View Full Version : Feathering an engine
Flanagan
May 5th 09, 05:07 PM
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.
Scott Skylane
May 5th 09, 08:06 PM
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
May 6th 09, 02:47 AM
Dear Scott,
It is so kind of you to reply, and your explanation is so interesting. Thank you!
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
May 6th 09, 02:48 AM
Dear Scott,
It is so kind of you to reply, and your explanation is so interesting. Thank you!
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
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
Orval Fairbairn[_2_]
May 6th 09, 04:16 AM
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.
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
Yep.
If the prop is stopped, then the area is the blade area.
Look up the derivation and proof of Betz' Law, which deals with the
energy to be derived from a wind turbine, which is what a prop becomes
when it is windmilling.
--
Jim Pennino
Remove .spam.sux to reply.
Tim[_8_]
May 6th 09, 06:38 AM
"Orval Fairbairn" > wrote in message
...
> 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?
vaughn
May 6th 09, 01:19 PM
"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
>
>
Tim[_8_]
May 6th 09, 01:24 PM
"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.
John E. Carty
May 6th 09, 02:16 PM
"Tim" > wrote in message
m...
>
> "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.
>
>
Vaughn is absolutely correct in stating that many aircraft with fixed-pitch
props will windmill all the way in, as you would have to be near or below
its rated stall speed for it to stop. Depends on the particular aircraft in
question :-)
Jim Logajan
May 6th 09, 05:37 PM
Orval Fairbairn > wrote:
> wrote:
>> 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.
>
> 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.
Three answers not entirely correct, none entirely wrong - how can this be?
Because as shown by simple empirical measurements, "it depends" as
indicated in this thesis:
http://www.goshen.edu/physics/PropellerDrag/thesis.htm
(Scroll down to review figures 11 through 14 if you are in a hurry. Figure
13 label provides a summary relevant to this thread.)
As the author of that thesis noted:
"The available publications and information in the area of propeller drag
are almost non-existent, not because of any difficulties of the research
sophistication, but because of the simplicity of it. To investigate
propeller drag one does not need electronics and a large grant, one only
needs a wind tunnel and a spring for a quick measurement. Therefore, most
of the research in this field was done before articles were indexed as they
are now. It was not until I found some journals from the 1930's that I
could actually piece together trails of research."
Tim[_8_]
May 6th 09, 05:47 PM
"John E. Carty" > wrote in message
...
>
>
> "Tim" > wrote in message
> m...
>>
>> "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.
>>
>>
>
> Vaughn is absolutely correct in stating that many aircraft with
> fixed-pitch props will windmill all the way in, as you would have to be
> near or below its rated stall speed for it to stop. Depends on the
> particular aircraft in question :-)
Perhaps, but that wasn't the question, and what does the phase of the moon
have to do with anything but starting a ****ing contest?
There is no doubt in my mind that all the singles I have flown will windmill
all the way in. I'm not aware of any direct drive, piston singles that
won't. You in fact have to be very, very slow to stop the prop, but it's not
difficult do to do. But even at airspeeds well above max glide, I have never
had a stopped prop restart against compression without at least bumping the
starter.
The point was how much do you gain by stopping a fixed pitch prop, as
opposed to letting it wind mill. I was taught many years ago, that if you
experience a power failure at high altitude, stopping the prop could mean
the difference in reaching a distant landing area. Some of the posts in this
thread suggests it makes no difference. I thought it might be to everyone's
benefit to clarify.
Orval Fairbairn[_2_]
May 6th 09, 05:59 PM
In article >,
"Tim" > wrote:
> "Orval Fairbairn" > wrote in message
> ...
> > 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?
That is correct!
--
Remove _'s from email address to talk to me.
Jim Logajan > wrote:
> Orval Fairbairn > wrote:
>> wrote:
>>> 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.
>>
>> 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.
>
> Three answers not entirely correct, none entirely wrong - how can this be?
> Because as shown by simple empirical measurements, "it depends" as
> indicated in this thesis:
>
> http://www.goshen.edu/physics/PropellerDrag/thesis.htm
>
> (Scroll down to review figures 11 through 14 if you are in a hurry. Figure
> 13 label provides a summary relevant to this thread.)
>
> As the author of that thesis noted:
> "The available publications and information in the area of propeller drag
> are almost non-existent, not because of any difficulties of the research
> sophistication, but because of the simplicity of it. To investigate
> propeller drag one does not need electronics and a large grant, one only
> needs a wind tunnel and a spring for a quick measurement. Therefore, most
> of the research in this field was done before articles were indexed as they
> are now. It was not until I found some journals from the 1930's that I
> could actually piece together trails of research."
True that propeller research went away around WWII, but wind turbine
research is currently a hot topic and that's what the propeller becomes
when the engine stops.
--
Jim Pennino
Remove .spam.sux to reply.
Jim Logajan
May 6th 09, 06:38 PM
wrote:
> True that propeller research went away around WWII, but wind turbine
> research is currently a hot topic and that's what the propeller
> becomes when the engine stops.
True, but if the propeller airfoil has asymmetrical camber then when the
engine stops, the relative wind is inverted (coming from the wrong side -
similar to inverted flight.) So it wouldn't be terribly efficient and
attributes like prop stall angle differ from engine on versus engine off.
Jim Logajan > wrote:
> wrote:
>> True that propeller research went away around WWII, but wind turbine
>> research is currently a hot topic and that's what the propeller
>> becomes when the engine stops.
>
> True, but if the propeller airfoil has asymmetrical camber then when the
> engine stops, the relative wind is inverted (coming from the wrong side -
> similar to inverted flight.) So it wouldn't be terribly efficient and
> attributes like prop stall angle differ from engine on versus engine off.
When the engine stops producing power, it becomes a frictional load to
the prop, which becomes a wind turbine.
There is nothing about the prop being attached to an airplane that
invalidates analysis as a wind turbine under that condition.
Whether it is an efficient wind turbine or not is irrelevant, it is
still a wind turbine when the engine is not producing power and air
is flowing past it.
--
Jim Pennino
Remove .spam.sux to reply.
On May 6, 2:00*pm, wrote:
> Jim Logajan > wrote:
> > wrote:
> >> True that propeller research went away around WWII, but wind turbine
> >> research is currently a hot topic and that's what the propeller
> >> becomes when the engine stops.
>
> > True, but if the propeller airfoil has asymmetrical camber then when the
> > engine stops, the relative wind is inverted (coming from the wrong side -
> > similar to inverted flight.) So it wouldn't be terribly efficient and
> > attributes like prop stall angle differ from engine on versus engine off.
>
> When the engine stops producing power, it becomes a frictional load to
> the prop, which becomes a wind turbine.
>
> There is nothing about the prop being attached to an airplane that
> invalidates analysis as a wind turbine under that condition.
>
> Whether it is an efficient wind turbine or not is irrelevant, it is
> still a wind turbine when the engine is not producing power and air
> is flowing past it.
>
> --
> Jim Pennino
>
> Remove .spam.sux to reply.
Yeah,, but. If the prop is not efficient enough to even rotate with
the wind passing over it it never really becomes a wind turbine....
Those need to spin to be called that. A non rotating prop is called ..
DRAG . A rotating prop not under power is called more DRAG.. IMHO
Ben.
wrote:
> On May 6, 2:00Â*pm, wrote:
>> Jim Logajan > wrote:
>> > wrote:
>> >> True that propeller research went away around WWII, but wind turbine
>> >> research is currently a hot topic and that's what the propeller
>> >> becomes when the engine stops.
>>
>> > True, but if the propeller airfoil has asymmetrical camber then when the
>> > engine stops, the relative wind is inverted (coming from the wrong side -
>> > similar to inverted flight.) So it wouldn't be terribly efficient and
>> > attributes like prop stall angle differ from engine on versus engine off.
>>
>> When the engine stops producing power, it becomes a frictional load to
>> the prop, which becomes a wind turbine.
>>
>> There is nothing about the prop being attached to an airplane that
>> invalidates analysis as a wind turbine under that condition.
>>
>> Whether it is an efficient wind turbine or not is irrelevant, it is
>> still a wind turbine when the engine is not producing power and air
>> is flowing past it.
>>
>> --
>> Jim Pennino
>>
>> Remove .spam.sux to reply.
>
> Yeah,, but. If the prop is not efficient enough to even rotate with
> the wind passing over it it never really becomes a wind turbine....
> Those need to spin to be called that. A non rotating prop is called ..
> DRAG . A rotating prop not under power is called more DRAG.. IMHO
>
> Ben.
And if the prop is in the special case of being motionless, it is just
an area equal to the frontal area of the prop.
There are three cases:
1. engine producing power and the prop spinning; prop has thrust X
2. engine not producing power and the prop spinning; prop has drag Y
3. engine not producing power and the prop stopped; prop has drag Z
Each is a different set of conditions and different net result.
--
Jim Pennino
Remove .spam.sux to reply.
Dave Doe
May 6th 09, 11:43 PM
In article <b4726e68-6571-4f76-8a3a-
>, says...
> On May 6, 2:00*pm, wrote:
> > Jim Logajan > wrote:
> > > wrote:
> > >> True that propeller research went away around WWII, but wind turbine
> > >> research is currently a hot topic and that's what the propeller
> > >> becomes when the engine stops.
> >
> > > True, but if the propeller airfoil has asymmetrical camber then when the
> > > engine stops, the relative wind is inverted (coming from the wrong side -
> > > similar to inverted flight.) So it wouldn't be terribly efficient and
> > > attributes like prop stall angle differ from engine on versus engine off.
> >
> > When the engine stops producing power, it becomes a frictional load to
> > the prop, which becomes a wind turbine.
> >
> > There is nothing about the prop being attached to an airplane that
> > invalidates analysis as a wind turbine under that condition.
> >
> > Whether it is an efficient wind turbine or not is irrelevant, it is
> > still a wind turbine when the engine is not producing power and air
> > is flowing past it.
> >
> > --
> > Jim Pennino
> >
> > Remove .spam.sux to reply.
>
> Yeah,, but. If the prop is not efficient enough to even rotate with
> the wind passing over it it never really becomes a wind turbine....
> Those need to spin to be called that. A non rotating prop is called ..
> DRAG . A rotating prop not under power is called more DRAG.. IMHO
Well if you can provide some evidence, that would be good.
Q. why is the prop windmilling in the first place?
Q2. I have a prop and I drag it through grease - as I do so it turns to
"allow" it it's passage through the grease. Now if I was to hold the
shaft so the prop does *not* rotate - surely that would be harder to
pull through the grease now. ?
--
Duncan
Dave Doe
May 6th 09, 11:44 PM
In article <o_r_fairbairn-B758D1.12591306052009@70-3-168-
216.pools.spcsdns.net>, says...
> In article >,
> "Tim" > wrote:
>
> > "Orval Fairbairn" > wrote in message
> > ...
> > > 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?
>
> That is correct!
Please provide some evidence.
--
Duncan
Morgans[_2_]
May 6th 09, 11:51 PM
"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[_2_]
May 6th 09, 11:51 PM
"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
a[_3_]
May 7th 09, 12:36 AM
On May 6, 6:44*pm, Dave Doe > wrote:
> In article <o_r_fairbairn-B758D1.12591306052009@70-3-168-
> 216.pools.spcsdns.net>, says...
>
>
>
>
>
> > In article >,
> > *"Tim" > wrote:
>
> > > "Orval Fairbairn" > wrote in message
> > ...
> > > > 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?
>
> > That is correct!
>
> Please provide some evidence.
>
> --
> Duncan- Hide quoted text -
>
> - Show quoted text -
Here is a URL to a thesis that addresses the question. The answer,
based on his evidence, is, it depends.
http://www.goshen.edu/physics/PropellerDrag/thesis.htm
Jim Logajan
May 7th 09, 12:39 AM
Dave Doe > wrote:
> Q2. I have a prop and I drag it through grease - as I do so it turns
> to "allow" it it's passage through the grease. Now if I was to hold
> the shaft so the prop does *not* rotate - surely that would be harder
> to pull through the grease now. ?
Sounds like a slick idea, but I think you'd have to deep fry an awful lot
of french fries before you'd have enough to perform the experiment over a
reasonable distance. That assumes you don't die from a coronary first, what
with having to dispose of all that greasy food first....
Dave Doe
May 7th 09, 01:54 AM
In article >,
says...
> Dave Doe > wrote:
> > Q2. I have a prop and I drag it through grease - as I do so it turns
> > to "allow" it it's passage through the grease. Now if I was to hold
> > the shaft so the prop does *not* rotate - surely that would be harder
> > to pull through the grease now. ?
>
> Sounds like a slick idea, but I think you'd have to deep fry an awful lot
> of french fries before you'd have enough to perform the experiment over a
> reasonable distance. That assumes you don't die from a coronary first, what
> with having to dispose of all that greasy food first....
Well Jim, when yer prepared to give me a scientific evidence based
answer.... :)
Hey ok, I admit that, the Reynolds numbers are quite different due to
the grease vs air (grease is almost 100% friction based drag, air is
largely pressure based drag). And perhaps therein lies the answer -
however I wanna see the maths.
Reading up on 'a's' link now...
http://www.goshen.edu/physics/PropellerDrag/thesis.htm
--
Duncan
Dave Doe
May 7th 09, 02:03 AM
In article <c8d0834f-8e51-42ad-add6-
>, says...
> On May 6, 6:44*pm, Dave Doe > wrote:
> > In article <o_r_fairbairn-B758D1.12591306052009@70-3-168-
> > 216.pools.spcsdns.net>, says...
> >
> >
> >
> >
> >
> > > In article >,
> > > *"Tim" > wrote:
> >
> > > > "Orval Fairbairn" > wrote in message
> > > ...
> > > > > 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?
> >
> > > That is correct!
> >
> > Please provide some evidence.
> >
> > --
> > Duncan- Hide quoted text -
> >
> > - Show quoted text -
>
> Here is a URL to a thesis that addresses the question. The answer,
> based on his evidence, is, it depends.
>
> http://www.goshen.edu/physics/PropellerDrag/thesis.htm
Thanks, so it really depends on the pitch of the propellor.
qv... you have a prop on the end of a shaft that has no engine, just a
braking mechanism (this is where I find it hard to get my head around
the maths! :) ...
You're say gliding through the air, the prop is freely spinning. Now,
we apply some braking to the shaft and slow down the prop. Basically
(and according to the maths you've shown), the drag will (dependent on
pitch, but for most fixed pitch props), increase. And "at the other
end" the brake will produce heat. The prop will slow and I would expect
the drag to *increase* and the aircraft attitude will need to be lowered
to maintain the same airspeed. But... according to the maths you've
shown, this is all dependent on the pitch of the prop. And, I *assume*
that fixed pitch props are too fine in pitch to be good windmills.
According to the maths, I assume that wind turbines are more efficient
if built really large, and spin slowly, rather than fast (which kinda
makes sense - certainly in known (expected) wind strengths.
--
Duncan
Dave Doe
May 7th 09, 02:07 AM
In article <c8d0834f-8e51-42ad-add6-
>, says...
> On May 6, 6:44*pm, Dave Doe > wrote:
> > In article <o_r_fairbairn-B758D1.12591306052009@70-3-168-
> > 216.pools.spcsdns.net>, says...
> >
> >
> >
> >
> >
> > > In article >,
> > > *"Tim" > wrote:
> >
> > > > "Orval Fairbairn" > wrote in message
> > > ...
> > > > > 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?
> >
> > > That is correct!
> >
> > Please provide some evidence.
> >
> > --
> > Duncan- Hide quoted text -
> >
> > - Show quoted text -
>
> Here is a URL to a thesis that addresses the question. The answer,
> based on his evidence, is, it depends.
>
> http://www.goshen.edu/physics/PropellerDrag/thesis.htm
Oh, BTW, it is not correct to for Orval (according to your link) to
*simply* say "that is correct" - as it is not.
Just looking at the conclusion...
.. Conclusions:
From the experimental results reported here we can conclude what we
could have figured out with a little thought: drag force increases with
length and wind velocity, and decreases with pitch. What is less clear
is how the drag force increases and decreases with these variables.
Does it increase linearly or quadradically with length and wind
velocity? When considering the pitch, does the windmilling drag force
also follow a cosine-squared curve? More accurate data are needed to
determine the characteristics of the crossover point. Does it depend on
wind velocity? Arguments both for and against rely on data that could
be drastically changed if just a couple of data points were moved.
Further work in this topic should begin either with an increase in the
range of the variables, or increasing the precision of the data.
Improving either one of these will help answer all of the questions
posed above.
The main goal of this investigation was simply to determine whether a
stationary or a windmilling propeller has more drag. The answer is
complicatedly simple: it depends. It is clear that it depends on the
pitch and length of the propeller, and it is probably independent of the
wind velocity. A crossover point was discovered where the drag forces
for the windmilling and stationary states were the same. This crossover
point is also dependent on the pitch, the length, and probably
independent of the wind velocity.
--
Duncan
Ron Garret
May 7th 09, 07:37 AM
In article >,
"Tim" > wrote:
> The point was how much do you gain by stopping a fixed pitch prop, as
> opposed to letting it wind mill.
A lot.
You can actually do this experiment in a plane with a variable-pitch
prop. Idle the engine, and play with the prop control. I did this
years ago in a 182RG during dead stick landing drills. The difference
in glide performance between the two extreme prop settings was quite
dramatic, almost like having an extra set of very fast acting flaps.
There's also the conservation of energy argument. If the engine is
turning, the energy to overcome friction and compression has to come
from somewhere.
rg
Mike Ash
May 7th 09, 03:22 PM
In article >,
Ron Garret > wrote:
> There's also the conservation of energy argument. If the engine is
> turning, the energy to overcome friction and compression has to come
> from somewhere.
I don't think this works. In the non-spinning case, you're dissipating
all that energy into the air, and there's no real limit as to how much
that could be. Now, it would seem that the conservation-of-energy
argument gets you the right answer, but IMO not for the right reasons.
--
Mike Ash
Radio Free Earth
Broadcasting from our climate-controlled studios deep inside the Moon
On May 7, 8:22*am, Mike Ash > wrote:
> In article >,
> *Ron Garret > wrote:
>
> > There's also the conservation of energy argument. *If the engine is
> > turning, the energy to overcome friction and compression has to come
> > from somewhere.
>
> I don't think this works. In the non-spinning case, you're dissipating
> all that energy into the air, and there's no real limit as to how much
> that could be. Now, it would seem that the conservation-of-energy
> argument gets you the right answer, but IMO not for the right reasons.
>
> --
> Mike Ash
> Radio Free Earth
> Broadcasting from our climate-controlled studios deep inside the Moon
I couldn't see, from those charts, that the spinning prop
developed a LOT more drag, like the flat plate some here claimed it
would be. A flat plate the diameter of the prop disc would be about
four times the flat-plate equivalent of the aircraft's profile, I
think, and would steepen the glide to some awesome angle.
I'm going to have to go up and do it again. Many years ago I
stopped the prop on a 150 and found that the glide was a hair steeper
for a given airspeed. The prop stopped, reluctantly, near the stall,
and diving the airplane to Vne would not restart it.
How many others here have actually tried it, besides me?
Dan
Tim[_8_]
May 7th 09, 06:26 PM
> wrote in message
...
I couldn't see, from those charts, that the spinning prop
developed a LOT more drag, like the flat plate some here claimed it
would be. A flat plate the diameter of the prop disc would be about
four times the flat-plate equivalent of the aircraft's profile, I
think, and would steepen the glide to some awesome angle.
I'm going to have to go up and do it again. Many years ago I
stopped the prop on a 150 and found that the glide was a hair steeper
for a given airspeed. The prop stopped, reluctantly, near the stall,
and diving the airplane to Vne would not restart it.
How many others here have actually tried it, besides me?
Dan
----------------------------------------------------------------------------------------
It was demonstrated to me during flight training many years ago. I did it a
few times later after I got my license just for fun, and an opportunity to
hear the airframe with no engine noise.
I never had a problem stopping the prop, but probably never exceed 100 kts
while gliding. In no situation did a prop ever attempt to restart it's self.
However, just a bump of the starter would send it wind milling again, even
with the mixture still closed.
Peter Dohm
May 7th 09, 11:13 PM
"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
Ron Garret
May 8th 09, 08:36 AM
In article >,
Mike Ash > wrote:
> In article >,
> Ron Garret > wrote:
>
> > There's also the conservation of energy argument. If the engine is
> > turning, the energy to overcome friction and compression has to come
> > from somewhere.
>
> I don't think this works. In the non-spinning case, you're dissipating
> all that energy into the air, and there's no real limit as to how much
> that could be. Now, it would seem that the conservation-of-energy
> argument gets you the right answer, but IMO not for the right reasons.
I'll grant you it's not a slam-dunk argument, but it sure seems
plausible that it takes a lot more energy to turn a dead engine than it
does to move a stopped prop through the air at ~100 knots.
rg
On May 8, 1:36 am, Ron Garret > wrote:
> I'll grant you it's not a slam-dunk argument, but it sure seems
> plausible that it takes a lot more energy to turn a dead engine than it
> does to move a stopped prop through the air at ~100 knots.
>
> rg
It would seem so, but a stopped prop still swallows energy. The
turbulence behind it translates into heating of the air. If you have a
sensitive thermometer in a beaker of water, and stir that water, its
temperature will rise.
Dan
Jason Warning Track Kendrick
May 9th 09, 03:39 PM
On Wed, 6 May 2009 11:47:18 -0500, Tim wrote:
>>>> 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.
>>>
>>>
>>
>> Vaughn is absolutely correct in stating that many aircraft with
>> fixed-pitch props will windmill all the way in, as you would have to be
>> near or below its rated stall speed for it to stop. Depends on the
>> particular aircraft in question :-)
>
> Perhaps, but that wasn't the question, and what does the phase of the moon
> have to do with anything but starting a ****ing contest?
Good point. Will U blow me?
--
That white softball comes at me. I am not afreed. I kill it.
To the warning track. I do this a lot. NO softball timidates me
if after me. I kill it. I am The Man, I play a kid's game.
http://tr.im/1f81
Bertie the Bunyip[_24_]
July 5th 09, 12:16 AM
Ron Garret > wrote in news:rNOSPAMon-
:
> In article >,
> "Tim" > wrote:
>
>> The point was how much do you gain by stopping a fixed pitch prop, as
>> opposed to letting it wind mill.
>
> A lot.
>
> You can actually do this experiment in a plane with a variable-pitch
> prop. Idle the engine, and play with the prop control. I did this
> years ago in a 182RG during dead stick landing drills. The difference
> in glide performance between the two extreme prop settings was quite
> dramatic, almost like having an extra set of very fast acting flaps.
>
> There's also the conservation of energy argument. If the engine is
> turning, the energy to overcome friction and compression has to come
> from somewhere.
>
> rg
Actualy, a pro that is spinning freely, with no compression, as in one that
is attached to a snapped crank, will cause more drag than one which is
driving all the internal bits in most cases.
Bertie
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