Page:Aerial Flight - Volume 1 - Aerodynamics - Frederick Lanchester - 1906.djvu/234

§ 153 curves, so clearly brought out by the experiments of Langley. It is possible that the form of the so-called “planes” employed by Dines is responsible for much of the disagreement. Dines employed slabs of triangular section (Fig. 100) (a), whereas Langley adopted a flat section (b), his “planes” having square edges, and being of about one-eighth inch thickness.

In Fig. 101 the curves are plotted B, B for a “plane” of square form, and (F) for one measuring 48 inches by 3 inches in pterygoid aspect, from Dines' paper (Proc. Royal Soc., Vol. 48). These curves incidentally cross one another, but there is nothing resembling Langley's reversal.

In experimental aerodynamics we are used to encountering discrepancies of various kinds, but a disagreement of the present extent is most unsatisfactory. On the whole, for planes at small and moderate angles, the author is disposed to accept Langley's data as the more reliable.

§ 154. Superposed Planes.—The effect of the proximity of one aeroplane to another has been investigated experimentally by Langley. In a series of experiments carried out by the aid of his whirling table and “Plane-Dropper,” Langley showed that two parallel planes, one above the other, will, at a given angle, support as great a load as if they were entirely independent, so long as they are separated by a certain minimum distance. In the actual experiments two pairs of planes, each 15 inches by 4 inches, were employed in pterygoid aspect (Fig. 102); it was found that so long as the angle did not exceed a certain maximum value a separation of four inches (i.e. equal to the fore and aft dimension