Surefly "Mag Checks"

[MisfitSELF]

For the folks who have installed the Surefly ignition system, how do the "mag checks" that you do pre-takeoff look like?  Does it behave like it would if you had two mags?  EG are the RPM drops and limits the same and do you still go through the both / right / both / left / both routine?

Thanks,

Bruce

[Ragsf15e]

45 minutes ago, MisfitSELF said:

For the folks who have installed the Surefly ignition system, how do the "mag checks" that you do pre-takeoff look like?  Does it behave like it would if you had two mags?  EG are the RPM drops and limits the same and do you still go through the both / right / both / left / both routine?

Thanks,

Bruce

Yes.  It’s largely the same although you might notice a very quick stumble depending on how your ignition switch is wired and where you put the SF.  Example, my SF is on the left and my switch is standard bendix.  When I switch from right back to both, it passes through left.  There is a very quick stumble as the SF takes something like 10ms to power back on.  This is a known and expected.  They have reduced the startup time on newer models so maybe not as noticeable.  The numbers you’re looking for are the same.

If you do an airborne mag check at full power, I’d recommend reducing power between switching mags instead of letting the stumble happen.  During a low power runup it’s just a miss, but I had a pretty good backfire when I did an airborne mag check.
 

[Ragsf15e]

Additionally, I don’t notice any difference on my preflight mag check from before I had the SF installed.  Still ~25-50 RPM drop.  I also watch egts and see uniform rise in them.

If your SF is set to advance timing, you’ll start to notice some difference as you climb below about 25”MP.  Say above 5000’ or so.  I noticed slightly higher temps.  Maybe 10deg f each cylinder at the same fuel flow.  The changes are very subtle.  Cruising ROP it’s pretty hard to notice any difference but maybe you’ll see the slightly higher temps.  LOP, I do see slightly higher speeds (maybe 2-3 kts) at a similar setting in degrees LOP.

Edited March 3, 2021 by Ragsf15e

[DXB]

RPM drop is similar, maybe slightly less on the Surefly side (assuming identical timing) given the longer spark duration on the Surefly.  Standard mag check at 1700rpm produces a slight stumble as you pass from right to left while going back to both (assuming Surefly on left).  The Surefly just doesn't kick in quite as fast as a regular mag.  When at cruise power, that tiny pause will produce a distinct backfire during an inflight mag check.  So one would have to pull the mixture out completely to avoid the backfire when going from right to left in flight. I don't do in flight mag checks any more.

[47U]

Same experience here as described above... Surefly replaced the left mag and the shower of sparks is history.

I too banged my exhaust pretty good doing an inflight mag check.  The ElectroAir rocker switch panel solves the problem latency problem of rotating through the positions R-L-B with the Bendix mag switch.

I didn’t have the panel space for the ElectroAir option, so I replaced the Bendix mag switch with a of couple of mil-spec DPDT toggle switches.  Works great.  My Bendix switch was in serious need of overhaul/replacement (after only 50+ years!).  You could pull the key out in any position.  Really unsafe.