Page:Aerial Flight - Volume 1 - Aerodynamics - Frederick Lanchester - 1906.djvu/233

Rh § 153. Planes in Pterygoid Aspect (Experimental).—The experimental information at present available relating to planes in pterygoid aspect is very unsatisfactory and conflicting.

In Fig. 99 we have a plotting given by Langley in the case of a plane 30 inches by 4.8 inches, with the curve for a square plane given for comparison. It was pointed out by Langley that the pressure on a plane in pterygoid aspect is greater for small angles the more extreme the proportion, but that this rule does not hold good when in the comparison of any two planes the angle exceeds a certain critical value. Thus in the figure the 30 inch by 4.8 inch curve crosses the 12 inch by 12 inch curve at an angle of about 23 degrees.

Curves as plotted by Langley are not fully comparable, in view of the fact, discovered by Dines, that the shape of the normal plane affects its pressure.

In his investigations on the influence of aspect. Dines has failed to show any trace of the “reversal,” or crossing, of the