Design study of a split-torque helicopter transmission

Abstract

A helicopter transmission with split-torque drive trains to the main rotor and tail rotor drive shaft is described. A design based on two 1200 kW engines supplying torque to a 350 r/min main shaft demonstrates a weight reduction of 40 per cent, extreme low height and reduced losses. Four double-helical pinions drive a combining gear and provide a 10:1 reduction ratio to the main shaft; flexible torque tubes, set by fine-difference splines, control the division of torque between pairs of pinions. Rotor loads bypass the transmission housings and pass to the fuselage through a large-diameter mast that encloses an integral sump and cooler.