The [stock] leading spark system provides a spark to both rotors at

the

same time.

A spark is provided for each rotor face (3), so when one rotor has

completed

its revolution it will have fired three times or once per eccentric

shaft

rev.  With two rotors this makes its twice per eccentric shaft rev as

Paul

indicated.

The leading spark catches one rotor in the right position for the
power/combustion stroke and the other is a "waste spark" that catches

the

second rotor during its exhaust cycle (so has no effect - a wasted

spark).

The [stock] trailing spark plug is slightly more complicated as it can

not

use the

"Waste Spark" approach of the leading igntion module and basically has

a

separate coil for each rotor.

Ed Anderson

Gordon Robertson wrote:

Ed,  Why can the trailing spark not use the same waste spark principle

as

the leading?

Gordon Robertson

Ed is gone for awhile and I have no idea why Mazda did it like that.
Waste spark systems use more electrical energy of course. Probably
a cost compromise on the part of Mazda. I suspect the trailing
plug actually needs more energy to fire the mixture effectively
therefore one coil per trailing plug was used.

In an airplane you would like to keep your battery
up for as long as possible in case of alternator failure. It is
best to use one coil per spark plug and fire it only when needed.
You could turn the trailing plug system off to limp to the nearest
airport.

Paul Lamar

Re:  Why no waste spark allowed on trailing plug:
Depending on the spark timing (which varies with RPM) there are times when a
waste spark on the trailing plug would spark the other rotor chamber which
has fuel air charge in it, i.e. the apex seal is on the "wrong" side of the
trailing plug.   Under some conditions, this could cause ignition which
would of course be bad for engine health.

Tracy Crook
tcrook@rotaryaviation.com
www.rotaryaviation.com

Thanks for the clarification on that Tracy.
You have been very quiet lately. I assume you are working hard on 
your new 3 rotor powered RV8. Will you make it to OSH with it?
If not OSH how is it coming? Just curious.

Paul Lamar
 
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