Detection And Analysis Of Interior And Exterior Noise Sources In A MD902 Helicopter

Exterior helicopter noise is often perceived as loud and unpleasant by people boarding the helicopter or people living in urban areas or close to airports where rotorcraft is flying. Excessive cabin noise in the helicopter is also an issue for passengers or crew flying the helicopter, especially for long duration flights. The objective of the paper is to investigate commercially available techniques for measuring and analyzing helicopter noise and ultimately help design engineers get insight into noise mechanisms in view of potential noise improvements. Exterior noise measurements were performed on a MD902 helicopter equipped with a Notar (No TAil Rotor) system. State-of-theart focalization and deconvolution techniques are presented to localize and rank dominant noise sources and identify aeroacoustic phenomena or mechanical devices responsible for the helicopter noise signature. Primary and secondary sources are clearly identified which provides guidance for possible noise reduction measures. Main rotor noise is found to be clearly dominating the overall noise spectra whereas Notar, engine exhaust and cooling system constitute secondary sources. Interior noise is also investigated for various flight conditions and dominant noise sources are localized in the cabin and some possible noise control treatments are suggested. It is shown here that the acoustic array technique is a very efficient and well suited tool to analyze both interior and exterior helicopter noise.