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Old 17th Jul 2011, 18:56
  #84 (permalink)  
bearfoil
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The earliest HPgas (jet) engines had piston engines driving the compressor, so the concept of drive/driven was established straightaway, imo. The thrust came from the exhaust. Long since retired, turbojets were noisy, wasteful, and high maintenance. So FANjets derive propulsion from the mechanical capture of the "exhaust", expressed in the Low Pressure Compressor (The Fan), which is driven by the Low Pressure Turbines at the back end. IMHO, and grateful to TD and barit1 to keep us all honest.

When a large wheel stops being driven, and starts to drive, bad things can happen. Worse things happen when drivers start to get driven (Turbine).
Or, a massive propellor in high Pitch in cruise that loses hydraulics and cycles to Low, (Flat) Pitch. Runaway Prop. Runaway Turbine. (Overspeed, nasty).