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Imagine a PT-6 in cruise flight. What would pushing the throttle forward for increased power show on the engine instruments? We know (I assume!) the prop RPM remains constant by varying the pitch, but what goes higher? Torque or TIT?

And what does the pilot do in descent for landing? Does pulling the throttle back for a long descent decrease the fuel flow to a point where it may not sustain combustion and cause flame out?

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Pushing the power lever forward will command more power. Fuel flow will increase, so will the TIT and torque.

  • To maintain the same RPM, more torque is needed as the prop blades will increase their angle.

Pulling all the way back does not cut the fuel flow (FF). The minimum FF required to sustain operation will be managed by the fuel control unit (FCU).

  • Sidenote on terminology: throttle, power, and thrust levers are the controls for piston, turbine, and jet engines respectively.

RE: Torque limits

It depends on the engine, but generally:

In cold weather conditions, torque limits can be exceeded while temperature limits are still within acceptable range. While in hot weather conditions, temperature limits may be exceeded without exceeding torque limits. In any weather, the maximum power setting of a turbine engine is usually obtained with the throttles positioned somewhat aft of the full forward position.


Related: Is turboshaft fuel efficiency affected by N2 loading?

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  • $\begingroup$ Thank you for your answer to my question. I am curious how the torque limits itself to maximum (say at 100%) while in cruise and before pushing forward the power lever it was already running near that, say 95%, as I have seen it in some videos? Thank you. $\endgroup$ – Hercules-63 Oct 10 '17 at 15:15
  • $\begingroup$ @Hercules-63 - check update. $\endgroup$ – ymb1 Oct 10 '17 at 15:22

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