A Hierarchical Approach to Adaptive Control for Improved Flight Safety

Following failures of primary aerodynamic actuators, safe flight can be maintained by introducing alternative actuation systems, such as secondary aerodynamic surfaces and propulsion, for critical stability and control augmentation. This paper presents an intelligent hierarchical flight control system architecture that is designed using nonlinear adaptive synthesis techniques and on-line learning neural networks. Pseudo-Control Hedging is used for proper adaptation in the presence of actuator saturation, rate limits and actuator failure. The hierarchical structure of the proposed approach incorporates non-active secondary actuation channels that are engaged after a failure of a primary control surface has occurred. These secondary channels are designed to account for the usually lower authority and degraded performance that can be expected with a secondary actuation system. The proposed flight control system is evaluated in a nonlinear flight simulation environment.