Medium-sized helicopter noise abatement flight test

An extensive flight test campaign was recently completed, which aims to reduce the operational noise generated by helicopters in an effort to improve community acceptance. Using a ground-based microphone array, acoustic measurements were acquired on helicopters in the medium-sized vehicle weight class over a number of flight conditions including steady level flight, steady descents, and approaches. While data were collected across four helicopters, the Leonardo AW139 and Sikorsky S-76D will be the focus of this paper. Source noise hemispheres are computed for the steady test points, but the ground noise contours measured during approach conditions cover only a small portion of the area impacted by noise because of practical constraints on the size of the deployed array. Thus, the Noise Informed Community Environment Operations Planning System (NICEOPS) in conjunction with the flight test data was used to estimate how changes in the approach procedures impact noise exposure over a larger ground area. It was found that even small longitudinal accelerations can have a substantial influence on the noise generation processes during approach and must be modeled appropriately to develop new flight procedures which minimize the acoustic impact on the ground.