Large envelope flight control satisfying H-infinity robustness and performance specifications

Abstract

A method of designing large envelope flight controllers for high performance aircraft is presented. The approach combines the simple two-degree of freedom architecture often referred to as a disturbance observer and recent advances in parameter-space control design techniques to form a new approach for large envelope flight control design. The procedure enables the designer to explicitly define the desired closed-loop dynamics and ensures that the closed-loop is stable and satisfies weighted frequency response magnitude (H-infinity) specifications. The result is a straightforward procedure that enables the design of a robust flight controller that "forces" the closed-loop dynamics to behave like the specified 'desired dynamics' despite disturbances, modeling uncertainties, and variations in aircraft dynamics due to changing flight conditions. The procedure is presented by designing a pitch-rate controller for the F-16 Variable Stability In-Flight Simulator Test Aircraft (VISTA). The controller provides predicted 'Level 1' flying qualities throughout the large design flight envelope, which is demonstrated using both linear simulations and a high fidelity, nonlinear simulation. Finally, the controller is compared to a 7th order and a 10th order linear parameter-varying (i.e. gain-scheduled) controller and found to provide better performance and robustness.