Ignition switch, what happen when Left or Right is selected

"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.?.

Already answered. Why are 'L' and 'R' often reversed on the switch?

moo



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

BTIZ wrote:
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.?.

Depends on the switch. Some switches ground out the RIGHT mag, some
leave both on. It also provides a contact for the starter solenoid.

Some more thoughts on selecting the correct mag for starting -

The impulse function on a mag provides a both a substantial timing
delay and a velocity enhancement for starting purposes. Both are
important. The timing delay of the impulse prevents an engine from
kicking back. That's why starting is done on one (the impulse) mag
only. Most aircraft have only one mag with an impulse, but even a
non-impulse mag may generate a spark at cranking speeds if the mag is
in good condition.

Two things to consider are

1) Be sure the only correct mag is selected if hand propping - and
never put your fingers over the back of the blade. I didn't once on a
TriPacer and still have a fortunately small scar on the tip of my index
finger when it kicked back mightily.

2) Consider that possibly the mag p leads might get reversed in
maintenance. The starter may be able to handle the cranking on the
wrong mag but it could be a hand propping accident waiting to happen.

That's why I won't hand prop a strange airplane for the first time.

Just running down the list in my head, I am going to take the opposite
position. Most aircraft have BOTH mags with an impulse; a small minority
have only one with an impulse.

Jim


Most aircraft have only one mag with an impulse