Vortex generators for increased maximum lift and enhanced high-α stability of a Zimmerman-wing MAV at low Reynolds number

The Micro Air Vehicle has a very small wingspan and low aspect ratio wing which operates at low Reynolds numbers. It flies in an environment which provides random turbulent gusts which exceed the size and energy of the MAV regularly, especially in built-up areas and forests, as discussed by Roth [1]. This means that stability and gust resistance is a key design point for the vehicle and should be maximised where possible to aid controllability and increase flight envelope. In this paper, comparisons between lift, drag, moment and angle of attack are used to determine the overall performance and static stability of the aircraft. The dynamic stability and controllability of the aircraft is investigated through flight testing, which is filmed for post-analysis. The 3D flow structure and aerodynamic forces are analysed using computational fluid dynamics, utilising Komega SST modelling to solve the RANS equations on a finite-volume multi-block mesh. In an attempt to improve the stability performance of the vehicle, vortex generating vanes are added to the upper wing surface near the leading edge. The effect of these is analysed using the above method to determine their effect on the performance of the MAV, specifically whether they increase Cl and high-α stability. It was found that vortex generators greatly increase the max Cl and stall-α of the MAV with negligible increase in cruise drag, and also increase the static stability at high-α. It is found that for the MAV, the largest contributing factor to instability is inaccurate centre of gravity (CG) placement, in particular having the CG too far aft.