Face Gear Development Under the Rotorcraft Drive System for the 21st Century Program

U.S. Army goals established for the Rotorcraft Drive Systems for the 21st Century Program were to achieve a 35% increase in horsepower to weight ratio, a 12dB reduction in gearbox generated noise, and 20% reductions in operating, support and acquisition cost. Boeing’s technology transition goals required that the operational endurance level of the face gearing and split-torque designs be validated to a TRL 7, and that analytical and manufacturing tools be validated. Face gear technology was developed during this project as a high power density gear set which splits torque evenly and quietly along two load paths to demonstrate the power density characteristics of the Boeing split torque face gear concept. Full scale system testing was conducted to verify the endurance of a concept demonstrator transmission, and statistical data were generated to substantiate face gear surface fatigue characteristics. The technologies were transitioned to the Boeing Apache Block III Program.