Simulation Study on Aerodynamic Characteristics of Combined Low Aspect Ratio UAV

Combined unmanned aerial vehicle (UAV) is a kind of new concept aircraft, which is composed of several small UAVs connected by their wingtips. It has both the high-aspect ratio aircraft's high-altitude and long endurance capability and the distributed mission utility of cluster UAV, and has great development potential. In this paper, a high-fidelity numerical simulation method for multi-body combined UAV based on unstructured polyhedral mesh is established, and the accuracy of the calculation method is verified by a standard example. Firstly, a low aspect ratio UAV configuration suitable for cluster combat is designed. Secondly, the lift-drag characteristics, longitudinal static stability and flow separation characteristics of the combination and each element are analyzed. Finally, the coupling mechanism of wingtip vortex induced drag and wing surface pressure differential drag in low aspect ratio configuration is explored. The results show that the wing tip connection can significantly improve the cruise lift-drag ratio of UAVs with low aspect ratio, and the increment of cruise lift-drag ratio and longitudinal static stability margin gradually decreases with the increase of the number of connections. The swept wing configuration combination is separated at a smaller angle of attack, while the flat wing and forward swept wing configuration combination have stronger drag to flow separation. The low aspect ratio configuration is significantly affected by the coupling effect of wingtip vorticity induceddrag and wing surface pressure differential drag. Only when the wingtips of five or more UAVs with low aspect ratio are connected, the drag coefficient of the combination is smaller than that of the single one.