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.

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

Dear Scott,

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

Originally Posted by Scott Skylane

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

Dear Scott,

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

Originally Posted by Scott Skylane

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

"Flanagan" wrote

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

In addition, I would add that though it seems counter intuitive, a rotating
unfeathered prop has more drag (much more) than a unfeathered prop that is
not rotating. The feathering has two bonuses, in sorts then.

An unfeathered prop has lower drag stopped, so feathering the prop stops the
prop for the first reduction in drag, and feathering it after it is (or
during stopping it) reduces drag even again.

The reasons given about lessening damage, although true, are a very very
distant reason on why to feather. The MOST important reason is to reduce
drag, increase time in the air and gliding distance, because both of those
reasons mean LIFE. Never seen a better reason than that one, yet. g
--
Jim in NC

"Morgans" wrote in message
...

"Flanagan" wrote

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

In addition, I would add that though it seems counter intuitive, a
rotating unfeathered prop has more drag (much more) than a unfeathered
prop that is not rotating. The feathering has two bonuses, in sorts then.

An unfeathered prop has lower drag stopped, so feathering the prop stops
the prop for the first reduction in drag, and feathering it after it is
(or during stopping it) reduces drag even again.

The reasons given about lessening damage, although true, are a very very
distant reason on why to feather. The MOST important reason is to reduce
drag, increase time in the air and gliding distance, because both of those
reasons mean LIFE. Never seen a better reason than that one, yet. g
--
Jim in NC

Very well said.

I am sorry that I cannot currently recall a source to document the
information. But considerable work has been done to document the rate and
angle of descent of light aircraft with a fixed pitch propeller idling,
windmilling, and stopped.

To the best of my recollection, the descent with the propeller stopped was
very similar to the descent with the engine idling; but the descent with the
propeller windmilling was considerably steeper.

In addition, some testing was docummented in one of the aviation magazines,
possibly Flying, in which a Cessna 172 or 152 (I have forgotten which) was
equipped with a steamlined fairing in place of the propeller and spinner.
The aircraft was towed then towed aloft and released so that the gilde
performance of the aircraft could be separated from the effects of the
engine and propeller.

However, in the particular case of the radial engines on the B17 and B24,
windmilling engines normally occurred in cruising flight as the result of a
loss of oil and consequently of oil pressure. In such cases, the engines
would overspeed until they seized and the propeller assembly would then
shear off of the affected engine. If you were lucky, it would then drop
straight down; but if you were not lucky considerable damage would
result--including serious injuries or deaths of crew members and
occasionally the loss of the aircraft. Bcak in the day--during the war--the
aircraft were in typically cruising in formation when that occurred, so
there was little opportunity to attempt anything other than to evacuate the
crew positions alligned with the propeller arc. Occassionally, in the
present time, something similar still happens involving the few remaining
DC3 and similar aircraft still in service; and the aircraft are frequently
lost by pilots attempting to avoid overspeeding the (failed) engine.

Peter

"Flanagan" wrote

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

In addition, I would add that though it seems counter intuitive, a rotating
unfeathered prop has more drag (much more) than a unfeathered prop that is
not rotating. The feathering has two bonuses, in sorts then.

An unfeathered prop has lower drag stopped, so feathering the prop stops the
prop for the first reduction in drag, and feathering it after it is (or
during stopping it) reduces drag even again.

The reasons given about lessening damage, although true, are a very very
distant reason on why to feather. The MOST important reason is to reduce
drag, increase time in the air and gliding distance, because both of those
reasons mean LIFE. Never seen a better reason than that one, yet. g
--
Jim in NC

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

In article
,
wrote:

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

YES! In aeronautical engineering analysis, a windmilling prop is
considered to be a flat disk, with drag numbers to match. Feathering the
prop greatly reduces drag.

--
Remove _'s from email address to talk to me.

"Orval Fairbairn" wrote in message
news
In article
,
wrote:

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

YES! In aeronautical engineering analysis, a windmilling prop is
considered to be a flat disk, with drag numbers to match. Feathering the
prop greatly reduces drag.


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?