Originally Posted by
SplineDrive
I wonder how that propellor gearbox likes sitting stationary in a vibrating environment? In a non-rotating state, some of the gear mesh and bearing rolling element contacts are direct metal-metal with no fluid film separating the surfaces. Could eventually get fretting damage. Presumably they’re doing something to keep the transmission at a reasonable operating temperature when it’s not spinning so when power is quickly clutched in, the system isn’t cold.
Good point. Another design flaw to add to the list. I have seen a bearing which had Brinelling (subtle impact damage to balls and races due to installation or handling errors) which spalled at locations around the circumference of the races at ball spacing intervals well before the overhaul/inspection interval. We have also seen what happens to an Airbus 225 when a transmission is dropped during shipping and the bearings not replaced (not proven, but a leading contender to have resulted in separation of the rotor).
The tail is a severe vibratory environment on any rotorcraft. More so on an ABC type with inherently brutal vibration levels. As all this is common knowledge, you would think Sikorsky would run the tail at no thrust while they expand their hover envelope if they could. Points to a serious drive system issue.