Effects of reynolds number and frequency parameter on control-surface buzz at high subsonic speeds

Abstract

Stiffness and damping hinge-moment derivatives have been measured on a two-dimensional aerofoil-flap combination model by a free-oscillation technique. The experiments were conducted in the N.P.L. 18 in x 14 in (0.46 m x 0.36 m) tunnel where it is possible to vary the stagnation pressure and hence the Reynolds number and frequency parameter. To separate the effects of Reynolds number and frequency, flaps of different inertias were used. Measurements were made only in the range of Mach number where control surface buzz oscillations started spontaneously. A method of controlling the flap oscillation was developed which depended on the use of fine air jets issuing from the model surface just forward of the flap. Although changes in Reynolds number produced only small changes in thederivatives, these changes were larger for low values of frequency parameter; the magnitude of the derivatives tended to increase with Reynolds number. The effect of frequency parameters was larger; the values of the limit cycle amplitude and both derivatives decreased numerically with increasing frequency.