Simviation Forums

Having spent my FSX time lately flying old piston propliners, I became intimately familiar with using torquemeters and RPM in combination to achieve the right power settings.

However, I recently got bored with the A2A stuff and started fooling around with the Digital Aviation Piper Cheyenne.

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So in real life turboprops, how does this work?

Ok, I was working on my experience, which was King Air gauging. It's all a little hazy. As I said, I haven't been near one in a few years!

Jets are soooo much less complicated! And I'm not a technical genius!

In the Airplane Flying Handbook, I'm reading that Gas Generator operation is monitored by the Gas generator tachometer, a separate instrument.

MSFS turbine modeling is pretty bad.

That accepted... the best we can do is piece things together and use what IS workable.

I'm no turbine expert, but I understand the differences between turbine and piston engines, when it comes to tourque and fuel-flow, and how they are effected by a constant-speed prop.

Your assumption:

I think that when reducing the RPM, the fuel flow should stay the same and the torque should change, not the other way around!

should be correct. Turbine fuel-flow is more throttle-position based, regardless of RPM; where piston fuel-flow IS RPM based regardless of throttle position. If the mixture is proper, RPMs determine the amount of air that passes through a piston intake system, hence the amount of fuel.

You "throttle" a piston engine by controlling the air-flow. You "throttle" a turbine by controlling the fuel-flow.

Ideally.. torque is not RPM related. It's HORSEpower that is a function of tourque/RPM. However, the reality of piston/crank geometry makes torque a slave to RPM (ie. tourque curve). That's one of the main advantages to a constant-speed prop (especially on a piston engine). It allows you to stay on a specific part of the torque curve (RPMwise), no matter the actual torque (power (MP))

There is no appreciable geometry to a turbine.. it just spins..

On reflection on my first post I was a bit wide of the mark.

I think that when reducing the RPM, the fuel flow should stay the same and the torque should change, not the other way around!

Indeed. Scouring back to the rear of my brain, ISTR that on reaching top of climb we'd set cruise power, bring back the RPM, then adjust the power back to cruise power again, which would fit in with your logic above.