The Effect Of Various Operating Parameters On The Noise Radiation Patterns From A Helicopter In Forward Flight

The in-flight noise radiation pattern and spectra were measured for a small helicopter over a range of rotor speeds, airspeeds, and main rotor thrust values, and for a wide range of distances snd azimuth angles. The resulting noise radiation patterns were distorted in the direction of flight; A 20-percent rotor speed reduction resulted in substantial noise level reductions. On the other hand, a 50-percent reduction in airspeed and a 17-percent reduction in main rotor thrust resulted in very little noise reduction.