Magnetos, Cars?

[Grapes]

I understand how mags work in aero engines but can someone enlighten me on how they work in car engines?

Thank you.

[Lu Zuckerman]

I would say that magnetos when used in automobile engines would perform in the same manner as those used on lawnmower engines and aircraft engines. However, there are slight differences between opposed aircraft engine magnetos and those used on radial aircraft engines. In radial engines the design of the cam that opens the points is not consistent in the placement of the lobes on the cam. This is called compensation and it is done to correct for the orbit of the articulating rod travel as opposed to the master rod travel. The master rod movement is circular and the articulating rod travel is elliptical.

------------------
The Cat

[Avro'ansome]

They don't ! :)
Not trying to be smart, but almost all cars use a standard electric ignition system to supply the spark. A high tension coil is used from the Batt. to provide initial current. A distributor, esentially a shaft driven off either the camshaft, or sometimes directly off the crankshaft has a switch/ contactor for each cylinder. As it rotates it disperses HT current to the appropriate spark plug via another HT lead.

The essential difference between this and a magneto system is that a mag needs no outside current ( essential in the event of an aircraft electrical failure).

Cars don't traditionally use mags 'cause firstly they are less safe (live mag senario), they cost more, they weigh more etc.

Aircraft don't generally used automotive ignitions 'cause a battery or electrical failure would also deprive the engine of it's spark ! ( not good !!!)

Most modern cars have developed electronic (smart) ignitions which used computer technology to optimise performance and eliminate problems like lead/ lag + vastly improve on reliability and performance.

Hope this all makes sense!

[Lu Zuckerman]

You are incorrect on two points. Although used in limited numbers there are electronic ignition systems available for opposed cylinder aircraft engines and also used in limited numbers there are magnetos that are available for automobiles. Both systems are used to improve performance and increase reliability. The electronic ignition systems used on aircraft require a second battery and each bank of spark plugs gets its primary power from its’ own battery power source.

------------------
The Cat

[Flight Safety]

The only type of autos where I've seen magnetos used in any numbers, is in dragsters.