Finite Element Contact Analysis and Redesign of Rotorcraft Planetary Gear Sets With Asymmetric Profiles

This article explores the use of asymmetric gear teeth for rotorcraft main rotor planetary gearsets. Two baseline designs having symmetric gear teeth were selected for redesign studies. Finite element-based contact analyses were used to compare designs. Bending stress predictions for the two existing baseline designs were compared to strain gage measurements to confirm the suitability of the modeling. The same modeling method is then used to assess design changes to improve the bending stress and contact pressure magnitudes using asymmetric tooth profiles. For the first redesign study, the selected gearset is mildly asymmetric, with a 4° difference in pressure angles between the two sides of a tooth. For the second redesign study, the selected gearset is strongly asymmetric with a 18° difference in pressure angles. The results demonstrate that the asymmetric tooth approach provides additional design flexibility toward balancing the contact stresses and bending stresses of the sun, planet, and ring members.