Meeting IFPCS control system design challenges with H∞

Future Advanced Short Take-Off and Vertical Landing (ASTOVL) aircraft which will replace the current Harrier will provide a challenging problem to the flight control systems design team. The combined requirements of supersonic flight and powered lift regimes provide very difficult constraints on the design of the aircraft, and as a result the dynamics are inherently much harder to control than for existing aircraft. In particular, a high degree of cross-coupling is expected when effecting changes in thrust magnitude and direction (nozzle angle). On the Harrier this cross-coupling is not that high, the thrust vector acting close to the centre of gravity. This enables the pilot to fly the aircraft without recourse to complex multiaxis feedback systems. However, even this moderate amount of cross-coupling does impact significantly on pilot workload. With increased coupling in future ASTOVL aircraft, feedback around all axes will be a requirement. This paper briefly discusses some of the issues facing the designer when applying the H_∞ method to more complex aircraft