This paper describes a control strategy to stabilize the position of a Vertical Takeoff and Landing (VTOL) Unmanned Aerial Vehicle (UAV) in wind gusts. The proposed approach takes advantage of the cascade structure of the system to design a hierarchical controller. The idea is to separate the controller in a High Level Controller devoted to position control and a Low Level Controller devoted to stabilization and attitude control. Both controllers are designed by means of backstepping techniques

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... that allow the stabilization of the vehicle's position while on-line estimation of the unknown aerodynamic forces. The global stability of the connected system is proven, and simulations as well as experimental results are presented. 0-7803-9505-0/06/$20.00 ©2006 IEEE