Abstract: The purpose of this paper is to prove the robustness of a scheme of model reference adaptive control system (MRACS) of pitching velocity to the unmodeled long period mode. A special form of state equation is deduced from a factorijed transfer function of longitudinal motion of aircraft. By means of transformation, the effect of the long period mode can be shown as an equivalent slowly varying disturbance acting on the approximate modle of the system considering only the effect of short period mode. By virtue of the performance of MRACS of accommodating the slow parameter perturbation of the plant and are suppre seed the slowly varying disturbances the robustness of the MRACS is to be assured.

Key words: Model reference control, Robustness, Longitudinal motion, Long period mode, Short period mode