Effects of horizontal tail ice on longitudinal aerodynamic derivatives

Abstract

Flight tests were performed with the NASA Lewis Research Center's DH-^6 icing research aircraft to determine the accuracy with which the effects of ice on aircraft longitudinal stability and control could be measured. Flights were made with both a clean (baseline) configuration and with simulated ice on the horizontal tail. At a given trim speed 45 repeat doublet maneuvers were performed in each of four test configurations to determine the ensemble variation of the estimated stability and control derivatives. Additional maneuvers were also performed in each configuration to determine the variation in the longitudinal derivative estimates over a wide range of trim speeds. Stability and control derivatives were estimated by a modified stepwise regression (MSR) technique. A measure of the confidence in the derivative estimates was obtained by comparing the standard error for the ensemble of repeat maneuvers to the average of the estimated standard errors predicted by the MSR program. The magnitude of icing effects on the derivative estimates was strongly dependent on flight speed and aircraft wing flap configuration. With wing flaps up, the estimated derivatives were degraded most at lower speeds corresponding to that configuration. With wing flaps extended to 10 deg, the estimated derivatives were degraded most at the higher corresponding speeds.