Abstract: The aircraft control surface defaults of rudders were mainly divided into jam fault and damage fault. On the basis of the relationship between motor toque and hinge moment, a new method of using the motor voltage was proposed to detect the control surface'faults of rudder. And the method could detect the damage degree of the faults. Torque motor was used to play the role of hinge moment. And the new method was simulated by Semi-Physical system which is consisted of dSPACE system, PC and simulated rudder actuator. The results show that, the damage faults and jam faults can be detected in 0.5s between 1.5s. And also it can detect the damage degree. According to the above, this method has good practical value.

Key words: diagnosis of actuator fault, jam fault, damage fault, dSPACE