The Aeroplane

by Claude Grahame-White; Harry Harper

	IN NORMAL FLIGHT. Fig. 53.—Machine “side-slipping” in a gust.
STRUCK BY AN ABNORMAL GUST.
MACHINE SLIPPING SIDEWAYS.

In such a predicament, two things only can save the airman; one his height above the ground, the other his nerve and presence of mind. If he is flying low when his machine side-slips, nothing can avert disaster. Falling at first sideways in a helpless lurch, then diving violently, the craft will strike ground with shattering force—completely beyond its pilot’s control. But if the airman is flying high, and granted he is a man of experience, he may escape even the worst of side-slips, and how he does so is as follows: as his machine slips he puts forward his elevating-lever as far as it will go, throws over his rudder to help the action of the elevator, and sets his motor at its fullest power—these actions seeming, in themselves, merely to aggravate the peril by causing the craft to fall more quickly. But the pilot knows what he is doing; he knows that, so long as his craft slips sideways, it is impossible for his controlling planes to act, seeing that they are effective only when the machine moves forward through the air. What he seeks to do, therefore, is to convert the side-slip into a forward dive. If he can do this—if he has space for the manœuvre before the machine strikes ground—he knows he can avert disaster.

In throwing over his elevating-lever, and accelerating his motor, his aim would be to make his machine fall forward more rapidly than it is slipping sideways; and, as a rule, under the combined thrust of the motor, and the extreme angles of elevating-plane and rudder, the craft will—after a sickening slip, perhaps of several hundred feet—begin to lose its sideway motion and plunge straight downward. His elevating plane will then become operative, tending to check this dive and bring up the bow of the machine; and at the same time, feeling he has regained control, the pilot will throttle down his motor so as to reduce the speed of his machine. In this way, responding to the action of its elevator, the craft will pause in its downward rush, and sweep forward again upon an even keel. But the actions of the pilot, in such a quandary, need to be accurately and boldly made; and unless his craft flies high, no skill can save it. If he has not a thousand feet or more below him, he will be dashed to death before his manœuvre has time to take effect.

The moral, therefore, lay in flying high, and it was one that pilots respected. Instead of passing across country at a few hundred feet, they began soon to ascend 3000 feet and more; and at such altitudes, apart from the greater safety in case of side-slip, an airman found usually a steadier and less gusty wind, and was in a better position to choose some landing-point should his motor fail suddenly.

When starting across country, particularly in the early days, a pilot had to consider very seriously the question of the failing of his motor. So long as he had an aerodrome below him, its smooth surface providing an alighting spot, he felt no great concern. But in flying across country, should his motor stop, he might find himself above a forest, or a sheet of water, or such rough and broken land that his machine would be damaged were he to alight upon it. But here again, as in the case of side-slip, altitude would tend to safety.

In the stoppage of its motor, when a craft is in flight, several factors need consideration; but one should clearly be understood: even if his engine does fail while he is passing through the air, a pilot is not helpless, nor does his machine fall to the ground. As he flies, of course, it is the thrust of his motor, acting through the medium of the propeller, that keeps his craft moving forward; and so long as this thrust is there, forcing his planes against the air and causing them to lift their load, the machine will fly ahead. But what happens should the engine fail, and the machine cease to be propelled? The first effect is that the craft begins to lose its speed, and as it does this its planes are less operative. Unless he can restore his forward speed, therefore, and so maintain the lift of his planes, the pilot is in peril. Were he merely to sit still after his engine failed, and do nothing to save himself, he would be in a position of the greatest risk. What would happen would be that his craft, having no power thrusting it against the air, would come gradually to a standstill; then, its planes exercising no further lift, it would lose equilibrium and fall.

But there is another force the airman can use, even when his motor fails entirely; and this is the downward pull of gravity, which acts unceasingly upon his machine. He must, at all costs, restore the speed of his craft; not only that its main-wings may bear their weight, but that its controlling-planes may continue operative, and enable him to steer towards a landing-point. What he does, therefore, when he hears his motor stop, is to tilt his elevating lever and send his machine upon a dive. Thus, even with no motor to propel him, he can still fly. It is gravity now that moves his machine, and so long as he keeps his lever forward, and sends his craft downward upon a gradually sloping path, he has perfect control and need not fear a fall. Air is still being forced under his planes; therefore, they bear their load; and, seeing that the machine is moving forward, its rudder and other controlling planes are able to do their work. The airman is, in fact, as much in command of his machine as he was before its motor stopped—save for one vital difference. While his motor ran he could fly where he pleased; but now he is obliged to glide downward. He is, indeed, in the same position as was Lilienthal, or any of the men who soared from hilltops. But, being say 1000 feet or more high when his engine stops, he has the advantage of a long glide before he reaches ground; and this gives him a chance, surveying the land below him, to pick a smooth landing-point that may lie in his path. If well-designed, an aeroplane will glide a long way after its motor has failed, as is indicated by [Fig. 54]. In this case, representing an actual test with a military machine, the motor has stopped at an altitude of between 1200 and 1400 feet, and the craft glides, before touching ground, a distance of nearly 9000 feet.

Fig. 54.—The gliding angle of a plane.