A Practical Approach to the Prediction of Oscillatory Pressure Distributions on Wings in Supercritical Flow

SUMMARY Brief consideration of current approaches to the prediction of unsteady wing loading in mixed subsonic and supersonic flow shows a wide variety of method and a clear need for economy in transonic aerodynamic calculations for flutter clearance in subsonic flight. In support of measurements of steady and oscillatory pressure distributions on a particular wing, an approximate theoretical treatment is devised in terms of non-linear steady surface pressures and linear oscillatcry loading. The steady data are taken either from transonic small-perturbation theory or from the static experiments. The resulting theoretical or semi-empirical calculations can take account of stream Mach number, mean incidence, mode of oscillation, frequency and amplitude. Like the dynamic experiments, the theoretical and semi-empirical results show large differences between oscillatory chordwise load distributions under subcritical and supercritical conditions, especially in the recompression region where the large and rapidly changing amplitude and phase of the measured loading are reproduced qualitatively in the calculations. The method should provide an economical indication of the importance of non-linear flutter aerodynamics in the lower transonic regime.