Proping Question

The engine is not designed to turn in a specific direction. Some
accessories are, such as mags, vacuum pumps, starter, alternator. The
engine itself will happily run in the other direction, several twins do
just that.



Mark T. Dame wrote:

Ron Natalie wrote:


The argument against it is that people claim it hurts the vacuum pump.


That was what I was taught many moons ago. I have never confirmed it,
but my brain tells me that the engine is designed to turn in one
direction, so don't turn it in the other. No real proof (I'm not an A&P
and have never played one on TV), but just my own logic.


Except when absolutely necessary (like to get the tow bar connected)
you shouldn't be turning the prop at all. There's no good reason to
justify the dangers.


If the engine is properly shutdown (boost pump off, throttle slightly
above idle, and mixture to cut off) the chances are greatly reduced than
if you just kill the engine by turn off the mags. Additionally, some
people recommend checking your mags before shutdown to make sure you
don't have a broken P lead which would also help. A flying club I used
to belong to had a "policy" (not a rule, just a suggestion that it would
be nice if you did it) of turning the prop vertical after parking it to
keep the birds from sitting on it and pooing on the plane.

Obviously the safest way to prevent an accidental fire while hand
turning the prop is to not do it. When I do turn a prob by hand, I try
to do it in the direction it turns while running, turn slowly to
minimize any compression (don't know if that is true either, just what I
was taught), and only use the palms of my hand on the face of the prop
to minimize the possibility of the prop smacking the back of my hand
should it fire. YMMV.


-m

"Barry" wrote in message
...
A flying club I used to belong to had a "policy" (not a rule, just a
suggestion that it would be nice if you did it) of turning the prop
vertical
after parking it to keep the birds from sitting on it and pooing on the
plane.

We turn the prop vertical in the winter to prevent water from pooling
inside
the spinner and then freezing into a block of ice. This happened to me
once,
and the vibration it caused was impressive. We shut down, pulled the
plane
into a heated hangar, turned the prop vertical, and waited for the ice to
melt
and drain out.


Interesting, and worth remembering.

There is also a much older version of the advise--recommending that wooden
props be left horizontal when parked for long periods so that moisture in
the wood will not migrate to one blade, causing an imbalance.

Peter

On May 15, 10:59 am, "Mark T. Dame" wrote:
Ron Natalie wrote:

The argument against it is that people claim it hurts the vacuum pump.

That was what I was taught many moons ago. I have never confirmed it,
but my brain tells me that the engine is designed to turn in one
direction, so don't turn it in the other. No real proof (I'm not an A&P
and have never played one on TV), but just my own logic.

Except when absolutely necessary (like to get the tow bar connected)
you shouldn't be turning the prop at all. There's no good reason to
justify the dangers.

If the engine is properly shutdown (boost pump off, throttle slightly
above idle, and mixture to cut off) the chances are greatly reduced than
if you just kill the engine by turn off the mags. Additionally, some
people recommend checking your mags before shutdown to make sure you
don't have a broken P lead which would also help. A flying club I used
to belong to had a "policy" (not a rule, just a suggestion that it would
be nice if you did it) of turning the prop vertical after parking it to
keep the birds from sitting on it and pooing on the plane.

Obviously the safest way to prevent an accidental fire while hand
turning the prop is to not do it. When I do turn a prob by hand, I try
to do it in the direction it turns while running, turn slowly to
minimize any compression (don't know if that is true either, just what I
was taught), and only use the palms of my hand on the face of the prop
to minimize the possibility of the prop smacking the back of my hand
should it fire. YMMV.


Although I agree with the dangers of accidental engine starts, what I
would like to know if there really have been any cases of inadvertant
engines starts when the prop is turned half a rotation with the
mixture in cut-off even if the magnetos were on. All the cases I am
aware of are related to hand-propping, which is not the same as
turning the prop to reposition the blades.

On May 15, 5:59 am, "Doug Palmer" wrote:
Several pilots found themselves in a debate at our field yesterday. The
issue is weather it is safer to move the propeller on a (parked) aircraft in
the direction of usual engine rotation, or opposite usual rotation. This is
assuming that the propeller needs to move for some reason.

The reasonings ranged from "you should not turn an engine backwards" to
"turning the engine backwards disarms the impulse coupling", to several
issues in between.

Any thoughts from the groups collective wisdom?

Of course turning it backward may damage the vac pump but I've never
flown a hand prop'ped airplane that had a vac system.
The problem with turning it backwards is that it can still on forward.
If you turn it and stop near the compression, it will then turn back
the other way. So, either way assume its hot.
Once you've been flying a hand propped airplane for awhile you will
realize that it is not safe or reasonable to use a full body kick
every time you turn the prop. So I would pull the prop through with an
open palm hand such that if the prop did start I would be ok (some of
the old guys actually start the plane this way). Then, when its time
to start, I hit the mags and do a full kick. If you primed the engine
correctly it should only take about an 1/8 of a turn for it to fire.
BTW: I would never hand prop a nosewheel plane.

-Robert

On May 15, 8:20 am, wrote:
We also check the mag grounding
at idle just before mixture cutoff.

Dan

What type of plane are you handpropping that has mixture cutoff? Must
not be the traditional Stromburg carb.

-Robert

"Newps" wrote in message
. ..

If the engine is properly shutdown (boost pump off, throttle slightly
above idle, and mixture to cut off) the chances are greatly reduced than
if you just kill the engine by turn off the mags. Additionally, some
people recommend checking your mags before shutdown to make sure you
don't have a broken P lead which would also help. A flying club I used
to belong to had a "policy" (not a rule, just a suggestion that it would
be nice if you did it) of turning the prop vertical after parking it to
keep the birds from sitting on it and pooing on the plane.

Obviously the safest way to prevent an accidental fire while hand turning
the prop is to not do it. When I do turn a prob by hand, I try to do it
in the direction it turns while running, turn slowly to minimize any
compression (don't know if that is true either, just what I was taught),
and only use the palms of my hand on the face of the prop to minimize the
possibility of the prop smacking the back of my hand should it fire.
YMMV.


That's only true with 2 cyclce engines, even then, ignition timing is a
factor. The rotational derection of a 4 cycle engine is determined by the
cam, valve and ignition timing. Twin engine aircraft with counter rotating
props/engines have beend designed specifically to do so. The engines as a
whole, are not interchangable.

Robert M. Gary wrote:
BTW: I would never hand prop a nosewheel plane.

Personally, I wouldn't hand prop any plane. I got too many nicks and
cuts as a kid finger propping model airplanes. (-:

Which reminds me of a story. One winter a few years ago the FBO had a
152 that was being stubborn in the cold weather, so one of the line guys
helped out by hand propping it for the pilot. He was wearing gloves and
when the plane started, one of his gloves came off. The prop threw the
glove about 30 feet and the pilot freaked out because he thought the
guy's hand was still in the glove! He shut the engine down to check on
him. The line guy wasn't happy about having to hand prop it again...


-m
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Doug Palmer wrote:
Several pilots found themselves in a debate at our field yesterday. The
issue is weather it is safer to move the propeller on a (parked) aircraft in
the direction of usual engine rotation, or opposite usual rotation. This is
assuming that the propeller needs to move for some reason.

The reasonings ranged from "you should not turn an engine backwards" to
"turning the engine backwards disarms the impulse coupling", to several
issues in between.

Any thoughts from the groups collective wisdom?

Never, ever turn a Rotax 912/914 backwards. It
will break the suction in the oil line. To regain
oil pressure you have to undo oil lines and refill
them.

Robert M. Gary wrote:
BTW: I would never hand prop a nosewheel plane.


Just out of curiosity, why does a nosewheel make a difference?

I used to have an old 172 (with the cheesey 20 amp generator) that required
a handprop after most night flights. I didn't seem any different than
handpropping a tailwheel equiped 170.

John Galban=====N4BQ (PA28-180)

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"Robert M. Gary" wrote in message
ps.com...
On May 15, 8:20 am, wrote:
We also check the mag grounding
at idle just before mixture cutoff.

Dan

What type of plane are you handpropping that has mixture cutoff? Must
not be the traditional Stromburg carb.

-Robert

This could be just a nomenclature issue. I was taught to call the lean
position of the mixture control "idle cut off" even though it really doesn't
cut anything off. However, it is too lean to keep the engine running at
1000 rpm.

I'm curious about what others think

Peter