Ignition switch, what happen when Left or Right is selected

"Guillermo" wrote in message
...
I was wondering what is exactly the function of the impulse-coupled
magneto.
I've read about them a little bit on the web, but I'd like somebody to
explain it in simple terms.

A regular non impulse magneto has the engine rotation directly attached to
the rotating part of the magneto, so at low cranking speeds, it may not be
going past the windings fast enough to generate a sufficient spark.

An impulse magneto has the generating part of the magneto designed just the
same as the regular magneto, but the trickery comes in, at how the magneto
is coupled to the engine.

In the impulse type, when the engine is being turned very slowly, there are
little counterweights that do not allow the generating portion to turn, but
instead, the rotation winds up a powerful spring. When it gets all the way
wound up, and the time has come to make a spark, it releases, and spins the
generating gizmo fast as the devil, creating a powerful spark, which sends
your piston scurrying down it's travel. The next time around, the mag will
be going fast enough to not wind up the spring, and it will behave just like
a regular magneto.

The winding up of the spring also serves to delay the spark until the piston
has barely gone past top dead center, rather than well before top dead
center. That is the reason you shut off the other regular mag; so it does
not possibly fire early, and make the starter have to work against the
attempted backwards combustion.

The impulse magneto is why rotating a prop can be so dangerous. If it has
the mags turned off, but the impulse mag has had it's ground path fail, it
will still wind up the spring. No matter how slowly the prop turns, if it
has a sufficient fuel air mix left in the cylinder and the impulse snaps
over center, the windings will send the spark on the way, thus starting the
engine.

By the way, at OSH, in the HB show area, the young men and women (Aviation
Explorers) helping you park your plane are NOT ALLOWED to touch your prop,
due to safety rules, because of this characteristic.

Clear enough? Ask if you need more clarification.
--
Jim in NC