Trajectory-Tracking Problem of an Airplane with Damaged Control Surfaces

Aircrafts may encounter various issues such as the reduction of control surface effectiveness. This might lead to a considerable danger for lives and materials. Such a problem requires the application of a Fault-Tolerant Control (FTC). This study aims to achieve a "trajectory-following" mission of an airplane, affected by multiple actuator failures. Two different fault scenarios are considered: a consecutive degradation in the effectiveness of control surfaces (one at a time), and an abrupt partial degradation in all control surfaces. A modified FTC strategy, known as Progressive Accommodation, is put forward. It combines the State-Dependent Riccati Equation and the Forward-Propagation Riccati-Equation. This study considers a nonlinear model of an airplane DC-8 with coupled longitudinal and lateral motions. The proposed strategy takes into account the complexity of the model and the control objectives. It preserves the stability of the airplane and allows it to follow a specific trajectory, despite its damaged control surfaces. Thus, the designed method can be a useful alternative to hardware redundancy in airplanes.