This report documents a flight test conducted on the experimental Beech 1900D, operated by Raytheon Aircraft. The flight test was conducted primarily to gain insight into the nature of the air-borne fuselage excitation due to the propellers. A secondary goal was to record wing spar vibrations as a measure of the contribution of structure-borne excitations from the wing and power plant to interior noise. A coarse interior noise survey was also conducted in the passenger section of the fuselage. Twenty flush-mounted microphones were attached to the fuselage exterior to monitor the air-borne excitation in the vicinity of the propellers. Four accelerometers recorded the fore and aft wing spar vibrations at the attachment to the fuselage. A reference microphone and a moveable, 8-microphone array were used to record interior noise. Data analysis has revealed that the point of highest sound pressure on the exterior lies forward of the propeller plane during all flight conditions. The magnitude of the excitation tends to decrease in proportion with the inverse of distance from the point of highest sound pressure. The relevance of this observation is that the excitation from a propeller can be very easily modeled in analysis.

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