eff ects. However , there is a linear dependence on contact width in a newer model of viscous drag [ 10]. If  there are actual changes in viscous drag due to the changing contact geometry, they would be captured in  the LQF and possibly misinterpreted as an increase in oil quantity . While it is possible that this would  account for the observed increase in LQF  in Figures 6 and 11, a thorough evaluation of viscous models is  beyond the scope of this work . Data from this study will be used in the future to test other models .  

Conclusion  

The distribution of oil in an operating angular contact bearing will depend on a number of competing forces .  These include mechanical forces,  such as centripetal accelerations and contact pressures, and surface  forces, such as the capillary action at the ball race interface and the surface tension gradient in a region of varying temperature. As a result, the quantity of lubricant in the rolling contact will depend on operational  and environmental conditions . And with it, many other bearing performance characteristics (for example,  thermal conductance and oil film thickness) will also depend on condition. This complex dependence is not  often taken into account when modeling dynamic bearing behavior, where the LQF is often taken as a fixed value . The results of this series of tests shows the significance of this effect and provides first -order  estimates of the degree of sensitivity to some important variables.   This report covered the LQF test data based on two  bearing types tests:  305- size hybrid and 305-size steel  bearings . Results showed that LQF was significantly impacted by average temperature (Figures 2, 3, 7,  and 8) , temperature gradient (F igures 4, 5, 9, and 10) and axial loads  (Figures 6 and 11) . We surmise that  these effects may be due to changes in the viscosity of the oil, affecting the volume of oil in the ball/race meniscus, or they may be due to changes in the thermal gradient in the vicinity of the contact, affecting the  flow of oil to the meniscus . While it is likely that the dependence on average bearing temperature is caused  by an actual change in the quantity of oil at the ball/race contact, the dependence on D T across the bearings  is more likely due to inadequacies in the drag torque model . The cause of the dependence on load remains  undetermined, but there are potential causes that are due to changes in actual oil volume and others due to errors in the drag torque model. Regardl ess of the cause, these dependencies should be considered  when applying the conventional drag model shown in E quation 6.    There are some differences in trends between the hybrid and all steel bearing. In the hybrid bearing, all  load conditions show a sensitivity of LQF to average temperature, but the degree of sensitivity is dependent on both temperature gradient and axial loads . The constant thermal gradient curves are NOT parallel in the  case of the hybrid bearings . This indicates that there is an interdependency between LQF and average  temperature, temperature gradient, and axial loads . The cause of differences between steel and hybrid are  the subject of future work . 

Acknowledgements    The authors  would like to acknowledge the management, Dr. Michael R. Hilton and Dr. Michael C. Lee for  their help on this project . This work would not be possible without their continued support.  

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