change in outer ring position provides excellent independence from thermally induced changes in outer  ring position. We conclude that this technique is suitable for the investigation of film starvation in grease  lubricated angular contact bearings.  Our initial investigation into film thickness with lubrica nts of immediate relevan ce to aerospace  applications shows that the steady state Coray oil film was approximately twice that of the Pennzane oil  film. Furthermore, the total Pennzane film thickness (9 /g80in) implies that the upper limit to the film  thickness of the inner ring was 3.6 /g80in. This is less than three  times the composite surfa ce roughness (3 x  2/g80in = 6 /g80in). This is also much less than the value predi cted using conventional starvation analytical  methods. Since the starvation analysis based upon surface tension driven resupply allows for an  arbitrarily small film under certain conditions [1, 10], we will continue to pursue quantitative analysis using these techniques. However, further testing will be required to establish the oil film thickness in the vicinity  of the contact ( h oil) before these methods can be used to produce a quantitative prediction.  Experiments with a large amount of Rheolube grease (1.1 g per row) show general agreement with other  comparisons of grease and oil film thicknesses in the literature. We found that the film thickness was approximately equal to the flooded oil film thickness (before run-in), where the literature generally shows  a typical grease to be slightly thicker before run-in. In contrast to the literature, however, we found that the  grease film thickness did not fall appreciably during th e nearly 400 hour test. We surmise that this is due  to benign operating conditions that did not stimulate regular changes in ball spin axis. With prolonged  periods of ball tracking, the depletion of grease from the ball surface was delayed, providing an  intermittent supply of oil and thickener to the contact. This produced an extended run-in transient with a  nearly 20 /g80in EHD film.  Experiments with a small amount of grease (0.14 g per row) show the results of a run-in that is more likely  to represent the conditions of a real application. With regular disturbances in speed and/or load experienced during an actual application, the high yield stress of the grease thickener would cause  channeling to the sides of the ball path on the races and more rapid depletion of thickener from the ball  surface. This would approach the situation that was artificially created with the reduced initial charge of  grease in this experiment. We found that the EHD film thickness fell over approximately 500 hours to  approximately the same level as the oil film thickness. This also contradicts many of the results shown in  the literature (for ball-on-plate interferometric film thickness instruments), which have shown a grease film thickness that is significantly reduced from the oil film thickness. However, it is possible that the film  thickness in these experiments would continue to fall with continued testing.  Acknowledgements  This work was supported by The Aerospace Corporation’s Independent Research and Development  Program funded by the Space and Missile Systems Center (SMC) of the USAF under contract number  FA8802-04-C-0001.  References  1. Cann, P.M. and Lubrecht, A.A. “An Analysis of the Mechanisms of Grease Lubrication in Rolling  Element Bearings” Lubrication Science, 11 (1999), 227-242  2. Tyler, J.C., Carper, H.J., and Ku, P.M. “EHD Film Thickness Behavior in DMA Bearings.  Part I –  Experimental and Computational Techniques” ASLE Transactions , 22(3) (1977), 201-212  3. Miettinen, J., Andersson, P., and Wikstrom, V.  “Analysis of Grease Lubrication Using Acoustic  Emission Measurement” I. Mech. E., J. Engr. Tribology,  215 (2000)  4. Qi, G.-P. “Development and Application of the Instruments for Rolling Bearing EHL Oil Film  Thickness Measurement” Modeliing, Measurement, and Control A: General Physics and  Electronics,  73(3) (2000), 40-46  5. Zheng, W., Zhang, Z, Sun, S. “The New Development of Measuring EHL Oil Film Thickness for  Thrust Bearing” Proc. 17 th IEEE Instrumentation and Measurement Technology , vol. 3 14091413, IEEE, Piscataway, NJ.  115