Flight system design: robust control and accommodation of failures

The goal of this presentation is to introduce new procedures for designing robust controllers for aircraft. The vehicle performs over a large variety of mission phases, flight and environmental conditions. Existing models have a limited capability for modeling of vehicles. Specifically, current models do not adequately model aerodynamics, environmental effects, flexible modes, disturbances, bifurcations, etc. This problem facilitates the use of uncertain models without sacrificing the aircraft dynamic quantities while minimizing analysis and design complexity. Uncertain models characterize the vehicle dynamics in a way that is instructive from physical and mathematical standpoints. Although many control methodologies have been derived, little effort has been directed to ensure robustness and stability with respect to nonlinear time-varying parameter uncertainties which represent the unmodeled vehicle dynamics, failures, environmental changes, etc. On the basis of the known bounds of parameter variations, structural and environmental changes, the robust controller is synthesized. The proposed control methodology is based on the dynamic programming method and Lyapunov´s concept which are familiar to control engineers. Modified Riccati equations are obtained. The application of the robust design for the AFTI/F-16 fighter is presented. The resulting closed-loop system achieves robust stability if the parameter variations and failures appear.