Interior Noise Source/Path Identification Technology

Excessive interior noise and vibration in propeller driven general aviation aircraft can result in poor pilot communications with ground control personnel and passengers, and, during extended flights, can lead to pilot and passenger fatigue. Noise source/path identification technology applicable to single engine propeller driven aircraft were employed to identify interior noise sources originating from structure-borne engine/propeller vibration, airborne propeller transmission, airborne engine exhaust noise, and engine case radiation. The approach taken was first to conduct a Principal Value Analysis (PVA) of an in-flight noise and vibration database acquired on a single engine aircraft to obtain a correlated data set as viewed by a fixed set of cabin microphones. A Conditioned Response Analysis (CRA), combining ground test noise source simulation frequency response function data with the in-flight PVA vectors, was then carried out to identify the relative contributions of each of the simulated sources to the cabin noise levels as measured by the fixed set of cabin microphones. Results of the analysis showed the aircraft interior noise to be generated from several airborne sources, including the propeller, exhaust, and engine case radiation. Structure-borne engine/propeller vibration was not found to be a significant contributor to interior noise. The major paths of noise propagation were identified to be the aircraft windshield and firewall.