Using P-U probes for the experimental vibro-acoustical modal analysis of a helicopter

Vibration reduction is an extremely important task to avoid fatigue and comfort problems; for this reason, the helicopter designer should make the spaced peaks of the input force spectrum coincide with the valleys of the structural frequency response functions. Experimental modal analysis is used for such a purpose. In order to provide the necessary insights, wide testing campaigns are very often carried out. The aim of the paper is to show the usefulness of the Microflown technology in this field, instead of classical methods such as accelerometers and scanning laser vibrometers. In particular an experimental vibro-acoustical modal analysis of an helicopter EC-135 is presented. The system has been excited by means of a low frequency loudspeaker located inside the cabin, and a 4x4 Microflown array has been used to measure pressures and particle velocities simultaneously. The results shown in this paper highlight the effectiveness of the Microflown technology in this context: in fact, with just one measurement, one gets the needed data allowing to carry out both a modal analysis and an acoustic intensity calculation for noise sources identification.