RJ said:
I doubt that the failure of the duplex bearing made much vibration, the TR servo end (non-rotating) would then be pushing on the TR spider shaft end (rotating) and that would be the only source of vibration. The duplex bearing is greased, but if oil leaked somehow into the shaft area (split O ring?) the oil would soften the grease and heat could destroy the bearing.
It depends on the dynamic range of the system used to measure the vibration, accelerometer location and mounting as to whether or not the system measured the fault. Actually failed bearing don't usually make much vibration amplitude when failing but they do give a definative signal that can be identified. Can't say whether the HUMS on this aircraft can do that or not due to the unkonwns listed above. But HUMS systems can find these type of faults.
Geoff said:
Yes, but that does not mean that there was any either!!
I'm not an engineer but I could imagine that a failed drive shaft would give vibes whereas a failed pitch change shaft may not.
Yes, a failed pitch shaft would give off vibrations, especially after it sheared inside the tail rotor shaft. In addition the bearing would have given off a distinct signal up to failure. All rotating parts give off some vibration. As mentioned above, it takes a system with a high dynamic range and a sensor installed where it can pick up the vibration. Not all HUMS are created equal...
Chuck