Life and Reliability Models for Helicopter Transmissions

Life and reliability models are oresen ted for planetary aear trains with a fixed ring gear, input applied to the sun gear, and output taken from the planet arm. For this transmission the input and output shafts are co-axial and the input and output torques are assumed to be coaxial with these shafts. Thrust and side loading are neglected. The reliability model is based on the Weibull distributions of the individual reliabilities of the main transmission components . The system model is also a Weibull distribution. The load versus life model for the system is a power relationship as are the models for the individual components. The load-life exponent and basic dynamic capacity are developed as functions of the component capacities. The computer models are used to compare three and four planet, 150 kw (200 horsepower), 5:1 reduction transmissions with 1500 RPM input speed to illustrate their use.