The Helicopter Transmission Design Process,

The purpose of the helicopter transmission or drive system is to deliver power from the engines to the rotors and also to accessories such as hydraulic pumps, generators, and air conditioner compressors. The design of a new helicopter drive system involves an extensive series of tasks that may take three or four years from predesign to qualification. Even after the new drive system is qualified, the transmission designer must keep himself aware of how the system is performing in the field to correct any service-related problems and to further his knowledge for the next design. The transmission design process involves six major tasks predesign, design, manufacturing coordination, bench testing, aircraft testing, and field service support.