Helicopter Transmission Noise Mechanisms, Analysis Methods, and Noise Reduction Techniques

摘要

Military and commercial helicopter transmissions are typically comprised of various gear reducingrnstages connected to bearing packages which are enclosed by metal housings. A schematic of arntransmission in the U.S. Army’s OH-58C helicopter reproduced from Coy et.al. [1] is shown in Figure 1.rnAn external motor powers an input shaft which rotates at a high speed. A spiral bevel gear at the end ofrnthe input shaft drives the gear reduction system, usually a planetary gearset, which then outputs power tornthe rotor at a much lower rotational speed. Since the gear geometries and alignments are never perfect,rnfluctuating forces are generated at many tooth, or gear meshing frequencies (GMF) when therntransmission operates. The forces are transmitted through the bearings and into the housing, which then:rn1. radiates sound directly from its surface into the cockpit, andrn2. transmits forces into the helicopter fuselage through its mounting connections, which in turn vibratesrnand radiates sound into the cockpit.