Proping Question

On 2007-05-15 05:59:05 -0700, "Doug Palmer" said:

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?

An engine can be made to run backwards. Model airplane engines do it
all the time, usually as a result of mixture that is too rich. Granted,
real airplane engines are different and have more safety systems, but I
could not say that it is impossible, especially given the enormous
variety in types of engines, magnetos, starters, and fuel systems you
see on airplanes.

I have never heard of an accident involving an engine running backward.
I haven't found one, either. You can be the first! :-)
--
Waddling Eagle
World Famous Flight Instructor

On May 16, 3:05 pm, "Morgans" wrote:
"Robert M. Gary" wrote

Because the top arch of the prop is close to my head. When teaching
students to hand prop the biggest challenge is to get them to stand
close enough to the prop. Standing too far back is much more dangerous
than standing too close. The worst thing that could happen is to fall
into the prop, something that can only happen if you are standing back
and leaning into it.

I was wrong. I had not heard that exact variation, before. g

Kicking though is still too close, even if you are swinging your body away
from the tip?
--
Jim in NC

In a tailwheel, as you pull the prop "down" during the kick you are
also moving toward yourself (because of the angle the taildragger sits
on the ground), which helps you maintain contact as you are moving
away from it. In a nose wheel plane you'd be pushing straight down on
the prop, causing your head to move down closer to the prop arch.

-Robert

"C J Campbell" wrote in message
news:2007051622171050878-christophercampbell@hotmailcom...

An engine can be made to run backwards. Model airplane engines do it all
the time, usually as a result of mixture that is too rich. Granted, real
airplane engines are different and have more safety systems, but I could
not say that it is impossible, especially given the enormous variety in
types of engines, magnetos, starters, and fuel systems you see on
airplanes.

I don't see how a four cycle engine can run backwards. If the crank is
turning backwards, the intake valve would be open while the piston is going
up, pushing the contents of the cylinder into the intake manifold. While the
exhaust valve is open, the piston would be going down, sucking whatever is
in the exhaust manifold into the cylinder. there would have to be a source
of fuel in the exhaust manifold for the engine to run.

Model engines are two stroke, so they can run backwards.

A long time ago, I bought a moped (also a two cycle). The timing was so far
retarded that it ran better backwards than forwards until I had it timed. It
couldn't pull me up the hill because it ran so badly. Once, it fired up
backwards and ran great. I rode it up the hill backwards.

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?

This is one issue where you don't want to get bogged down in the
technicalities involving vacuum pumps and impulse couplings.
The bottom line on this issue is that you should NEVER.....EVER......
trust
a propeller not to kill you if you turn it by hand IN EITHER DIRECTION
while
it's attached to the airplane.
Dudley Henriques

People will say it is technically impossible, but I think it is wishful
thinking. An engine may not run backwards very well, but I have seen
too many malfunctioning magnetos to believe that it could never happen.
It might be improbable, but I would not bet my life on the idea that it
is impossible.
--
Waddling Eagle
World Famous Flight Instructor

It doesn't really have to "run" to hit you, it only has to "kick" once. And
that is cold comfort indeed, since immediate death is far from the worst
thing that can happen to a person.

(rant omitted)
Peter

"C J Campbell" wrote in message
news:2007051622001427544-christophercampbell@hotmailcom...

People will say it is technically impossible, but I think it is wishful
thinking. An engine may not run backwards very well, but I have seen too
many malfunctioning magnetos to believe that it could never happen. It
might be improbable, but I would not bet my life on the idea that it is
impossible.
--

On a 2 cycle engine, ignition time is all it takes. Some golf carts actually
work that way. The starter and ignition time is selectable by the direction
indicatior on the dash.

But on a 4 cycle engine, the valve timing would have you intaking through
the exhaust, and exhausting through the intake.

"C J Campbell" wrote in message
news:2007051622001427544-christophercampbell@hotmailcom...
On 2007-05-15 07:46:15 -0700, "Dudley Henriques"
said:


"Doug Palmer" wrote in message
ink.net...
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?

This is one issue where you don't want to get bogged down in the
technicalities involving vacuum pumps and impulse couplings.
The bottom line on this issue is that you should NEVER.....EVER......
trust
a propeller not to kill you if you turn it by hand IN EITHER DIRECTION
while
it's attached to the airplane.
Dudley Henriques

People will say it is technically impossible, but I think it is wishful
thinking. An engine may not run backwards very well, but I have seen too
many malfunctioning magnetos to believe that it could never happen. It
might be improbable, but I would not bet my life on the idea that it is
impossible.
--
Waddling Eagle
World Famous Flight Instructor


Rule number one for me has always been "never give the machinery an
advantage".
If it CAN kill me, it just MIGHT kill me, so I treat it that way.
:-)))
Dudley Henriques

On May 16, 8:26 pm, Dana M. Hague
d(dash)m(dash)hague(at)comcast(dot)net wrote:
On Tue, 15 May 2007 17:47:01 -0400, "Morgans"

wrote:
Why no hand propping a nose dragger for you?

I've done it a few times but found it very awkward, as the prop on,
say, a C-150 or 172 is much lower than the prop on a taildragger like
my T-Craft.

On the T-Craft turning it backwards was the standard way of clearing
it if it was flooded... but there was no impulse coupling nor vacuum
pump.

I haven't yet seen a Continental or Lycoming lightplane engine
without an impulse coupling on at least one mag. That impulse
mechanism is necessary for starting because it snaps the mag over fast
so it'll generate a spark, but it also retards the spark to at or near
top dead center so that the engine doesn't kick back. The usual firing
position on an A-65 is 30 degrees before top dead center. The other,
non-impulse mag won't fire at hand-propping speeds, but will sometimes
fire immediately after the engine catches and will stop it or kick it
backwards or make it hammer frightfully until the RPM comes up to
idle. Some pilots will set the mag switch to the impulse mag only
while hand-propping, going to Both after the engine is running. Much
safer. I have two impulse mags on mine and it behaves itself.
I hand-prop using one hand only. As I pull down I fold
myself so that my weight is carried back a little. The trick, as has
been mentioned, is to get pretty close to begin with. And make sure of
your footing. Anything slippery like snow or ice or wet grass, or
gravel on the pavement, can let you slide into the prop.
I don't prime my A-65 unless the temp is down around
freezing. It floods way too easily. Mags on, throttle at idle, and it
will catch on the sixth to eighth blade.

Dan

In article .com,
wrote:

On May 16, 8:26 pm, Dana M. Hague
d(dash)m(dash)hague(at)comcast(dot)net wrote:
On Tue, 15 May 2007 17:47:01 -0400, "Morgans"

wrote:
Why no hand propping a nose dragger for you?

I've done it a few times but found it very awkward, as the prop on,
say, a C-150 or 172 is much lower than the prop on a taildragger like
my T-Craft.

On the T-Craft turning it backwards was the standard way of clearing
it if it was flooded... but there was no impulse coupling nor vacuum
pump.

I haven't yet seen a Continental or Lycoming lightplane engine
without an impulse coupling on at least one mag. That impulse
mechanism is necessary for starting because it snaps the mag over fast
so it'll generate a spark, but it also retards the spark to at or near
top dead center so that the engine doesn't kick back.

.........

Both mags on the O-435 Lycoming in my Johnson Rocket are non-impulse.

Orval Fairbairn wrote:
In article .com,
wrote:

On May 16, 8:26 pm, Dana M. Hague
d(dash)m(dash)hague(at)comcast(dot)net wrote:
On Tue, 15 May 2007 17:47:01 -0400, "Morgans"

wrote:
Why no hand propping a nose dragger for you?

I've done it a few times but found it very awkward, as the prop on,
say, a C-150 or 172 is much lower than the prop on a taildragger like
my T-Craft.

On the T-Craft turning it backwards was the standard way of clearing
it if it was flooded... but there was no impulse coupling nor vacuum
pump.

I haven't yet seen a Continental or Lycoming lightplane engine
without an impulse coupling on at least one mag. That impulse
mechanism is necessary for starting because it snaps the mag over fast
so it'll generate a spark, but it also retards the spark to at or near
top dead center so that the engine doesn't kick back.

........

Both mags on the O-435 Lycoming in my Johnson Rocket are non-impulse.

Both mags on the O-320 Lycoming in my Beech Musketeer are non-impulse.

--
Don Poitras

wrote:

I haven't yet seen a Continental or Lycoming lightplane engine
without an impulse coupling on at least one mag.

They're out there. In addition to the impuse system, there was a starting
system called "shower of sparks" that used a gadget called a vibrator to
provide the low rpm spark. Unlike the impulse system, the vibrator required
electrical power from the battery to make a spark.

I've usually seen these on older models.

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

--
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