ADVANCED ROTORCRAFT TRANSMISSION DEVELOPMENT - A TECHNOLOGY RECONVERSION PROGRAM

McDonnell Douglas Helicopter Systems with Lucas Western, Inc. as part of the Army/NASA Advanced Rotorcraft Transmission (ART) Program developed a transmission design that made use of face-gears for a torque splitting concept. Recently, a Technology Reconversion Program (TRP) was proposed by and awarded to the MDHS/LWI team to design, build and test a full size split torque demonstrator transmission. The development of a grinding process for the face-gears is also under way as part of this program. This grinding capability will allow use of case-hardened, aerospace quality face-gears. This paper presents the key design concepts of the demonstrator transmission. Two designs have been evaluated. The first design is a modified version of the three-stage ART transmission. The face-gears were arranged over and under the flexibly-mounted pinion to provide an equal division of power. The second design is a closed-loop high gear-ratio face-gear stage followed by a planetary system. In this design, the equal torque division is achieved through the use of idler pinions. Both designs significantly reduce the size, weight, and the number of reduction stages required. To substantiate the initial concept, durability tests and split torque tests were performed on one-half scale shaper-cut face-gears. The tests demonstrated the feasibility of using face-gears in high-speed, high-load applications and for uses requiring accurate splitting of torque. This paper also presents the new experimental test programs on the surface-hardened gears and the analysis methods which support the development of the TRP transmission demonstrator. The success of this new transmission will provide significant advancements in face-gear design, manufacture and application.