Measurement of lift, pitching moment and hinge moment on a two-dimensional cambered aerofoil to assist the estimation of camber derivatives

Abstract

Aerodynamic camber derivatives are used in predicting three-dimensional control characteristics, in estimating wind-tunnel interference and in applying model data to full scale. Knowledge of these derivatives has been discussed in R. & M. 2820 (1950), from which it was apparent that experiments were needed to confirm empirical formulae for the derivatives of lift and pitching moment and to check widely differing formulae for the hinge-moment derivative. A two-dimensional RAE 102 aerofoil with a 4 per cent parabolic centre-line and plain control surfaces of chord ratios 0.2 and 0.4 has been tested at a low speed and Reynolds number 0.95 x 10power6. Particular attention is given to the effect of bmmdary-layer transition. Aerodynamic coefficients are obtained from measured forces and moments and from the pressure distribution at one section. The measured pressures compare fairly well with calculated distributions when the experimental circulation is used. Most of the coefficients from the integrated pressures are consistent with the balance measurements. The empirical formulae for the camber derivatives of lift and pitching moment are consistent within about 6 per cent. A new formula for the hinge-moment derivative is suggested, which, though at times 25 per cent different from experiment, is believed to correspond to an aerodynamic camber as it normally operates on a lifting surface in incompressible viscous flow.