3. Danger.—The airplane is by no means so dangerous as the public has been led to think from the exploits of the daredevil circus performers of the past 10 years; with careful manipulation it will make trips day after day without any damage. However, it is not a foolproof machine and there remains an element of danger on this account, which it is hoped will one day be eliminated.
Future Uses of the Airplane.—Future uses of the airplane are many after the war is over. The postal service of several governments are considering this means of mail delivery; the sports use as in the past will continue to flourish; express carrying may be expected in inaccessible countries where railroads and roads do not give access and where high-speed delivery by countless airplanes would aid materially in the development of newly opened countries. For airplane transportation will require no expensive right-of-way, rubber-tire renewals, etc. Minor uses of airplanes are on such duties as forest-fire patrol, working at life-saving stations, etc.
American Airplane Industries.—The magnitude of the airplane industry in this country is great, although not so great as in Europe. Leading business men have invested in this industry with the firm belief that it will become a profitable one, irrespective of war. We see a number of leading bankers and also automobile manufacturers in various parts of the country putting their money into this new industry. Now that a great demand has sprung up on our side of the water for airplanes, we will expect to see this industry increase more rapidly still. The only result can be, from all the interest and importance attached to aviation, that after the war is over, large commercial uses will develop which will offer employment to those who go into the work at this time for military reasons. No one can predict exactly what turn the situation will take, but there is every indication that aviation has graduated from the primary class of experimental work and is to be considered now as an industry along with the automobile business, motor-boat business, etc.
CHAPTER III
PRINCIPLES OF FLIGHT
Support of an Airplane by Its Wings.—An airplane is supported just as definitely as though on top of a post, and by the same law, namely reaction. If you try to sweep the air downward with a wing held at a slight angle, the air just before it consents to be pushed downward, delivers a momentary reaction which is upward. If you have a bag of air in your hand it exerts no push upward of course; but the minute you give it a quick push downward it resists, due to its inertia, thus delivering an upward “reaction” against your hand.
Whenever you move anything, it reacts an amount just equal to the force that is moving it; if you move a bullet out of a gun, just before starting the bullet reacts and you have “kick.” If you should shoot a thousand guns downward, the reaction would be considerable, and for the instant might be sufficient to support heavy weight.
The airplane is a device for pushing downward millions of little bullets, made out of air and exceedingly small and light. The wing of an airplane sweeps through these bullets, or molecules, of air like a horizontal plow, wedges the particles downward in vast numbers and in a continual stream, making up in amount what is lacking in weight, so that as long as the airplane rushes along, there are many thousands of cubic feet of air forced down beneath its wings, delivering up a reaction that results in complete support for the machine. This reaction is just as definite and secure as though the machine were supported from the ground on wheels, but it disappears entirely when the airplane is at rest. Part of the whir of a training machine as it glides back to earth is made by the air driven downward from the wings; the same phenomenon may be noticed when a bat flies close to your ears at night, and if you were a few feet below the airplane as it flew, you would feel the rush of air driven downward from its wings (see Fig. [16]).
The net result of all the reactive pushes from this air is lift. It may amount to several pounds for every square foot of the wing surface.
This is all that need be said about why the air supports an airplane; all you have to remember is that as long as you have the forward sweeping movement, you will have the lift.
The forward movement is absolutely essential, however, and to maintain it requires a lot of horsepower and gasoline. For it is by means of the engine and propeller that this forward movement is maintained. The engine is a device for creating forward movement—the propeller drives the machine ahead in exactly the same way as is the case in a torpedo, or steamboat.