Page:Aerial Flight - Volume 1 - Aerodynamics - Frederick Lanchester - 1906.djvu/232

§ 152 may predict the general character of the resulting flow (Fig. 98) (a), which in all probability would be accounted for by the Kirchhoff-Rayleigh analysis. There is, however, some probability that when the inclination of the plane is small the viscous drag ejects the dead-water from the region above the plane, as in the case of the stream-line body, so that the motion will be approximately as represented in Fig. 98 (b), in which a small remnant of the dead-water alone remains immediately above the front edge of the plane. The resulting type of motion from a hydrodynamic standpoint is somewhat obscure; that a cyclic component exists there can be no doubt, but it is difficult to frame a régime which is in strict accord with hydrodynamic principles. It is possible that the surface of junction of the two streams, when they meet at the after edge of the plane, contains rotation, there being a finite difference between the velocities, and that this region of rotation modifies the lines of flow of the cyclic system in a manner that remains for future investigation.

If the author's theory is correct in its present application, the Kirchhoff-Rayleigh result will break down for small angles, in the direction of showing too low a reaction; for it is evident that the arrangement of flow (b) (Fig. 98) will result in a greater downward velocity being given to the air than in case (a). Experimental evidence on this point is at present inconclusive.