Advancements Toward Oil-Free Rotorcraft Propulsion

NASA and the Army have been working for over a decade to advance the state-of-the-art (SOA) in Oil-Free Turbmachinery with an eye toward reduced emissions, and maintenance, and increased performance and efficiency among other benefits. Oil-Free Turbomachinery is enabled by Oil-Free gas foil bearing technology and relatively new high-temperature tribological coatings. Rotorcraft propulsion is a likely candidate to apply Oil-Free bearing technology because the engine size class matches current SOA for foil bearings and because foil bearings offer the opportunity for higher speeds and temperatures and lower weight, all critical issues for rotorcraft engines. This paper describes an effort to demonstrate gas foil journal bearing use in the hot section of a full-scale helicopter engine core. A production engine hot core location is selected as the candidate foil bearing application. Rotordynamic feasibility, bearing sizing, and load capability are assessed. The results of the program will help guide future analysis and design in this area by documenting the steps required and the process utilized for successful application of Oil-Free Technology to a full-scale engine.