A video-based experimental investigation of wing rock

Abstract

The primary objective of this research was to develop a definitive theory on the cause of wing rock. The study was based on dynamic measurements in both a water tunnel and a wind tunnel on a sharp-edged delta wing with an 80° leading-edge sweep angle. Experimental data were compared with analytical results from a mathematical model and a fourth order Runge-Kutta integration. In the water tunnel tests, conducted at a=35° and Reynolds numbers from 3 x 10⁴/ft to 7.5 x 10 ⁴ /ft, the movement of the leading-edge vortices and the model motion were simultaneously tracked and analyzed using a video-based motion analysis system, ExpertVision. Quantified vortex movement data were not obtained in the wind tunnel study; however, an extensive investigation of wing rock dynamics was performed at angles of attack from 24 ° to 50 ° and Reynolds numbers from 1.09 x 10⁵/ft to 3.44 x 10⁵/ft. The initial phase of the study validated ExpertVision accuracy using stationary and forced oscillation tests on 70° and 80° delta wings. Vortex trajectory, core velocity, and burst point results from stationary tests were in good agreement with published data. Forced oscillation tests proved that ExpertVision could simultaneously track and analyze the movement of leading-edge vortices and model motion. Wing rock is caused by the dynamic behavior of the leading-edge vortices. Specifically, the alternate lift-off and reattachment of the vortices generate an asymmetry in vortex lift and cause changes in rolling moment that initiate and sustain roll oscillations. Since wind tunnel and water tunnel tests showed opposite direction hysteresis loops, it was concluded that roil damping could not be the primary aerodynamic mechanism that sets the limit on roll amplitude..