Airframe aerodynamic noise—total radiated acoustic power approach

Abstract

During flight the noise radiated by aircraft is emanating from two distinct types of sources. One source is the propulsion system and the other is the nonpropulsion system noise, or airframe noise, associated with movement of the aircraft through the atmosphere. The purpose of this effort was to study airframe noise using a total radiated acoustic power approach. Methodology was developed to accurately calculate the total acoustic power by using measurements from an array of microphones during aircraft flyover. This methodology was applied to Schweizer 2–32 glider flyovers and it was found that for an aerodynamic configuration (no flaps, wheels, wheel wells, etc.) the total acoustic power can be obtained from one flyover measurement by assuming the directivity is nearly equal in all directions. This assumption was shown to be valid for the glider and is assumed valid for any aircraft in an aerodynamic configuration. The detailed methodology developed is still useful since most commercial aircraft land in a nonaerodynamic configuration and thus their directivity is not equal in all directions. The results from the glider tests were compared to data in the literature and found to agree well. Variation of the total power with aircraft velocity followed a V6 law. The parameter which best normalizes the overall acoustic power from different aircraft was found to be the wing area.