Formulation, implementation and verification of novel transition control strategy for VTOL hybrid UAV

Abstract This research is focused on the formulation, implementation and verification of novel transition control strategy for an originally designed tail-sitter VTOL hybrid UAV. A differential thrust transition vehicle was designed to achieve wide-envelope flight control by using four actuators. Attitude-tracking and altitude-hold controllers were developed to provide adequate control actuation for smooth transition between different flight modes. The control system was formulated for flight dynamic model of the aircraft, and implemented in MATLAB/Simulink environment for flight simulations. Tilt-angle-based feedback control was employed to calculate attitude errors. Altitude errors were obtained by direct comparison of commanded signal with the vehicle’s response. To maintain the desired altitude and attitude, required total thrust and differential thrust were calculated from the output of the altitude and attitude controllers, respectively. High-fidelity aerodynamic analysis was performed over the entire flight envelope to obtain the aerodynamic coefficients of the aircraft. Motor dynamics, propeller effects and airframe aerodynamics were incorporated in the flight dynamics model of the vehicle. Flight simulations verified effectiveness of the flight control system in tracking attitude and altitude-hold commands. The flight modes transition manoeuvre was successfully accomplished with the designed transition control system. The control technique for takeoff, hover and landing was successfully validated on manufactured prototype.