Possio's subsonic derivative theory and its application to flexural-torsional wing flutter parts 1 and 2

Abstract

Part I. Possio's Derivative Theory for an Infinite Aerofoil Moving at Subsonic Speeds. The derivative theory due to C. Possio for an infinite aerofoil moving at subsonic speeds is reviewed, and certain modifications are proposed. Derivative values are calculated for a Mach number of 0.7, and for values of the frequency parameter lambda ranging from 0 to 5.0. For lambda < 1 the derivative values based on a three-point collocation method are in fair agreement with those given by Possio. For the range 1.0 < 2 < 2.0 five-point collocation is necessary, while for lambda = 5.0 even seven-point collocation may prove unsatisfactory. The numerical results obtained are applied in Part II to estimate the influence of compressibility and flying height on the critical speed for flutter of a tapered cantilever wing. Part II. Influence of Compressibility on the Flexural-Torsional Flutter of a Tapered Cantilever Wing Moving at Subsonic Speed. Calculations based on Possio's subsonic derivative theory and:on vortex strip theory were made to obtain preliminary information on the influence of compressibility and flying height on the critical speed for flexural torsional flutter. The results are summarised by curves corresponding to constant altitude H, which show the variation of N with wing stiffness ratio r, where N denotes the ratio of the critical speed for flutter of the wing in compressible air at a Math number of 0.7 to the critical speed for flutter of the same wing in incompressible air. The results indicate that for 1 =< r =<3 the compressibility correction is insignificant at sea level, and that N is of the order 0.95 to 0.92 at H = 30,000 ft. More extensive test calculations are very desirable.