To: rba194
Some automotive engines have over speed limiters, which either cut off the fuel supply or cut the ignition. On an automotive engine when you stop ignition or fuel the rear/front wheels through the transmission are still back driving the engine.
On the Robbie or any other helicopter the internal combustion engine is isolated by the free wheeling unit and when any overspend device were actuated the engine would most likely stop.
To put some type of limiter on an existing engine it would require re certification or that an STC be issued which would require much less paperwork than a full re certification.
Many years ago the US Army took delivery of a brand new H-34. A new pilot was transitioning from H-13s to the H-34. He started the engine while twisting or untwisting the throttle trying to get fuel pumped into the engine. The throttle canceller switch was misrigged and the engine caught with the throttle wide open. The engine went to 2800 RPM and there was so much force in the hydromechanical clutch that it broke and the engine was connected to the driveline. It took only one second under those conditions to make that brand new H-34 a write-off and it was taken to the training school as a training aid.
