Aggressive Longitudinal Aircraft Trajectory Tracking Using Nonlinear Control

Flight-control system designs are complicated if the aircraft dynamics are nonlinear and nonminimum phase. The nonminimum phase property can result from the choice of output vector and coupling between the moment generating actuators and the aerodynamic forces on the aircraft. In this paper we study a flight-control problem for a conventional aircraft longitudinal dynamic model that explicitly includes the coupling between the moment generating actuators and the aerodynamic forces. In particular, we study the execution of a maneuver for which the aircraft is intended to track a given motion in a vertical plane. We formulate the problem as a nonlinear tracking control problem. Controllers are developed for an aggressive maneuver that requires the use of a two-degrees-of-freedom controller design. We demonstrate the value of this control architecture in order to achieve aggressive maneuvering with good tracking performance. Our approach throughout is to make use of nonlinear control theory. Our analysis is complicated by the nonminimum phase characteristics of the flight model.