Vibration analysis and experiment of the helicopter rotor test stand transmission

The transmission vibration characteristics of the helicopter test stand was analyzed using the transfer matrix method, including the torsional vibration and the lateral vibration. The torsional vibration modal frequencies and the modal shapes of each order were obtained by analyzing the torsional vibration of the rotor test stand transmission; What´s more, each order natural frequency and the relationship between the lateral vibration and the supported stiffness of the test stand transmission were obtained by analyzing the lateral vibration of the transmission of the rotor test stand. While the rotor velocity ran from 200rpm to 960rpm, the axis vibrations of X, Y, Z were being measured in the experiment. After the rotor ran over the resonance of the test stand (about 780rpm) to the spindle speed of 960rpm, the test stand would have been in steady run for about 2-3 seconds then the vibration went diverge, and the peak would be about 4g. That frequency of the spindle speed leading to vibration diverge was just right the 1^st order natural frequency of the lateral vibration. Based on the analyzed of the torsional vibration and the lateral vibration of the transmission of the rotor test stand, it was concluded that the less of the supported stiffness of the rotor test stand transmission leaded to the vibration diverge, and two methods of dealing this malfunction were given: improve the supported stiffness or let the rotor run over the resonance area fast including the test stand and the transmission.