Number: 105
Date: 18 Dec 1996
From:Bill Bruckman
Test results for mount 3 bearing serial #7448-5 and mount 4 bearing serial #58989-3
Stiffness measurements were made for both mounts 3 and 4 on 11/14/96. Measurements were made using two precision electronic levels which have 0.1 arc-second resolution. The levels were mounted to strain free bars - one spanning the outer race of the bearing and one spanning the inner race. An 1100 lb load was applied horizontally at and along the elevation axis. The load direction is reversed to give a second data set. Results for mount 3 bearing serial #7448-5 are shown in Charts ONE and TWO. Results for mount 4 bearing serial #58989-3 are shown in Charts THREE and FOUR. For an 1100 lb load applied at the elevation axis the relative tilt across the bearing should not exceed 0.49 arc-seconds per our bearing specification. This means that the change in the "Delta" from the unloaded to loaded to condition should not change by more than 0.49 arc-seconds. This is clearly the case for in Charts TWO, THREE and FOUR. For mount 3 with the load to the right (Chart ONE) it is less clear that the relative deflection is always less than 0.49 arc-seconds, but the results are generally close to this value.
Results for the friction and stiffness tests for mount 3 bearing serial #7448-5 and mount 4 bearing serial #58989-3 are identified in Chart FIVE. Friction measurements were made on several different occasions. The dates and results are shown on Charts FIVE and SIX. The peak friction for the mount 3 bearing serial #7448-5 was 1375 ft-lb. The peak friction for the mount 4 bearing serial #58989-3 was 1210 ft-lb. Our specification is 3200 ft-lb. For friction variation all results for mount 4 have been within the values allowed by our specification. Two test points for mount 3 lie beyond our limit on variation. See charts FIVE and SIX. All friction measurements were done by moving the antenna 30 degrees in azimuth, stopping for 10 to 15 seconds, and then pulling through a dynamometer on a bar until the antenna just begins to move. The peak reading on the dynamometer is then recorded. Readings are taken every 30 degrees.
