Accurate mathematical model for describing electrohydraulic loading system of helicopter pitch adjusting hydromechanical servos

This paper deals with the establishment of the exact mathematical model for describing the electro-hydraulic load system which is applied to the earth-experiment of the hydromechanical servomechanism (hydraulic assistor) for the helicopter pitch adjusting. Based on the working principle analysis of the electro-hydraulic load system, the accurate mathematical model of electric-hydraulic loading system is established and the influence of the model on the system characteristics is deeply analyzed. It is proved that surplus force is concerned with not only the velocity but also the acceleration of rudderpost. Moreover, the traditional structure invariance principle is improved. Experiments in the paper validate the correctness of complex mathematical model, of which the guiding effect in eliminating the extraneous force is revealed also.