Feathering System

[SkySBA]

Hi,

When a turbo-prop taxies out of the terminal (referencing the EMB-120 especially), the pilots test the auto-feather and manual feathering systems.

It seems it stays in "feathered" position (but still rotating) for several seconds. I'm assuming they're not testing the full feathering, otherwise the prop would stop, correct?

Thanks!

 

[heywatchthis]

otherwise the prop would stop, correct?

Why would the prop stop? It goes into "feather". What was your question again?

 

[SlapShot]

Why would the prop stop? At least on the SAAB, testing the auto-coarsen system (as it is called because the Sweedes just want to be difficult) does not stop the engine. The power turbine is still spinning, therefore the prop still turns.

 

[paulsalem]

I was flying a C90 with a guy one day (me in the right seat) and he feathered the right prop on me, keeping the egine running. Looked pretty odd to see the blades all flat out there.

 

[SkySBA]

Why would the prop stop? It goes into "feather". What was your question again?

Isn't the purpose of feathering a prop to stop it from spinning?

 

[paulsalem]

Well it stops it from spinning when the engine is not running. In free turbine turbo prop it has enough power to keep it spinning (although the RPMs will drop). If the engine fails, then feathering the prop will make it stop rotating.

Basically you don't use feather unless the engine dies.

Not sure how it works in a turboprop that isn't a free turbine, or in a piston.

If you just put the prop into feather on a piston what would happen?

 

[Floatplane]

It is called a free turbine engine.

Hi,

When a turbo-prop taxies out of the terminal (referencing the EMB-120 especially), the pilots test the auto-feather and manual feathering systems.

It seems it stays in "feathered" position (but still rotating) for several seconds. I'm assuming they're not testing the full feathering, otherwise the prop would stop, correct?

Thanks!

Free Turbine or dual spool engines are not directly connected to the propeller, hense the term free. The propeller is definitely in the fully feathered position when these tests are performed. The propeller will not stop on this type of engine/propeller configuration. Infact, the ATR has an option for a propeller brake that can bring the propeller to a complete stop and the engine can remain running. Hope this helps clear up any confussion you may have.

 

[HatWearer]

Dash 8 auto-feather test feathers prop fully and takes RPM below 300 rpm. At start the PW120 was in feather, and also, the engine can be put into feather and operated that way on the ground...can't remember quite how low the RPM goes, but I remember the fuel flow drops off. Back in the day it was good for sitting in PHL waiting for a gate...

 

[ultrarunner]

Free Turbine or dual spool engines are not directly connected to the propeller, hense the term free. The propeller is definitely in the fully feathered position when these tests are performed. The propeller will not stop on this type of engine/propeller configuration. Infact, the ATR has an option for a propeller brake that can bring the propeller to a complete stop and the engine can remain running. Hope this helps clear up any confussion you may have.

SKySBA...when one speaks of a 'free turbine', as Floatplane says, it's like this.

There is a compressor sections and a power section of the engine. The power section is the propeller/gearbox section.

The connection is aerodynamic, meaning that the compressor spins so fast, that it, in turn, spins or turns the powersection.

When you start this type of engine, you're starting the compressor section. The spinning prop you see is a byproduct.

The power section is independent. So, if you feather the prop, the engine is still running. There is still enough spinning of the compressor to turn the power section, with the prob in feather.

this is true on the ground or in flight.

Direct drive turboprop (turbo shaft) engines are a different beast. Such as the TFE's.

HTH

 

[paulsalem]

To add to ultra runner..

you could go hold still the prop of a free turbine (like a king air) while the pilot started the engine and it would still start.

 

[SkySBA]

Thanks!

Free Turbine or dual spool engines are not directly connected to the propeller, hense the term free. The propeller is definitely in the fully feathered position when these tests are performed. The propeller will not stop on this type of engine/propeller configuration. Infact, the ATR has an option for a propeller brake that can bring the propeller to a complete stop and the engine can remain running. Hope this helps clear up any confussion you may have.

Thank you all for your explanations. It makes sense now. I guess I was confused as I've only flow in a piston-powered twin. What got me is the fact that propeller control, or condition lever as they call it, controls the prop only not affecting the turbine section.

 

[bugchaser]

What got me is the fact that propeller control, or condition lever as they call it

Two different things. Prop controls prop, condition is fuel.

 

[Yudso]

Auto-coarsen and auto-feather are two different things.

 

[SkySBA]

Two different things. Prop controls prop, condition is fuel.

So condition levers are similar to mixture controls on a prop plane?

 

[Yudso]

Depends on the aircraft.

 

[Captjiggles]

Skysba,

To answer your question about the EMB-120. The Hamilton Standard 14RF-9 propeller does not fail to a feathered position if oil is lost, like in an engine failure. However there are four different ways to feather the prop.
1.Autofeather
2.Electric feather
3.Manual feather
4.Fire handle

At GIA we are required to test the autofeather and test the manual feather during our "after engine start'(before taxi) checklist. If any parameters are not met with the feathering test the airplane is grounded until rectified.

Hope this helps.

 

[embpic1]

So condition levers are similar to mixture controls on a prop plane?

Not really. The condition levers control fuel and propeller RMP. In the EMB-120, when the condition levers are fully retarded, that is the fuel cutoff position. During engine start the condition levers are pushed to the first detent which is (fuel on, propellers feathered). The engines will run all day in feather spinning at about 300 RPM(I think). When you are ready to taxi the condition levers are pushed to the next detent (min RPM). This is about 58% RPM or so (All RPMs are in % in the 120). When you are ready for takeoff the condition levers are pushed full forward. This will govern the props at 100% when the power levers are advanced for takeoff. We leave them there until we set cruise power. We will pull the condition levers back to about 85% NP for cruise. Without getting too technical, the condition levers basically are used to turn the fuel on or off to the engine. Then they are used to set propeller RPM. The "fuel mixture" is handled by the HMUs and EECs (manual and electronic fuel controls) which work automatically.

 

[SkySBA]

I appreciate your time everyone, thanks again.

 

[T-prop]

Buy "Turbine Pilots Manual" it explains how various/generic turbo-prop and turbo-jet engines and other systems work. Even has nice diagrams and even a CD-ROM with animation to better visualize the information in the book. It's actually a pretty easy-read. Unlike most aviation technical manuals.

 

[T-prop]

Two different things. Prop controls prop, condition is fuel.

Some turbines have the two combined into one lever. Saab's, anything with a garrett, ATR's, EMB-120s, and a few others have only 2 levers/engine. Whereas, anything with a PT-6 (kingair) has 3 levers/engine.