Feasibility of Gas Bearings for Small High-Performance Aircraft Gas Turbines

Abstract

High temperatures, pressures, and speeds of future Army propulsion systems will impose severe, perhaps intolerable, operating requirements on oil-lubricated engine bearings. Accordingly, air-lubricated (gas) bearings are being investigated as a possible approach to alleviating the lubrication problems. This paper presents results of a study to apply gas bearings to a two-spool gas generator for an advanced 4.5-lb/sec engine. It is shown that gas-lubricated journal and thrust bearings can be designed to carry the maximum loads imposed by flight and landing conditions. Additionally, the resulting engine configuration has promising attributes of compactness and mechanical simplicity. Potential problem areas are identified to be rotor-bearing system stability, LP-spool balancing, and LP-spool seal leakage. One area where feasibility has not been established is durability of the bearing construction materials. Material testing at the high-temperature, high-stress operating conditions of the bearings, including the effects of momentary high-speed bearing contacts, is urgently needed so that the question of material feasibility can be critically assessed.