Heading Adjustment by Admittance Control for Lifting-Wing Quadcopters in Strong Winds

Wind disturbance is a critical challenge for uninhabited aerial vehicles (UAVs), particularly for hybrid vertical takeoff and landing (VTOL) UAVs such as lifting-wing quadcopters, which are prone to aerodynamic disturbances like gusts and turbulence due to their wing structure. Existing control strategies often treat wind effects as generic disturbances, neglecting the unique characteristics of hybrid UAVs. This letter evaluates the wind rejection capability of lifting-wing quadcopters by introducing the wind rejection degree (WRD), a novel metric that quantifies both the rejection capability and the control margins under wind disturbances. Based on the analysis, we propose an innovative control strategy to resist the undesired effects of wind disturbances for hover flight, which integrates admittance control with disturbance estimation, enabling automatic alignment of the aircraft's heading with the wind direction. Outdoor experiments under varying wind conditions, including strong winds with a peak speed of 9.4 m/s, were conducted on a small-sized lifting-wing quadcopter. The results demonstrate significant improvements in hover accuracy and disturbance rejection compared to conventional PID and APM flight control methods, validating the effectiveness of the proposed approach.