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A novel adaptive backstepping control scheme based on invariant manifolds for unmanned aerial vehicles in the presence of some uncertainties in the aerodynamic coefficients is presented in this article. This scheme is used for command tracking of the angle of attack, the sideslip angle, and the bank angle of the aircraft. The control law has a modular structure, which consists of a control module and a recently developed non-linear estimator. The estimator is based on invariant manifolds, which allows for prescribed dynamics to be assigned to the estimation error. The adaptive backstepping control law combined with the estimator covers the entire flight envelope and does not require accurate aerodynamic parameters. The stability of the whole closed-loop system is analyzed using the Lyapunov stability theory. The full six-degree-of-freedom non-linear model of a small unmanned aerial vehicle is used to demonstrate the effectiveness of the proposed control law. The numerical simulation result shows that this method can yield satisfying command tracking despite some unknown aerodynamic parameters.

The main contribution of this article is the proposal of a path-following method for fixed-wing unmanned aerial vehicles. This path-following method employs the multi-loop framework that consists of an outer guidance loop and an inner control loop. The guidance loop relies on the idea of tracking a virtual target. The virtual target is assumed to travel along the defined path and its speed is explicitly specified. This guidance law guarantees the asymptotic convergence to the desired path and can anticipate the transition of the flight path in advance, which reduces the command for the inner control loop. In the inner control loop, the flight control law based on dynamic surface control is derived to overcome the 'explosion of complexity' problem in the backstepping design. The numerical simulation result illustrates the effectiveness of the proposed method.