An L₁ adaptive backup flight control law for transport aircraft with vertical-tail damage

This paper presents a backup lateral-directional flight control law for mid-sized trans- port aircraft with severe vertical-tail damage. In particular, the damage case scenarios considered in this work are characterized by a total loss of directional control via rudder, in addition to potential changes in the mass and aerodynamic properties of the aircraft. To compensate for the loss of rudder control, the proposed flight control law uses antisymmet- ric thrust and asymmetric spoiler deflection as directional control effectors. The design of the alternate control law relies on a frequency-shaped approach that accounts for the slow dynamics of the engines, and prevents excessive lift reduction resulting from continued large deflection of the aircraft’s spoilers. In addition, the flight control law incorporates an L₁ adaptive augmentation loop that is designed to restore prescribed flying qualities for a family of uncertain aircraft models with vertical-tail damage. Both batch and piloted simulation results with NASA’s Transport Class Model demonstrate that the developed alternate flight control law is able to recover directional control and provide satisfactory flying and handling qualities of the impaired aircraft.