Feathering an engine

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
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!

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

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
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!

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

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
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!

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