Experimental Investigation of Wing Rock on a Low Aspect Ratio Flying Wing Micro Aerial Vehicle using Pyramidal Balance

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Wing rock phenomenon on low aspect ratio Flying Wing Micro Aerial Vehicle (FWMAV) has been experimentally investigated at varying angles of attack using 6 strain gauge pyramidal balance. This research has experimentally investigated the wing rock phenomenon at very low speeds without the use of the Free To Roll (FTR) sting balance. In this research, we have predicted the onset of wing rock with sinusoidal behavior of rolling moment coefficient with angle of attack instead of monitoring roll angle change history with time. Wind tunnel experiments were conducted at a Reynolds number of 1.16x10^5 on an FWMAV having a mean aerodynamic chord of 0.17m. Experiments were conducted at three speeds (5m/s, 7m/s, and 10m/s) and angles of attack were progressively increased from -10º to +20º in a step of +1 deg. Conventional trends of aerodynamic coefficients were obtained, however, the rolling moment coefficient reflected a non-periodic sinusoidal behavior with varying amplitudes and frequencies at all speeds. This non-uniform oscillatory behavior of the rolling moment coefficient reflected the onset of the wing rock phenomenon. The most probable cause of wing rock seemed to be the unsymmetrical pressure and hence lift distribution over both wings at low angles of attack, however, unsymmetrical forebody vortices and their breakdown in an unsymmetrical manner could be the case in high angles of attack regime. Wing rock being non-linear in nature was observed to start in the pre-stall region which is unprecedented, undocumented, and demands further investigations. It is concluded, that low aspect ratio flying wings at low speeds can exhibit wing rock even at low angles of attack. Additionally, the onset of the wing rock phenomenon can be detected using pyramidal balance and FTR sting balance is not necessarily required.