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Feathering an engine



 
 
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  #1  
Old May 5th 09, 05:07 PM
Flanagan Flanagan is offline
Junior Member
 
First recorded activity by AviationBanter: May 2009
Posts: 3
Default Feathering an engine

I am an historian who is writing a nonfiction book involving WWII B-24 airmen. I have done considerable research on B-24s, but I am not a pilot. In my book, I tell of an incident in which an engine died and was feathered. I have been repeatedly told, and have repeatedly read, that feathering is done to reduce drag generated by a propeller in a dead engine. But a pilot with whom I was conversing said that he believed that part of the problem in a dead, unfeathered engine is the windmilling driving the dead engine, not just the angle of the prop.

Can anyone clarify this? Does one feather an engine simply to reduce the drag generated by the angle of the propeller, or it is also to stop the engine from turning? If the latter is correct, why?

Thanks to everyone.
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  #2  
Old May 5th 09, 08:06 PM posted to rec.aviation.piloting
Scott Skylane
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Posts: 150
Default Feathering an engine

Flanagan wrote:
/snip/
Can anyone clarify this? Does one feather an engine simply to reduce
the drag generated by the angle of the propeller, or it is also to stop
the engine from turning? If the latter is correct, why?

Thanks to everyone.




Flanagan,

To clarify, the term "feathering an engine" actually means "feathering
the propeller". The blades of the prop are twisted in the hub such that
they are parallel with the airflow, and thus present minimal drag, to
assist the aircraft in continuing flight with one less powerplant in
operation. As a result of this, no lift is generated by the blades, and
thus the prop, and the engine it's attached to, stops rotating. As an
aside, the drag created by a windmilling propeller, i.e. one not
feathered and attached to a dead engine, creates as much drag as a flat
plate the same size as the area of the prop arc.

To answer your question, yes, stopping engine rotation is desireable for
several reasons. If the engine was experiencing some sort of internal
failure, stopping rotation will contain damage to whatever component was
affected, and hopefully preserve the rest for future use. If the engine
was on fire, and the aircraft is equipped with fire fighting agent, you
want to stop the airflow from the prop, as it tends to dissipate the
agent, instead of letting it do it's work. And obviously in the case of
fire, a turning engine may well pump more fuel in to the conflagration
to begin with.

Hope this helps.

Happy Flying!
Scott Skylane
  #3  
Old May 6th 09, 02:47 AM
Flanagan Flanagan is offline
Junior Member
 
First recorded activity by AviationBanter: May 2009
Posts: 3
Default

Dear Scott,

It is so kind of you to reply, and your explanation is so interesting. Thank you!

Quote:
Originally Posted by Scott Skylane View Post
Flanagan wrote:
/snip/
Can anyone clarify this? Does one feather an engine simply to reduce
the drag generated by the angle of the propeller, or it is also to stop
the engine from turning? If the latter is correct, why?

Thanks to everyone.




Flanagan,

To clarify, the term "feathering an engine" actually means "feathering
the propeller". The blades of the prop are twisted in the hub such that
they are parallel with the airflow, and thus present minimal drag, to
assist the aircraft in continuing flight with one less powerplant in
operation. As a result of this, no lift is generated by the blades, and
thus the prop, and the engine it's attached to, stops rotating. As an
aside, the drag created by a windmilling propeller, i.e. one not
feathered and attached to a dead engine, creates as much drag as a flat
plate the same size as the area of the prop arc.

To answer your question, yes, stopping engine rotation is desireable for
several reasons. If the engine was experiencing some sort of internal
failure, stopping rotation will contain damage to whatever component was
affected, and hopefully preserve the rest for future use. If the engine
was on fire, and the aircraft is equipped with fire fighting agent, you
want to stop the airflow from the prop, as it tends to dissipate the
agent, instead of letting it do it's work. And obviously in the case of
fire, a turning engine may well pump more fuel in to the conflagration
to begin with.

Hope this helps.

Happy Flying!
Scott Skylane
  #4  
Old May 6th 09, 02:48 AM
Flanagan Flanagan is offline
Junior Member
 
First recorded activity by AviationBanter: May 2009
Posts: 3
Default

Dear Scott,

It is so kind of you to reply, and your explanation is so interesting. Thank you!

Quote:
Originally Posted by Scott Skylane View Post
Flanagan wrote:
/snip/
Can anyone clarify this? Does one feather an engine simply to reduce
the drag generated by the angle of the propeller, or it is also to stop
the engine from turning? If the latter is correct, why?

Thanks to everyone.




Flanagan,

To clarify, the term "feathering an engine" actually means "feathering
the propeller". The blades of the prop are twisted in the hub such that
they are parallel with the airflow, and thus present minimal drag, to
assist the aircraft in continuing flight with one less powerplant in
operation. As a result of this, no lift is generated by the blades, and
thus the prop, and the engine it's attached to, stops rotating. As an
aside, the drag created by a windmilling propeller, i.e. one not
feathered and attached to a dead engine, creates as much drag as a flat
plate the same size as the area of the prop arc.

To answer your question, yes, stopping engine rotation is desireable for
several reasons. If the engine was experiencing some sort of internal
failure, stopping rotation will contain damage to whatever component was
affected, and hopefully preserve the rest for future use. If the engine
was on fire, and the aircraft is equipped with fire fighting agent, you
want to stop the airflow from the prop, as it tends to dissipate the
agent, instead of letting it do it's work. And obviously in the case of
fire, a turning engine may well pump more fuel in to the conflagration
to begin with.

Hope this helps.

Happy Flying!
Scott Skylane
  #5  
Old May 6th 09, 03:36 AM posted to rec.aviation.piloting
[email protected]
external usenet poster
 
Posts: 1,130
Default Feathering an engine

On May 5, 1:06 pm, Scott Skylane wrote:
As an aside, the drag created by a windmilling propeller, i.e. one not
feathered and attached to a dead engine, creates as much drag as a flat
plate the same size as the area of the prop arc.


Nope. The blades cannot be everywhere at once, and so the area
affected is no larger than the blade area.

Dan


  #9  
Old May 6th 09, 01:19 PM posted to rec.aviation.piloting
vaughn
external usenet poster
 
Posts: 93
Default Feathering an engine


"Tim" wrote in message
m...


So you are saying if I loose power at high altitude in a fixed pitch prop
aircraft, like a Skyhawk, I will have less drag if I stop the prop, as
opposed to letting it windmill?


Yes, but with a fixed pitch prop you may or may not be able to stop the prop
by slowing down to a near stall. Once stopped, it may or may not stay
stopped at best glide speed. It would depend on the pitch of your prop, the
compression of your engine, your plane's best glide speed, the quality of
the pilot's speed control, and the phase of the moon.

Vaughn




  #10  
Old May 6th 09, 01:24 PM posted to rec.aviation.piloting
Tim[_8_]
external usenet poster
 
Posts: 27
Default Feathering an engine


"vaughn" wrote in message
...

"Tim" wrote in message
m...


So you are saying if I loose power at high altitude in a fixed pitch prop
aircraft, like a Skyhawk, I will have less drag if I stop the prop, as
opposed to letting it windmill?


Yes, but with a fixed pitch prop you may or may not be able to stop the
prop by slowing down to a near stall. Once stopped, it may or may not
stay stopped at best glide speed. It would depend on the pitch of your
prop, the compression of your engine, your plane's best glide speed, the
quality of the pilot's speed control, and the phase of the moon.

Vaughn


Are you high?
Have you actually done it?
I can assure you, all aspects of it are much easier than you imply.



 




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