Turbo props running in feather before shutdown

smig

Well-Known Member
Can someone tell my why many turboprops run in feather for a half minute or so before shutdown? What would happen if you didn't wait and shut it down right away.
 

subpilot

Squawking 7600
I am sure every aircraft out there will have its own procedures and reasons for doing stuff that is unique. With that said, I can only speak for a SAAB 340B. We have no requirement to feather before shutdown. You may notice the engine feathered during taxi because we are using that engine to provide HP air for air conditioning. The only requirement in respects to shutting down our engines was a 2 minute cool down after operating the HP air.
 

vheissu

Well-Known Member
Could just be the crew running checklists, and waiting for things to stabilize before shutting things down.
 

RomeoTango

New Member
Im not a turbine driver but the PT6 [free turbine] feathers on shutdown I beleive the reason may be to avoid the prop windmilling and turning the gearbox while the oil pump ,conected to the compressor section, is not delivering oil.Im sure there is people here that can give you a much better explanation:)
 

Polar742

All the responsibility none of the authority
Welcome smig!!

I think it depends on the type of tprop.

Free-power turbines, such as the PT-6 on the King Air and the GE on the SAAB, don't require that the prop turns in order to start the engine. So it's easier to let them bleed off to feather, or some procedures (I'm reaching way back) and systems are designed to place the prop to feather prior to shutdown. Usually bringing the condition levers to cutoff will feather the engine as it shuts down (I think this is the way it was in the King Airs - again, I'm reaching deep in the memory, so I could be completely off base)

Direct-drive turboprops, such as the Garrett TPE331 series found on J31s, MU2s and Aerocommanders and the Rolls-Royce Darts found on the old F27 whistle pigs and the YS-11s, require the blades to be in fine pitch during start. Otherwise, the drag on the blades would be too great for the starter to get the engine going. The physics is the same, so if the oil pressure drops, the prop wants to feather. There are usually pins that are inserted into the prop hub, that as the engine spins down, the centrifugal force that holds them away, reduces allowing the pins to fall into position. Forcing the prop to stay in the flat pitch can be done by several procedures. If you hear a TPE331 start up, after the engines get spooled, you'll hear a quick burst of reverse pitch. That backs the hub off the pins allowing them to retract, allowing the prop to coarsen the pitch.
 

ZapBrannigan

Old School
If you hear a TPE331 start up, after the engines get spooled, you'll hear a quick burst of reverse pitch. That backs the hub off the pins allowing them to retract, allowing the prop to coarsen the pitch.
Whoa... flashbacks. "Johnstown tower, Chautauqua 4204, braking action nil..."
 

smig

Well-Known Member
I understand that a feathered prop will slow down faster on shutdown, but why do they run the prop in feather for a prolonged period? The Dash for example runs in feather for about a minute before shutdown. I have never seen one shut down right away.
 

USMC-SSGT

Well-Known Member
1. It allows it to cool down and spool down a bit before just being stopped abruptly
2. We always leave number 2 spinning until we have ground power hooked up because the dash 8 is an electricity hog and will not survive long on batteries alone.
 

spilot

Well-Known Member
Remembering from Caravan training, the word is to feather, to allow the oil otherwise used in the prop hub, to flow back into the oil reservoir and keep the scavenge pumps and stuff lubricated (having more oil there for startup).

Also, brushes used to transfer electricity to the prop heat elements, are prone to damage if the prop is spinning the opposite direction of normal, thus, when feathering, the wind will likely not be turning the prop while parked without securing the prop.

I haven't heard about feathering and then leave it running for 30 seconds. I'd imagine it may cause warm exhaust gases to heat up the exterior fuselage and melt stuff. Very bad. The oil cooler and the engine also enjoys airflow from the prop. So I feather, and shut down within a few seconds.
 

smig

Well-Known Member
1. It allows it to cool down and spool down a bit before just being stopped abruptly
But does a free power turbines compressor cool down and spool down with the prop in feather? I would think the compressor would run at the same speed and temp regardless since it is not connected to the prop. Am I thinking about this too hard?
 

400A

New Member
I understand that a feathered prop will slow down faster on shutdown, but why do they run the prop in feather for a prolonged period? The Dash for example runs in feather for about a minute before shutdown. I have never seen one shut down right away.

In paticular to the Dash, there is a time limitation that the engine has to be in feather before shutdown, something like 30 seconds (I'm pulling way deep in the memory banks for that one). It has to do with stabilizing the oil temps in the gear box and on the bearings throught the engine. It is more of a prevenative mx thing than anything, ie less wear and tear.
 

subpilot

Squawking 7600
But does a free power turbines compressor cool down and spool down with the prop in feather? I would think the compressor would run at the same speed and temp regardless since it is not connected to the prop. Am I thinking about this too hard?
You are correct. You could leave a free power turbine engine in the feather condition until the cows come home.
 

SpiraMirabilis

Possible Subversive
In the dash-8 we pull condition levers back to start feather, and then 30 seconds later to fuel cut off. Why? Well, its in the checklist to do it that way.
 

Turbo Mcfloat

Well-Known Member
In the shorts (PT-6) we have no company procedure to feather before shutdown, but it is on the after shutdown checklist to bring the props to feather to prevent them from coming out of feather on startup. You are right about the compressor speed and temp, doesnt change on a free turbine. Are you asking about a direct drive plane you saw? I don't think it matters with a free
 

smig

Well-Known Member
I mostly see it on the dash, I see them a lot. They always feather for a prolonged period before shutdown.
 

E_Dawg

Moderator
In the Brasilia it's so the Aux oil pump fills such that you can do the aux feather pump test prior to the next engine start, if need be.


But, I've flown the Brasilia at 2 companies now... and the last company just had us shut 'em down when we wanted. And we never had an issue with the aux feather pump not being full.

So, who knows! Cuz they pay me, and they tell me to, I guess.
 

Teller1900

Well-Known Member
I mostly see it on the dash, I see them a lot. They always feather for a prolonged period before shutdown.
Short answer, that's because the checklists says props in fx minimum 30 seconds before selecting fuel off. The explanation they gave us is so that it will allow the engine and gearbox to cool down/stabilize before you shut it down. If it's run in feather any longer than 30 seconds, it's probably because we're using it for electricity/air conditioning until they get the ground services hooked up.
 
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