Development of a Graphite/Polyimide Composite Transmission Housing

Research and development have been conducted to achieve reductions in helicopter drive system weight and cost and to improve reliability and system performance. A major effort in this area has been the design, fabrication, and test of a high-modulus composite transmission housing. The material system used for this composite transmission housing was graphite fibers in a polyimide matrix. The potential advantages of a composite transmission housing include thermal stability, excellent specific strength and stiffness, and resistance to corrosion, when compared to current magnesium housings. The gearbox selected for this investigation was the CH-47D engine-mounted nose box. This gearbox is a single-bevel-mesh unit with a reduction ratio of 1.23 to 1 and a power capability of 4,600 horsepower at an input speed of approximately 15,000 rpm. A filament-winding fabrication procedure was selected to minimize production cost through the elimination of hand layups, multiple cure cycles, and secondary bonds. Several composite housings were fabricated, machined, and tested during this program. Testing was both static and dynamic through a wide range of operating conditions. The results of this development program, including fabrication and test experience, are presented in this paper.