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 d esign is presented. The methodology begins with a reduced-order linear, dyn amic-inversion technique that is scheduled over the flight envelope. The re duced order dynamic inverter can offer a significant reduction in the numbe r of state variables to be sensed or estimated as compared to typical appli cations of inverse dynamic control. The technique can provide desired input -output characteristics including control decoupling. The required gain sch eduling of the reduced order dynamic inversion Is straightforward. Uncertai nty is introduced by perturbing the stability derivatives in the vehicle mo del at each of the flight conditions considered. The effects of uncertainty are then reduced by additional feedback loops involving a diagonal compens ation matrix obtained through application of a loop shaping procedure based upon a quantitative feedback theory predesign technique. The tendency of q uantitative feedback theory to produce high-bandwidth conservative designs is mitigated by the scheduling and decoupling associated with the dynamic i nversion. Finally, handling qualities and pilot-induced oscillation tendenc ies are evaluated using a structural model of the human pilot implemented i n an interactive computer program that can include the effects of nuisance nonlinearities such as actuator saturation. The proposed methodology is app lied to the design of a lateral-directional flight control system for a pil oted supermaneuvarable fighter aircraft.