Predefined-Time Adaptive Flight Control of a Coaxial Compound Helicopter Against Input Saturation and Perturbations

Controlling coaxial compound helicopters is particularly challenging due to perturbations and input saturation, which can compromise stability and maneuverability. Current methods often fall short in ensuring robust performance under these conditions, highlighting a gap in the literature for adaptive control strategies that guarantee predefined-time convergence of tracking errors. In this study, we propose a predefined-time adaptive control scheme that combines a model reference adaptive control (MRAC) law with a trajectory control law specifically designed for coaxial compound helicopters. The MRAC law incorporates explicit stability conditions to achieve predefined-time convergence of the tracking error, even under saturated input conditions. To enhance maneuverability, we develop a trajectory control law based on sliding mode control, which, when integrated with the MRAC law, ensures effective longitudinal and lateral-directional control of the helicopter. The efficacy of this combined control scheme is validated through comparative simulations using a benchmark linear angular rate system under various scenarios, and further evaluated against representative maneuvers from the ADS-33E specification. The results demonstrate that the proposed control scheme effectively addresses the challenges of perturbations and input saturation, offering superior predefined-time convergence and enhanced maneuverability for coaxial compound helicopters.