1 School of Aeronautics, Northwestern Polytechnical University, Xi'an 710072, China; National Key Laboratory of Aircraft Configuration Design, Xi'an 710072, China. Electronic address: wangban@nwpu.edu.cn.
2 School of Aeronautics, Northwestern Polytechnical University, Xi'an 710072, China; National Key Laboratory of Aircraft Configuration Design, Xi'an 710072, China. Electronic address: huiminzhao@mail.nwpu.edu.cn.
3 School of Aeronautics, Northwestern Polytechnical University, Xi'an 710072, China; National Key Laboratory of Aircraft Configuration Design, Xi'an 710072, China. Electronic address: xinyuehu@mail.nwpu.edu.cn.
4 Department of Electrical and Computer Engineering, Concordia University, Montreal H3G 1M8, Canada. Electronic address: y_shen@encs.concordia.ca.
5 School of Aeronautics, Northwestern Polytechnical University, Xi'an 710072, China; National Key Laboratory of Aircraft Configuration Design, Xi'an 710072, China. Electronic address: lini@nwpu.edu.cn.

In this study, an innovative adaptive sliding mode fault-tolerant control approach is developed for an over-actuated vertical takeoff and landing (VTOL) fixed-wing unmanned aerial vehicle (UAV) with the capability to suppress overestimation of adaptive parameters. This method is designed to effectively address model uncertainties and actuator faults without relying on any previous information regarding the specifics of faults or the boundaries of uncertainties. An innovative adaptive sliding mode control (SMC) mechanism is designed which can autonomously adjust to compensate for the unpredictable nature of these challenges, ensuring the stability and reliability of the UAV system under various operational conditions. Taking into account the over-actuated characteristics of the studied VTOL UAV, a control allocation module is further designed to efficiently distribute the control signals produced by the adaptive SMC scheme. It is noteworthy that the designed adaptive control approach can effectively prevent the overestimation of adaptive parameters, thereby reducing the occurrence of undesired control chattering. Finally, the superiority and efficacy of the designed control technique are convincingly illustrated through an extensive range of comparative hardware-in-the-loop simulation tests.