Page:Aerial Flight - Volume 2 - Aerodonetics - Frederick Lanchester - 1908.djvu/426

App. VIIIb. The theory of the flight of a boomerang has not been fully worked out. Probably the most advanced work that has been done on the subject is contained in a memoir by G. T. Walker, in which an attempt is made to deal with the problem by mathematical analysis. It appears to the present author that this memoir, in spite of its unquestionable value, is not altogether sound in its initial premises; the results, however, speaking generally, are of the right kind.

In the discussion that follows no attempt is made to deal with the question quantitatively, but rather to elucidate the principles

Fig. 189 (1/3 full size).

on which the peculiarities of the flight of the boomerang depend, regarding the latter as an example of the practical application of gyroscopic action for the maintenance of stability in flight.

Let us first examine the case of a circular flat disc. Fig. 191, projected edgewise, horizontally, with a rotary motion. Then the disc will begin to fall, and after a short time we may regard its weight as sustained by the aerodynamic reaction. But we know that the centre of pressure will then be in advance of the centre of gravity; consequently there will be a couple or torque tending to lift the leading edge, and this couple, counter-clock in Fig. 191, will give rise to angular momentum of like sense.