Acoustical signature analysis of a helicopter cabin in steady-state and run up operational conditions

The noise situation inside modern helicopter cabins is still unsatisfying in comparison to modern jet. The requirement of a quieter helicopter needs a systematic study of its NVH (Noise Vibration Harshness) behaviour. In this context, the authors have performed a wide experimental vibro-acoustic campaign in a helicopter cabin, which aims at evaluating the importance of the noise contribution produced by the jet engines with respect to the gearbox as well as finding possible noise sources and leakage points on the cabin surface. The results show that the main noise and vibration sources are the jet engines and the gearbox. Furthermore, the contribution of the jet engines is dominant with respect to the contribution of the gearbox, in terms of sound quality parameters. Finally, the paper suggests a fast and efficient experimental tool for leakage point detection and relative quantification on the cabin, very useful for noise control and quality check.