Aircraft flight control system analysis and design

In-flight loss-of-control (LOC) has been the leading cause of fatal aircraft accidents in the past two decades. Aircraft LOC recovery is an extremely challenging and formidable task for the pilots. The reaction time for recovery usually is very limited, and the pilots need to act quickly, correctly, and avoid deepening the crisis. Under these emergency and critical situations, pilots certainly need help from a sophisticated new-generation flight computer/control system that can correctly diagnose the problem and provide an accommodation solution in time. In this work, a 12-state full nonlinear aircraft flight dynamics model is employed as a test bed to investigate the flight dynamics and control theory regarding to the loss-of-control or upset conditions like nose dive, spins, falling leaf, roll-pitch coupling oscillations, etc. Aircraft usually are operating at or around one trim (equilibrium) at a time. Smooth trim-to-trim transition is a common practice in normal aircraft flight mode switching, for example, from a straight/level flight to a climb or a descent, from a coordinated turn to a straight level flight, etc. We are particularly interested in the trim switching and robust control system design relevant to aircraft loss-of-control prevention and recovery. Through the study of aircraft flight dynamics at loss-of-control conditions together with the virtual aircraft flight experiments at a variety of trims, we have gained more understanding on what factors are relevant to the occurrence of loss-of-control conditions. These factors include the trim condition, initial state, external disturbances, and the inherent properties of the aircraft dynamics like damping ratio and natural frequencies, etc. The study also reveals that the trim selection and feedback control strategies are critical in loss-of-control prevention and recovery. This line of research may lead to practical and effective solutions for LOC prevention/recovery that would make the flight of aircraft much safer.