A Review of Noise and Vibration Control Technologies for Rotorcraft Transmissions

An expanded commercial use of rotorcraft can alleviate runway congestion and improve the accessibility of routine air travel. To date, commercial use has been hindered by excessive cabin noise. The primary noise source is structure-borne vibration originating from the main rotor gearbox. Despite significant advancements in gear design, the gear mesh tones generated often exceed 100 dB. This paper summarizes the findings of a literature survey of vibration control technologies that serve to attenuate this vibration near the source, before it spreads into the airframe and produces noise. The scope is thus limited to vibration control treatments and modifications of the gears, driveline, housing structures, and the strut connections to the airframe. The findings of the literature are summarized and persistent and unresolved issues are identified. An emphasis is placed on components and systems that have been demonstrated in flight vehicles. Then, a discussion is presented of emerging technologies that have the potential to make significant advancements over the state of the art.