Design Analysis of Pericyclic Variable-Speed Transmission System for a 600 HP Class Unmanned Rotorcraft

摘要

Speed variation mechanisms in rotorcraft transmission systems can introduce weight penalties to the system. It is significant to explore innovative, light-weight, reliable and efficient transmission concepts for the variable rotor-speed rotorcraft systems. The Pericyclic Variable-speed Transmission (PVT) is a nutating gear train, which is capable of being driven by a variable speed mechanism. The PVT enables very high reduction ratios in a compact design. An integrated design analysis has been developed. Kinematics, gear tooth bending stress, bearing contact stresses, bearing roller deformations and mesh efficiencies are analyzed. The use of the PVT system for a conceptual 600 HP Unmanned Rotorcraft is explored. The candidate transmission has a 7:1 ratio variable speed PVT stage with 50% speed capability, and a 14:1 fixed speed stage. Within the estimated design space, the minimum total weight of the PVT gears is 52 lb (4 inches diameter at the first stage and 8 inches at the second) and the maximum is 128 lb (7 inches diameter at the first stage and 12 inches at the second). The efficiency of the PVT is estimated based on the published friction coefficients, the PVT kinematics. The averaged efficiency of the conceptual Unmanned Rotorcraft PVT system is approximately 98%.