Modeling and Control of a Tailsitter UAV

Unconventional UAVs are being proposed to combine the benefits of fixed-wing and rotary-wing aircraft. Among these are tailsitter aircraft, which are fixed-wing aircraft with vertical landing capability. In this work, we present the development of a real-time simulation of a commercial radio-controlled tailsitter aircraft, along with a single controller that is capable of executing vertical takeoff, level flight, and vertical landing. The model accounts for progressive stall, the effect of large control surface deflections, as well as the drag generated by the aircraft's structural components. The thruster model accounts for changes in battery voltage, inflow velocity, and predicts slipstream effects. A ground contact model is also implemented to allow simulation of the takeoff and landing phases. A cascaded quaternion-based controller is then implemented in this simulated environment to control the tailsitter in a typical flight mission, with promising results. The transition from level flight to hover proves to be the most challenging aspect in the control of this aircraft.