Effects of impulsiveness on noisiness of helicopter noise

An experiment was conducted to examine the effects of impulsiveness on the noisiness of helicopters. Subject groups located outdoors and inside two houses listened to and judged the noisiness of two helicopters and a propeller airplane, which was used as a reference. The impulsive characteristics of one of the helicopters was controlled by varying the main rotor rotational rate while maintaining a constant airspeed which resulted in other characteristics of the noise being held relatively constant. Other controlled variables included altitude and sideline distance. Preliminary analyses indicate that within each altitude and sideline distance condition, the level of impulsiveness is positively correlated with noisiness. Across helicopter types and flight conditions, however, the addition of an impulsive correction factor did not significantly improve the correlation between the noisiness judgments and noise units such as EPNL which is being considered as an international standard. Comparisons of results between subject groups within the houses, while reasonably correlated, indicate significant effects of the orientation of the rooms with respect to the aircraft flightpaths.