Ceramic Hybrid Bearings in Air-Cycle Machines

Extensive research in the field of ceramic rolling contact bearings has been conducted over the past several years. The results of this research indicate that silicon nitride may offer significant improvements in rolling fatigue life and a possible increase in operating temperature. AlliedSignal Aerospace Systems & Equipment (ASE) and the Air Force Item Management Engineering Branch at Tinker Air Force Base are conducting a development program under contract to ARPA to introduce ceramic hybrid bearings into existing F-15, F-111, and C-130 aircraft fleets in a near-term program involving retrofitting mature air-cycle machines with such bearings. The air-cycle machine (ACM) is a complex bearing application, operating at very high speeds (up to 100,000 rpm) and at high temperatures. In more severe military ACM applications, mean times between failures (MTBFs) of 2000 and 3000 hours are common. The fleet would see an immediate benefit from improved bearing life. This paper describes the analytical approach to evaluating and comparing ceramic to steel bearings, describes the laboratory test program to verify performance, and discusses the life-cycle cost improvement and the flight test program.