High-Temperature Hybrid Foil Bearing for Unmanned Aerial System Gas Turbines

Small unmanned aerial systems (UAS) are a critical element in current military operations, and their use will increase substantially in the future. The propulsion system is a key design constraint in any UAS, and current small gas turbines for these vehicles are limited by the conventional oil-lubricated rolling element bearings used to suspend their high-speed rotating assemblies. Gas-lubricated foil bearings offer a potentially attractive alternative, but despite their very successful commercial application to aircraft air cycle machines, they have not been widely used in gas turbine systems due to limitations with high-temperature operation, cost, and a variety of other issues. The objective of the proposed project is to develop a new hybrid foil bearing concept that has the potential to address the key issues inhibiting broad application of foil bearings to small gas turbines. In Phase I, we worked with a small turbine engine manufacturer to define the ideal requirements for such a bearing, developed a design, fabricated a prototype, and tested it in an existing room-temperature test rig. In Phase II, we will further develop the novel foil bearing concept, develop a high-temperature test rig, and evaluate the hybrid foil journal bearing under representative small gas turbine operating conditions.