Page:Aerial Flight - Volume 1 - Aerodynamics - Frederick Lanchester - 1906.djvu/392

§ 241 special design, Fig. 152, the supporting member being a plane whose centre of pressure is known from independent experiment. The tail plane is divided into two portions arranged so as to be as little as possible affected by the wake disturbance; this is essential on account of the fact that the angle between the supporting plane and the tail plane is assumed to be the angle made by the former by the line of flight. The computation of $$\xi$$ is made from gliding data, the whole surface being assumed as subject to skin-friction, or an allowance may be made in respect of the supporting plane on the lines laid down in §§ 182, 183 and 184.

(3) The Method of the Ballasted Aeroplane.—Reference has already been made to this method (§ 162). A number of planes are prepared of exactly the same size and total weight, but with their centres of gravity situated at different distances from their geometrical centres. Trial flights are made, and the resulting data give simultaneous equations from which the values of the constant may be deduced.