Design of the lateral adaptive nonlinear guidance law for unpowered unmanned aerial vehicle gliding

Unmanned aerial vehicle (UAV) is regarded as a glider when it loses its power. Because the phugoid mode plays a major role, it makes the regulating time to the steady state become longer. That will cause the obvious influence between the longitudinal and lateral guidance. The more important is that UAV without power is more sensitive to the wind. This paper presents a method of the lateral adaptive nonlinear guidance to track a given falling spiral. First the guidance law is obtained by the geometric relationship. Then the guidance law is transformed to a two-order viscous system with damp and oscillation, while the characteristic of this system is related to the system's natural frequency. The authors design an adaptive scheme for the guidance laws in order to improve the convergence time of the system and its anti-wind ability. Finally the presented method is used to track the falling spiral when the UAV loses the thrust. The simulation results show that, compared with other non-adaptive method, the proposed method improves the tracking accuracy of the system, no matter whatever there is the constant wind disturbance or not.