Measured Sound Levels of the Raisbeck Quiet Turbofan Propellers on Medium-Twin Aircraft

Judicious application of state-of-the-art technologies in aerodynamics and materials has been coupled with newly available CAD/CAM techniques in engine/propeller/airframe integrations to bring about a new class of propellers for general aviation turboprop twins. These new propellers, coined “Quiet Turbofans,” are being retrofitted to today's currently flying general aviation turboprop aircraft, measurably reducing total airplane noise and vibration.

This paper details the results of two distinct applications of these technologies. The Raisbeck Quiet Turbofan System, manufactured by Hartzell Propeller Products, has brought about certified reductions in FAR Part 36 flyover sound levels of approximately 5 dBA for the Beechcraft Super King Air 200/B200 and the deHavilland of Canada DHC-6-300 Twin Otter. Associated cabin and cockpit sound levels have been reduced 7 to 13 dBA, while at the same time increasing the overall performance of these aircraft, Future applications at the new aircraft design level allow virtual elimination of propeller noise and vibration as overriding design considerations.