Unified Approach for Velocity Control and Flight State Transition of Unmanned Tiltwing Aircraft

This paper presents a unified approach for velocity control of tiltwing UAV within their entire flight envelope ranging from hovering flight to wing-borne flight. With their capability of VTOL operation and hovering in combination with long endurance and high payload capacity a tiltwing aircraft offers multiple benefits in UAV applications. Due to significant changes in flight mechanical characteristics during transition from thrust-borne to wing-borne flight the control of a tiltwing, in particular for fully automated flight, is challenging. The presented velocity and flight state transition controller includes a mapbased feedforward controller to maintain trimmed straight-lined flight and utilizes virtual control surfaces to provide a unified attitude control scheme. Changes of flight state are conducted by a dedicated flight state transition controller. Flight state trajectories are defined deterministically and safely with respect to flight envelope limitations. The control concept avoids any differentiation between discrete flight states. The implementation for the RWTH Aachen unmanned tiltwing demonstrator is based on characteristic flight mechanics data gathered in wind tunnel investigations. Flight tests were conducted and results indicate very good performance of the controller within the entire flight envelope.