Ignition switch, what happen when Left or Right is selected

"Bill Zaleski" wrote in message
...
You are shorting the magneto that is not selected, therefore
inhibiting it's operation.

And that's one of the dangerous things of a magneto system. They are hot on
their own, unless shorted. So if the wiring gets loose in the key switch, or
something else along the circuit gets disconnected, actually you may have a
hot prop, which is very dangerous.
If when you do a magneto check you notice NO RPM drop, then either the
grounding is not correct, or the other magneto is not working at all.

"Guillermo" wrote in message
...
And that's one of the dangerous things of a magneto system. They are hot
on
their own, unless shorted.

Well, yes and no. I mean, yes...a hot prop can be dangerous, depending on
the engine and airplane.

But compared to the hazard of having a broken wire disable your magneto,
it's a pretty minor danger. The "short the magneto" design is that way for
a reason, and I think most people would agree with that reason.

There are lots of "dangerous things" about airplanes. This just happens to
be one of them, and it's not really that big of a deal as things go.

[...]
If when you do a magneto check you notice NO RPM drop, then either the
grounding is not correct, or the other magneto is not working at all.

Yup. Of course, it's easy enough to determine which it is, when you go to
test the other magneto.

Pete

Guillermo wrote:
"Bill Zaleski" wrote in message
...

You are shorting the magneto that is not selected, therefore
inhibiting it's operation.


And that's one of the dangerous things of a magneto system. They are hot on
their own, unless shorted. So if the wiring gets loose in the key switch, or
something else along the circuit gets disconnected, actually you may have a
hot prop, which is very dangerous.
If when you do a magneto check you notice NO RPM drop, then either the
grounding is not correct, or the other magneto is not working at all.


Or things are severely mistimed.

But the fact there is a drop on L and R doesn't tell you things
are working properly in the OFF position.

"Guillermo" wrote in message
...
And that's one of the dangerous things of a magneto system. They are hot
on
their own, unless shorted. So if the wiring gets loose in the key switch,
or
something else along the circuit gets disconnected, actually you may have
a
hot prop, which is very dangerous.
If when you do a magneto check you notice NO RPM drop, then either the
grounding is not correct, or the other magneto is not working at all.


That's a good thing to pay attention to. You can also check it at
idle before shut down by briefly turning the switch to "OFF" and
see if the engine starts to shut down.

"OtisWinslow" wrote in message
m...
That's a good thing to pay attention to. You can also check it at
idle before shut down by briefly turning the switch to "OFF" and
see if the engine starts to shut down.

Emphasis on "at idle", of course.

"Peter Duniho" wrote in message
...
"OtisWinslow" wrote in message
m...
That's a good thing to pay attention to. You can also check it at
idle before shut down by briefly turning the switch to "OFF" and
see if the engine starts to shut down.

Emphasis on "at idle", of course.


Yes. At idle. And I should have added that if it starts to shudder and
die don't turn it back on. When I do it it's just a brief switch to the
OFF position and back on.

Yes. At idle. And I should have added that if it starts to
shudder and
die don't turn it back on.

It WILL start to shudder and die if you turn it off, unless there's a
bad P-lead connection or mag switch. You want it back on so you can
shut the engine off with mixture, not ignition.
I get really annoyed when students go to "Off" during the runup
and mag testing. We try to get them to hold the key firmly, not by its
edges, so that it won't inadvertently snap over to "Off" when they
select "R." They almost always immediately turn it on again (instead of
letting it spool to a stop and restarting) and the exhaust makes an
almighty BANG and I have to look closely at that muffler and piping
during inspections to find the cracks that often result.
That was the big joke when we were young, right? Turn of the
auto's ignition and back on again to get the big boom from the exhaust
system. Doesn't work anymore with fuel injection. Saves exhaust
systems, no doubt.

Dan

I get annoyder when they go the other way and grind the starter bendix. I'm
not sure which one is more expensive to fix.

{;-)

Jim


I get really annoyed when students go to "Off" during the runup
and mag testing.

My point was that if it gets past the point where it's going to keep
running, just leave it off. A quick flick of the switch to OFF and back ON
it
will certainly quit firing and lose a few rpm, but it won't die. I've been
doing these as long as I've been flying (the 70s) and I think it's
important to know the mags aren't hot. It's part of my shut down.
You should simply use any method you feel comfortable with to
check the P leads.


wrote in message
ups.com...

It WILL start to shudder and die if you turn it off, unless there's a
bad P-lead connection or mag switch. You want it back on so you can
shut the engine off with mixture, not ignition.

Dan

Exactly. I learned to fly in the early '70s and they didn't
teach us to look for a hot mag. I learned that when upgrading some
years ago. Doing this, I found that one of our 172's mag switches would
allow the mags to keep firing if the key was forced against the "Off"
stop, and upon investigation found an AD against any of those switches
that did that (76-07-12). Bet there are still a lot of them out there.
As far as the discussion about a single impulse mag rather than
two: Lycoming may have recommended a change to one to get rid of the
impulse coupling on one mag. The springs in these things have been
known to fail, and with two mags one might fail and not be readily
noticed if the pilot is a careless twit who doesn't do a decent runup;
if the other spring then failed as well the timing on both would go to
near zero BTDC. Power output would be low indeed. Corrosion has been a
problem in engines seldom flown or flown on very short flights, and the
springs, being a high-carbon steel, corrode quickly. The Bendix dual
mag (one housing, one gear and impulse coupling, two mags) had an AD
against it to replace that spring with a better one, since its failure
could and did cause accidents.

Dan