Sun Gear Fault Detection on an OH-58C Helicopter Transmission

Detecting seeded faults on a full-scale helicopter transmission is the focus of this paper. Two methods to isolate the dynamics of an individual sun gear, in an effort to assess its condition, are developed and validated on an OH-58C helicopter transmission's planetary reduction stage. Planetary indexing is used to geometrically synchronize dynamic measurements with the positions of the meshing teeth. This provides the opportunity for source/signal mapping that can lead to increased sensitivity, allowing faults to be detected earlier and thus increasing the available time for corrective action. Special measurement and data processing techniques are needed to filter out the effects of the planet gears, bearings, input spiral bevel stage, and other components in and around the gearbox. Two sun gears, which were damaged in previous fatigue tests, serve as the focus of this current work. A vibration separation (VS) algorithm, for the non-sequential OH-58C transmission was developed and the resulting signals analyzed. A non-VS based method, which uses only the time synchronously averaged data and takes advantage of the signal/source mapping required for VS is also developed. The FM4 condition indicator is used to compare the two damaged cases with the baseline. Both algorithms were successful in identifying the damage on the sun gear with multiple faults. Sun gear damage was confirmed by the presence of sun mesh groups.