Determination of Turboprop Reduction Gearbox System Fatigue-Life and Reliability From Computer Generated Tests

Two computational models for the fatigue life and reliability of a turboprop gearbox are compared with each other and with field data. The two models are (1) Monte Carlo simulation of randomly selected lives of individual bearings and gears comprising a gearbox and (2) life analysis of the bearings and gears in the gearbox using the two-parameter Weibull distribution and the Lundberg-Palmgren life theory. These results were compared with field life results from 75 gearbox failures. Field data for the gearbox resulted in an L₁₀ life of 2100 hrs. and a Weibull slope of 1.3. The Lundberg-Palmgren method resulted in a calculated L₁₀ life of 1735 hours and a Weibull slope of 1.17. For the life estimation produced by the Monte Carlo method, the median L₁₀ life approached 1775 hours and the Weibull slope approached a value of 1.21. There is reasonably good engineering correlation between the life results obtained from the field data and those predicted from the Lundberg-Palmgren analysis and the Monte Carlo simulation.