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.