Multichannel coherence analysis of helicopter vibrations

To understand the mechanisms that delineate helicopter vibrations has been an challenge existing for decades. We use multichannel coherence analysis to examine the flight data of a four-blade helicopter, including lateral and vertical vibrations at the center of 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.