Variation in Helicopter Noise During Approach Maneuvers

The Helicopter Association International (HAI) "Fly Neighborly" program aims to provide helicopter pilots with recommendations to effectively reduce the noise of their operations. One aspect of this program encourages the development of approach trajectories that avoid airspeed and flight path angle combinations associated with high levels of noise generation. These trajectories necessarily involve changes in speed and flight path angle; i.e., there is an acceleration. To understand the effect of acceleration on noise, a parametric sweep of both longitudinal acceleration and time rate of change of flight path angle (vertical acceleration) were completed for a model of the Sikorsky S-76D helicopter. This was done utilizing a PSU noise prediction system that is a coupled flight simulation (PSUHeloSim), rotor comprehensive analysis (CHARM), and noise prediction code (PSU-WOPWOP). These sweeps are compared with noise predictions for trajectories processed through the PSU noise prediction system that follow flight test data collected in the 2019 joint NASA/FAA/Army flight test.