Power Vs. Condition Levers

[tperry]

Just a quick question -
What exactly do the condition levers do on a turboprop engine? I know it controls the fuel supply, and high hidle and low idle, but how does that differ from the power levers, which controls torque through fuel flow?

[Sulako]

You basically only touch the condition levers a few times per flight, while you touch the power levers all the time. It's *sort* of like the mixture control, but it's really just a glorified on-off switch for delivering fuel - condition levers have no metering function and turboprops have fuel control computers to automatically lean your fuel.

When you start the Garrett you pull the condition levers out of cut-off to low idle. Then you leave them in low idle til you are just about to take off, when you put them in flight mode, (high idle). You leave them until you land and are ready to taxi, then you put em back in low idle. When you shut down, you bring the condition levers back to cut-off.

[just curious]

On the Twin Otter, the condition lever has only on, and off as postitions. Since it only has two it is refered to as a fuel lever. Want more than just idle? Push up the power levers.

On Garretts, (Beech turbines have this installed as well) if you like, the condition lever sets the idle for an engine. Off, idle at 50% or idle at 70%. Setting condition levers to high means if you start your takeoff roll, and decide to reject, the engines will be set to develop higher levels of reverse right now. Ensuring the condition levers on a Beech for landing on a level paved, dry runway will ensure max reverse available on touchdown. You would want them in low for taxi, or you would be riding the brakes and the airplane would be howling like a banshee.
So, more than on/off, condition levers; fuel on/off- fuel levers.
.

[tperry]

Makes perfect sense. Thanks, guys.

[BTD]

If you learn how a free turbine works and then transition to a fixed shaft turbine, learning it can make you cry.

With the Garretts on the Metro, there are no condition levers. Only power levers and "Speed Levers". The speed levers work as condition levers and prop control levers depending on where the power levers are positioned. It can make your head spin. But eventually it makes sense.

BTD

[. .]

The condition levers on some Pt6's have a high and low idle setting. The low idle setting being for on ground operations, and the high idle setting being for in flight. You could easily fly an entire flight with them in low idle and notice no difference what so ever. The only time you'd notice would be with the power levers at idle, you'd typically get about 3-5% lower Ng speed.

A note on the fuel control units in Pt6's. There is no computer at all, it's all an elaborate set of bellows, and linkages which control fuel flow. If you're interested you can find pictures of it, but the bellow and linkage system moves two cylinders which both have holes in them. Depending on the power needed the cylinders will align in different patterns to enlarge or shrink the hole allowing more or less fuel to enter the engine.

The FADEC on more complex jets is computerized and is powered off of fixed magnet alternators which will keep power to the FADEC computers even if all other power in the jet is lost. Something which diamond should have had installed on the twin star. They had an incident of dual engine failure due to a power break to the FADEC computers.

[iflyforpie]

If you learn how a free turbine works and then transition to a fixed shaft turbine, learning it can make you cry.

With the Garretts on the Metro, there are no condition levers. Only power levers and "Speed Levers". The speed levers work as condition levers and prop control levers depending on where the power levers are positioned. It can make your head spin. But eventually it makes sense.

BTD

Then go to the Allison 501s where there are no condition levers or prop levers. You have one power lever that controls thrust and reverse, an on/off switch, a feather button, and a speed switch for changing between ground and flight idle.

On the Convair 580 these are scattered around the cockpit between the overhead panel and pedestal.