Vibration Measurements on Planetary Gears of Aircraft Turbine Engines

Abstract

Planetary reduction gear stages are an efficient, compact, and lightweight means of speed reduction and are, therefore, used in many aircraft turbine engines. In the PT6 engines, of which more than 13,000 have been produced, the planetary reduction gearboxes allow a speed reduction from more than 30,000 to about 6000 rpm in turboshaft and 1210-2200 rpm in turboprop applications. These gearboxes have been developed to a high level of reliability. The continuing demand for uprated or new higher powered designs requires a good understanding of the design factors that play a role in the dynamic gear loads and motions. The theoretical dynamic analysis of a planetary gear stage is quite complex due to the multiple, nonlinear gear meshes. Therefore, the development of these gearboxes depends to a high degree upon engine running experience and detailed dynamic measurements. A variety of dynamic measurements taken on PT6 reduction gearboxes over a number of years is reviewed. Peculiar behavior found in these tests is discussed, such as load sharing among planets, responses due to gear errors, and a dynamic instability.