and therefore the + lift, becoming less than the weight, when, of course, the aeroplane must + fall, i.e., side-slip. + </p> + <p> + When making a very sharp turn it is necessary to bank very steeply indeed. + If, at the same time, the longitudinal axis of the aeroplane remains + approximately horizontal, then there must be a fall, and the direction of + motion will be the resultant of the thrust and the fall as illustrated + above in sketch A. The lifting surfaces and the controlling surfaces are + not then meeting the air in the correct attitude, with the result that, in + addition to falling, the aeroplane will probably become quite + unmanageable. + </p> + <p> + The Pilot, however, prevents such a state of affairs from happening by + “nosing-down,” i.e., by operating the rudder to turn the nose of the + aeroplane downward and towards the direction of motion as illustrated in + sketch B. This results in the higher wing, which is on the outside of the + turn, travelling with greater velocity, and therefore securing a greater + reaction than the lower wing, thus tending to tilt the aeroplane over + still more. The aeroplane is now almost upside-down, but its attitude + relative to the direction of motion is correct and the controlling + surfaces are all of them working efficiently. The recovery of a normal + attitude relative to the Earth is then made as illustrated in sketch C. + </p> + <p> + The Pilot must then learn to know just the angle of bank at which the + margin of lift is lost, and, if a sharp turn necessitates banking beyond + that angle, he must “nose-down.” + </p> + <p> + In this matter of banking and nosing-down, and, indeed, regarding + stability and control generally, the golden rule for all but very + experienced pilots should be: Keep the aeroplane in such an attitude that + the air pressure is always directly in the pilot's face. The aeroplane is + then always engaging the air as designed to do so, and both lifting and + controlling surfaces are acting efficiently. The only exception to this + rule is a vertical dive, and I think that is obviously not an attitude for + any but very experienced pilots to hanker after. + </p> + <p> + SPINNING.—This is the worst of all predicaments the pilot can find + himself in. Fortunately it rarely happens. + </p> + <p> + It is due to the combination of (1) a very steep spiral descent of small + radius, and (2) insufficiency of keel-surface behind the vertical axis, or + the jamming of the rudder end or elevator into a position by which the + aeroplane is forced into an increasingly steep and small spiral. + </p> + <p> + Owing to the small radius of such a spiral, the mass of the aeroplane may + gain a rotary momentum greater, in effect, than the air pressure of the + keel-surface or controlling surfaces opposed to it; and, when once such a + condition occurs, it is difficult to see what can be done by the pilot to + remedy it. The sensible pilot will not go beyond reasonable limits of + steepness and radius when executing spiral descents. + </p> + <p> + GLIDING DESCENT WITHOUT PROPELLER THRUST.—All aeroplanes are, or + should be, designed to assume their gliding angle when the power and + thrust is cut off. This relieves the pilot of work, worry, and danger + should he find himself in a fog or cloud. The Pilot, although he may not + realize it, maintains the correct attitude of the aeroplane by observing + its position relative to the horizon. Flying into a fog or cloud the + horizon is lost to view, and he must then rely upon his instruments—(1) + the compass for direction; (2) an inclinometer (arched spirit-level) + mounted transversely to the longitudinal axis, for lateral stability; and + (3) an inclinometer mounted parallel to the longitudinal axis, or the + airspeed indicator, which will indicate a nose-down position by increase + in air speed, and a tail-down position by decrease in air speed. + </p> + <p> + The pilot is then under the necessity of watching three instruments and + manipulating his three controls to keep the instruments indicating + longitudinal, lateral, and directional stability. That is a feat beyond + the capacity of the ordinary man. If, however, by the simple movement of + throttling down the power and thrust, he can be relieved of looking after + the longitudinal stability, he then has only two instruments to watch. + That is no small job in itself, but it is, at any rate, fairly + practicable. + </p> + <p> + Aeroplanes are, then, designed, or should be, so that the centre of + gravity is slightly forward of centre of lift. The aeroplane is then, as a + glider, nose-heavy—and the distance the C.G. is placed in advance of + the C.L. should be such as to ensure a gliding angle producing a velocity + the same as the normal flying speed (for which the strength of + construction has been designed). + </p> + <p> + In order that this nose-heavy tendency should not exist when the thrust is + working and descent not required, the centre of thrust is placed a little + below the centre of drift or resistance, and thus tends to pull up the + nose of the aeroplane. + </p> + <p> + 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 + C.G. being forward of the C.L. + </p> + <p> + LOOPING AND UPSIDE DOWN FLYING.—If a loop is desired, it is best to + throttle the engine down at point A. The C.G. being forward of the C.P., + then causes the aeroplane to nose-down, and assists the pilot in making a + reasonably small loop along the course C and in securing a quick recovery. + If the engine is not throttled down, then the aeroplane may be expected to + follow the course D, which results in a longer nose dive than in the case + of the course C. + </p> + <p> + A steady, gentle movement of the elevator is necessary. A jerky movement + may change the direction of motion so suddenly as to produce dangerous air + stresses upon the surfaces, in which case there is a possibility of + collapse. + </p> + <p> + If an upside-down flight is desired, the engine may, or may not, be + throttled down at point A. If not throttled down, then the elevator must + be operated to secure a course approximately in the direction B. If it is + throttled down, then the course must be one of a steeper angle than B, or + there will be danger of stalling. + </p> + <p> + Diagram p. 88.—This is not set at quite the correct angle. Path B + should slope slightly downwards from Position A. + </p> + <p> + <a name="link2HCH0003" id="link2HCH0003"> + <!-- H2 anchor --> </a> + </p> + <div style="height: 4em;"> + <br /><br /><br /><br /> + </div> + <h2> + CHAPTER III. RIGGING + </h2> + <p> + In order to rig an aeroplane intelligently, and to maintain it in an + efficient and safe condition, it is necessary to possess a knowledge of + the stresses it is called upon to endure, and the strains likely to + appear. + </p> + <p> + STRESS is the load or burden a body is called upon to bear. 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 + body. + </p> + <p> + Thus, if, for instance, the object illustrated above contains 4 square + inches of cross-sectional area, and the total load it is called upon to + endure is 10 tons, the stress would be expressed as 2 1/2 tons. + </p> + <p> + STRAIN is the deformation produced by stress. + </p> + <p> + THE FACTOR OF SAFETY is usually expressed by the result found by dividing + the stress at which it is known the body will collapse, by the maximum + stress it will be called upon to endure. For instance, if a control wire + be called upon to endure a maximum stress of 2 cwts., and the known stress + at which it will collapse is 10 cwts., the factor of safety is then 5. + </p> + <p> + [cwts. = centerweights = 100 pound units as in cent & century. + Interestingly enough, this word only exists today in abbreviation form, + probably of centreweights, but the dictionary entries, even from a hundred + years ago do not list this as a word, but do list c. or C. as the previous + popular abbreviation as in Roman Numerals] The word listed is + “hundredweight. Michael S. Hart, 1997] + </p> + <p> + COMPRESSION.—The simple stress of compression tends to produce a + crushing strain. Example: the interplane and fuselage struts. + </p> + <p> + TENSION.—The simple stress of tension tends to produce the strain of + elongation. Example: all the wires. + </p> + <p> + BENDING.—The compound stress of bending is a combination of + compression and tension. + </p> + <p> + The above sketch illustrates a straight piece of wood of which the top, + centre, and bottom lines are of equal length. We will now imagine it bent + to form a circle, thus: + </p> + <p> + The centre line is still the same length as before being bent; but the top + line, being farther from the centre of the circle, is now longer than the + centre line. That can be due only to the strain of elongation produced by + the stress of tension. The wood between the centre line and the top line + is then in tension; and the farther from the centre, the greater the + strain, and consequently the greater the tension. + </p> + <p> + The bottom line, being nearest to the centre of the circle, is now shorter + than the centre line. That can be due only to the strain of crushing + produced by the stress of compression. The wood between the centre and + bottom lines is then in compression; and the nearer the centre of the + circle, the greater the strain, and consequently the greater the + compression. + </p> + <p> + It then follows that there is neither tension nor compression, i.e., no + stress, at the centre line, and that the wood immediately surrounding it + is under considerably less stress than the wood farther away. This being + so, the wood in the centre may be hollowed out without unduly weakening + struts and spars. In this way 25 to 33 per cent. is saved in the weight of + wood in an aeroplane. + </p> + <p> + The strength of wood is in its fibres, which should, as far as possible, + run without break from one end of a strut or spar to the other end. A + point to remember is that the outside fibres, being farthest removed from + the centre line, are doing by far the greatest work. + </p> + <p> + SHEAR STRESS IS such that, when material collapses under it, one part + slides over the other. Example: all the locking pins. + </p> + <p> + Some of the bolts are also in shear or “sideways” stress, owing to lugs + under their heads and from which wires are taken. Such a wire, exerting a + sideways pull upon a bolt, tries to break it in such a way as to make one + piece of the bolt slide over the other piece. + </p> + <p> + TORSION.—This is a twisting stress compounded of compression, + tension, and shear stresses. Example: the propeller shaft. + </p> + <p> + NATURE OF WOOD UNDER STRESS.—Wood, for its weight, takes the stress + of compression far better than any other stress. For instance: a + walking-stick of less than 1 lb. in weight will, if kept perfectly + straight, probably stand up to a compression stress of a ton or more + before crushing; whereas, if the same stick is put under a bending stress, + it will probably collapse to a stress of not more than about 50 lb. That + is a very great difference, and, since weight is of the greatest + importance, the design of an aeroplane is always such as to, as far as + possible, keep the various wooden parts of its construction in direct + compression. Weight being of such vital importance, and designers all + trying to outdo each other in saving weight, it follows that the factor of + safety is rather low in an aeroplane. The parts in direct compression + will, however, take the stresses safely provided the following conditions + are carefully observed. + </p> + <p> + CONDITIONS TO BE OBSERVED: + </p> + <p> + 1. All the spars and struts must be perfectly straight. + </p> + <p> + The above sketch illustrates a section through an interplane strut. If the + strut is to be kept straight, i.e., prevented from bending, then the + stress of compression must be equally disposed about the centre of + strength. If it is not straight, then there will be more compression on + one side of the centre of strength than on the other side. That is a step + towards getting compression on one side and tension on the other side, in + which case it may be forced to take a bending stress for which it is not + designed. Even if it does not collapse it will, in effect, become shorter, + and thus throw out of adjustment the gap and all the wires attached to the + top and bottom of the strut, with the result that the flight efficiency of + the aeroplane will be spoiled. + </p> + <p> + The only exception to the above condition is what is known as the Arch. + For instance, in the case of the Maurice Farman, the spars of the + centre-section plane, which have to take the weight of the nacelle, are + arched upwards. If this was not done, it is possible that rough landings + might result in the weight causing the spars to become slightly distorted + downwards. That would produce a dangerous bending stress, but, as long as + the wood is arched, or, at any rate, kept from bending downwards, it will + remain in direct compression and no danger can result. + </p> + <p> + 2. Struts and spars must be symmetrical. By that I mean that the + cross-sectional dimensions must be correct, as otherwise there will be + bulging places on the outside, with the result that the stress will not be + evenly disposed about the centre of strength, and a bending stress may be + produced. + </p> + <p> + 3. Struts, spars, etc., must be undamaged. Remember that, from what I have + already explained about bending stresses, the outside fibres of the wood + are doing by far the most work. If these get bruised or scored, then the + strut or spar suffers in strength much more than one might think at first + sight; and, if it ever gets a tendency to bend, it is likely to collapse + at that point. + </p> + <p> + 4. The wood must have a good, clear grain with no cross-grain, knots, or + shakes. Such blemishes produce weak places and, if a tendency to bend + appears, then it may collapse at such a point. + </p> + <p> + 5. The struts, spars, etc., must be properly bedded into their sockets or + fittings. To begin with, they must be of good pushing or gentle tapping + fit. They must never be driven in with a heavy hammer. Then again, a strut + must bed well down all over its cross-sectional area as illustrated above; + otherwise the stress of compression will not be evenly disposed about the + centre of strength, and that may produce a bending stress. The bottom of + the strut or spar should be covered with some sort of paint, bedded into + the socket or fitting, and then withdrawn to see if the paint has stuck + all over the bed. + </p> + <p> + 6. The atmosphere is sometimes much damper than at other times, and this + causes wood to expand and contract appreciably. This would not matter but + for the fact that it does not expand and contract uniformly, but becomes + unsymmetrical, i.e., distorted. I have already explained the danger of + that in condition 2. This should be minimized by WELL VARNISHING THE WOOD + to keep the moisture out of it. + </p> + <p> + FUNCTION OF INTERPLANE STRUTS.—These struts have to keep the lifting + surfaces or “planes” apart, but this is only part of their work. They must + keep the planes apart, so that the latter are in their correct attitude. + That is only so when the spars of the bottom plane are parallel with those + of the top plane. Also, the chord of the top plane must be parallel with + the chord of the bottom plane. If that is not so, then one plane will not + have the same angle of incidence as the other one. At first sight one + might think that all that is necessary is to cut all the struts to be the + same length, but that is not the case. + </p> + <p> + Sometimes, as illustrated above, the rear spar is not so thick as the main + spar, and it is then necessary to make up for that difference by making + the rear struts correspondingly longer. If that is not done, then the top + and bottom chords will not be parallel, and the top and bottom planes will + have different angles of incidence. Also, the sockets or fittings, or even + the spars upon which they are placed, sometimes vary in thickness owing to + faulty manufacture. This must be offset by altering the length of the + struts. The best way to proceed is to measure the distance between the top + and bottom spars by the side of each strut, and if that distance, or “gap” + as it is called, is not as stated in the aeroplane's specifications, then + make it correct by changing the length of the strut. This applies to both + front and rear interplane struts. When measuring the gap, always be + careful to measure from the centre of the spar, as it may be set at an + angle, and the rear of it may be considerably lower than its front. + </p> + <p> + BORING HOLES IN WOOD.—It should be a strict rule that no spar be + used which has an unnecessary hole in it. Before boring a hole, its + position should be confirmed by whoever is in charge of the workshop. A + bolt-hole should be of a size to enable the bolt to be pushed in, or, at + any rate, not more than gently tapped in. Bolts should not be hammered in, + as that may split the spar. On the other hand, a bolt should not be slack + in its hole, as, in such a case, it may work sideways and split the spar, + not to speak of throwing out of adjustment the wires leading from the lug + or socket under the bolt-head. + </p> + <p> + WASHERS.—Under the bolt-head, and also under the nut, a washer must + be placed—a very large washer compared with the size which would be + used in all-metal construction. This is to disperse the stress over a + large area; otherwise the washer may be pulled into the wood and weaken + it, besides possibly throwing out of adjustment the wires attached to the + bolt or the fitting it is holding to the spar. + </p> + <p> + LOCKING.—Now as regards locking the bolts. If split pins are used, + be sure to see that they are used in such a way that the nut cannot + possibly unscrew at all. The split pin should be passed through the bolt + as near as possible to the nut. It should not be passed through both nut + and bolt. + </p> + <p> + If it is locked by burring over the edge of the bolt, do not use a heavy + hammer and try to spread the whole head of the bolt. That might damage the + woodwork inside the fabric-covered surface. Use a small, light hammer, and + gently tap round the edge of the bolt until it is burred over. + </p> + <p> + TURNBUCKLES.—A turnbuckle is composed of a central barrel into each + end of which is screwed an eye-bolt. Wires are taken from the eyes of the + eye-bolt, and so, by turning the barrel, they can be adjusted to their + proper tension. Eye-bolts must be a good fit in the barrel; that is to + say, not slack and not very tight. Theoretically it is not necessary to + screw the eye-bolt into the barrel for a distance greater than the + diameter of the bolt, but, in practice, it is better to screw it in for a + considerably greater distance than that if a reasonable degree of safety + is to be secured. + </p> + <p> + Now about turning the barrel to secure the right adjustment. The barrel + looks solid, but, as a matter of fact, it is hollow and much more frail + than it appears. For that reason it should not be turned by seizing it + with pliers, as that may distort it and spoil the bore within it. The best + method is to pass a piece of wire through the hole in its centre, and to + use that as a lever. When the correct adjustment has been secured, the + turnbuckle must be locked to prevent it from unscrewing. It is quite + possible to lock it in such a way as to allow it to unscrew a quarter or a + half turn, and that would throw the wires out of the very fine adjustment + necessary. The proper way is to use the locking wire so that its direction + is such as to oppose the tendency of the barrel to unscrew, thus: + </p> + <p> + WIRES.—The following points should be carefully observed where wire + is concerned: + </p> + <p> + 1. Quality.—It must not be too hard or too soft. An easy practical + way of learning to know the approximate quality of wire is as follows: + </p> + <p> + Take three pieces, all of the same gauge, and each about a foot in length. + One piece should be too soft, another too hard, and the third piece of the + right quality. Fix them in a vice, about an inch apart and in a vertical + position, and with the light from a window shining upon them. Burnish them + if necessary, and you will see a band of light reflected from each wire. + </p> + <p> + Now bend the wires over as far as possible and away from the light. Where + the soft wire is concerned, it will squash out at the bend, and this will + be indicated by the band of light, which will broaden at that point. In + the case of the wire which is too hard, the band of light will broaden + very little at the turn, but, if you look carefully, you will see some + little roughnesses of surface. In the case of the wire of the right + quality, the band of light may broaden a very little at the turn, but + there will be no roughnesses of surface. + </p> + <p> + By making this experiment two or three times one can soon learn to know + really bad wire from good, and also learn to know the strength of hand + necessary to bend the right quality. + </p> + <p> + 2. It must not be damaged. That is to say, it must be unkinked, rustless, + and unscored. + </p> + <p> + 3. Now as regards keeping wire in good condition. Where outside wires are + concerned, they should be kept WELL GREASED OR OILED, especially where + bent over at the ends. Internal bracing wires cannot be reached for the + purpose of regreasing them, as they are inside fabric-covered surfaces. + They should be prevented from rusting by being painted with an anti-rust + mixture. Great care should be taken to see that the wire is perfectly + clean and dry before being painted. A greasy finger-mark is sufficient to + stop the paint from sticking to the wire. In such a case there will be a + little space between the paint and the wire. Air may enter there and cause + the wire to rust. + </p> + <p> + 4. Tension of Wires.—The tension to which the wires are adjusted is + of the greatest importance. All the wires should be of the same tension + when the aeroplane is supported in such a way as to throw no stress upon + them. If some wires are in greater tension than others, the aeroplane will + quickly become distorted and lose its efficiency. + </p> + <p> + In order to secure the same tension of all wires, the aeroplane, when + being rigged, should be supported by packing underneath the lower surfaces + as well as by packing underneath the fuselage or nacelle. In this way the + anti-lift wires are relieved of the weight, and there is no stress upon + any of the wires. + </p> + <p> + As a general rule the wires of an aeroplane are tensioned too much. The + tension should be sufficient to keep the framework rigid. Anything more + than that lowers the factor of safety, throws various parts of the + framework into undue compression, pulls the fittings into the wood, and + will, in the end, distort the whole framework of the aeroplane. + </p> + <p> + Only experience will teach the rigger what tension to employ. Much may be + done by learning the construction of the various types of aeroplanes, the + work the various parts do, and in cultivating a touch for tensioning wires + by constantly handling them. + </p> + <p> + 5. Wires with no Opposition Wires.—In some few cases wires will be + found which have no opposition wires pulling in the opposite direction. + For instance, an auxiliary lift wire may run from the bottom of a strut to + a spar in the top plane at a point between struts. In such a case great + care should be taken not to tighten the wire beyond barely taking up the + slack. + </p> + <p> + Such a wire must be a little slack, or, as illustrated above, it will + distort the framework. That, in the example given, will spoil the camber + (curvature) of the surface, and result in changing both the lift and the + drift at that part of the surface. Such a condition will cause the + aeroplane to lose its directional stability and also to fly one wing down. + </p> + <p> + I cannot impress this matter of tension upon the reader too strongly. It + is of the utmost importance. When this, and also accuracy in securing the + various adjustments, has been learned, one is on the way to becoming a + good rigger. + </p> + <p> + 6. Wire Loops.—Wire is often bent over at its end in the form of a + loop, in order to connect with a turnbuckle or fitting. These loops, even + when made as perfectly as possible, have a tendency to elongate, thus + spoiling the adjustment of the wires Great care should be taken to + minimize this as far as possible. The rules to be observed are as follows: + </p> + <p> + (a) The size of the loop should be as small as possible within reason. By + that I mean it should not be so small as to create the possibility of the + wire breaking. + </p> + <p> + (b) The shape of the loop should be symmetrical. + </p> + <p> + (c) It should have well-defined shoulders in order to prevent the ferrule + from slipping up. At the same time, a shoulder should not have an angular + place. + </p> + <p> + (d) When the loop is finished it should be undamaged, and it should not + be, as is often the case, badly scored. + </p> + <p> + 7. Stranded Wire Cable.—No splice should be served with twine until + it has been inspected by whoever is in charge of the workshop. The serving + may cover bad work. + </p> + <p> + Should a strand become broken, then the cable should be replaced at once + by another one. + </p> + <p> + Control cables have a way of wearing out and fraying wherever they pass + round pulleys. Every time an aeroplane comes down from flight the rigger + should carefully examine the cables, especially where they pass round + pulleys. If he finds a strand broken, he should replace the cable. + </p> + <p> + The ailerons' balance cable on the top of the top plane is often + forgotten, since it is necessary to fetch a high pair of steps in order to + examine it. Don't slack this, or some gusty day the pilot may unexpectedly + find himself minus the aileron control. + </p> + <p> + CONTROLLING SURFACES.—The greatest care should be exercised in + rigging the aileron, rudder, and elevator properly, for the pilot entirely + depends upon them in managing the aeroplane. + </p> + <p> + The ailerons and elevator should be rigged so that, when the aeroplane is + in flight, they are in a fair true line with the surface in front and to + which they are hinged. + </p> + <p> + If the surface to which they are hinged is not a lifting surface, then + they should be rigged to be in a fair true line with it as illustrated + above. + </p> + <p> + If the controlling surface is, as illustrated, hinged to the back of a + lifting surface, then it should be rigged a little below the position it + would occupy if in a fair true line with the surface in front. This is + because, in such a case, it is set at an angle of incidence. This angle + will, during flight, cause it to lift a little above the position in which + it has been rigged. 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 slack, because that would cause it to bind against the + pulleys and make the operation of it too hard for the pilot. 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 front. Remember + that this only applies when it is hinged to a lifting surface. The greater + the angle of incidence (and therefore the lift) of the surface in front, + then the more the controlling surface will have to be rigged down. + </p> + <p> + As a general rule it is safe to rig it down so that its trailing + </p> + <p> + edge is 1/2 to 3/4 inch below the position it would occupy if in a fair + line with the surface in front; or about 1/2 inch down for every 18 inches + of chord of the controlling surface. + </p> + <p> + When making these adjustments the pilot's control levers should be in + their neutral positions. It is not sufficient to lash them. They should be + rigidly blocked into position with wood packing. + </p> + <p> + The surfaces must not be distorted in any way. If they are held true by + bracing wires, then such wires must be carefully adjusted. If they are + distorted and there are no bracing wires with which to true them, then + some of the internal framework will probably have to be replaced. + </p> + <p> + The controlling surfaces should never be adjusted with a view to altering + the stability of the aeroplane. Nothing can be accomplished in that way. + The only result will be to spoil the control of the aeroplane. + </p> + <p> + FABRIC-COVERED SURFACES.—First of all make sure that there is no + distortion of spars or ribs, and that they are perfectly sound. Then + adjust the internal bracing wires so that the ribs are parallel to the + direction of flight. The ribs usually cause the fabric to make a ridge + where they occur, and, if such ridge is not parallel to the direction of + flight, it will produce excessive drift. As a rule the ribs are at right + angles to both main and rear spars. + </p> + <p> + The tension of the internal bracing wires should be just sufficient to + give rigidity to the framework. They should not be tensioned above that + unless the wires are, at their ends, bent to form loops. In that case a + little extra tension may be given to offset the probable elongation of the + loops. + </p> + <p> + The turnbuckles must now be generously greased, and served round with + adhesive tape. The wires must be rendered perfectly dry and clean, and + then painted with an anti-rust mixture. The woodwork must be well + varnished. + </p> + <p> + If it is necessary to bore holes in the spars for the purpose of + receiving, for instance, socket bolts, then their places should be marked + before being bored and their positions confirmed by whoever is in charge + of the workshop. All is now ready for the sail-maker to cover the surface + with fabric. + </p> + <p> + ADJUSTMENT OF CONTROL CABLES.—The adjustment of the control cables + is quite an art, and upon it will depend to a large degree the quick and + easy control of the aeroplane by the pilot. + </p> + <p> + The method is as follows: + </p> + <p> + After having rigged the controlling surfaces, and as far as possible + secured the correct adjustment of the control cables, then remove the + packing which has kept the control levers rigid. Then, sitting in the + pilot's seat, move the control levers SMARTLY. Tension the control cables + so that when the levers are smartly moved there is no perceptible snatch + or lag. Be careful not to tension the cables more than necessary to take + out the snatch. If tensioned too much they will (1) bind round the pulleys + and result in hard work for the pilot; (2) throw dangerous stresses upon + the controlling surfaces, which are of rather flimsy construction; and (3) + cause the cables to fray round the pulleys quicker than would otherwise be + the case. + </p> + <p> + Now, after having tensioned the cables sufficiently to take out the + snatch, place the levers in their neutral positions, and move them to and + fro about 1/8 inch either side of such positions. If the adjustment is + correct, it should be possible to see the controlling surfaces move. If + they do not move, then the control cables are too slack. + </p> + <p> + FLYING POSITION.—Before rigging an aeroplane or making any + adjustments it is necessary to place it in what is known as its “flying + position.” I may add that it would be better termed its “rigging + position.” + </p> + <p> + 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 laterally. This position is + found by placing a straight-edge and a spirit-level across the engine + foundations (both longitudinally and laterally), and great care should be + taken to see that the bubble is exactly in the centre of the level. The + slightest error will assume magnitude towards the extremities of the + aeroplane. Great care should be taken to block up the aeroplane rigidly. + In case it gets accidentally disturbed while the work is going on, it is + well to constantly verify the flying position by running the straight-edge + and spirit-level over the engine foundations. The straight-edge should be + carefully tested before being used, as, being generally made of wood, it + will not remain true long. Place it lightly in a vice, and in such a + position that a spirit-level on top shows the bubble exactly in the + centre. Now slowly move the level along the straight-edge, and the bubble + should remain exactly in the centre. If it does not do so, then the + straight-edge is not true and must be corrected. THIS SHOULD NEVER BE + OMITTED. + </p> + <p> + In the case of aeroplanes fitted with engines of the rotary type, the + “flying position” is some special attitude laid down in the aeroplane's + specifications, and great care should be taken to secure accuracy. + </p> + <p> + ANGLE OF INCIDENCE.—One method of finding the angle of incidence is + as follows: + </p> + <p> + First place the aeroplane in its flying position. The corner of the + straight-edge must be placed underneath and against the CENTRE of the rear + spar, and held in a horizontal position parallel to the ribs. This is + secured by using a spirit-level. The set measurement will then be from the + top of the straight-edge to the centre of the bottom surface of the main + spar, or it may be from the top of the straight-edge to the lowest part of + the leading edge. 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 level. + Remember that all this will be useless if the aeroplane has not been + placed accurately in its flying position. + </p> + <p> + This method of finding the angle of incidence must be used under every + part of the lower surface where struts occur. It should not be used + between the struts, because, in such places, the spars may have taken a + slight permanent set up or down; not, perhaps, sufficiently bad to make + any material difference to the flying of the machine, but quite bad enough + to throw out the angle of incidence, which cannot be corrected at such a + place. + </p> + <p> + If the angle is wrong, it should then be corrected as follows: + </p> + <p> + If it is too great, then the rear spar must be warped up until it is + right, and this is done by slackening ALL the wires going to the top of + the strut, and then tightening ALL the wires going to the bottom of the + strut. + </p> + <p> + If the angle is too small, then slacken ALL the wires going to the bottom + of the strut, and tighten ALL the wires going to the top of the strut, + until the correct adjustment is secured. + </p> + <p> + Never attempt to adjust the angle by warping the main spar. + </p> + <p> + The set measurement, which is of course stated in the aeroplane's + specifications, should be accurate to 1/16 inch. + </p> + <p> + LATERAL DIHEDRAL ANGLE.—One method of securing this is as follows, + and this method will, at the same time, secure the correct angle of + incidence: + </p> + <p> + The strings, drawn very tight, must be taken over both the main and rear + spars of the top surface. They must run between points on the spars just + inside the outer struts. The set measurement (which should be accurate to + 1/16 inch or less) is then from the strings down to four points on the + main and rear spars of the centre-section surface. These points should be + just inside the four centre-section struts; that is to say, as far as + possible away from the centre of the centre-section. Do not attempt to + take the set measurement near the centre of the centre-section. + </p> + <p> + The strings should be as tight as possible, and, if it can be arranged, + the best way to accomplish that is as shown in the above illustration, + i.e., by weighting the strings down to the spars by means of weights and + tying each end of the strings to a strut. This will give a tight and + motionless string. + </p> + <p> + However carefully the above adjustment is made, there is sure to be some + slight error. This is of no great importance, provided it is divided + equally between the left- and right-hand wings. In order to make sure of + this, certain check measurements should be taken as follows: + </p> + <p> + Each bay must be diagonally measured, and such measurements must be the + same to within 1/16 inch on each side of the aeroplane. As a rule such + diagonal measurements are taken from the bottom socket of one strut to the + top socket of another strut, but this is bad practice, because of possible + inaccuracies due to faulty manufacture. + </p> + <p> + The points between which the diagonal measurements are taken should be at + fixed distances from the butts of the spars, such distances being the same + on each side of the aeroplane, thus: + </p> + <p> + It would be better to use the centre line of the aeroplane rather than the + butts of the spars. It is not practicable to do so, however, as the centre + line probably runs through the petrol tanks, etc. + </p> + <p> + THE DIHEDRAL BOARD.—Another method of securing the dihedral angle, + and also the angle of incidence, is by means of the dihedral board. It is + a light handy thing to use, but leads to many errors, and should not be + used unless necessary. The reasons are as follows: + </p> + <p> + The dihedral board is probably not true. If it must be used, then it + should be very carefully tested for truth before-hand. Another reason + against its use is that it has to be placed on the spars in a position + between the struts, and that is just where the spars may have a little + permanent set up or down, or some inaccuracy of surface which will, of + course, throw out the accuracy of the adjustment. The method of using it + is as follows: + </p> + <p> + The board is cut to the same angle as that specified for the upward + inclination of the surface towards its wing-tips. It is placed on the spar + as indicated above, and it is provided with two short legs to raise it + above the flanges of the ribs (which cross over the spars), as they may + vary in depth. A spirit-level is then placed on the board, 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 level. This operation must be + performed in respect of each bay both front and rear. The bays must then + be diagonally measured as already explained. + </p> + <p> + YET ANOTHER METHOD of finding the dihedral angle, and at the same time the + angle of incidence, is as follows: + </p> + <p> + A horizontal line is taken from underneath the butt of each spar, and the + set measurement is either the angle it makes with the spar, or a fixed + measurement from the line to the spar taken at a specified distance from + the butt. This operation must be performed in respect of both main and + rear spars, and all the bays must be measured diagonally afterwards. + </p> + <p> + Whichever method is used, be sure that after the job is done the spars are + perfectly straight. + </p> + <p> + STAGGER.—The stagger is the distance the top surface is in advance + of the bottom surface when the aeroplane is in flying position. The set + measurement is obtained as follows: + </p> + <p> + Plumb-lines must be dropped over the leading edge of the top surface + wherever struts occur, and also near the fuselage. The set measurement is + taken from the front of the lower leading edge to the plumb-lines. It + makes a difference whether the measurement is taken along a horizontal + line (which can be found by using a straight-edge and a spirit-level) or + along a projection of the chord. The line along which the measurement + should be taken is laid down in the aeroplane's specifications. + </p> + <p> + If a mistake is made and the measurement taken along the wrong line, it + may result in a difference of perhaps 1/4 will, in flight, be nose-heavy + or tail-heavy. + </p> + <p> + After the adjustments of the angles of incidence, dihedral, and stagger + have been secured, it is as well to confirm all of them, as, in making the + last adjustment, the first one may have been spoiled. + </p> + <p> + OVER-ALL ADJUSTMENTS.—The following over-all check measurements + should now be taken. + </p> + <p> + The straight lines AC and BC should be equal to within 1/8 inch. The point + C is the centre of the propeller, or, in the case of a “pusher” aeroplane, + the centre of the nacelle. The points A and B are marked on the main spar, + and must in each case be the same distance from the butt of the spar. The + rigger should not attempt to make A and B merely the sockets of the outer + struts, as they may not have been placed quite accurately by the + manufacturer. The lines AC and BC must be taken from both top and bottom + spars—two measurements on each side of the aeroplane. + </p> + <p> + The two measurements FD and FE should be equal to within 1/8 inch. F is + the centre of the fuselage or rudder-post. D and E are points marked on + both top and bottom rear spars, and each must be the same fixed distance + from the butt of the spar. Two measurements on each side of the aeroplane. + </p> + <p> + If these over-all measurements are not correct, then it is probably due to + some of the drift or anti-drift wires being too tight or too slack. It may + possibly be due to the fuselage being out of truth, but of course the + rigger should have made quite sure that the fuselage was true before + rigging the rest of the machine. Again, it may be due to the internal + bracing wires within the lifting surfaces not being accurately adjusted, + but of course this should have been seen to before covering the surfaces + with fabric. + </p> + <p> + FUSELAGE.—The method of truing the fuselage is laid down in the + aeroplane's specifications. After it has been adjusted according to the + specified directions, it should then be arranged on trestles in such a way + as to make about three-quarters of it towards the tail stick out + unsupported. In this way it will assume a condition as near as possible to + flying conditions, and when it is in this position the set measurements + should be confirmed. If this is not done it may be out of truth, but + perhaps appear all right when supported by trestles at both ends, as, in + such case, its weight may keep it true as long as it is resting upon the + trestles. + </p> + <p> + THE TAIL-PLANE (EMPENNAGE).—The exact angle of incidence of the + tail-plane is laid down in the aeroplane's specifications. 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 + Fuselage. If the spars are tapered, then make sure that their centre lines + are horizontal. + </p> + <p> + UNDERCARRIAGE.—The undercarriage must be very carefully aligned as + laid down in the specifications. + </p> + <p> + 1. The aeroplane must be placed in its flying position and sufficiently + high to ensure the wheels being off the ground when rigged. When in this + position the axle must be horizontal and the bracing wires adjusted to + secure the various set measurements stated in the specifications. + </p> + <p> + 2. Make sure that the struts bed well down into their sockets. + </p> + <p> + 3. Make sure that the shock absorbers are of equal tension. In the case of + rubber shock absorbers, both the number of turns and the lengths must be + equal. + </p> + <p> + HOW TO DIAGNOSE FAULTS IN FLIGHT, STABILITY, AND CONTROL. + </p> + <p> + DIRECTIONAL STABILITY will be badly affected if there is more drift (i.e., + resistance) on one side of the aeroplane than there is on the other side. + The aeroplane will tend to turn towards the side having the most drift. + This may be caused as follows: + </p> + <p> + 1. The angle of incidence of the main surface or the tail surface may be + wrong. The greater the angle of incidence, the greater the drift. The less + the angle, the less the drift. + </p> + <p> + 2. If the alignment of the fuselage, fin in front of the rudder, the + struts or stream-line wires, or, in the case of the Maurice Farman, the + front outriggers, are not absolutely correct—that is to say, 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 course. + </p> + <p> + 3. If any part of the surface is distorted, it will cause the aeroplane to + turn off its course. The surface is cambered, i.e., curved, to pass + through the air with the least possible drift. If, owing perhaps to the + leading edge, spars, or trailing edge becoming bent, the curvature is + spoiled, that will result in changing the amount of drift on one side of + the aeroplane, which will then have a tendency to turn off its course. + </p> + <p> + LATERAL INSTABILITY (FLYING ONE WING DOWN).—The only possible reason + for such a condition is a difference in the lifts of right and left wings. + That may be caused as follows: + </p> + <p> + 1. The angle of incidence may be wrong. If it is too great, it will + produce more lift than on the other side of the aeroplane; and if too + small, it will produce less lift than on the other side—the result + being that, in either case, the aeroplane will try to fly one wing down. + </p> + <p> + 2. Distorted Surfaces.—If some part of the surface is distorted, + then its camber is spoiled, and the lift will not be the same on both + sides of the aeroplane, and that, of course, will cause it to fly one wing + down. + </p> + <p> + LONGITUDINAL INSTABILITY may be due to the following reasons: + </p> + <p> + 1. The stagger may be wrong. The top surface may have drifted back a + little owing to some of the wires, probably the incidence wires, having + elongated their loops or having pulled the fittings into the wood. If the + top surface is not staggered forward to the correct degree, then + consequently the whole of its lift is too far back, and it will then have + a tendency to lift up the tail of the machine too much. The aeroplane + would then be said to be “nose-heavy.” + </p> + <p> + A 1/4-inch area in the stagger will make a very considerable difference to + the longitudinal stability. + </p> + <p> + 2. If the angle of incidence of the main surface is not right, it will + have a bad effect, especially in the case of an aeroplane with a lifting + tail-plane. + </p> + <p> + If the angle is too great, it will produce an excess of lift, and that may + lift up the nose of the aeroplane and result in a tendency to fly + “tail-down.” If the angle is too small, it will produce a decreased lift, + and the aeroplane may have a tendency to fly “nose-down.” + </p> + <p> + 3. The fuselage may have become warped upward or downward, thus giving the + tail-plane an incorrect angle of incidence. If it has too much angle, it + will lift too much, and the aeroplane will be “nose-heavy.” If it has too + little angle, then it will not lift enough, and the aeroplane will be + “tail-heavy.” + </p> + <p> + 4. (The least likely reason.) The tail-plane may be mounted upon the + fuselage at a wrong angle of incidence, in which case it must be + corrected. If nose-heavy, it should be given a smaller angle of incidence. + If tail-heavy, it should be given a larger angle; but care should be taken + not to give it too great an angle, because the longitudinal stability + entirely depends upon the tail-plane being set at a much smaller angle of + incidence than is the main surface, and if that difference is decreased + too much, the aeroplane will become uncontrollable longitudinally. + Sometimes the tail-plane is mounted on the aeroplane at the same angle as + the main surface, but it actually engages the air at a lesser angle, owing + to the air being deflected downwards by the main surface. There is then, + in effect, a longitudinal dihedral as explained and illustrated in Chapter + I. + </p> + <p> + CLIMBS BADLY.—Such a condition is, apart from engine or propeller + trouble, probably due to (1) distorted surfaces, or (2) too small an angle + of incidence. + </p> + <p> + FLIGHT SPEED POOR.—Such a condition is, apart from engine or + propeller trouble, probably due to (1) distorted surfaces, (2) too great + an angle of incidence, or (3) dirt or mud, and consequently excessive + skin-friction. + </p> + <p> + INEFFICIENT CONTROL is probably due to (1) wrong setting of control + surfaces, (2) distortion of control surfaces, or (3) control cables being + badly tensioned. + </p> + <p> + WILL NOT TAXI STRAIGHT.—If the aeroplane is uncontrollable on the + ground, it is probably due to (1) alignment of undercarriage being wrong, + or (2) unequal tension of shock absorbers. + </p> + <p> + <a name="link2HCH0004" id="link2HCH0004"> + <!-- H2 anchor --> </a> + </p> + <div style="height: 4em;"> + <br /><br /><br /><br /> + </div> + <h2> + CHAPTER IV. THE PROPELLER, OR “AIR-SCREW” + </h2> + <p> + The sole object of the propeller is to translate the power of the engine + into thrust. + </p> + <p> + The propeller screws through the air, and its blades, being set at an + angle inclined to the direction of motion, secure a reaction, as in the + case of the aeroplane's lifting surface. + </p> + <p> + This reaction may be conveniently divided into two component parts or + values, namely, Thrust and Drift. + </p> + <p> + The Thrust is opposed to the Drift of the aeroplane, and must be equal and + opposite to it at flying speed. If it falls off in power, then the flying + speed must decrease to a velocity, at which the aeroplane drift equals the + decreased thrust. + </p> + <p> + The Drift of the propeller may be conveniently divided into the following + component values: + </p> + <p> + Active Drift, produced by the useful thrusting part of the propeller. + </p> + <p> + Passive Drift, produced by all the rest of the propeller, i.e., by its + detrimental surface. + </p> + <p> + Skin Friction, produced by the friction of the air with roughnesses of + surface. + </p> + <p> + Eddies attending the movement of the air caused by the action of the + propeller. + </p> + <p> + Cavitation (very marked at excessive speed of revolution). A tendency of + the propeller to produce a cavity or semi-vacuum in which it revolves, the + thrust decreasing with increase of speed and cavitation. + </p> + <p> + THRUST-DRIFT RATIO.—The proportion of thrust to drift is of + paramount importance, for it expresses the efficiency of the propeller. It + is affected by the following factors: Speed of Revolution.—The + greater the speed, the greater the proportion of drift to thrust. This is + due to the increase with speed of the passive drift, which carries with it + no increase in thrust. For this reason propellers are often geared down to + revolve at a lower speed than that of the engine. + </p> + <p> + Angle of Incidence.—The same reasons as in the case of the aeroplane + surface. + </p> + <p> + Surface Area.—Ditto. + </p> + <p> + Aspect Ratio.—Ditto. + </p> + <p> + Camber.—Ditto. + </p> + <p> + In addition to the above factors there are, when it comes to actually + designing a propeller, mechanical difficulties to consider. For instance, + the blades must be of a certain strength and consequent thickness. That, + in itself, limits the aspect ratio, for it will necessitate a chord long + enough in proportion to the thickness to make a good camber possible. + Again, the diameter of the propeller must be limited, having regard to the + fact that greater diameters than those used to-day would not only result + in excessive weight of construction, but would also necessitate a very + high undercarriage to keep the propeller off the ground, and such + undercarriage would not only produce excessive drift, but would also tend + to make the aeroplane stand on its nose when alighting. The latter + difficulty cannot be overcome by mounting the propeller higher, as the + centre of its thrust must be approximately coincident with the centre of + aeroplane drift. + </p> + <p> + MAINTENANCE OF EFFICIENCY. + </p> + <p> + The following conditions must be observed: + </p> + <p> + 1. PITCH ANGLE.—The angle, at any given point on the propeller, at + which the blade is set is known as the pitch angle, and it must be correct + to half a degree if reasonable efficiency is to be maintained. + </p> + <p> + This angle secures the “pitch,” which is the distance the propeller + advances during one revolution, supposing the air to be solid. The air, as + a matter of fact, gives back to the thrust of the blades just as the + pebbles slip back as one ascends a shingle beach. Such “give-back” is + known as Slip. If a propeller has a pitch of, say, 10 feet, but actually + advances, say, only 8 feet owing to slip, then it will be said to possess + 20 per cent. slip. + </p> + <p> + Thus, the pitch must equal the flying speed of the aeroplane plus the slip + of the propeller. For example, let us find the pitch of a propeller, given + the following conditions: + </p> +<pre xml:space="preserve"> + Flying speed.............. 70 miles per hour. + Propeller revolutions..... 1,200 per minute. + Slip...................... 15 per cent. +</pre> + <p> + First find the distance in feet the aeroplane will travel forward in one + minute. That is— + </p> +<pre xml:space="preserve"> + 369,600 feet (70 miles) + ———————————— = 6,160 feet per minute. + 60 “ (minutes) +</pre> + <p> + Now divide the feet per minute by the propeller revolutions per minute, + add 15 per cent. for the slip, and the result will be the propeller pitch: + </p> +<pre xml:space="preserve"> + 6,160 + ——- + 15 per cent. = 5 feet 1 3/5 inches. + 1,200 +</pre> + <p> + In order to secure a constant pitch from root to tip of blade, the pitch + angle decreases towards the tip. This is necessary, since the end of the + blade travels faster than its root, and yet must advance forward at the + same speed as the rest of the propeller. For example, two men ascending a + hill. One prefers to walk fast and the other slowly, but they wish to + arrive at the top of the hill simultaneously. Then the fast walker must + travel a farther distance than the slow one, and his angle of path (pitch + angle) must be smaller than the angle of path taken by the slow walker. + Their pitch angles are different, but their pitch (in this case altitude + reached in a given time) is the same. + </p> + <p> + In order to test the pitch angle, the propeller must be mounted upon a + shaft at right angles to a beam the face of which must be perfectly level, + thus: + </p> + <p> + First select a point on the blade at some distance (say about 2 feet) from + the centre of the propeller. At that point find, by means of a protractor, + the angle a projection of the chord makes with the face of the beam. That + angle is the pitch angle of the blade at that point. + </p> + <p> + Now lay out the angle on paper, thus: + </p> + <p> + 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 + pitch, which is, or should be, marked upon the boss of the propeller. + </p> + <p> + Now find the circumference of the propeller where the pitch angle is being + tested. For example, if that place is 2 feet radius from the centre, then + the circumference will be 2 feet X 2 = 4 feet diameter, which, if + multiplied by 3.1416 = 15.56 feet circumference. + </p> + <p> + Now mark off the circumference distance, which is represented above by + A-B, and reduce it in scale for convenience. + </p> + <p> + The distance a vertical line makes between B and the chord dine is the + pitch at the point where the angle is being tested, and it should coincide + with the specified pitch. You will note, from the above illustration, that + the actual pitch line should meet the junction of the chord line and top + line. + </p> + <p> + The propeller should be tested at several points, about a foot apart, on + each blade; and the diagram, provided the propeller is not faulty, will + then look like this: + </p> + <p> + At each point tested the actual pitch coincides with the specified pitch: + a satisfactory condition. + </p> + <p> + A faulty propeller will produce a diagram something like this: + </p> + <p> + At every point tested the pitch angle is wrong, for nowhere does the + actual pitch coincide with the specified pitch. Angles A, C, and D, are + too large, and B is too small. The angle should be correct to half a + degree if reasonable efficiency is to be maintained. + </p> + <p> + A fault in the pitch angle may be due to (1) faulty manufacture, (2) + distortion, or (3) the shaft hole through the boss being out of position. + </p> + <p> + 2. STRAIGHTNESS.—To test for straightness the propeller must be + mounted upon a shaft. Now bring the tip of one blade round to graze some + fixed object. Mark the point it grazes. Now bring the other tip round, and + it should come within 1/8 inch of the mark. If it does not do so, it is + due to (1) faulty manufacture, (2) distortion, or (3) to the hole through + the boss being out of position. + </p> + <p> + 3. LENGTH.—The blades should be of equal length to inch. + </p> + <p> + 4. BALANCE.—The usual method of testing a propeller for balance is + as follows: Mount it upon a shaft, which must be on ball-bearings. Place + the propeller in a horizontal position, and it should remain in that + position. If a weight of a trifle over an ounce placed in a bolt-hole on + one side of the boss fails to disturb the balance, then the propeller is + usually regarded as unfit for use. + </p> + <p> + The above method is rather futile, as it does not test for the balance of + centrifugal force, which comes into play as soon as the propeller + revolves. It can be tested as follows: + </p> + <p> + The propeller must be in a horizontal position, and then weighed at fixed + points, such as A, B, C, D, E, and F, and the weights noted. The points A, + B, and C must, of course, be at the same fixed distances from the centre + of the propeller as the points D, E, and F. Now reverse the propeller and + weigh at each point again. Note the results. The first series of weights + should correspond to the second series, thus: + </p> +<pre xml:space="preserve"> + Weight A should equal weight F. + “ B “ “ “ E. + “ C “ “ “ D. +</pre> + <p> + There is no standard practice as to the degree of error permissible, but + if there are any appreciable differences the propeller is unfit for use. + </p> + <p> + 5. SURFACE AREA.—The surface area of the blades should be equal. + Test with callipers thus: + </p> + <p> + The points between which the distances are taken must, of course, be at + the same distance from the centre in the case of each blade. + </p> + <p> + There is no standard practice as to the degree of error permissible. If, + however, there is an error of over 1/8 inch, the propeller is really unfit + for use. + </p> + <p> + 6. CAMBER.—The camber (curvature) of the blades should be (1) equal, + (2) decrease evenly towards the tips of the blades, and (3) the greatest + depth of the curve should, at any point of the blade, be approximately at + the same percentage of the chord from the leading edge as at other points. + </p> + <p> + It is difficult to test the top camber without a set of templates, but a + fairly accurate idea of the concave camber can be secured by slowly + passing a straight-edge along the blade, thus: + </p> + <p> + The camber can now be easily seen, and as the straight-edge is passed + along the blade, the observer should look for any irregularities of the + curvature, which should gradually and evenly decrease towards the tip of + the blade. + </p> + <p> + 7. THE JOINTS.—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 flight, and then carefully examining the joints to see if they + have opened. It is not likely, however, that the reader will have the + opportunity of making this test. He should, however, examine all the + joints very carefully, trying by hand to see if they are quite sound. + Suspect a propeller of which the joints appear to hold any thickness of + glue. Sometimes the joints in the boss open a little, but this is not + dangerous unless they extend to the blades, as the bolts will hold the + laminations together. + </p> + <p> + 8. CONDITION OF SURFACE.—The surface should be very smooth, + especially towards the tips of the blades. Some propeller tips have a + speed of over 30,000 feet a minute, and any roughness will produce a bad + drift or resistance and lower the efficiency. + </p> + <p> + 9. MOUNTING.—Great care should be taken to see that the propeller is + mounted quite straight on its shaft. Test in the same way as for + straightness. If it is not straight, it is possibly due to some of the + propeller bolts being too slack or to others having been pulled up too + tightly. + </p> + <p> + FLUTTER.—Propeller “flutter,” or vibration, may be due to faulty + pitch angle, balance, camber, or surface area. It causes a condition + sometimes mistaken for engine trouble, and one which may easily lead to + the collapse of the propeller. + </p> + <p> + CARE OF PROPELLERS.—The care of propellers is of the greatest + importance, as they become distorted very easily. + </p> + <p> + 1. Do not store them in a very damp or a very dry place. + </p> + <p> + 2. Do not store them where the sun will shine upon them. + </p> + <p> + 3. Never leave them long in a horizontal position or leaning up against a + wall. + </p> + <p> + 4. They should be hung on horizontal pegs, and the position of the + propellers should be vertical. + </p> + <p> + If the points I have impressed upon you in these notes are not attended + to, you may be sure of the following results: + </p> + <p> + 1. Lack of efficiency, resulting in less aeroplane speed and climb than + would otherwise be the case. + </p> + <p> + 2. Propeller “flutter” and possible collapse. + </p> + <p> + 3. A bad stress upon the propeller shaft and its bearings. + </p> + <p> + TRACTOR.—A propeller mounted in front of the main surface. + </p> + <p> + PUSHER.—A propeller mounted behind the main surface. + </p> + <p> + FOUR-BLADED PROPELLERS.—Four-bladed propellers are suitable only + when the pitch is comparatively large. + </p> + <p> + For a given pitch, and having regard to “interference,” they are not so + efficient as two-bladed propellers. + </p> + <p> + The smaller the pitch, the less the “gap,” i.e., the distance, measured in + the direction of the thrust, between the spiral courses of the blades. + </p> + <p> + If the gap is too small, then the following blade will engage air which + the preceding blade has put into motion, with the result that the + following blade will not secure as good a reaction as would otherwise be + the case. It is very much the same as in the case of the aeroplane gap. + </p> + <p> + For a given pitch, the gap of a four-bladed propeller is only half that of + a two-bladed one. Therefore the four-bladed propeller is only suitable for + large pitch, as such pitch produces spirals with a large gap, thus + offsetting the decrease in gap caused by the numerous blades. + </p> + <p> + The greater the speed of rotation, the less the pitch for a given + aeroplane speed. Then, in order to secure a large pitch and consequently a + good gap, 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-shaft. + </p> + <p> + <a name="link2HCH0005" id="link2HCH0005"> + <!-- H2 anchor --> </a> + </p> + <div style="height: 4em;"> + <br /><br /><br /><br /> + </div> + <h2> + CHAPTER V. MAINTENANCE + </h2> + <p> + CLEANLINESS.—The fabric must be kept clean and free from oil, as + that will rot it. To take out dirt or oily patches, try acetone. If that + will not remedy matters, then try petrol, but use it sparingly, as + otherwise it will take off an unnecessary amount of dope. If that will not + remove the dirt, then hot water and soap will do so, but, in that case, be + sure to use soap having no alkali in it, as otherwise it may injure the + fabric. Use the water sparingly, or it may get inside the planes and rust + the internal bracing wires, or cause some of the wooden framework to + swell. + </p> + <p> + The wheels of the undercarriage have a way of throwing up mud on to the + lower surface. This should, if possible, be taken off while wet. It should + never be scraped off when dry, as that may injure the fabric. If dry, then + it should be moistened before being removed. + </p> + <p> + Measures should be taken to prevent dirt from collecting upon any part of + the aeroplane, as, otherwise, excessive skin-friction will be produced + with resultant loss of flight speed. The wires, being greasy, collect dirt + very easily. + </p> + <p> + CONTROL CABLES.—After every flight the rigger should pass his hand + over the control cables and carefully examine them near pulleys. Removal + of grease may be necessary to make a close inspection possible. If only + one strand is broken the wire should be replaced. Do not forget the + aileron balance wire on the top surface. + </p> + <p> + Once a day try the tension of the control cables by smartly moving the + control levers about as explained elsewhere. + </p> + <p> + WIRES.—All the wires should be kept well greased or oiled, and in + the correct tension. When examining the wires, it is necessary to place + the aeroplane on level ground, as otherwise it may be twisted, thus + throwing some wires into undue tension and slackening others. The best + way, if there is time, is to pack the machine up into its “flying + position.” + </p> + <p> + If you see a slack wire, do not jump to the conclusion that it must be + tensioned. Perhaps its opposition wire is too tight, in which case slacken + it, and possibly you will find that will tighten the slack wire. + </p> + <p> + Carefully examine all wires and their connections near the propeller, and + be sure that they are snaked round with safety wire, so that the latter + may keep them out of the way of the propeller if they come adrift. + </p> + <p> + The wires inside the fuselage should be cleaned and regreased about once a + fortnight. + </p> + <p> + STRUTS AND SOCKETS.—These should be carefully examined to see if any + splitting has occurred. + </p> + <p> + DISTORTION.—Carefully examine all surfaces, including the + controlling surfaces, to see whether any distortion has occurred. If + distortion can be corrected by the adjustment of wires, well and good; but + if not, then some of the internal framework probably requires replacement. + </p> + <p> + ADJUSTMENTS.—Verify the angles of incidence; dihedral, and stagger, + and the rigging position of the controlling-surfaces, as often as + possible. + </p> + <p> + UNDERCARRIAGE.—Constantly examine the alignment and fittings of the + undercarriage, and the condition of tyres and shock absorbers. The latter, + when made of rubber, wear quickest underneath. Inspect axles and skids to + see if there are any signs of them becoming bent. The wheels should be + taken off occasionally and greased. + </p> + <p> + LOCKING ARRANGEMENTS.—Constantly inspect the locking arrangements of + turnbuckles, bolts, etc. Pay particular attention to the control cable + connections, and to all moving parts in respect of the controls. + </p> + <p> + LUBRICATION.—Keep all moving parts, such as pulleys, control levers, + and hinges of controlling surfaces, well greased. + </p> + <p> + SPECIAL INSPECTION.—Apart from constantly examining the aeroplane + with reference to the above points I have made, I think that, in the case + of an aeroplane in constant use it is an excellent thing to make a special + inspection of every part, say once a week. This will take from two to + three hours, according to the type of aeroplane. In order to carry it out + methodically, the rigger should have a list of every part down to the + smallest split-pin. He can then check the parts as he examines them, and + nothing will be passed over. This, I know from experience, greatly + increases the confidence of the pilot, and tends to produce good work in + the air. + </p> + <p> + WINDY WEATHER.—The aeroplane, when on the ground, should face the + wind; and it is advisable to lash the control lever fast, so that the + controlling surfaces may not be blown about and possibly damaged. + </p> + <p> + “VETTING” BY EYE.—This should be practiced at every opportunity, + and, if persevered in, it is possible to become quite expert in diagnosing + by eye faults in flight efficiency, stability and control. + </p> + <p> + The aeroplane should be standing upon level ground, or, better than that, + packed up into its “flying position.” + </p> + <p> + Now stand in front of it and line up the leading edge with the main spar, + rear spar, and trailing edge. Their shadows can usually be seen through + the fabric. Allowance must, of course, be made for wash-in and wash-out; + otherwise, the parts I have specified should be parallel with each other. + </p> + <p> + Now line up the centre part of the main-plane with the tail-plane. The + latter should be horizontal. + </p> + <p> + Next, sight each interplane front strut with its rear strut. They should + be parallel. + </p> + <p> + Then, standing on one side of the aeroplane, sight all the front struts. + The one nearest to you should cover all the others. This applies to the + rear struts also. + </p> + <p> + Look for distortion of leading edges, main and rear spars, trailing edges, + tail-plane and controlling surfaces. + </p> + <p> + This sort of thing, if practiced constantly, will not only develop an + expert eye for diagnosis of faults, but will also greatly assist in + impressing upon the memory the characteristics and possible troubles of + the various types of aeroplanes. + </p> + <p> + MISHANDLING OF THE GROUND.—This is the cause of a lot of unnecessary + damage. The golden rule to observe is: PRODUCE NO BENDING STRESSES. + </p> + <p> + Nearly all the wood in an aeroplane is designed to take merely the stress + of direct compression, and it cannot be bent safely. Therefore, in packing + an aeroplane up from the ground, or in pulling or pushing it about, be + careful to stress it in such a way as to produce, as far as possible, only + direct compression stresses. For instance, if it is necessary to support + the lifting surface, 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 designed. Such supports should be covered + with soft packing in order to prevent the fabric from becoming damaged. + </p> + <p> + When pulling an aeroplane along, if possible, pull from the top of the + undercarriage struts. If necessary to pull from elsewhere, then do so by + grasping the interplane struts as low down as possible. + </p> + <p> + Never lay fabric-covered parts upon a concrete floor. Any slight movement + will cause the fabric to scrape over the floor with resultant damage. + </p> + <p> + Struts, spars, etc., should never be left about the floor, as in such + position they are likely to become scored. I have already explained the + importance of protecting the outside fibres of the wood. Remember also + that wood becomes distorted easily. This particularly applies to + interplane struts. If there are no proper racks to stand them in, then the + best plan is to lean them up against the wall in as near a vertical + position as possible. + </p> + <p> + TIME.—Learn to know the time necessary to complete any of the + various rigging jobs. This is really important. Ignorance of this will + lead to bitter disappointments in civil life; and, where Service flying is + concerned, it will, to say the least of it, earn unpopularity with senior + officers, and fail to develop respect and good work where men are + concerned. + </p> + <p> + THE AEROPLANE SHED.—This should be kept as clean and orderly as + possible. A clean, smart shed produces briskness, energy, and pride of + work. A dirty, disorderly shed nearly always produces slackness and poor + quality of work, lost tools and mislaid material. + </p> + <p> + <a name="link2H_GLOS" id="link2H_GLOS"> + <!-- H2 anchor --> </a> + </p> + <div style="height: 4em;"> + <br /><br /><br /><br /> + </div> + <h2> + GLOSSARY + </h2> + <h3> + Aeronautics—The science of aerial navigation. + </h3> + <p> + Aerofoil—A rigid structure, of large superficial area relative to + its thickness, designed to obtain, when driven through the air at an angle + inclined to the direction of motion, a reaction from the air approximately + at right angles to its surface. Always cambered when intended to secure a + reaction in one direction only. As the term “aerofoil” is hardly ever used + in practical aeronautics, I have, throughout this book, used the term + SURFACE, which, while academically incorrect, since it does not indicate + thickness, is a term usually used to describe the cambered lifting + surfaces, i.e., the “planes” or “wings,” and the stabilizers and the + controlling aerofoils. + </p> + <p> + Aerodrome—The name usually applied to a ground used for the practice + of aviation. It really means “flying machine,” but is never used in that + sense nowadays. + </p> + <p> + Aeroplane—A power-driven aerofoil with stabilizing and controlling + surfaces. + </p> + <p> + Acceleration—The rate of change of velocity. + </p> + <p> + Angle of Incidence—The angle at which the “neutral lift line” of a + surface attacks the air. + </p> + <p> + Angle of Incidence, Rigger's—The angle the chord of a surface makes + with a line parallel to the axis of the propeller. + </p> + <p> + Angle of Incidence, Maximum—The greatest angle of incidence at + which, for a given power, surface (including detrimental surface), and + weight, horizontal flight can be maintained. + </p> + <p> + Angle of Incidence, Minimum—The smallest angle of incidence at + which, for a given power, surface (including detrimental surface), and + weight, horizontal flight can be maintained. + </p> + <p> + Angle of Incidence, Best Climbing—That angle of incidence at which + an aeroplane ascends quickest. An angle approximately halfway between the + maximum and optimum angles. + </p> + <p> + Angle of Incidence, Optimum—The angle of incidence at which the + lift-drift ratio is the highest. + </p> + <p> + Angle, Gliding—The angle between the horizontal and the path along + which an aeroplane at normal flying speed, but not under engine power, + descends in still air. + </p> + <p> + Angle, Dihedral—The angle between two planes. + </p> + <p> + Angle, 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-tips. + </p> + <p> + Angle, 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 them. + </p> + <p> + Angle, Rigger's Longitudinal Dihedral—Ditto, but substituting + “chords” for “neutral life lines.” + </p> + <p> + Angle, Pitch—The angle at any given point of a propeller, at which + the blade is inclined to the direction of motion when the propeller is + revolving but the aeroplane stationary. + </p> + <p> + Altimeter—An instrument used for measuring height. + </p> + <p> + Air-Speed Indicator—An instrument used for measuring air pressures + or velocities. It consequently indicates whether the surface is securing + the requisite reaction for flight. Usually calibrated in miles per hour, + in which case it indicates the correct number of miles per hour at only + one altitude. 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 + altitude. It would be more correct to calibrate it in units of air + pressure. + </p> + <p> + Air Pocket—A local movement or condition of the air causing an + aeroplane to drop or lose its correct attitude. + </p> + <p> + Aspect-Ratio—The proportion of span to chord of a surface. + </p> + <p> + Air-Screw (Propeller)—A surface so shaped that its rotation about an + axis produces a force (thrust) in the direction of its axis. + </p> + <p> + Aileron—A controlling surface, usually situated at the wing-tip, the + operation of which turns an aeroplane about its longitudinal axis; causes + an aeroplane to tilt sideways. + </p> + <p> + Aviation—The art of driving an aeroplane. + </p> + <p> + Aviator—The driver of an aeroplane. + </p> + <p> + Barograph—A recording barometer, the charts of which can be + calibrated for showing air density or height. + </p> + <p> + Barometer—An instrument used for indicating the density of air. + </p> + <p> + Bank, to—To turn an aeroplane about its longitudinal axis (to tilt + sideways) when turning to left or right. + </p> + <p> + Biplane—An aeroplane of which the main lifting surface consists of a + surface or pair of wings mounted above another surface or pair of wings. + </p> + <p> + Bay—The space enclosed by two struts and whatever they are fixed to. + </p> + <p> + Boom—A term usually applied to the long spars joining the tail of a + “pusher” aeroplane to its main lifting surface. + </p> + <p> + Bracing—A system of struts and tie wires to transfer a force from + one point to another. + </p> + <p> + Canard—Literally “duck.” The name which was given to a type of + aeroplane of which the longitudinal stabilizing surface (empennage) was + mounted in front of the main lifting surface. Sometimes termed + “tail-first” aeroplanes, but such term is erroneous, as in such a design + the main lifting surface acts as, and is, the empennage. + </p> + <p> + Cabre—To fly or glide at an excessive angle of incidence; tail down. + </p> + <p> + Camber—Curvature. + </p> + <p> + Chord—Usually taken to be a straight line between the trailing and + leading edges of a surface. + </p> + <p> + Cell—The whole of the lower surface, that part of the upper surface + directly over it, together with the struts and wires holding them + together. + </p> + <p> + Centre (Line) of Pressure—A line running from wing-tip to wing-tip, + and through which all the air forces acting upon the surface may be said + to act, or about which they may be said to balance. + </p> + <p> + Centre (Line) of Pressure, Resultant—A line transverse to the + longitudinal axis, and the position of which is the resultant of the + centres of pressure of two or more surfaces. + </p> + <p> + Centre of Gravity—The centre of weight. + </p> + <p> + Cabane—A combination of two pylons, situated over the fuselage, and + from which anti-lift wires are suspended. + </p> + <p> + Cloche—Literally “bell.” Is applied to the bell-shaped construction + which forms the lower part of the pilot's control lever in a Bleriot + monoplane, and to which the control cables are attached. + </p> + <p> + Centrifugal Force—Every body which moves in a curved path is urged + outwards from the centre of the curve by a force termed “centrifugal.” + </p> + <p> + Control Lever—A lever by means of which the controlling surfaces are + operated. It usually operates the ailerons and elevator. The “joy-stick”. + </p> + <p> + Cavitation, Propeller—The tendency to produce a cavity in the air. + </p> + <p> + Distance Piece—A long, thin piece of wood (sometimes tape) passing + through and attached to all the ribs in order to prevent them from rolling + over sideways. + </p> + <p> + Displacement—Change of position. + </p> + <p> + Drift (of an aeroplane as distinct from the propeller)—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 + “detrimental” surface PLUS resistance due to “skin-friction.” Sometimes + termed “head-resistance.” + </p> + <p> + Drift, Active—Drift produced by the lifting surface. + </p> + <p> + Drift, Passive—Drift produced by the detrimental surface. + </p> + <p> + Drift (of a propeller)—Analogous to the drift of an aeroplane. It is + convenient to include “cavitation” within this term. + </p> + <p> + Drift, to—To be carried by a current of air; to make leeway. + </p> + <p> + Dive, to—To descend so steeply as to produce a speed greater than + the normal flying speed. + </p> + <p> + Dope, to—To paint a fabric with a special fluid for the purpose of + tightening and protecting it. + </p> + <p> + Density—Mass of unit volume, for instance, pounds per cubic foot. + </p> + <p> + Efficiency—Output Input + </p> + <p> + Efficiency (of an aeroplane as distinct from engine and propeller)— + </p> +<pre xml:space="preserve"> + Lift and Velocity + Thrust (= aeroplane drift) +</pre> + <p> + Efficiency, Engine—Brake horse-power + </p> +<pre xml:space="preserve"> + Indicated horse-power +</pre> + <p> + Efficiency, Propeller— + </p> +<pre xml:space="preserve"> + Thrust horse-power + Horse-power received from engine + (= propeller drift) +</pre> + <p> + NOTE.—The above terms can, of course, be expressed in foot-pounds. + It is then only necessary to divide the upper term by the lower one to + find the measure of efficiency. + </p> + <p> + Elevator—A controlling surface, usually hinged to the rear of the + tail-plane, the operation of which turns an aeroplane about an axis which + is transverse to the direction of normal horizontal flight. + </p> + <p> + Empennage—See “Tail-plane.” + </p> + <p> + Energy—Stored work. For instance, a given weight of coal or + petroleum stores a given quantity of energy which may be expressed in + foot-pounds. + </p> + <p> + Extension—That part of the upper surface extending beyond the span + of the lower surface. + </p> + <p> + Edge, Leading—The front edge of a surface relative to its normal + direction of motion. + </p> + <p> + Edge, Trailing—The rear edge of a surface relative to its normal + direction of motion. + </p> + <p> + 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 bear. + </p> + <p> + Fineness (of stream-line)—The proportion of length to maximum width. + </p> + <p> + Flying Position—A special position in which an aeroplane must be + placed when rigging it or making adjustments. It varies with different + types of aeroplanes. Would be more correctly described as “rigging + position.” + </p> + <p> + Fuselage—That part of an aeroplane containing the pilot, and to + which is fixed the tail-plane. + </p> + <p> + Fin—Additional keel-surface, usually mounted at the rear of an + aeroplane. + </p> + <p> + Flange (of a rib)—That horizontal part of a rib which prevents it + from bending sideways. + </p> + <p> + Flight—The sustenance of a body heavier than air by means of its + action upon the air. + </p> + <p> + Foot-pound—A measure of work representing the weight of 1 lb. raised + 1 foot. + </p> + <p> + Fairing—Usually made of thin sheet aluminum, wood, or a light + construction of wood and fabric; and bent round detrimental surface in + order to give it a “fair” or “stream-like” shape. + </p> + <p> + Gravity—Is the force of the Earth's attraction upon a body. It + decreases with increase of distance from the Earth. See “Weight.” + </p> + <p> + Gravity, Specific—Density of substance Density of water. Thus, if + the density of water is 10 lb. per unit volume, the same unit volume of + petrol, if weighing 7 lb., would be said to have a specific gravity of + 7/10, i.e., 0.7. + </p> + <p> + Gap (of an aeroplane)—The distance between the upper and lower + surfaces of a biplane. In a triplane or multiplane, the distance between a + surface and the one first above it. + </p> + <p> + Gap, Propeller—The distance, measured in the direction of the + thrust, between the spiral courses of the blades. + </p> + <p> + Girder—A structure designed to resist bending, and to combine + lightness and strength. + </p> + <p> + Gyroscope—A heavy circular wheel revolving at high speed, the effect + of which is a tendency to maintain its plane of rotation against + disturbing forces. + </p> + <p> + Hangar—An aeroplane shed. + </p> + <p> + Head-Resistance—Drift. The resistance of the air to the passage of a + body. + </p> + <p> + Helicopter—An air-screw revolving about a vertical axis, the + direction of its thrust being opposed to gravity. + </p> + <p> + Horizontal Equivalent—The plan view of a body whatever its attitude + may be. + </p> + <p> + Impulse—A force causing a body to gain or lose momentum. + </p> + <p> + Inclinometer—A curved form of spirit-level used for indicating the + attitude of a body relative to the horizontal. + </p> + <p> + Instability—An inherent tendency of a body, which, if the body is + disturbed, causes it to move into a position as far as possible away from + its first position. + </p> + <p> + Instability, Neutral—An inherent tendency of a body to remain in the + position given it by the force of a disturbance, with no tendency to move + farther or to return to its first position. + </p> + <p> + Inertia—The inherent resistance to displacement of a body as + distinct from resistance the result of an external force. + </p> + <p> + Joy-Stick—See “Control Lever.” + </p> + <p> + Keel-Surface—Everything to be seen when viewing an aeroplane from + the side of it. + </p> + <p> + King-Post—A bracing strut; in an aeroplane, usually passing through + a surface and attached to the main spar, and from the end or ends of which + wires are taken to spar, surface, or other part of the construction in + order to prevent distortion. When used in connection with a controlling + surface, it usually performs the additional function of a lever, control + cables connecting its ends with the pilot's control lever. + </p> + <p> + 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 motion. + </p> + <p> + Lift, Margin of—The height an aeroplane can gain in a given time and + starting from a given altitude. + </p> + <p> + Lift-Drift Ratio—The proportion of lift to drift. + </p> + <p> + Loading—The weight carried by an aerofoil. Usually expressed in + pounds per square foot of superficial area. + </p> + <p> + Longeron—The term usually applied to any long spar running + length-ways of a fuselage. + </p> + <p> + Mass—The mass of a body is a measure of the quantity of material in + it. + </p> + <p> + Momentum—The product of the mass and velocity of a body is known as + “momentum.” + </p> + <p> + Monoplane—An aeroplane of which the main lifting surface consists of + one surface or one pair of wings. + </p> + <p> + Multiplane—An aeroplane of which the main lifting surface consists + of numerous surfaces or pairs of wings mounted one above the other. + </p> + <p> + Montant—Fuselage strut. + </p> + <p> + Nacelle—That part of an aeroplane containing the engine and pilot + and passenger, and to which the tail plane is not fixed. + </p> + <p> + Neutral Lift Line—A line taken through a surface in a forward + direction relative to its direction of motion, and starting from its + trailing edge. If the attitude of the surface is such as to make the said + line coincident with the direction of motion, it results in no lift, the + reaction then consisting solely of drift. The position of the neutral lift + line, i.e., the angle it makes with the chord, varies with differences of + camber, and it is found by means of wind-tunnel research. + </p> + <p> + Newton's Laws of Motion—1. If a body be at rest, it will remain at + rest; or, if in motion, it will move uniformly in a straight line until + acted upon by some force. + </p> + <p> + 2. The rate of change of the quantity of motion (momentum) is proportional + to the force which causes it, and takes place in the direction of the + straight line in which the force acts. If a body be acted upon by several + forces, it will obey each as though the others did not exist, and this + whether the body be at rest or in motion. + </p> + <p> + 3. To every action there is opposed an equal and opposite reaction. + </p> + <p> + Ornithopter (or Orthopter)—A flapping wing design of aircraft + intended to imitate the flight of a bird. + </p> + <p> + Outrigger—This term is usually applied to the framework connecting + the main surface with an elevator placed in advance of it. Sometimes + applied to the “tail-boom” framework connecting the tail-plane with the + main lifting surface. + </p> + <p> + Pancake, to—To “stall ” + </p> + <p> + Plane—This term is often applied to a lifting surface. Such + application is not quite correct, since “plane” indicates a flat surface, + and the lifting surfaces are always cambered. + </p> + <p> + Propeller—See “Air-Screw.” + </p> + <p> + Propeller, Tractor—An air-screw mounted in front of the main lifting + surface. + </p> + <p> + Propeller, Pusher—An air-screw mounted behind the main lifting + surface. + </p> + <p> + Pusher—An aeroplane of which the propeller is mounted behind the + main lifting surface. + </p> + <p> + Pylon—Any V-shaped construction from the point of which wires are + taken. + </p> + <p> + Power—Rate of working. + </p> + <p> + Power, Horse—One horse-power represents a force sufficient to raise + 33,000 lbs. 1 foot in a minute. + </p> + <p> + Power, Indicated Horse—The I.H.P. of an engine is a measure of the + rate at which work is done by the pressure upon the piston or pistons, as + distinct from the rate at which the engine does work. The latter is + usually termed “brake horse-power,” since it may be measured by an + absorption brake. + </p> + <p> + Power, Margin of—The available quantity of power above that + necessary to maintain horizontal flight at the optimum angle. + </p> + <p> + Pitot Tube—A form of air-speed indicator consisting of a tube with + open end facing the wind, which, combined with a static pressure or + suction tube, is used in conjunction with a gauge for measuring air + pressures or velocities. (No. 1 in diagram.) + </p> + <p> + Pitch, Propeller—The distance a propeller advances during one + revolution supposing the air to be solid. + </p> + <p> + Pitch, to—To plunge nose-down. + </p> + <p> + Reaction—A force, equal and opposite to the force of the action + producing it. + </p> + <p> + Rudder—A controlling surface, usually hinged to the tail, the + operation of which turns an aeroplane about an axis which is vertical in + normal horizontal flight; causes an aeroplane to turn to left or right of + the pilot. + </p> + <p> + Roll, to—To turn about the longitudinal axis. + </p> + <p> + Rib, Ordinary—A light curved wooden part mounted in a fore and aft + direction within a surface. The ordinary ribs give the surface its camber, + carry the fabric, and transfer the lift from the fabric to the spars. + </p> + <p> + Rib, Compression—Acts as an ordinary rib, besides bearing the stress + of compression produced by the tension of the internal bracing wires. + </p> + <p> + Rib, False—A subsidiary rib, usually used to improve the camber of + the front part of the surface. + </p> + <p> + Right and Left Hand—Always used relative to the position of the + pilot. When observing an aeroplane from the front of it, the right hand + side of it is then on the left hand of the observer. + </p> + <p> + Remou—A local movement or condition of the air which may cause + displacement of an aeroplane. + </p> + <p> + Rudder-Bar—A control lever moved by the pilot's feet, and operating + the rudder. + </p> + <p> + Surface—See “Aerofoil.” + </p> + <p> + Surface, Detrimental—All exterior parts of an aeroplane including + the propeller, but excluding the (aeroplane) lifting and (propeller) + thrusting surfaces. + </p> + <p> + Surface, Controlling—A surface the operation of which turns an + aeroplane about one of its axes. + </p> + <p> + Skin-Friction—The friction of the air with roughness of surface. A + form of drift. + </p> + <p> + Span—-The distance from wing-tip to wing-tip. + </p> + <p> + Stagger—The distance the upper surface is forward of the lower + surface when the axis of the propeller is horizontal. + </p> + <p> + Stability—The inherent tendency of a body, when disturbed, to return + to its normal position. + </p> + <p> + Stability, Directional—The stability about an axis which is vertical + during normal horizontal flight, and without which an aeroplane has no + natural tendency to remain upon its course. + </p> + <p> + Stability, Longitudinal—The stability of an aeroplane about an axis + transverse to the direction of normal horizontal flight, and without which + it has no tendency to oppose pitching and tossing. + </p> + <p> + Stability, Lateral—The stability of an aeroplane about its + longitudinal axis, and without which it has no tendency to oppose sideways + rolling. + </p> + <p> + Stabilizer—A surface, such as fin or tail-plane, designed to give an + aeroplane inherent stability. + </p> + <p> + Stall, to—To give or allow an aeroplane an angle of incidence + greater than the “maximum” angle, the result being a fall in the + lift-drift ratio, the lift consequently becoming less than the weight of + the aeroplane, which must then fall, i.e., “stall” or “pancake.” + </p> + <p> + Stress—Burden or load. + </p> + <p> + Strain—Deformation produced by stress. + </p> + <p> + Side-Slip, to—To fall as a result of an excessive “bank” or “roll.” + </p> + <p> + Skid, to—To be carried sideways by centrifugal force when turning to + left or right. + </p> + <p> + Skid, Undercarriage—A spar, mounted in a fore and aft direction, and + to which the wheels of the undercarriage are sometimes attached. Should a + wheel give way the skid is then supposed to act like the runner of a + sleigh and to support the aeroplane. + </p> + <p> + Skid, Tail—A piece of wood or other material, orientable, and fitted + with shock absorbers, situated under the tail of an aeroplane in order to + support it upon the ground and to absorb the shock of alighting. + </p> + <p> + Section—Any separate part of the top surface, that part of the + bottom surface immediately underneath it, with their struts and wires. + </p> + <p> + Spar—Any long piece of wood or other material. + </p> + <p> + Spar, Main—A spar within a surface and to which all the ribs are + attached, such spar being the one situated nearest to the centre of + pressure. It transfers more than half the lift from the ribs to the + bracing. + </p> + <p> + Spar, Rear—A spar within a surface, and to which all the ribs are + attached, such spar being situated at the rear of the centre of pressure + and at a greater distance from it than is the main spar. It transfers less + than half of the lift from the ribs to the bracing. + </p> + <p> + Strut—Any wooden member intended to take merely the stress of direct + compression. + </p> + <p> + Strut, Interplane—A strut holding the top and bottom surfaces apart. + </p> + <p> + Strut, Fuselage—A strut holding the fuselage longerons apart. It + should be stated whether top, bottom, or side. If side, then it should be + stated whether right or left hand. Montant. + </p> + <p> + Strut, Extension—A strut supporting an “extension” when not in + flight. It may also prevent the extension from collapsing upwards during + flight. + </p> + <p> + Strut, Undercarriage— + </p> + <p> + Strut, Dope—A strut within a surface, so placed as to prevent the + tension of the doped fabric from distorting the framework. + </p> + <p> + Serving—To bind round with wire, cord, or similar material. Usually + used in connection with wood joints and wire cable splices. + </p> + <p> + Slip, Propeller—The pitch less the distance the propeller advances + during one revolution. + </p> + <p> + Stream-Line—A form or shape of detrimental surface designed to + produce minimum drift. + </p> + <p> + Toss, to—To plunge tail-down. + </p> + <p> + Torque, Propeller—The tendency of a propeller to turn an aeroplane + about its longitudinal axis in a direction opposite to that in which the + propeller revolves. + </p> + <p> + Tail-Slide—A fall whereby the tail of an aeroplane leads. + </p> + <p> + Tractor—An aeroplane of which the propeller is mounted in front of + the main lifting surface. + </p> + <p> + Triplane—An aeroplane of which the main lifting surface consists of + three surfaces or pairs of wings mounted one above the other. + </p> + <p> + Tail-Plane—A horizontal stabilizing surface mounted at some distance + behind the main lifting surface. Empennage. + </p> + <p> + Turnbuckle—A form of wire-tightener, consisting of a barrel into + each end of which is screwed an eyebolt. Wires are attached to the + eyebolts and the required degree of tension is secured by means of + rotating the barrel. + </p> + <p> + Thrust, Propeller—See “Air-Screw.” + </p> + <p> + Undercarriage—That part of an aeroplane beneath the fuselage or + nacelle, and intended to support the aeroplane when at rest, and to absorb + the shock of alighting. + </p> + <p> + Velocity—Rate of displacement; speed. + </p> + <p> + Volplane—A gliding descent. + </p> + <p> + Weight—Is a measure of the force of the Earth's attraction (gravity) + upon a body. The standard unit of weight in this country is 1 lb., and is + the force of the Earth's attraction on a piece of platinum called the + standard pound, deposited with the Board of Trade in London. At the centre + of the Earth a body will be attracted with equal force in every direction. + It will therefore have no weight, though its mass is unchanged. Gravity, + of which weight is a measure, decreases with increase of altitude. + </p> + <p> + Web (of a rib)—That vertical part of a rib which prevents it from + bending upwards. + </p> + <p> + Warp, to—To distort a surface in order to vary its angle of + incidence. To vary the angle of incidence of a controlling surface. + </p> + <p> + Wash—The disturbance of air produced by the flight of an aeroplane. + </p> + <p> + Wash-in—An increasing angle of incidence of a surface towards its + wing-tip. + </p> + <p> + Wash-out—A decreasing angle of incidence of a surface towards its + wing-tip. + </p> + <p> + Wing-tip—The right- or left-hand extremity of a surface. + </p> + <p> + Wire—A wire is, in Aeronautics, always known by the name of its + function. + </p> + <p> + Wire, Lift or Flying—A wire opposed to the direction of lift, and + used to prevent a surface from collapsing upward during flight. + </p> + <p> + Wire, Anti-lift or Landing—A wire opposed to the direction of + gravity, and used to sustain a surface when it is at rest. + </p> + <p> + Wire, Drift—A wire opposed to the direction of drift, and used to + prevent a surface from collapsing backwards during flight. + </p> + <p> + Wire, Anti-drift—A wire opposed to the tension of a drift wire, and + used to prevent such tension from distorting the framework. + </p> + <p> + Wire, Incidence—A wire running from the top of an interplane strut + to the bottom of the interplane strut in front of or behind it. It + maintains the “stagger” and assists in maintaining the angle of incidence. + Sometimes termed “stagger wire.” + </p> + <p> + Wire, Bracing—Any wire holding together the framework of any part of + an aeroplane. It is not, however, usually applied to the wires described + above unless the function performed includes a function additional to + those described above. Thus, a lift wire, while strictly speaking a + bracing wire, is not usually described as one unless it performs the + additional function of bracing some well-defined part such as the + undercarriage. It will then be said to be an “undercarriage bracing lift + wire.” It might, perhaps, be acting as a drift wire also, in which case it + will then be de-scribed as an “undercarriage bracing lift-drift wire.” It + should always be stated whether a bracing wire is (1) top, (2) bottom, (3) + cross, or (4) side. If a “side bracing wire,” then it should be stated + whether right- or left-hand. + </p> + <p> + Wire, Internal Bracing—A bracing wire (usually drift or anti-drift) + within a surface. + </p> + <p> + Wire, Top Bracing—A bracing wire, approximately horizontal and + situated between the top longerons of fuselate, between top tail booms, or + at the top of similar construction. + </p> + <p> + Wire, Bottom Bracing—Ditto, substituting “bottom” for “top.” + </p> + <p> + Wire, Side Bracing—A bracing wire crossing diagonally a side bay of + fuselage, tail boom bay, undercarriage side bay or centre-section side + bay. This term is not usually used with reference to incidence wires, + although they cross diagonally the side bays of the cell. It should be + stated whether right- or left-hand. + </p> + <p> + Wire, Cross Bracing—A bracing wire, the position of which is + diagonal from right to left when viewing it from the front of an + aeroplane. + </p> + <p> + Wire, Control Bracing—A wire preventing distortion of a controlling + surface. + </p> + <p> + Wire, Control—A wire connecting a controlling surface with the + pilot's control lever, wheel, or rudder-bar. + </p> + <p> + Wire, Aileron Gap—A wire connecting top and bottom ailerons. + </p> + <p> + Wire, Aileron Balance—A wire connecting the right- and left-hand top + ailerons. Sometimes termed the “aileron compensating wire.” + </p> + <p> + Wire, Snaking—A wire, usually of soft metal, wound spirally or tied + round another wire, and attached at each end to the framework. Used to + prevent the wire round which it is “snaked” from becoming, in the event of + its displacement, entangled with the propeller. + </p> + <p> + Wire, Locking—A wire used to prevent a turnbuckle barrel or other + fitting from losing its adjustment. + </p> + <p> + Wing—Strictly speaking, a wing is one of the surfaces of an + ornithopter. The term is, however, often applied to the lifting surface of + an aeroplane when such surface is divided into two parts, one being the + left-hand “wing,” and the other the right-hand “wing.” + </p> + <p> + Wind-Tunnel—A large tube used for experimenting with surfaces and + models, and through which a current of air is made to flow by artificial + means. + </p> + <p> + Work—Force X displacement. + </p> + <p> + Wind-Screen—A small transparent screen mounted in front of the pilot + to protect his face from the air pressure. + </p> + <p> + <a name="link2H_FOOT" id="link2H_FOOT"> + <!-- H2 anchor --> </a> + </p> + <div style="height: 4em;"> + <br /><br /><br /><br /> + </div> + <h2> + FOOTNOTES:] + </h2> + <p> + <a name="linknote-1" id="linknote-1"> + <!-- Note --></a> + </p> + <p class="foot"> + 1 (<a href="#linknoteref-1">return</a>)<br /> [ Propeller Slip: As the + propeller screws through the air, the latter to a certain extent gives + back to the thrust of the propellor blades, just as the shingle on the + beach slips back as you ascend it. Such “give-back” is known as “slip,” + and anyone behind the propellor will feel the slip as a strong draught of + air.] + </p> + <p> + <a name="linknote-2" id="linknote-2"> + <!-- Note --></a> + </p> + <p class="foot"> + 2 (<a href="#linknoteref-2">return</a>)<br /> [ Helicopter. An air-screw + revolving upon a vertical axis. If driven with sufficient power, it will + lift vertically, but having regard to the mechanical difficulties of such + construction, 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 axis.] + </p> + <p> + <a name="linknote-3" id="linknote-3"> + <!-- Note --></a> + </p> + <p class="foot"> + 3 (<a href="#linknoteref-3">return</a>)<br /> [ Pancakes: Pilot's slang for + stalling an aeroplane and dropping like a pancake.] + </p> + <p> + <a name="linknote-4" id="linknote-4"> + <!-- Note --></a> + </p> + <p class="foot"> + 4 (<a href="#linknoteref-4">return</a>)<br /> [ Morane parasol: 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 earth.] + </p> + <p> + <a name="linknote-5" id="linknote-5"> + <!-- Note --></a> + </p> + <p class="foot"> + 5 (<a href="#linknoteref-5">return</a>)<br /> [ Skin friction is that part + of the drift due to the friction of the air with roughnesses upon the + surface of the aeroplane.] + </p> + <p> + <a name="linknote-6" id="linknote-6"> + <!-- Note --></a> + </p> + <p class="foot"> + 6 (<a href="#linknoteref-6">return</a>)<br /> [ Banking: 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 turn. + To minimize such action the pilot banks, i.e., tilts, the aeroplane + sideways in order to oppose the underside of the planes to the air. The + aeroplane will not then skid outwards beyond the slight skid necessary to + secure a sufficient pressure of air to balance the centrifugal force.] + </p> + <p> + <a name="linknote-7" id="linknote-7"> + <!-- Note --></a> + </p> + <p class="foot"> + 7 (<a href="#linknoteref-7">return</a>)<br /> [ An explanation of the way + in which the wash-out is combined with a wash-in to offset propellor + torque will be found on p. 82.] + </p> + <p> + <a name="linknote-8" id="linknote-8"> + <!-- Note --></a> + </p> + <p class="foot"> + 8 (<a href="#linknoteref-8">return</a>)<br /> [ A.M.'s: Air Mechanics.] + </p> + <p> + <a name="linknote-9" id="linknote-9"> + <!-- Note --></a> + </p> + <p class="foot"> + 9 (<a href="#linknoteref-9">return</a>)<br /> [ Butt means to thicken at + the end. Screw means to machine a thread on the butt-end of the wire, and + in this way the wire can make connection with the desired place by being + screwed into a metal fitting, thus eliminating the disadvantage of the + unsatisfactory loop.] + </p> + <p> + <a name="linknote-10" id="linknote-10"> + <!-- Note --></a> + </p> + <p class="foot"> + 10 (<a href="#linknoteref-10">return</a>)<br /> [ Deviation curve: A curved + line indicating any errors in the compass.] + </p> + <p> + <a name="linknote-11" id="linknote-11"> + <!-- Note --></a> + </p> + <p class="foot"> + 11 (<a href="#linknoteref-11">return</a>)<br /> [ A propeller screws + through the air, and the distance it advances during one revolution, + supposing the air to be solid, is known as the pitch. The pitch, which + depends upon the angle of the propeller blades, must be equal to the speed + of the aeroplane, plus the slip, and if, on account of the rarity of the + air the speed of the aeroplane increases, then the angle and pitch should + be correspondingly increased. Propellers with a pitch capable of being + varied by the pilot are the dream of propeller designers. For explanation + of “slip” see Chapter IV. on propellers.] + </p> + <p> + <a name="linknote-12" id="linknote-12"> + <!-- Note --></a> + </p> + <p class="foot"> + 12 (<a href="#linknoteref-12">return</a>)<br /> [ Getting out of my depth? + Invading the realms of fancy? Well, perhaps so, 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 altitude.] + </p> + <p> + <a name="linknote-13" id="linknote-13"> + <!-- Note --></a> + </p> + <p class="foot"> + 13 (<a href="#linknoteref-13">return</a>)<br /> [ Box-kite. The first crude + form of biplane.] + </p> + <p> + <a name="linknote-14" id="linknote-14"> + <!-- Note --></a> + </p> + <p class="foot"> + 14 (<a href="#linknoteref-14">return</a>)<br /> [ See Newton's laws in the + Glossary at the end of the book.] + </p> + <p> + <a name="linknote-15" id="linknote-15"> + <!-- Note --></a> + </p> + <p class="foot"> + 15 (<a href="#linknoteref-15">return</a>)<br /> [ See “Aerofoil” in the + Glossary.] + </p> + <p> + <a name="linknote-16" id="linknote-16"> + <!-- Note --></a> + </p> + <p class="foot"> + 16 (<a href="#linknoteref-16">return</a>)<br /> [ “In effect” because, + although there may be actually the greatest proportion of keel-surface In + front of the vertical axis, such surface may be much nearer to the axis + than is the keel-surface towards the tail. The latter may then be actually + less than the surface in front, but, being farther from the axis, it has a + greater leverage, and consequently is greater in effect than the surface + in front.] + </p> + <p> + <br /><br /> + </p> +<pre xml:space="preserve"> + + + + + +End of the Project Gutenberg EBook of The Aeroplane Speaks, by H. Barber + +*** END OF THIS PROJECT GUTENBERG EBOOK THE AEROPLANE SPEAKS *** + +***** This file should be named 818-h.htm or 818-h.zip ***** +This and all associated files of various formats will be found in: + http://www.gutenberg.org/8/1/818/ + +Produced by Charles Keller, and David Widger + +Updated editions will replace the previous one--the old editions +will be renamed. + +Creating the works from public domain print editions means that no +one owns a United States copyright in these works, so the Foundation +(and you!) can copy and distribute it in the United States without +permission and without paying copyright royalties. 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