It’s been a rainy day here so I couldn’t get out and fly. My idle mind has come up with a few questions about how an electronic advance/retard system works on our modern day ignition systems.

The instructions on a CH Electronics Syncro Spark (CTC) equipped system say to set the ignition to spark at 28-32 degrees before top dead center while slowly rotating the prop. I did this using a degree wheel and the engine runs just fine. My assumption is that while the engine is running at idle, the CTC senses the crankshaft at 28 degrees (my timing) and delays producing the spark until around 4 degrees BTDC (retarded condition). As the engine is advanced in RPM the delay is reduced until at about 4000 RPM where the advance is back to 28 degrees BTDC. With the ignition initially timed for 28 degrees BTDC, what keeps the engine from trying to knock my hand off the first time that it fires? At this point the CTC doesn’t know anything about RPM or rotational rate since it has only sensed one pulse.

On my ZDZ80RV engine equipped with the Falkon ignition the timing instructions say to mechanically set the sensor at a specific distance (6 mm) from the center of the magnet with the engine at TDC. The engine runs fine with this setting. I put a degree wheel on the engine just to see where the spark occurred. It was at 4 degrees BTDC. This makes sense to me from a starting standpoint. The only reference that the ignition has for timing is the relationship of the sensor to the magnet. This means that to advance the timing the only thing that the electronics can do is to delay the spark a certain number of degrees, based on engine RPM, after the initial pulse from the sensor. As far as I know there isn’t an anticipator circuit to know when to fire. If the engine starts out at idle at 4 degrees BTDC then, as the engine increases in RPM, the delay before spark occurs will decrease from as an example: 356 degrees, 350 degrees, 345 degrees, etc. This is absolute degrees of delay.

It seems that these two systems are operating on a different principals. I very well may be all wet in my suppositions and that is where I would like for you ignition wizards to straighten me out.

Ken