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65 decibels absolute coefficient acceptable actually aerodynamic Aeronautical Aeronautical Laboratory airplane noise airports altitude Angle of attack application approximately Arthur assumed axis blade calculated Chief Cleveland compared complete conventional decibels decibels higher demonstrated desirable determined developed diameter difference direction Director distance drag Efficiency engine feet Field figure five-blade propeller flight Force frequency given ground horsepower inches increased indicates John Langley Light Airplanes loudness level maximum measurements miles per hour modified airplane modified test airplanes muffler NACA TN necessary noise level Office operating performance personal airplanes Pitch Positive pounds presented pressure problem produce quiet rated ratio reduction reference relating relative REPORT Research response Rotating scale shown in figure shows sound SOUND-LEVEL sound-pressure level speed standard SYMBOLS take-off theoretical thrust tion two-blade propeller United unmodified Vice President weight wooden
Page 6 - Aeronautical Laboratory, National Advisory Committee for Aeronautics, Langley Field, Va., February 12, 1958.