Helicopter transmission research Available to Purchase

CURRENT HELICOPTER MAIN TRANSMISSION SYSTEMS must reduce the gas‐turbine engine speed by a typical ratio of 80:1 to drive the main rotor. Existing technology dictates that this ratio is achieved in 3 or 4 stages of gearing, where each stage is either an epicyclic gear assembly, a spiral bevel gear pair or a helical gear pair. Gear tooth reaction forces can be as high as 20,000lbf (90kN) both axially and radially, so large gears and as many as 3 heavy duty rolling elements bearings per gear shaft are required. Transmission systems thus typically account for 10 per cent of all‐up‐weight, the main gearbox taking up 75 per cent of this and the bearings accounting for 20 per cent of the gearbox weight. Scheduled overhaul periods are seldom more than 1,000 flying hr due partly to the likelihood of rolling element bearing fatigue failure and many require overhaul before this time is reached. Thus the research effort on transmission systems, and specifically on gearboxes, is directed in general terms towards achieving:—