Utilization of Differential Thrust for Lateral/Directional Stability of a Commercial Aircraft with a Damaged Vertical Stabilizer

This thesis investigates the utilization of differential thrust to help a commercial aircraft with a damaged vertical stabilizer regain its lateral/directional stability. In the event of an aircraft losing its vertical stabilizer, the consequential loss of the lateral/directional stability is likely to cause a fatal crash. In this thesis, the damaged aircraft model is constructed, and the lateral/directional dynamic stability and frequency domain analyses are conducted. The propulsion dynamics of the aircraft are modeled as a system of differential equations with engine time constant and time delay terms to study the engine response time with respect to a differential thrust input. The novel differential thrust control module is presented to map the rudder input to differential thrust input. Then, the differential thrust based control strategies such as linear quadratic regulator (LQR), model reference adaptive system (MRAS), and H∞ loop-shaping based robust control system are proposed to be utilized to help maintain stability and control of the damaged aircraft. For each type of control system design, robustness and sensitivity analysis is also conducted to test the performance of each control system in the presence of noise and uncertainty. Results demonstrate successful applications of such control methodologies as the damaged aircraft can achieve stability under feasible control efforts and without any actuator saturation. Finally, a comparison study of three control systems is conducted to investigate the merits and limits of each control system. Overall, the H∞ loop-shaping based robust control system was found to have the most remarkable results for stabilizing and saving the damaged aircraft