Design of longitudinal adaptive nonlinear guidance law for unpowered UAV helix gliding

For the longitudinal guidance problem that how to track a helix path when the UAV loses power, we present a method of the nonlinear adaptive longitudinal guidance to track a given falling spiral. Firstly, the guidance law is obtained with the geometric relationship. Secondly, the guidance law is transformed to a two-order viscous system with damping and oscillation, based on which the guidance stability is proved. Then we design an adaptive scheme for the guidance laws in order to improve the convergence time of the system and its anti-disturbance rejection capability. Finally the presented method is used to track the falling spiral when the UAV loses the thrust. The simulation results and their analysis show preliminarily that, compared with other non-adaptive method as, the proposed method improves the tracking accuracy of the system, despite being constantly subjected to wind disturbance.