Engineering Wonders of the World
Volume III

THE THEORY AND PRINCIPLES OF THE AEROPLANE. THE physical laws governing the suc- cessful operation of an aeroplane are at the present time still being ex- plored. Much valuable research work has been done by Lilienthal, Chanute, Maxim, Phillips, Lanchester, Langley, the Wrights, and others ; and conclusions, capable of ex- perimental proof, have been arrived at, so that human flight has moved from the posi- tion of mere aspiration into the region of accomplished fact. A great deal remains to be done, however, before man will rival the birds in this latest form of locomotion. The scientific literature dealing with aero- statics is as yet comparatively scanty, and of a nature which may well scare the unscientific reader. It is our desire to avoid here tiresome technicalities, formulae, and equations, and to present, in as simple a form as possible, the physical facts and problems with which experimenters have to deal. Most of us have handled the toy kite, a very simple apparatus which is subservient to essentially the same laws as is the aeroplane. When a kite is launched in a wind sufficiently strong to lift it at all, it speedily rises to a cer- tain elevation, at which it re- The Kite, mains so long as the velocity of the wind does not change. The steadiness of the kite implies an equilibrium of the forces acting upon it. These forces, as shown in Fig. 1, are : G, gravity, which remains prac- tically unaltered under all conditions ; W, the pressure of wind, acting perpendicularly to the oblique surface of the kite ; and P, the pull of the string. The force W may be resolved into two other forces. One of these, known as drift, tends to move the kite horizontally in the direction of the wind ; the other, called lift, to raise the kite vertically in opposition to gravity. In practice, if not in theory, the drift is augmented by the direct resistance offered by edges, excrescences, and roughnesses of the kite. If the wind sinks, the kite sinks also, in- creasing its angle with the horizontal. This causes it to capture and force downwards more