F117-PW-100 Hybrid Ball Bearing Ceramic Technology Insertion

Results of an Advanced Research Projects Agency (ARPA) sponsored project to demonstrate the operational benefits of incorporating advanced structural ceramic ball elements into the F117-PW-100 aircraft gas turbine engine high rotor thrust bearings is described. This program consists of design, fabrication, and experimental evaluation of candidate hybrid ball bearing designs in Pratt & Whitney and MRC Bearings test facilities. The bearing design criteria and development test conditions utilized for the project are compatible with the requirements of the F117-PW-100 engine system application. Two hybrid bearing designs were produced by analytically varying internal geometry features such as M-50 race curvatures and contact angles to optimize for the modulus of elasticity of the ceramic balls. CERBEC grade NBD 200 silicon nitride ceramic balls (1 1/8 in. size) demonstrated integrity and a quadruple rolling contact fatigue life improvement versus state-of-the-art M-50 steel balls in single ball test rigs. Thermal performance data obtained in full-scale bearing rig performance testing with 178 mm size hybrid and all-steel baseline bearings shows comparable characteristics. The hybrid bearing displayed a distinct survivability benefit in bearing liquid lubricant starvation testing. Two dozen hybrid bearings will be fabricated for full-scale bearing rig endurance tests to be conducted in 1995–1996 as a prerequisite to validation in operating F117-PW-100 engines in 1996–1997.