Adaptive safety attitude control of a hybrid VTOL UAV under transition flight subject to multiple faults and uncertainties

Hybrid VTOL UAVs combine the configuration advantages of fixed-wing UAVs and rotary-wing UAVs, offering great environmental adaptability and improved forward flight efficiency, but they also impose more stringent demands on UAVs' safety attitude control, particularly during the transition mode. To address this issue, this paper proposes an adaptive safety attitude control strategy for a hybrid VTOL UAV to compensate for multiple faults and uncertainties under transition flight. Firstly, dynamic modeling and control allocation scheme design of the studied UAV are performed. Then, a novel reaching law-based sliding mode control strategy is developed, ensuring robust tracking performance under model uncertainties while mitigating control chattering. Following this, an adaptive fault-tolerant control strategy is formulated for the VTOL UAV, which is capable to simultaneously address model uncertainties and actuator faults in both rotors and control surfaces, while effectively preventing the overestimation of adaptive control parameters and avoiding control chattering. Finally, simulation tests of the UAV's transition flight under multiple faults and uncertainties are conducted. The quantitative comparison results demonstrate the effectiveness of the proposed strategy for enhancing attitude control safety.