Development of an Air-launched Tail-Sitter Unmanned Aerial Vehicle

Abstract

This paper describes the development and flight testing of the first-ever air-launched tail-sitter UAV platform. Integrated with VTOL capability, the platform can be launched from various platforms, perform long-endurance loiter tasks and low-speed or hover flight, and land vertically in limited spaces. This work covers the experimental exploration of possible rotatable-fin designs, which then converge to a coaxial thrust vectoring design. A platform featuring a coaxial propeller and a thrust-vectoring mechanism is combined with a conventional fixed-wing design to accomplish both vertical and horizontal flights. An innovative bird-wing-inspired wing folding mechanism is also proposed in this work. A control strategy capable of handling both vertical and horizontal flight has been proposed. A cascaded feedback control strategy was implemented on a 1.7-gram custom-designed autopilot to stabilize the vehicle attitude. The proposed platform uses the coaxial rotors and the thrust-vectoring mechanism to accomplish the control in pitch, roll, and yaw for both vertical and horizontal flight. An indoor flight test with aggressive pilot inputs was successfully performed to demonstrate the controllability of the aircraft. Additionally, transition flight testing has successfully demonstrated the vehicle's capability of transition flight using the proposed thrust-vectoring mechanism.