High-Order Fully Actuated System Approach-Based Controller Design for Tailsitter in Flight Mode Transitions

A fan-powered tailsitter is capable of operating in both rotary-wing and fixed-wing flight modes. The transition between these modes is critical due to strong disturbances and considerable control complexity. This article investigates a predefined-time stability tracking control problem for tailsitters subject to parameter uncertainties and external disturbances. Based on the second-order dynamic model and high-order fully actuated (HOFA) system approach, a high-order robust controller is first developed to address the limitations of existing mode transitions, particularly in terms of control accuracy and disturbance suppression capabilities. On this basis, a novel predefined-time HOFA scheme is proposed by introducing adjustable parameters, which enables the system states to converge into a small neighborhood of the desired equilibrium within a prescribed time, while providing flexible tuning of the convergence time to adapt to varying mission and environmental requirements. Theoretical analysis and numerical simulations demonstrate that the proposed scheme achieves enhanced control accuracy, faster convergence, and improved robustness compared with conventional approaches. In contrast to existing approaches, the proposed HOFA-based predefined-time framework allows explicit tuning of the convergence time and provides robustness guarantees under parameter uncertainties, an aspect that has not been sufficiently addressed in the current literature.