Robust flight control design with handling qualities constraints using scheduled linear dynamic inversion and loop-shaping

A technique for obtaining a full-envelope decoupled linear flight control design is presented. The methodology begins with a reduced-order linear dynamic-inversion technique that is scheduled over the flight envelope. The reduced order dynamic inverter can offer a significant reduction in the number of state variables to be sensed or estimated as compared to typical applications of inverse dynamic control. The technique can provide desired input-output characteristics including control decoupling. The required gain scheduling of the reduced order dynamic inversion is straightforward. Uncertainty is introduced by perturbing the stability derivatives in the vehicle model at each of the flight conditions considered. The effects of uncertainty are then reduced by additional feedback loops involving a diagonal compensation matrix obtained through application of a loop shaping procedure based upon a quantitative feedback theory predesign technique. The tendency of quantitative feedback theory to produce high-bandwidth conservative designs is mitigated by the scheduling and decoupling associated with the dynamic inversion. Finally, handling qualities and pilot-induced oscillation tendencies are evaluated using a structural model of the human pilot implemented in an interactive computer program that can include the effects of nuisance nonlinearities such as actuator saturation. The proposed methodology is applied to the design of a lateral-directional flight control system for a piloted supermaneuvarable fighter aircraft.