Guaranteed trajectory tracking of a small-size autonomous helicopter in a smooth uncertain environment

This paper deals with the problem of disturbance (wind gusts) reconstruction acting on a scale autonomous helicopter in 3D flight. A general class of disturbance is addressed, namely any uniform time-varying tridimensional wind gust occurring in the vicinity of the UAV. Using an unknown input observer, it is shown that the disturbance can be accurately reconstructed online. Singular perturbation assumption is made to separate translational and rotational dynamics. Robust backstepping techniques are then used to stabilize each subsystems by taking into account the disturbance estimation procedure. Using a Lyapunov analysis, it is proven that the closed loop system coupling two non linear controllers with two nonlinear observers converges to an asymptotical set of which radius may be tuned as small as desired by increasing some gains. Simulation results validate the work.