Dynamic Analysis of Rotorcraft Planetary Gears Using a Finite Element/Contact Mechanics Model

This study investigates the vibration of the OH-58A and OH-58C planetary gear stages at operating conditions using a finite element/contact mechanics model. These two planetary gears have identical sun, planet, and ring gears. They differ in the number of planets, the planet spacing, and the mesh phasing, which results in substantial differences in their vibration characteristics. The elastic vibrations at fixed points on the ring outer diameter of both planetary gears have spectra with frequency content in clusters near each harmonic of mesh frequency. The OH-58A planetary gear, which has equally-spaced planets and in-phase meshes, has the same frequency components near each harmonic of mesh frequency. They include response at mesh frequency harmonics and upper and lower sidebands at multiples of the planet pass frequency. The OH-58C planetary gear has different frequency content than the OH-58A because it has diametrically-opposed planet spacing and gear meshes that are out-of-phase. The frequency content near odd harmonics of mesh frequency differs from that near even harmonics. There is no response at odd harmonics of mesh frequency, and upper and lower sideband frequencies are prominent. Response occurs at even harmonics of mesh frequency. Upper and lower sideband frequencies occur at multiples of twice the carrier frequency. The amplitudes of the sideband frequencies are sensitive to the system's input torque.