Feathering an engine

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

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....

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