Design and Implementation of a Thrust-Vectored Unmanned Tail-Sitter with Reconfigurable Wings

In this paper, we present the development of a reconfigurable hybrid unmanned aerial vehicle (UAV): U-Lion [Ang et al., 11th IEEE Int. Conf. Control Automation (ICCA), pp. 750–755]. U-Lion is a small-scale UAV that is capable of vertical takeoff and landing (VTOL) and fixedwing Cruise modes through its unique mechanical design. Mainly built with carbon fiber and expanded polyolefin (EPO) foam, U-Lion is equipped with an array of 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 tail-sitter 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 Cruise mode. The maximum thrust provided by the motor can be as high as 40N and it provides six degree of motion controls in VTOL mode. U-Lion has a few special internal designs to empower its capabilities: (1) Reconfigurable wings allow the U-Lion to adapt to different flying modes. (2) Adaptive center of gravity (CG) by adjusting the battery position to fulfill the different requirements of CG for VTOL mode and Cruise mode. (3) Unique contra-rotating thrust-vectored propulsion system. 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.