Abstract: The synthesis of frequency-shaped weighting matrixes in the quadratic cost functional and the theory of implicit model-following is presented and the approach to select frequency-shaped weighting matrixes is studied. The procedure using this method to design flight control law is given. In the synthesis the stability, desided transient and ste-ady-state response characteristics and robustness of system are considered so as to get the satisfactory synthetic results. This mehtod is used to design a flight control law for a fight aircraft. In comparison with the flight control law designed by using normal linear quadratic method, the flight control law designed by using this method has not only satisfying stability and transient response characteristics but robustness is also improved. The structural mode response of the aircraft is well suppressed. These results are proved by digital simulation and real-time microprocessor realization.

Key words: optimal linear-quadratic, optimal quadratic with frequency-shaped weighting matrixes, implicit model-following, flight control system