Turbo props running in feather before shutdown

[smig]

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]

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]

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

[RomeoTango]

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]

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]

Originally Posted by Polar742

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..."

[USMC-SSGT]

This is an easy one.

Because the checklist says "condition levers".... "start / feather"

[smig]

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]

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]

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]

Originally Posted by USMC-SGT

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]

Originally Posted by smig

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]

Originally Posted by smig

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]

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]

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]

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

[E_Dawg]

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]

Originally Posted by smig

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.

[SRA_kbad]

Its already been answered, but long story short...

To scavenge oil and cool the gearbox, period

[SierraPilot123]

Originally Posted by SRA_kbad

Its already been answered, but long story short...

To scavenge oil and cool the gearbox, period

Yep, that is why we do it on the Brasilia.

[SpiraMirabilis]

I did a little research in my systems book and asked someone else and came to this conclusion --

In the Dash-8 there is a prohibited/yellow RPM range (500-780rpm) which the ECU will keep Nh set as such to either be above or below it. Above feather/disc the ECU will keep the Nh up to keep the RPM above 780rpm. Going to feather allows the Nh to stabilize temperatures for fuel cut off.

[MikeOH58]

Procedures I use are:

van- feather, 400 Prop RPM condition cutoff

200- cutoff, feather during spool down.

[bareman]

A feathered prop is also much quieter than an unfeathered one on a prolonged taxi. Also in the Saab you will see your prop gearbox oil temps spike in the unfeathered position if you are sitting still on the ground on a warm day. Feathering allows oil back to the reservoir which = cooler oil.

As previously mentioned, CJC's procedure to help keep the cabin cool is to run the high pressure bleed valves with one engine feathered and the compressor spooled up a bit. This is why so often you see the Saabs taxiing with one engine unfeathered and one feathered. We are in there sweating like a cub scout at neverland ranch.

[RightSeatGirl]

Also on the Dash we do it for the purpose of the mighty quick turn...If we didn't let the engine cool at feather for 30 seconds in all likelihood, especially in the summer, we'd have to motor the engine to bring the ITT down within starting limitations before adding fuel. That's really hard on the starter and batteries even with the APU running. And it's also time limited to 30 seconds which may not be adequate.

[smig]

Originally Posted by RightSeatGirl

we'd have to motor the engine to bring the ITT down within starting limitations before adding fuel.

which series dash is this?