Windmilling and electrical power

If a prop is feathered and an engine is shut down, will the engine
windmill at all?

I assume that a windmilling prop still turns the engine (i.e., no
clutch disconnects it from the engine, at least on a piston
powerplant). If so, can windmilling drive an alternator enough to
provide useful electrical power?

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Mxsmanic wrote:
If a prop is feathered and an engine is shut down, will the engine
windmill at all?

I assume that a windmilling prop still turns the engine (i.e., no
clutch disconnects it from the engine, at least on a piston
powerplant). If so, can windmilling drive an alternator enough to
provide useful electrical power?

You'll never know until you get into a plane. A real plane. your
question... Some will. Some won't. Again, stop cross posting. At best,
you're a student. At worst, you're not even human.

Rip

Do you know the difference between a windmilling prop and one that is
feathered? Try looking this up first before wasting more electrons.

Rip writes:

You'll never know until you get into a plane.

Oh, I think someone who knows the answer will eventually tell me. I
have to put up with a bit of background noise, but there are still a
few qualified and sensible people on these newsgroups.

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Viperdoc writes:

Do you know the difference between a windmilling prop and one that is
feathered?

Yes. I also know that not all props have adjustable pitch, and that
the fully feathered position on a prop will not necessarily be exactly
parallel to the wind.

I suppose the question can apply to jet engines as well, but someone I
doubt that they would windmill with speed sufficient to generate
useful power, and I'm not sure which stage of the engine drives
generators, anyway.

Obviously windmilling itself is practical, since some aircraft have a
tiny deployable windmill specifically for this purpose.

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On Feb 6, 7:53 pm, Mxsmanic wrote:
Yes. I also know that not all props have adjustable pitch, and that
the fully feathered position on a prop will not necessarily be exactly
parallel to the wind.

Sorry everyone but I am gonna feed the troll here.Most of the props
that I have seen fethered are actually feathered enough to stop or
spin very slowly.

I suppose the question can apply to jet engines as well, but someone I
doubt that they would windmill with speed sufficient to generate
useful power, and I'm not sure which stage of the engine drives
generators, anyway.

Not sure what you are asking here, but a jet engine will not
feather .The fan blades are not adjustable.The compressor section
drives the generator, but it will not spin fast enough to generate
electricity (Even with a CSD).What is interesting is that it will
indicate oil pressure and with this indication (And the absence of
vibration) a restart is recomended.

Obviously windmilling itself is practical, since some aircraft have a
tiny deployable windmill specifically for this purpose.

All of the ER versions of 2 engine transport category jets have this
function.

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Sorry about feeding the troll guys, but he ask a question that I
actually knew something about.

What is interesting is that
it will
indicate oil pressure and with this indication (And the absence of
vibration) a restart is recomended.


That is interesting and usefull, although I'll never personally have
any occasion to use it.

On 2007-02-07, Mxsmanic wrote:
If a prop is feathered and an engine is shut down, will the engine
windmill at all?

I assume that a windmilling prop still turns the engine (i.e., no
clutch disconnects it from the engine, at least on a piston
powerplant). If so, can windmilling drive an alternator enough to
provide useful electrical power?

With piston engines, when the prop is feathered (hence blades are more
nearly parallel with the wind) there is usually enough compression in the
engine to prevent the blades from turning. This might also depend upon how
completely the blades feathered.

So even if the prop turned at all there would not be enough rotation for the
alternator to be of any use. Also, in an emergency all electrics may be
turned off anyway to prevent fire hazards.

With turboprop engines there are two types. Engines like Garretts have the
props connected by planetary gears to a shaft and both the compressor and
exhaust turbine blades are connected to the same shaft with no breaks in the
shaft. Accessories, such as starter/generators and other pumps are connected
to this via gears. This is called a fixed shaft turbine.

My experience is with a Commander 840 with -10 Garretts and when the props
are feathered there is a very slow turning of the props, but not enough to
effect any generation of current.

The second type of turboprop would be like the Pratts where the prop is
free-wheeling (free turbine) and the connection to the actual engine is via
two sets of blades positioned in front of each other, one set on the shaft
to the engine and the other set to the prop. I'm not as familiar with this
engine, but whether or not the prop rotated, it isn't connected to
accessories anyway so of no use.

Remember than when an engine is shut down in flight, whether intentional or
not, all electrical to the engine might be shut down, including any fuel
pumps, generators, etc., (and usually is) in handling the emergency to
prevent other problems, such as fire.

....Edwin
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"Once you have flown, you will walk the earth with your eyes
turned skyward, for there you have been, there you long to
return."-da Vinci http://bellsouthpwp2.net/e/d/edwinljohnson

Edwin Johnson writes:

With piston engines, when the prop is feathered (hence blades are more
nearly parallel with the wind) there is usually enough compression in the
engine to prevent the blades from turning. This might also depend upon how
completely the blades feathered.

So even if the prop turned at all there would not be enough rotation for the
alternator to be of any use. Also, in an emergency all electrics may be
turned off anyway to prevent fire hazards.

With turboprop engines there are two types. Engines like Garretts have the
props connected by planetary gears to a shaft and both the compressor and
exhaust turbine blades are connected to the same shaft with no breaks in the
shaft. Accessories, such as starter/generators and other pumps are connected
to this via gears. This is called a fixed shaft turbine.

My experience is with a Commander 840 with -10 Garretts and when the props
are feathered there is a very slow turning of the props, but not enough to
effect any generation of current.

The second type of turboprop would be like the Pratts where the prop is
free-wheeling (free turbine) and the connection to the actual engine is via
two sets of blades positioned in front of each other, one set on the shaft
to the engine and the other set to the prop. I'm not as familiar with this
engine, but whether or not the prop rotated, it isn't connected to
accessories anyway so of no use.

Remember than when an engine is shut down in flight, whether intentional or
not, all electrical to the engine might be shut down, including any fuel
pumps, generators, etc., (and usually is) in handling the emergency to
prevent other problems, such as fire.

Thanks for the detailed answers. It is interesting that some turboprops don't
have a solid connection to the prop--it seems that this could come in handy if
the prop is blocked or hits something, as it might help preserve the engine
(with no solid connection, the engine would not be violently immobilized).

It has also been pointed out to me (in e-mail) that the question is a bit moot
because: (1) if you have a twin, the other engine is presumably still running,
so you don't need the electricity that might hypothetically be generated by
the alternator on the dead engine, and (2) if you have a single, you'll
probably be on the ground before the battery goes dead, one way or another.
This would be true for both jets and props, of course.

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An imposter of "Mxsmanic" writes:

Thanks for the detailed answers. It is interesting that some people
continue answering my stupid questions.

How about dancing for me too.

You need to use correct punctuation if you wish to be believable. Also, I
have a fairly consistent style to my writing that you fail to emulate.

It seems odd to me that the very people who complain about my posts here
would double the apparent traffic from them by pretending to be me. Perhaps
Ms. Nowak has peers on this newsgroup.


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