Multichannel coherence analysis of helicopter vibrations

To understand the mechanisms that delineate helicopter vibrations has been an existing,challenge for decades. In this paper, we used multichannel coherence analysis to examine the flight data of a four-blade helicopter, including lateral and vertical vibrations at the center gravity and blade flapwise bending at 17% and 73% from the center. The linear relationship between multiple harmonics of 1/rev were clearly and quantitatively described using the suggested analysis'. The finding is also consistent with the known mechanical structure of the helicopter.