Windmilling Turbines

[BlatantLiar]

From day one you're taught to not let a PT6 windmill in the wind due to the bearings not receiving pressurized oil. During short breaks between operations I'll put the prop 'brake' on if I think theres a chance it will spin. However, the other day it occurred to me. Airliners at gates between turnarounds, be it 30 minutes to a few hours, happily have their N1 shaft rotate in the wind.

What's the difference? Is it different bearings, the lack of gearbox or something else?

Keen to hear an explanation on this one.

[Car RAMROD]

Not sure about other engines, but a windmilling prop on a PT6 does not rotate the accessory gearbox, and isn't that where the oil pump is located?

[BlatantLiar]

Not sure about other engines, but a windmilling prop on a PT6 does not rotate the accessory gearbox, and isn't that where the oil pump is located?

Correct. I'm of the belief that on most turbofans oil is circulated when the N2 is spinning but not the Fan.

[Brian Abraham]

Think you may perhaps have your N1/N2 confused. N1 is the compressor spool and N2 is the power output spool (what drives the prop). N2 will be rotating if wind is driving the prop, N1 maybe/maybe not depending on airflow through the engine. The accessories gear box (and oil pump) are driven by the N1.

A feathered engine (on King Air at least) will slowly rotate, so doubt anything detremental happening, but check with your maintenance people.

http://vid101.photobucket.com/albums/m56/babraham227/Video_zpsd6911dfd.mp4

http://www.pwc.ca/files/en/Know_your_PT6A.pdf

[Blueskymine]

That's interesting Brian. Generally in multiple shaft turbine engines, combusted exhaust gasses pass into the turbine section driving N2. The expansion of combustion gasses drives N1 (free power turbine) which either has a fan or a prop attached to it.....

It's certainly the case with the jet engine I operate.

[Oakape]

fuel goes into the turbine section

That is also interesting! I thought the fuel went into the combustion section.

[Brian Abraham]

It's certainly the case with the jet engine I operateI was addressing the PT6 in particular in my post. You are correct though that in jet engines the nomenclature is somewhat different. A triple spool for example,
N1 = low pressure spool (fan)
N2 = intermediate spool
N3 = high pressure spool

[ChaseIt]

I have witnessed engineers put straps on the fan blades to stop them from spinning after the last flight of the day... Perhaps with what residual oil their is and the time it takes to turn around the aircraft it isn't viable to strap them up at every chance. However that is only an assumption!

[43Inches]

I think Brian was right in the first instance, in the PT-6 the Ng = N1, Np = N2. My understanding is it's all about which compressor/spool sees the airflow through the "jet engine" pump first. In a typical Turbofan the LP compressor or large forward fan sees the airflow first so is N1, then through N2 etc. In a Turbo-prop the prop is not part of the pump, so the first part of the engine that compresses air is the gas generator (Ng) making it N1. The airflow doesn't reach the prop driving part until last in the turbine stage. The PT-6 though is different to same other turbo-shafts as the Np shaft is separate to the Ng shaft, unlike a CT-7 for instance where the prop shaft is more conventionally placed through the Ng shaft and airflow goes in the correct direction.

[waren9]

9 posts and 6 of them are more interested in arguing the naming conventions than answering the op's question.

typical australians. :rolleyes:

to the op

you'll get a wider, more informed audience if you post in tech log

[yr right]

It's just good practice to strap the prop on any turbine. It's as simple as that. Just as you lock the flying controls.

[Jack Ranga]

:=:= Matey, having travelled extensively overseas & talked to multiple pilots I think you will find that Australians are easily the best pilots in the world :D

The level of respect for our paperwork, procedures, redtape & beauracracy is astounding :ok:

[Wally Mk2]

Spot on 'JR', we are good at all that crap!:ok::ok:

'W9' I was thinking the same thing to some degree but like most threads they always tend to drift off somewhat but no harm done:).

Windmilling props are a danger to personal, nothing to do with the bearings because if it where then the manufacturers would have far more stringent measures in place to stop same.
After many many years of operating prop turbines I'd like a buck for every time I saw a windmilling PT-6:ok:


Wmk2

[BlatantLiar]

I think there is a reason PW refers to the spools of a PT6 by letters rather than numbers guys...

It's just good practice to strap the prop on any turbine. It's as simple as that. Just as you lock the flying controls.

I agree, but I'm not after a lesson on airmanship and recommend practice. Out of pure curiosity I want to know why a PT6 prop should not be allowed to spin with hot oil recently distributed through its bearings and gearbox whilst fans are allowed to spin willynilly during turnarounds?

Or is it purely an OWT of sorts taught to pilots so that they dont run off and forget to strap it after a days work?

you'll get a wider, more informed audience if you post in tech log

Good option, I'll let this brew a bit longer.

[drunk_pilot]

I think there is a reason PW refers to the spools of a PT6 by letters rather than numbers guys...

It's numbered on a King Air... N1, not Ng like some others.

[BlatantLiar]

It's numbered on a King Air... N1, not Ng like some others.

Interesting, cheers.

[Jamair]

Apart from any technical rationale, another reason to not allow the prop on a turbine to windmill is the potential for injury or damage to or from the now silent but moving blades.

[BlatantLiar]

Apart from any technical rationale, another reason to not allow the prop on a turbine to windmill is the potential for injury or damage to or from the now silent but moving blades.

http://www.berryreview.com/wp-content/uploads/2012/01/facepalm.jpg

[HarleyD]

I was recently in Mojave to do some work and noticed that a crew was readying an L1011 for a job. This aircraft has been sitting with wind blowing through the engines which has provided a clanking noise for several months while they have be been windmilling. Seriously, there is NO issue with this, but a pt6 needs its prop tied all the time?

I does get windy at Mojave. Clank clank clank clank clank clank and so on and so on.

BTW I was seriously shaken to see Mikes Roadhouse Diner boarded up.......WTF .......where else can i get coconut cream pie ( which i always thought was a fictional product of the Gilligans Island script writers) in Mojave?

HD

[Lumps]

I'll have a go...

If the main bearing on the Np shaft is a plain bearing, as in it requires oil under pressure to provide clearance between metal surfaces, then in my books it's the same as motoring a piston engine sloooowly with the oil pump removed. Probably take a long time to kill it, but not cool.

If.

[TURIN]

Jamair has a point.

I used to see the left prop secured while loading passengers through D1L.

[Lumps]

Jamair has a point.

No he doesn't

[TURIN]

Oh is it pantomime season?


All together now at the back...

"Oh yes he does" :bored:

[Arm out the window]

I remember hearing years ago about some speed record car driver, might have been Ken Warby?, who bought an Avon engine from Pearce and stuck it on a truck to bring it back east. Apparently it windmilled all the way across the country and by the time it got to its destination it was rooted, to use a technical term.


In my book N1 (Ng) is gas generator speed, N2 (Np) is free turbine speed (what's connected to the output shaft), for what it's worth.

[yr right]

It's the airframe manufacture that calls the shots to either n1 or NG or n2 or n2 np etc. that is until you get into the P&W mm then they call n1 etc. the prop gear box in a pt6 has both plain and and roller bearings. The plain bearing has its oil supply from the prop gov all the other bearings are supplied by the oil
Pumps. The oil pumps are in the cold section. And as such the prop is free to spin and will not have any oil supplied to any bearings when the cold section is not spinning. But still at the end of the day it's just good practice to strap any turbine and cover any fan to stop the spinning.

[maxgrad]

Yr right Yr right

[Jack Ranga]

And his grammar & sentence construction has improved out of sight!