The Aeroplane Speaks.

by H. Barber.

MOTIVE

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_ a.s.sistance to the Pilot and his invaluable a.s.sistant 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.

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.

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 ill.u.s.trations reproduced at the end of this book.

PROLOGUE

PART I

THE ELEMENTARY PRINCIPLES AIR THEIR GRIEVANCES

The Lecture Hall at the Royal Flying Corps School for Officers was deserted. The pupils had dispersed, and the Officer Instructor, more f.a.gged than any pupil, was out on the aerodrome watching the test of a new machine.

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 an ill.u.s.tration thus:

[Ill.u.s.tration]

"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."

"Quite right," said the Angle. "That's me, and I'm the famous Angle of Incidence."

"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."

"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.

[Ill.u.s.tration: The action of the surface upon the air.]

"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 ma.s.s of air displaced, but also the result of the Speed and consequent Force 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 alt.i.tudes and consequent density of air they at present experience, I increase at about the Square of the Speed.

"Oh, I'm a most complex and interesting personality, I a.s.sure 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."

[Ill.u.s.tration]

"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 or Weight, then--there you are--Flight! And nothing mysterious about it at all."

"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 a.s.sure you that I'm not to be won quite so easily."

"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."

"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."

[Ill.u.s.tration]

"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.

"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.

"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 a.s.sure you, to make me quite perfect and of infinite service to Miss Efficiency."

[Ill.u.s.tration]

"That's not practical politics," said the Surface. "The way you talk one would think you were drawing 400 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."

"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."

"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."

"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."

"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."

"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:

[Ill.u.s.tration]

"Well, what do you think of that?" they all cried to the Drift.

"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."

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:

[Ill.u.s.tration]

Said the Blackboard, "That's not half bad! It really begins to look something like the real thing, eh?"

"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.

"Oh, dear! Oh, dear!" she cried. "I'm always getting into trouble. What _will_ the Designer say?"

"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."