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Feathering an engine



 
 
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  #31  
Old May 7th 09, 03:39 PM posted to rec.aviation.piloting
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Posts: 1,130
Default Feathering an engine

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
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  #32  
Old May 7th 09, 06:26 PM posted to rec.aviation.piloting
Tim[_8_]
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Posts: 27
Default Feathering an engine


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.


  #33  
Old May 7th 09, 11:13 PM posted to rec.aviation.piloting
Peter Dohm
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Posts: 1,754
Default Feathering an engine

"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



  #34  
Old May 8th 09, 08:36 AM posted to rec.aviation.piloting
Ron Garret
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Posts: 199
Default Feathering an engine

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
  #35  
Old May 8th 09, 03:07 PM posted to rec.aviation.piloting
[email protected]
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Posts: 1,130
Default Feathering an engine

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
  #36  
Old May 9th 09, 03:39 PM posted to rec.aviation.piloting
Jason Warning Track Kendrick
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Posts: 2
Default Feathering an engine

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
 




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