Design of robust controllers for a fighter aircraft using individual channel design

Controllers are designed for a fighter aircraft using individual channel design (ICD). In ICD the structure of a multivariable system depends on the multivariable structure function γ(s). If the Nyquist plot of γ(s) is close to the (1,0) point at frequencies in the region of and below the gain crossover frequencies of the channel transmittances then it is necessary to improve the structure of the system. Two controllers are designed for the system one using near diagonal pre-compensation and the other using near diagonal pre-compensation together with feedforward control to improve structure. It is shown that the first is robust to plant structured uncertainty only whereas the second is also robust to plant unstructured uncertainty