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Old 09-26-2019, 08:11 PM
vlittle's Avatar
vlittle vlittle is offline
Join Date: Jan 2005
Location: Victoria, Canada
Posts: 2,164

Originally Posted by rv6ejguy View Post
The LOP button is designed to be used when you lean the engine to LOP. This advances the timing (usually 3-5 degrees) and picks up some of the power lost when running lean of peak due to the slower burn rate of the mixture.

Usually see 3-6 knots come back over fixed mag timing, depending on airframe and how far LOP you are.

The amount of advance for LOP is user programmable as are the basic RPM and MAP timing curves. In fact, almost every parameter right down to cranking retard and coil charge times can be changed.

This is the "Last Word" in aircraft EI systems where you want full control of your timing and not a canned curve like most other EIs offer.
I'm not from Missouri (actually from Victoria), but all of these claims about ignition timing made me skeptical. I have an IO540 9.2:1 running one magneto and an Electroair electronic ignition.

I have a switch that cuts off the MAP sensor so I can have baseline timing or advanced timing. That also provided me a convenient spot to intercept the advance signal and massage it with an arduino controller.

So I wrote a sketch that allowed me to add or subtract ignition timing in flight and test some of the claims.

The first test was to try changing the timing with a rich 'best power' mixture at 8500 PA. Stock timing from the Electroair was 33 degrees. I tried between 27 and 38 degrees with no measureable change in airspeed of 201 knots.

The second test was to go LOP around 180 knots and find the best timing. Baseline was 177 knots at 33 degrees and 180 knots at 38 degrees. Yeah!

So, based on this rather elementary test, it looks like the 'canned' curve is a bit too conservative LOP, thus proving Ross's assertion. But I also had to watch CHTs in the climb, so maybe it was too agressive ROP. I can always turn off the advance with the switch, though.

So maybe I can change the shape of my advance curve with some simple programming... less advance when ROP and more advance when LOP. I can figure this out from the Dynon serial data stream.

V e r n. ====
RV-9A complete
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Victoria, BC (Summer)
Chandler, Az (Winter)
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