Development testing of hybrid bearings with M.50 rings and HIPed silicon nitride balls in small high-speed turbojet engines was carried out for several minutes at speeds up to 110,000 rpm. The main rotor system comprised an overhung radial compressor and turbine monorotor assembly with a pair of preloaded 101-size bearings. Estimated aerodynamic thrust of up to 750 N (170 lb) was added to the 200 N (45 lb) preload on the bearing adjacent to the compressor. Some testing was carried out with MIL-L-7808 air/oil mist and some with JP-10 fuel supplied in a similar fashion. After each test phase the bearings were removed for examination and re-used or replaced. Four of the bearings were submitted to inspection with special equipment to measure operating contact angles, as evidenced by the visible ball tracks, and any wear present. Contact angles and other operating characteristics estimated with the Jones, “SHABERTH,” and “ADORE” computer codes were compared with the experimental data.

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