MINISTRY OF AVIATION SUPPLY AERONAUT/CA1 RESEARCH COUNCIL CURRENT PAPERS Scale Effects on Oscillatory Control-Surface Derivatives

Scale Effects on Oscillatory Control-Surfeoe Derivatives-By-A. Y/. Moore Aerod.ynsmlcs Division NPL The limited evidence availahle concerning scale effects on Control-surface derivatives suggests a general tendency for in-phase hinge-moment derivatives to increase when Reynolds number increases but to decrease sharply when boundary-layer transition is artificially fixed. Damping (in-quadrature) derivatives in two-dimensional tests seem to follow a similar pattern, but with three-dimensional models, neither an increase in Reynolds number nor fixing boundary-layer transition appears to have any significant effect. It is therefore tentatively concluded that provided boundary-layer separation is not a feature of the flow, wind-tunnel tests should be done without fifing boundary-layer transition. However, it is emphasised that this conclusion is based on results from a limited number of papers and further measurements should be made, in which Reynolds number is systematically varied over a wide range with and without a means for fixing boundary-layer transition.