Unified Velocity Control and Flight State Transition of Unmanned Tilt-Wing Aircraft

This paper presents an approach for velocity control of tilt-wing aircraft over their entire flight envelope, ranging from hovering flight to wing-borne flight. With their capability of vertical takeoff and landing operation in combination with efficient cruise flight, tilt-wing aircraft offer multiple benefits in unmanned aerial vehicle applications. Control of tilt-wing aircraft, in particular for fully automated flight, is challenging because along with their versatility comes significant variations in flight mechanics characteristics. Known approaches to this problem subdivide tilt-wing flight into discrete aircraft configurations. The presented control concept omits discrete configurations and instead allows for continuous flight state transitions over a unified flight configuration space. Actuation that is unique to tilt-wing aircraft, for example, tilt angle control, is not only used as an aircraft configuration parameter but also as a full-fledged motion control device. The concept includes a map-based feedforward controller to maintain trimmed straight-lined flight and uses virtual control devices for motion control independent of the flight state. Flight state transitions are conducted along state trajectories that are defined deterministically and safely with respect to flight envelope limitations. The controller is implemented for an unmanned tilt-wing demonstrator and evaluated in flight. Compared to prior results, velocity response is considerably improved.