Detection of Naturally Occurring Gear and Bearing Faults in a Helicopter Drivetrain

Report No. ARL-TR-6795
Authors: Kelsen E. LaBerge; Eric C. Ames; Brian D. Dykas
Date/Pages: January 2014; 26 pages
Abstract: A high-load endurance test was performed on the tail drivetrain of an H-60 Blackhawk helicopter to determine the resistance to gear tooth fracture under power levels exceeding the maximum continuous rating. During posttest inspection, it was found that a tooth had broken off of the tail takeoff spiral bevel gear. In addition, a moderate spall was found on the outer race of the intermediate gearbox input gear shaft support bearing. There were no obvious indications of the gear tooth failure during the duration of the test, making the determination of the time of tooth fracture critical to understanding the resistance of the H-60 tail drivetrain to overloads. This report analyzes vibration data sampled periodically throughout the test to determine the initiation time of these two specific mechanical failures. Both faults occurred naturally in a system environment, making the dataset of particular interest. Several existing gear and bearing vibration analysis techniques were utilized. These methods clearly identified the time of initiation of both the spiral bevel gear tooth fracture and the bearing spall. The capability of the different analysis methods relative to predicting gear tooth crack and bearing spall initiation are compared.
Distribution: Approved for public release
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Last Update / Reviewed: January 1, 2014