Output tracking of VTOL aircraft with delayed attitude measurements

In this paper we consider the flight-trajectory tracking problem of an input-disturbed non-minimum phase vertical takeoff and landing (VTOL) aircraft with delayed attitude measurements. By applying the first-order Pade¿ approximation method to deal with the time delays, the problem is reduced to the output tracking of a new high-order non-minimum phase system without delay, whose dynamics are then separated into minimum-phase and non-minimum-phase parts. By using Devasia´s stable noncausal inversion method, the ideal internal states of the non-minimum-phase subsystem are obtained and two error subsystems are ultimately constructed. We propose two low-dimensional sliding mode controllers to stabilize the error subsystems, which can render the overall closed-loop system stable in spite of the existence of disturbances. Simulations are performed to show the main results of this paper.