Experimental guidelines for NVH improvements in helicopter vibro-acoustic comfort

The noise of helicopters has started to become an important issue and the next level technical challenge is to include new design parameters such as vibro-acoustic comfort in the design process of a modern rotorcraft. In this scenario a wide experimental campaign has been performed on a EC-135 helicopter cabin in order to assess the effectiveness of several techniques for NVH (Noise Vibration and Harshness) improvements. Vibro-acoustical modal analyses of the cabin internal and external surface as well as a pure acoustical modal analysis of the cabin enclosure have been performed in order to verify the vibro-acoustical coupling between the cabin cavity and the cabin mechanical structure. Secondly a detailed leakage point detection on the cabin walls has been carried out by a few techniques finding out possible noise sources. Through such experimental analyses, some guidelines are suggested as well as particular techniques/instrumentations in order to improve human comfort on the helicopter cabin.