Airframe Noise Flight Test Measurements Using an Electret Condenser Microphone Array

An extensive collection of airframe noise flight test data has been acquired for a regional jet class of aircraft using a ground-based electret condenser microphone phased array system. The measurements were conducted at the Wallops Flight Facility for the NASA Aeronautics Research Mission Directorate's Fundamental Aeronautics Program. Gulfstream G450 and G550 aircraft were used as the test beds for the study. The phased array employed for the measurements consisted of a spiral clustering of 167 Panasonic WM-61A quarter-inch, omni-directional electret microphones. The innermost 49 sensors of the array were flush-mounted on a rigid aluminum plate with the remaining sensors flush-mounted on individual 16-inch circular Plexiglas platters. The aluminum plate and platters were deployed on the overrun area of runway 4 at Wallops. Airframe noise measurements were performed with the aircraft flying a ?racetrack? pattern simulating the approach path to landing as is passed over the phased array. A distributed data acquisition system was used to acquire simultaneous time history data from the array and was synchronized with instrumentation onboard the aircraft. This presentation will discuss the design of the phased array, the calibration and deployment of the microphones, a sampling of the measurements obtained from the system, and lessons learned from the deployment.