Robust nonlinear dynamic inversion method for an aircraft motion control

Abstract

A control law design approach that robustifies the nonlinear dynamic inversion method for an aircraft performing nonlinear maneuvers is proposed. The robustness condition is based upon Lyapunov stability theory and multiple time scale dynamic inversion. The algorithm is analytically developed to be robust to a specified level of parameter uncertainty. A smoothed sliding mode control condition is introduced to provide linear stability of a closedloop system and maintain a specified level of command trajectory tracking accuracy. The method is demonstrated via an application to a twin-engined high performance aircraft performing the Cobra maneuver and a 360 degrees stability axis roll at high angle of attack while asymmetrically dropping external stores or experiencing thrust loss of one engine. Simulation results are presented to show the closedloop system dynamics using both the proposed algorithm and the conventional nonlinear dynamic inversion method.