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So, I was skiing sometime ago, and unfortunately, another skier got injured. So, a heli was flown up to get the injured skier. The rotor blades were stationary, but I still heard some sort of engine like sound. Does anyone know any helicopters capable of doing this sort of thing?

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Yes, many helicopters (but not all) can do this. There are 2 main methods:

  • a clutch between engine and rotor system
  • for turbines only: a rotor brake on the engine output shaft. The engine contains a free turbine (i.e. a turbine stage that isn't attached to the compressor) that drives the rotor system. If you brake this shaft, the engine can run without spinning the rotors.
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  • $\begingroup$ I can't seem to find any of these of the Bell 412 or AS350 for example. Any documentation? $\endgroup$ – lpydawa Dec 19 '19 at 10:47
  • $\begingroup$ Bell 412 engines: euravia.aero/engine-detail/pt6t-3df $\endgroup$ – Hobbes Dec 19 '19 at 11:00
  • $\begingroup$ Also, is there a term for this method of stopping blades while engine is running? $\endgroup$ – lpydawa Dec 19 '19 at 11:34
  • $\begingroup$ so technically I can run the engines at idle, and apply rotor brake? And does that mean that the 412 has no clutches? $\endgroup$ – lpydawa Dec 19 '19 at 11:35
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    $\begingroup$ The brake is called a rotor brake. The procedure would depend on the helicopter, but generally, yes I'd expect you can idle the engine and apply the rotor brake. Some rotor brakes are automatic, I see. $\endgroup$ – Hobbes Dec 19 '19 at 11:42

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