Proping Question

On May 15, 2:08 pm, "Peter Dohm" wrote:
"Robert M. Gary" wrote in glegroups.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

In the C140, the Aeronca, and the J-3 the carbs (probably all
Stromburg), pulling the mixture all the way out at idle had no effect
at all on the engine. The mixture control only affected the engine at
power.

-Robert

Robert M. Gary wrote:

In the C140, the Aeronca, and the J-3 the carbs (probably all
Stromburg), pulling the mixture all the way out at idle had no effect
at all on the engine. The mixture control only affected the engine at
power.


With the Marvel-Schebler carbs found on the average (post 1950s) light
singles, pulling the mixture all the way back will cut off fuel to the idle
circuit as well as the main jet.

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

--
Message posted via AviationKB.com
http://www.aviationkb.com/Uwe/Forums...ation/200705/1

"Robert M. Gary" wrote

BTW: I would never hand prop a nosewheel plane.

I think I know the reason for this opinion, but I would still be interested
in hearing your reasoning.

Why no hand propping a nose dragger for you?
--
Jim in NC

On May 15, 10:21 am, "Robert M. Gary" wrote:
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

We were talking about turning the prop backward to reposition
it, not handpropping to start it. All our training airplanes have
starters and idle cutoff mixture controls. My own old Jodel with its
A-65 has to be handpropped, and has the old Stromberg with cruise
mixture control that has no effect on idle mixture. I shut the fuel
off and wait a bit for the bowl to run dry when I shut it down.

Dan

On May 15, 10:02 am, Newps wrote:
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.

That backward-running engine has a different camshaft, mags and
oil pump to allow it to run that way. Engines won't run backwards just
because we try to start them backwards. The intake/compression/power/
exhaust strokes MUST happen in that order, and a backward-turned
engine has them all messed up.

Dan

On May 15, 10:18 am, Andrew Sarangan wrote:


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.- Hide quoted text -

- Show quoted text -

Yes, engines have hurt people. You can kill it with the idle
mixture cutoff, but if someone has fooled with the primer (or boost
pump on an injected system), fuel will be present and any spark could
set it off. An example is a failed start attempt, due either to a
flooded engine or cold weather. That prop will be dangerous with the
mags on. Turning it forward is insane.

Dan

On May 15, 4:11 pm, wrote:
On May 15, 10:02 am, Newps wrote:

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.

That backward-running engine has a different camshaft, mags and
oil pump to allow it to run that way. Engines won't run backwards just
because we try to start them backwards. The intake/compression/power/
exhaust strokes MUST happen in that order, and a backward-turned
engine has them all messed up.

Dan

Forgot to mention: an alternator generates just fine when run
backwards. I did it on an inboard boat I built, because there was no
room in that tight compartment for the alternator to sit alonside the
engine in its usual spot and had to be mounted backwards in front. An
alternator generates alternating curent that is internally rectified,
and the direction of rotor rotation is irrelevant. The only
consideration is the cooling fan blade angle; installing an older fan
with straight radial blades solves the problem.
The DC generator must be turned in one direction only.

Dan

Andrew Sarangan wrote:


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.

Start no, kick over a turn or two, yes. Even with the engine cut
off with the mixture, there can end up with just enough fuel in the
system to fire the thing over a turn. I've had it happen on a 172N
we had in the club.

Interesting topic, interesting discussion... but if I may expand on
the original question a bit?

The Original piper POH that came with my bird ('67 PA-28-140) actually
recommends that that prop be pulled through two complete rotations
backwards any time the engine is started after sitting for a long time
(it actually says its a good idea for every flight, but should be
mandatory any time the engine's been sitting for a while).

I've NEVER heard or seen this advice anywhere else... I've never
practiced it... It seems almost insane to me... but the book says
what the book says.

Anyone have any clue why?

I can get the exact wording tpmogjt ... its in the 'preflight and
takeoff' section of the book.

Andrew Sarangan wrote:
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.

Early in my piloting career, while my instructor deftly distracted me
with questions about the cruising speed of an unladen swallow, I managed
to turn the mags off before pulling the engine to cutoff, so that it
stopped because the ignition died. Spotting my mistake, my instructor
asked me to run the starter over, and the engine gleefully spat to life
on the very first blade, and ran for another 5-10 seconds.

Then he asked me if I wouldn't mind terribly putting the plane away myself.

Take any aircraft X and put renter A before you who does something
similar but doesn't catch the mistake, and you too can become another
statistic by trusting that the prop is dead, that the p-lead works, and
that the cylinders are dry.

TheSmokingGnu