Page:Aerial Flight - Volume 1 - Aerodynamics - Frederick Lanchester - 1906.djvu/245

Rh

Fig. 105 illustrates the manner in which $$c$$ may be plotted as a function of the aspect ratio $$n$$. The values of $$c$$ are at present not known with any pretence to accuracy; $$c$$ is probably different in the case of an aeroplane from what it is in the case of a pterygoid aerofoil. For the former Langley found that variations in $$n$$ gave rise to very considerable variations in $$c$$ (Fig. 99); Dines failed to discover any variation at all (Fig. 101).

The values given in Fig. 105 are “plausible values” (see Chap. VIII.) for a pterygoid aerofoil. The same data have been laid out in Fig. 106, where abscissae give angle and ordinates pressure reaction.

In addition to the equation, Rh

we may also formulate as a direct consequence of the small angle hypothesis, Rh

and from the resolution of forces we have, Rh

where $$y =$$ aerodynamic resistance.

Consequently, A.F.