New bearing system could cut costs

  • Published
  • By Michael Kelly
  • Air Force Research Laboratory Propulsion Directorate
Advances in bearing systems for engines powering target drones and cruise missiles could cut costs by 20 percent and increase fuel efficiency.

Scientists and engineers in the Air Force Research Laboratory's Propulsion Directorate are testing a bearing using a compliant foil -- a thin, flexible sheet of metal -- rather than conventional parts like balls or rollers.

An air foil bearing developed by experts from Mohawk Innovative Technology Inc., is being tested in a target drone engine at Williams International, in Walled Lake, Mich. Tests are expected to be completed in June.

The advanced bearings support an engine's rotor on an air film, eliminating the need for traditional bearings and their related lubrication system, said Matt Wagner, the project's manager and a mechanical engineer in the directorate's turbine engine division.

"Conventional rolling element bearings produce frictional drag and require cooling, both of which decrease engine performance," he said. "Eliminating the current oil-mist lubrication system and roller bearing from the WJ24-8 (engine) could reduce engine weight by as much as 10 percent."

Bearing lubrication systems in aerial targets or drones, and cruise missiles typically account for 10 to 30 percent of the engine cost and weight, as well as a large portion of maintenance Wagner said. In contrast, air foil bearings require no lubrication system; need little cooling and produce much less friction than their predecessor.

Air foil bearings also operate at much higher speeds and temperatures, which helps next generation engines with greater capabilities and efficiencies built in, Wagner said.

Foil air bearings have been around since the 1970s and used primarily in aircraft air cycle machines circulating air through the cabin for environmental control. They have historically been limited in size, load capacity and high temperature operation -- until now, Wagner said.

Recent research programs conducted by the propulsion directorate and NASA experts addressed each of these areas, he said. The bearing has been successfully developed for future testing in the Joint Expendable Turbine Engine Concept engine demonstrator, known as the XTL-87.

The WJ24-8 tests demonstrated stable operation of the air foil bearing throughout a series of cyclic and mission simulation testing, Wagner said. The data from these tests will be used to assess the use of foil bearings on other gas turbine engines for military and commercial systems. (Courtesy of Air Force Materiel Command News Service)