Passive mitigation of roll stall for low aspect ratio wings

Abstract

This investigation addresses an issue with the lateral stability and control of Micro Aerial Vehicles (MAVs) which is created by the presence of ‘roll stall’ and its effects on the aircraft’s stability derivatives. This behavior is a result of the developing tip vortex asymmetry of a low aspect ratio (LAR) wing in sideslip which creates an asymmetric spanwise load and a resulting roll moment. Experimental wind tunnel results indicate that roll stall produces a roll stability derivative, , for both the MAV models tested as well as canonical tapered flat wing cases; furthermore, even at small sideslip angles, the cross-coupled derivative links the longitudinal aerodynamics and the lateral loads of LAR wings, effects which are not present for large aircraft. The roll stall creates nonlinearites in lateral loads in an angle of attack regime in which the lift variation is linear; thus, control techniques for MAVs must consider the fact that lateral and longitudinal equations of motion can not necessarily be linearized about the same equilibrium flight conditions. Finally, the addition of winglets below the plane of the wing is seen to reduce by at least 50% in some cases, as well as essentially eliminating the derivative for a taper ratio of . This provides a passive control technique which can potentially be employed to significantly reduce the lateral instabilities of MAVs.