H∞-design of robust flight controllers to meet flying quality specifications

The design of a longitudinal control sytem for a fighter aircraft using H_∞-norm minimization is considered. The nonlinear aircraft model is linearized at various flight conditions. A linear controller is designed at each flight condition and these linear controllers are then scheduled. The outputs available for control are the pitch rate and the normal acceleration. The elevator deflection is the only control input. For this design, it is recommended that six basic flying quality metrics be met. Some of these flying qualities are expressed in the time domain while others are expressed in the frequency domain. The linearized state-space model of the longitudinal motion of the aircraft at a particular operating condition is given