Feathering an engine

"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 :-)

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."

"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.

In article ,
"Tim" wrote:

"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?

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.

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.

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