Enhanced Transition Control for Tail-Sitter UAVs: An Integrated NDI-ADRC Approach

To address the challenges posed by significant changes in dynamic characteristics and strong coupling during the flight mode transition from vertical takeoff and landing to horizontal cruise in tail-sitter unmanned aerial vehicles (UAVs), this paper proposes a control architecture that integrates Nonlinear Dynamic Inversion (NDI) with Active Disturbance Rejection Control (ADRC). Focusing on inner-loop attitude control, the approach utilizes NDI to achieve precise linearization of the UAV's nonlinear nominal model, thereby establishing an ideal basis for tracking response. An Extended State Observer (ESO) is subsequently designed to estimate and dynamically compensate for disturbances. Comparative experiments were conducted in the MATLAB/Simulink simulation environment. To validate the effectiveness of the proposed method, a transition corridor for a tail-sitter quadrotor UAV was designed. The safety and performance of transition control were evaluated against this predefined corridor. Experimental results demonstrate that, compared with conventional pure NDI control, the proposed scheme achieves smoother, faster, and more accurate transition trajectory tracking, with a reduction in altitude tracking error of approximately 1.5% and a decrease in transition time of about 40%.