Ceramic hybrid bearings are like conventional bearings, except that the steel rolling elements have been replaced with ceramic elements. The ceramic rolling elements in hybrid bearings offer many benefits, including low density, high hardness, low thermal growth effect, corrosion resistance,
and favorable frictional characteristics. However, damage detection for ceramic hybrid bearings has been an issue in the aerospace industry since their introduction. In the aerospace industry, the lack of effective and reliable silicon nitride detection devices limits the immediate use of
ceramic hybrid bearings to applications that do not depend on continuous and automatic health monitoring devices, but instead require monitoring by maintenance personnel. One such application is the helicopter tail rotor drive shaft hanger bearing. Typically, tail rotor drive shaft hanger
bearings have no in‐flight damage detection system. Bearing damage is detected by manually rotating the bearing and feeling for any perceived roughness. Hanger bearings are often configured as sealed grease packed bearings. Many of these bearings also have means provided for regreasing.
The objective of this paper is to present the results of a series of tests designed to determine the suitability of ceramic hybrid bearings in helicopter hanger bearing applications. The discussion includes the results of 100‐ and 200‐h side‐by‐side hybrid and steel
bearing endurance tests. In addition, the results of a 100‐h run‐dry hybrid bearing test, conducted at the same load and speed as the endurance test, are presented. Finally, ceramic hybrid bearing failure modes are discussed, damage detection methods for hanger bearing applications
are proposed, and data taken from a single, extreme load test are discussed.
Technical Resource Specialist, Staff Engineer, Bell Helicopter Textron, Inc., Fort Worth, TX
Publication date: July 1, 2009
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