Air/gas foil bearings (AFB) have shown a promise in high-speed micro to mid-sized turbomachinery. Compared to rolling element bearings, AFBs do not require oil lubrication circuits and seals, allowing the system to be less complicated and more environment-friendly. Due to the smaller number of parts required to support the rotor and no lubrication/seal system, AFBs provide compact solution to oil-free turbomachinery development.While foil bearing technology is mature in small industrial machines and power generation turbines, its application to aero-propulsion systems has been prohibited due to the reliability issues relevant to unique aero-propulsion environments such as severe rubbing due to the very slow acceleration of typically heavy rotors. This paper presents a hybrid air foil bearing (a combination of hydrostatic and hydrodynamic) with 102 mm in diameter designed for aero-propulsion applications, and preliminary test results on start-stop friction characteristics and thermal behavior at low speeds below 10,000 rpm are presented. The bearing could withstand 1000 start/stop cycles with 6 rev/s2 acceleration under a static load of 356 N (43.4 kPa).

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