Originally Posted by
Gordy
Resurrecting this thread as I am new to the 76, (literally just finished initial training).
What am I missing? Trying to figure out why you would lose TR thrust if you shut down #1 engine.
Gordy I suppose this is a hypothetical situation where a specific combination of failures of gears inside the Main Gearbox meant that the #1 Engine was the only thing driving the Tail Rotor output shaft. The #2 Engine would still be driving the Main Rotor through its surviving gears but not the Tail Rotor, and the #1 Engine would still be driving the Tail Rotor but not the Main Rotor. So shutdown of the #1 Engine would cause loss of tail rotor thrust.
I'm not knowledgeable enough of the internals of the MGB to say whether this is actually possible or not the way the gears are arranged inside.
I do vaguely remember hearing a story years ago at a FlightSafety recurrent that during the initial design of the S76 MGB, an engineer messed up the design for the fastener for one of the internal gears. It was supposed to be reverse threaded to prevent it backing off when the gear was spinning under load. It was designed conventionally threaded and the fastener backed out during operation, and subsequently the gear came off in flight. I believe the story was that the engine continued to drive the MGB lubrication pump and hydraulic pump but provided no power to the main rotor or tail rotor. I'm probably wrong on the details - it was a long time ago I heard that story.