Calculation of flutter derivatives for wings of general plan-form

Abstract

The vortex-lattice method of calculating flutter derivatives presented in this note is an extension to higher frequencies of the work on stability derivatives reported in R. & M. 2922. The method is a modified form of the scheme outlined in R. & M. 2470 and is suggested as an alternative to the latter method since it gives a simpler routine calculation for wings of general plan-form. Derivatives are calculated for the following wings, describing plunging and pitching oscillations: (a) Delta wings of aspect ratio A = 1.2 and 3 and with a taper ratio 1/7. (b) Arrowhead wing of aspect ratio 1.32 with a taper ratio 7/18 and angle of sweep of 63.4 deg at quarter-chord. The results for the delta wing A = 1.2 and the arrowhead wing are compared with values of the pitching derivatives obtained in low-speed tests; those for the delta wing A = 3 with the values calculated in R. & M. 2841. The comparison indicates that the present method gives reasonable accuracy for low-aspect-ratio wings in incompressible flow; the method may be sufficiently reliable for use with the equivalent wing theory suggested in R. & M. 2855 for the calculation of flutter derivatives in compressible subsonic flow.