LATERAL OSCILLATIONS OF AN AIRCRAFT MODEL AT HIGH ANGLES OF ATTACK

Abstract

Lateral oscillations occurring on the aircraft model of NASA TP 1803 at angles of attack ranging from 25° to 60° have been investigated in a low-speed wind tunnel for configurations including fuselage with wing or with a combination of wing and leading-edge extension (LEX). The wind tunnel experiment was conducted in the range of Mach number from 0·1 to 0·2, and the range of the Reynolds number based on the body diameter from 2·8×10 5to 5·6×10 5. The time-varying side force coefficients, which may represent the displacements of oscillation in the lateral direction, were measured to obtain the root-mean-square values and the power spectra. Flow visualization of the vortices generated from the forebody, wing and LEX of the model has also been performed in a water tunnel. It was found that the entire system of the flow and the sting-supported model locks-in at the resonant oscillation frequency as the lateral oscillation occurs. The presence of LEX significantly enhances the oscillation amplitude especially at high enough angles of attack, i.e., α>40 °.The enhancement of the lateral oscillation, as suggested by the water tunnel visualization, seems closely related to the breakdown of the LEX vortices in general and the location of breakdown in particular. The power spectra of the test model with wind and LEX exhibit a transition from weakly nonlinear to broad band oscillations as αis increased from 45° to 60°. The appearance of a broad range of frequencies around or below the dominant frequency, that can be indicative of possible chaotic oscillation, corresponds to a sharp drop of the lateral oscillation amplitude. The effect of Reynolds number is notable only at α>50°.Variation of the sideslip angle between 0 and 10° appears to have no discernible effects on the amplitude of lateral oscillation for the test model with wing and LEX.