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."
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.
"Bit b.u.mpy 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 s.p.a.ce.
"My eye!" e.j.a.c.u.l.a.t.es 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 s.p.a.ce. 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, crowned with white filmy lace-like streaks of vapour. And withal the increasing sense with alt.i.tude of vast, clean, silent solitudes of s.p.a.ce.
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.
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.
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!
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 mult.i.tudes of men shall awake, and by their unceasing toil and the spirit within them produce marvels of which the Aeroplane is but the harbinger.
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.
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 pa.s.s 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."
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 alt.i.tude 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."
"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 alt.i.tude and rarity of air_, and there is no limit to the speed through s.p.a.ce if only our strength remains. And with oxygen for pilot and pa.s.sengers and a steeper pitch[11]
for the Propeller we may then circle the Earth in a day!"
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 ma.s.s of the aeroplane become terrific. And, bearing that in mind, remember that with alt.i.tude _gravity decreases_. There may yet be literally other worlds to conquer.[12]
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 a.s.sumes 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 Compa.s.s 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.
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.
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. "Crash, Bang, Rattle----!----!----!" and worse than that, yells the Exhaust, and the Aeroplane, who is a gentleman and not a box kite,[13] 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!"
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 lower 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.
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!
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.
The Struts and the Spars, which felt so awkward at first, have bedded themselves in their sockets, and are taking the compression stresses uncomplainingly.
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.
"Well, what result?" calls the Flight-Commander to the Pilot.
"A hundred miles an hour and a thousand feet a minute," he briefly replies.
"And a very good result too," says the Aeroplane, complacently, as he is carefully wheeled into his shed.
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.
[Footnote 8: A.M."s: Air Mechanics.]
[Footnote 9: b.u.t.t means to thicken at the end. Screw means to machine a thread on the b.u.t.t-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.]
[Footnote 10: Deviation Curve: A curved line indicating any errors in the compa.s.s.]
[Footnote 11: 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.]
[Footnote 12: Getting out of my depth? Invading the realms of fancy?
Well, perhaps so, but at any rate it is possible that extraordinary speed through s.p.a.ce may be secured if means are found to maintain the impulse of the engine and the thrust-drift efficiency of the propeller at great alt.i.tude.]
[Footnote 13: Box-kite. The first crude form of biplane.]
PART IV
"CROSS COUNTRY
The Aeroplane had been designed and built, and tested in the air, and now it stood on the Aerodrome ready for its first "cross-country flight.
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.
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.
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 alt.i.tudes to bother the Pilot, and the air none too clear for the observation of landmarks.
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!"
"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 very 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!"
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, "Tanks full of petrol and oil?"
"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."