Measurement of Rotor Noise Levels and Evaluation of Porous Blade Tips on a CH -47A Helicopter

Abstract : Two sets of acoustical data were correlated. Relative blade tip-path plane positions influence noise levels more than other operating parameters such as rotor speed or gross weight. Porous blade tips were installed on the test aircraft. The tips reduced noise levels in hover but had no consistent effect in forward flight. However, the tips tended to decrease the sharpness of the acoustical signature at all airspeeds.