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.