A Flow Visualization Study of LEX Generated Vortices on a Scale Model of a F/A-18 Fighter Aircraft at High Angles of Attack

Abstract

A water tunnel flow visualization investigation was performed into the high angle of attach aerodynamics of a 2% scale model of the F/A-18 fighter aircraft. The main focus of this study was the effect of pitch rate on the development and bursting of vortices generated from the leading edge extensions in the high angle of attack range with and without yaw. Results of this investigation indicate that that the vortex bursting point (relative to the static case) moves rearward with increasing pitch-up motion and forward with increasing pitch-down motion. For the same pitch rate, vortex bursting was found to occur earlier for the pitch-down motion than for the pitch-up motion, implying aerodynamic hysteresis effects. Yawing the model generated significant vortex asymmetries due to the delayed vortex breakdown on the leeward side for yaw angles of less than 10' . The presence of these asymmetric vortices led to undesirable side forces and yawing moments.