Happy 4th of July but No Joy in Mudville

Over the last few days I have been trying several things and thought I'd catch it up, before going out for a 4th of July picnic.

Air gap - I had the scope out the other day and a couple of people much smarter than me. We were getting the miss, on the ground, at WOT. The Electromotive manual says to have the sensor air gap set to .030 to .060, depending on the trigger wheel style. At various times, I had been running it in the .030 to .040 range. Just for grins we tried setting it to .060 and it ran worse.

Then we went the other way and set it to .020". (Remember, I have a run out of .003" for the mounted trigger wheel.) Unbelievably, the miss disappeared (on the ground). Then we tried setting it to .017" and it was still fine.

Unfortunately, the subsequent test flight failed. Got to altitude and running on the ignition only and the miss was still bad.

Terry Crouch urged me to go the extra mile and "make the sensor support strong enough that you can hang the airplane on it, without it flexing". So, I trundled down to the lumbar yard and bought some 1/8" angle iron. I fashioned a stiffener to the sensor plate and mounted it on the two nose bolts. No lightening holes. This tractor quality part does not flex. (I still have yet to try rebar reinforced concrete, but that may have to be next).

Today's flight test - failure. No change in the miss characteristics. Rats. The engine actually backfired when I was switching from BOTH to IGN.

Talking to Terry some more, we wondered if somehow the backup sensor might be interfering with the primary. The plan is to make a single flight with the backup sensor removed from the system and see if that has any effect.

A couple of you have inquired about variations in the air gap due to wobble in the crank or prop extension. I haven't checked this relationship yet, and promise I will on the next visit.

Happy 4th of July

Sam