Page:Aerial Flight - Volume 1 - Aerodynamics - Frederick Lanchester - 1906.djvu/230

§ 151 that (in absolute units) $$P = C\ \rho\ V^2$$ where $$P$$ is the normal pressure on the plane for any angle.

There is some doubt as to the correct plotting of the Langley curves owing to the fact that this observer was unaware of the variation to which the $$C$$ of the normal plane equation is subject, as dependent upon the shape of the plane.

§ 152. The Infinite Lamina in Pterygoid Aspect.—The case of the inclined infinite lamina in pterygoid aspect has been examined by Kirchhoff and Rayleigh on the Helmholtz hypothesis. According to this investigation the pressure is given by the equation: $$P = \frac{\pi\ \sin \beta}{4 + \pi\ \sin \beta}\ \rho\ V^2$$ from which the curve (Fig. 97)