Low Noise Propeller Technology Demonstration
Final technical rept. 15 Feb 1973-Jan 1974
LOCKHEED-CALIFORNIA CO BURBANK
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Quiet aircraft used for covert aerial night reconnaissance employ low tip speed propellers to achieve a minimum acoustic noise signature. This study was initiated when certain unexpected and anomalous trends in the measured propeller noise of such aircraft were compared to predictions of noise made by the Air Force Propeller Noise Prediction Program. Large discrepancies in both trends and levels were noted between measured and predicted noise. Therefore, the goal of this study was the modification of an existing Air Force computer program such that accurate predictions of far field noise for low tip speed propellers can be made. Empirical data from previous quiet airplane experiments were used to develop modifications to both rotational and vortex noise prediction methods for propellers operating in the tip speed range from Mach 0.2 to 0.4.