Integrated flight and propulsion control of a future V/STOL aircraft concept

A robust integrated flight and propulsion control (IFPC) system is designed and analysed for an experimental vertical/short take-off and landing (V/STOL) aircraft configuration, using multivariable design techniques. The model used for the design is based on the DERA VAAC Harrier wide envelope model (WEM) airframe with a Rolls-Royce Spey engine. This provides a detailed, large-scale, interacting full-envelope, nonlinear simulation model, thought likely to be representative of the next generation of V/STOL aircraft. The centralised IFPC system is evaluated in piloted simulation trials on DERA's real-time all-vehicle simulator (RTAVS), the results of which indicate that level 1 or 2 handling qualities are achieved over the low-speed powered-lift region of the flight envelope. The application of the structured singular value, , and the -gap metric to the problem of evaluating the robustness properties of this multivariable IFPC system is presented. The centralised controller is subsequently partitioned into decentralised lower-order airframe and engine subcontrollers, in order to address implementation and testing issues. The partitioned system is seen to retain largely both the performance and robustness properties of the centralised system. Due to the particular implementation structure used for the centralised H loop shaping controller, the partitioning procedure described can be applied to general two-degree-of-freedom control systems. A scheme to guarantee maximum limits on safety-critical engine variables is developed and applied, to preserve the structural integrity of the engine during extreme manoeuvres. As the system frequently operates on the position limits of the engine actuators, an anti-windup scheme is implemented to maintain the performance of the system during actuator saturation.