Aerovee Ignition Question

[Bill63C]

I’m new to the Aerovee/Sonex world. I purchased a tri-gear sport trainer with the Aerovee engine. When I do my initial run up before flying, I get very little, if any, drop in rpm’s between the mag and secondary ignition. After a lap around the patch and a warm engine, there is a substantial drop when the secondary ignition is switched off. The engine will run extremely rough. Any ideas would be welcome.

Thanks,
Bill

[mike.smith]

Hi, Bill:

You should see about a +/- 50 rpm max difference between the secondary and the primary on the ground. All the ground check does is confirm the engine does not quit when the secondary is turned off, so you know you have two ignition systems operating. In my experience even a 100 rpm drop on the ground is not indicative of a problem. The proof is in the in-flight check. In the air, in cruise, there should be little difference between the two. If there is, or if there is a large swing in CHT numbers, then the secondary ignition may be too advanced or retarded. You can only check that in flight; it doesn't work to check that on the ground.

I turn off my secondary ignition in flight (not needed, and the battery charges better without), and when on the ground (to save the drain on the battery from the coils). With the secondary turned off on the ground, it will run rougher than when both ignitions are turned on. I simply bump up the throttle a tad when I shut off the secondary.

From the AeroVee manual (page 46 of the 2018 manual):
Ground Check: A mag check at 1600-2000 rpm should reveal little or no change in rpm. If a change of 50 rpm or greater is noted, the magnet cap should be rotated slightly one way or the other.
In Flight Check: Under normal cruise power (2900-3400 rpm):
1. Turn off the secondary ignition and observe the cylinder head temperature.
2. Turn on the secondary ignition and turn off the primary ignition. Observe the cylinder head temperature.
If the CHT rises when operating with only the secondary ignition, the secondary ignition is advanced. Retard the secondary ignition by turning the magnet cap slightly clockwise, as viewed from the flywheel end of the engine.

I get more then a 50 rpm drop on the ground, but the secondary nearly matches the primary in flight, with no change in CHTs. When I adjusted the magnet cap to get a 50 rpm or less drop, the engine ran worse in flight on the secondary. So I'm happy with a 100 rpm drop on the ground since in every other mode of flight the secondary works perfectly.

Hope this helps. If you have more questions let us know.

[Bill63C]

Mike,
Thanks for all the info. I will do the inflight tests and see what happens there. I just bought her Friday and still learning.

Bill

[bvolcko38]

Why can't an old fashioned automotive timing light be used to time the secondary ignition?

[XenosN42]

Hi all,

I agree with Michael Smith, the best way to verify your secondary ignition (coils) timing is in the air at a normal cruise RPM setting.

I produced a video last fall which demonstrates one method. Even if your plane doesn't have a MGL EFIS you may still pick up some valuable tips on how to check your timing.

https://www.youtube.com/watch?v=bMWfEA8s8so&feature=youtu.be

[Bill63C]

My issue seems to be with the Primary ignition. On the ground before flying, everything checks out. After a short flight and a warm engine, the engine will barely run on the primary. Runs fine on the secondary alone. As it is now, I don’t think I would turn of the secondary in flight.

Bill

[mike.smith]

My issue seems to be with the Primary ignition. On the ground before flying, everything checks out. After a short flight and a warm engine, the engine will barely run on the primary. Runs fine on the secondary alone. As it is now, I don’t think I would turn of the secondary in flight.

Sounds like a magneto or spark problem. The primary timing is fixed by the flywheel, so you can't change it. A cold or warm engine should have no impact on the primary ignition. You may need to readjust the magneto gap (page 33 in the manual), or you may need to verify the magnetos are operating; operating properly; check you don't have have an issue with the wires (like cracks, or the end of the wire where it meets the magneto is loose); securing of the spark plug boots to the spark plugs (there should be a small "snap" when they engage the electrode); or the spark plug gaps (correct gaps, and not fouled by lead or carbon). More than likely you would only have an issue with one magneto, which runs two of the cylinders. Highly unlikely to have an issue with two magnetos.

Do you have the AeroVee manual?
http://www.aeroconversions.com/support/ ... Manual.pdf

[Bill63C]

Thanks again Mike, I do have an Aerovee manual. Strange, I flew it home from Minnesota last Friday with no issues at all. I will keep looking.

Bill

[mike.smith]

I also ran a ground wire from each mag, rather than depending on the metal to metal contact. If yours have ground wires, check to see if they are attached and have continuity.

Flywheel magnet still firmly in place?

Mag switch OK (not defective, or loose wire)?

Just grabbing at straws for you...

[radfordc]

Why can't an old fashioned automotive timing light be used to time the secondary ignition?

It can if you are comfortable snuggling up to a 56" Cuisinart blade. Even if the timing light shows agreement between the ignitions I would still do the in flight check to confirm that all is correct. I found that running my engine on just the magnetrons usually reduced engine temps by 5-10 degrees no matter how the secondary was set. I think that the guys who designed the engine knew where to put the plugs for best operation.