Development of an unmanned tail-sitter with reconfigurable wings: U-Lion

In this paper, we present the development of a reconfigurable hybrid unmanned aerial vehicle (UAV): U-Lion. U-Lion is a small-scale UAV that is capable of vertical takeoff and landing (VTOL) and fixed-wing flight modes through its unique mechanical design. Mainly built with carbon fiber and Expanded PolyOlefin (EPO) foam, U-Lion is equipped with an array of electronic avionic components which enable stable control of the UAV both in VTOL and Cruise modes. It was employed by the National University of Singapore (NUS) Unmanned System Research Group to participate in the 2013 UAV Grand Prix (UAVGP) competition held in Beijing, China. Its design adopts a reconfigurable wing and a tailsitter structure, which combines the advantages of a fixed-wing plane and a rotor helicopter effectively. U-Lion could transit from vertical takeoff to a hovering stage before flying in cruise mode to realize efficient long duration flight. The propulsion of U-Lion comes from a self-fabricated contra-rotating motor fixed on a gimbal mechanism which can change the direction of the motor for the required thrust. This thrust-vectored propulsion system primarily provides control in the VTOL mode but also enhances flight capabilities in the cruise mode. The detailed design and implementation procedure have been presented in this paper along with our Computational Fluid Dynamics (CFD) simulation results, real flight tests and competition performance.