Helicopter noise reduction through gearing modifications

摘要

A transmission is provided wherein selected configurational parameters of interacting spur gearing are modified to abate the vibration levels thereof due to the effects of differential thermal expansion of the gearbox housing. The chordal addenda of the gear teeth of the interacting spur gearing are extended by a predetermined amount, based upon the computed relative radial displacement of the centerlines thereof due to the differential thermal expansion effects, to provide modified interacting spur gearing having increased outside diameters. Such modified spur gearing provides an effective centerline spacing for the transmission such that the interacting spur gearing thereof has an operating contact ratio greater than the design contact ratio at engine start up. As the transmission reaches stabilized operating conditions the operating contact ratio of the modified spur gearing is substantially equal to the design contact ratio due to the effects of differential thermal expansion on the transmission gearbox housing. In addition, the helix angle of the interacting spur gearing is substantially increased to counteract the effects of differential thermal expansion on the gearbox housing.