Experimental Determination of AH-64 Apache Tailshaft Hanger Bearing Vibration Characteristics with Seeded Faults

Report No. ARL-TR-4865
Authors: Brian Dykas, Timothy Krantz, Harry Decker, and David Lewicki
Date/Pages: June 2009; 30 pages
Abstract: A series of seeded fault experiments are conducted to evaluate the characteristics of degraded AH-64 Apache helicopter forward hanger bearings, which support the tail rotor drive shaft. This bearing is one of a handful of maintenance-intensive components originally identified for condition-based maintenance proof of principle. Several fault modes are simulated in the test specimens including salt water corrosion, sand contamination, and trench flaws on the races. The vibration characteristics of the faulted bearings are then recorded in a component-level bearing test stand, and analyzed to corroborate or modify current fault detection methodology in the aircraft. For the bearings with substantial amounts of damage or removed material, the vibration response showed increase content in a portion of the spectrum not monitored by the condition indicators now in use. Impact experiments suggest this is a result of the bearing vibration exciting the hanger assembly natural frequencies.
Distribution: Approved for public release
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Last Update / Reviewed: June 1, 2009