Ignition switch, what happen when Left or Right is selected

Hello,

Here is my question:

On regular aircrafts, like C150, C172, PA28, when we perform the
magneto check where we select Left, than Right, while looking for RPM
drop... what is the switch doing?

When we select Left or Right, do we short that particular magneto or
are we shorting the other one?

I checked all my books and cannot find the answer.

Thanks in advance,

Martin

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


On Tue, 17 May 2005 22:49:09 -0400, Martin B
wrote:

Hello,

Here is my question:

On regular aircrafts, like C150, C172, PA28, when we perform the
magneto check where we select Left, than Right, while looking for RPM
drop... what is the switch doing?

When we select Left or Right, do we short that particular magneto or
are we shorting the other one?

I checked all my books and cannot find the answer.

Thanks in advance,

Martin

"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.

and now the other part of that question... for most key switches that have
"Off" "Left" "Right" "Both" "Start" positions.. what happens when you go to
the "Start" position.?.

BT

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


On Tue, 17 May 2005 22:49:09 -0400, Martin B
wrote:

Hello,

Here is my question:

On regular aircrafts, like C150, C172, PA28, when we perform the
magneto check where we select Left, than Right, while looking for RPM
drop... what is the switch doing?

When we select Left or Right, do we short that particular magneto or
are we shorting the other one?

I checked all my books and cannot find the answer.

Thanks in advance,

Martin

"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

"BTIZ" wrote in message
news:uhzie.7310$Db6.649@okepread05...
and now the other part of that question... for most key switches that have
"Off" "Left" "Right" "Both" "Start" positions.. what happens when you go
to the "Start" position.?.

Assuming just one magneto with an impulse coupling, the other magneto is
shorted and the starter is engaged (by electrical relay, generally...I'm not
aware of any airplane starter that runs the current straight through the mag
switch).

Note also that this is true only of systems that use an impulse coupling for
starting.

Of course, you could have just posted that information, rather than turning
into a pop-quiz.

Pete

"BTIZ" wrote in message
news:uhzie.7310$Db6.649@okepread05...
and now the other part of that question... for most key switches that have
"Off" "Left" "Right" "Both" "Start" positions.. what happens when you go
to
the "Start" position.?.

BT

Usually, the propeller starts turning and after a seond or two the noise
level increases. Sorry, couldn't pass that one up.

most correct answer...

"Peter Duniho" wrote in message
...
"BTIZ" wrote in message
news:uhzie.7310$Db6.649@okepread05...
and now the other part of that question... for most key switches that
have "Off" "Left" "Right" "Both" "Start" positions.. what happens when
you go to the "Start" position.?.

Assuming just one magneto with an impulse coupling, the other magneto is
shorted and the starter is engaged (by electrical relay, generally...I'm
not aware of any airplane starter that runs the current straight through
the mag switch).

Note also that this is true only of systems that use an impulse coupling
for starting.

Of course, you could have just posted that information, rather than
turning into a pop-quiz.

Pete

a good answer... but missing essential elements.. LOL

See Pete's answer
BT

"Dave Stadt" wrote in message
m...

"BTIZ" wrote in message
news:uhzie.7310$Db6.649@okepread05...
and now the other part of that question... for most key switches that
have
"Off" "Left" "Right" "Both" "Start" positions.. what happens when you go
to
the "Start" position.?.

BT

Usually, the propeller starts turning and after a seond or two the noise
level increases. Sorry, couldn't pass that one up.

What's the logic of grounding the non impulse-coupled mag during starting?
(Not a "pop quiz" - I'd like to know).

G Faris



In article ,
says...

Assuming just one magneto with an impulse coupling, the other magneto is
shorted and the starter is engaged (by electrical relay, generally...I'm not
aware of any airplane starter that runs the current straight through the mag
switch).

Note also that this is true only of systems that use an impulse coupling for
starting.

Of course, you could have just posted that information, rather than turning
into a pop-quiz.

Pete