Three flexure pivot pad bearings (FPBs) with different preloads are evaluated foruse in high performance applications by comparing them to a hybrid hydrostatic bearing(HHB). One application of these bearings is in turbopumps for liquid rocket engines.To evaluate bearing performance, the lift-off speed of the shaft from the bearing surfaceis experimentally determined. Experimental data of lift-off are collected using a circuitrunning through the shaft and the designed bearing. Other methods for measuring liftoffspeeds were attempted but did not yield consistent results. Water is used as alubricant to simulate a low viscosity medium.In comparison to load-capacity-based predictions for FPBs, the experimentalresults showed lower lift-off speeds, higher load capacities, higher eccentricity ratios,and lower attitude angles. The bearings? predicted load capacity determined lift-offspeed predictions, but the experimental results show no clear trend relating lift-off speedto load capacity. This was for a range of running speeds, with the design speed definedas the final speed in a particular test case.At 0.689 bar supply pressure and for a design speed of 3000 rpm, the HHBshowed greater load capacities and lower eccentricities than the FPBs, but the FPBs hadlower lift-off speeds and attitude angles. In fact, the FPBs in the load-between-padorientation outperformed the HHB in the load-on-pocket orientation with lower lift-offspeeds for the shaft weight-only case. An increased supply pressure lowered the lift-offspeeds in the HHB tests. If the load in the bearing application remains relatively small, aFPB could be substituted for an HHB.
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