Thickness and Loading Noise from Helicopter Rotor at various Pitch Angles

Noises from the helicopter rotor model are calculated numerically at various pitch angles. The aerodynamic data are calculated by using prescribed wake model and unsteady panel method. The distribution of aerodynamic loads on the blade surface are obtained from 0o to 9o pitch angles with equiangular increments of 1.5o. Although thickness noise is not related to the change of pitch angles, loading noise level increases about 3~4dBA every 1.5o increment of pitch angle. The additive noise level shows sufficient value to perceive the loudness. From the result of directivity pattern the sound level at the lower region of the blade disc plane is higher than that of the upper region.