Tail-Propeller Assisted UAV Perching Control System Design & Verification

Fixed-Wing Unmanned Aerial Vehicles (FW-UAVs), requiring a runway for landing, provide better performance than multi-rotor UAVs and Vertical Take-Off and Landing (VTOL)-FW-UAVs in endurance, range and energy efficiency. To benefit from the efficiency of a FW-UAV and the convenience of a VTOL-UAV, this work proposes a runway-less landing approach by executing a fare and perching manoeuvre. The landing trajectory is optimised by solving the optimal control problem for the perching manoeuvre. Open-loop experiments revealed significant deviations from the target fight path and a high pitch angle at touchdown as expected. This paper introduces a Time-Varying Linear Quadratic Regulator (TVLQR) controller designed to correct deviations of the fight path from the optimal trajectory. The TVLQR reduces the mean absolute error of the deviations and increases the success rate to 60%. It shows, however, the final pitch angle remains as high as 57◦, leading to tail collisions. Introducing a tail rotor with a 45◦ activation threshold further improves the performance, reducing the final pitch angle to 25◦ and increasing the success rate to 77%. The performance of the system is evaluated and presented including it’s ability to maintain pitch stability under wind disturbances. Data from 120 indoor fight tests confirm the effectiveness of combining feedback control with auxiliary thrust, demonstrating robustness to aerodynamic disturbances.