Page:Aerial Flight - Volume 1 - Aerodynamics - Frederick Lanchester - 1906.djvu/389

Rh subject matter of the later volume, “Aerodouetics,” and only certain experiments having an immediate bearing on the aerodynamics of flight will be dealt with at the present juncture.

A method of experiment that the author has used to some advantage involves the employment of gliding models. Up to the present time the whole question of the stability of such models has been but little understood, and it is necessary to some extent to anticipate the conclusions of the later portion of the work.

It is currently believed that the equilibrium of a bird in flight is essentially maintained by the intervention of the brain and nerve centres, and that an aerodrome or aerodone, in order that it should possess stability, must be fitted with parts capable of ready and rapid adjustment, and furnished with some “brain equivalent,” or be immediately directed by an aeronaut. It may be stated at once that no such provision is necessary, and that a properly designed rigid structure is capable of maintaining its own equilibrium, and possesses complete stability within prearranged limits; and further, that such a rigid structure (or aerodone) may be designed to automatically simulate many of the apparently life-like movements of birds in flight or at will glide steadily at its natural velocity at a constant angle of flight path.

The above are mere bald statements of fact, that will be fully substantiated in the subsequent volume. The behaviour and stability of an aerodone in flight will for the present be taken for granted, an indication of the underlying principles having been given in § 162 on the Ballasted Aeroplane.

§ 240. Scope of Experiments.—The scope of the present series of experiments has been in the main confined to the determination of $$\xi$$ by a variety of methods.

This quantity, which has been frequently stated to be negligible, is (as has been demonstrated in the present work) one of very