Surefly electronic ignition

[kiljoy]

Here's our Surefly experience so far:

I'd decided to replace some of the slick mags on our club's 172s with Surefly.

The install is easy although we did have to install mp, fuel flow, pressure etc etc to get the full benefit but it was bangin' from day one. You can just keep leaning and leaning. Saved us at least 1 gph on our O320-D2J. As stated before it does highlight inefficiencies. Needed aluminum tape to block about 15% of our oil cooler duct as it was stealing air from cylinder #3, replace some baffle rubber, etc

It didnt turn out all roses (yet) though. We wound up having to send it back to Surefly to go through a service cycle as we were having problems of momentary engine stutter (~.5-1sec).

Full story: A pilot squawked that there was a very short but noticeable engine stutter that'd happen every 20 minutes or so. I test flew her for an hour, same altitude, relatively same conditions and experienced nothing of course. Our club mechanic and I went through and replaced pretty much everything we could think from the plugs back to the switch including at Surefly's behest switching to the mag harness they recommend.

We switched back to two slicks and hadn't had an issue while waiting for the surefly to come back.

As an aside: The mag check was interesting as when you went from right (slick) to left (surefly) we saw a half second stutter as the surefly came alive... or at least that's what we're thinking it is. Has anyone else experienced that?

[MiserBird]

Originally Posted by kiljoy

As an aside: The mag check was interesting as when you went from right (slick) to left (surefly) we saw a half second stutter as the surefly came alive... or at least that's what we're thinking it is. Has anyone else experienced that?

Yes, and from what I've read that's completely normal. I think the SureFly is programed to make two revolutions to determine direction of rotation before it resumes firing.

[Carl Froehlich]

For me the main advantage of pMags is the advanced timing (jumper in). Over the years I find they provide superb service for my primary mission, high efficiency LOP cruise.

In other words, for me fixing the timing at 25 degrees (or whatever) for an EI takes away the primary reason for having it.

One note on leaving off the manifold pressure sense line. If this is all you do, you still get timing advance as you go up in altitude. Consider a typical cruise at 8000?, WOT. The manifold pressure will very close to atmospheric pressure - and your EI timing will advance per it?s programmed curve.

I know of one Lancair builder that does just this. He spends 99% of his time high, WOT and LOP. He just left off the manifold line as he did not what to add another firewall penetration.

Carl

[norcal64d]

Originally Posted by rv6ejguy

Perhaps I'm not understanding here but I hope Surefly isn't saying that best power is made at 38 BTDC?

This flies in the face of plenty of dyno and flight data saying that isn't so. 38 will give you way less power, high CHTs and detonation almost for sure.

They are still mulling over the data before they give me an answer, but their immediate thought was it should only give you more power, so in essence, yes. I asked if they had any test data for high DA and that info wasn't available.

Just to be clear my setup is one Slick and one Surefly. I think for me its fairly clear to me that their advance is probably terrible for us people trying to get off the ground in Colorado. The plane sure starts nicely though!

[Mike S]

Tim, welcome aboard the good ship VAF

[vlittle]

Let me see if I understand this:

A canned timing curve that looks at MAP and RPM has no knowledge of mixture and therefore flame speed. So a best power mixture at 8500 DA may need less advance than a best economy mixture.

Is this why Ross at SDS has an LOP switch that advances timing for economy operation?

Vern

[Toobuilder]

Originally Posted by vlittle

Let me see if I understand this:

A canned timing curve that looks at MAP and RPM has no knowledge of mixture and therefore flame speed. So a best power mixture at 8500 DA may need less advance than a best economy mixture.

Is this why Ross at SDS has an LOP switch that advances timing for economy operation?

Vern

Yes.

Except that best power mixture WILL (not may) need less advance than best economy mixture. There is no merit to debate on this - it's fact. If a canned advance curve is optimized for LOP, then best power will suffer. Conversely, if the canned curve is optimized for best power, LOP will suffer. They are two very different requirements, and you need two curves to satisfy both conditions.

[DanH]

Originally Posted by vlittle

Let me see if I understand this:
A canned timing curve that looks at MAP and RPM has no knowledge of mixture and therefore flame speed. So a best power mixture at 8500 DA may need less advance than a best economy mixture. Is this why Ross at SDS has an LOP switch that advances timing for economy operation?
Vern

Yes again.

If I may add to Mike's illustration...

If your EI choice is not switchable between best power and best economy ignition advance schedules, install a best power schedule.

Yes, that advice flies in the face of claims made repeatedly. Humor me a moment.

Many EI users conflate two separate EI factors. One is the ability to light less-than-optimum mixtures, a function of spark duration, energy, and wide gap. The other is the incorporation of variable advance. A user will install an EI, and then gush about his new lower fuel burn, easier starting, etc, while silently pondering his new higher CHTs. He often fails to understand that most of what he loves about his new EI is due to the spark, and much of what he dislikes is due to the timing of that spark.

Two weekends ago I found myself flying side by side with another RV-8. The nice young man was a relatively new owner, with a limited grasp of things in-cowl. Beautiful airplane...with very high CHTs. Before we went flying, I took a look under the cowl at his request. Yep, it had all the usual baffle seal errors, and lots of leaky spots, and a blast tube, and even two totally empty holes in the rear wall. I explained the needed corrections and stuck some aluminum tape on the worst spots, just so he could observe a difference when we went aloft for a visit to another airport.

The ignition? One Slick, and a P-Mag, with no jumper, which means an advance schedule beginning around 28 and maxing at 38 degrees BTDC. I suggested at least installing the jumper to subtract 5 degrees or so, and offered to do so, but the owner said no, not without consulting his own expert, who had apparently blessed the whole setup at least once before. Hey, no problem here...just don't forget.

So, we're cruising about 3500 and 150 knots TAS, the hot CHT airplane leading because he doesn't want to push CHTs. He was throttled, so MAP was low, so the P-Mag was advancing. The numbers? 11 GPH and 360-380F for a 360 parallel valve, vs 7.5 and ~315F for my 390 with an EI at a fixed 23 degrees. He was flying at 3500 because climbing got things too hot too quickly, and slow and full rich to keep cruise CHT below 400.

Sorry, that's just dumb as dirt.

Yes, I can hear keyboards warming right now. Yes, I'm sure you enjoy wonderful efficiency with your highly advanced EI after slowly climbing to some rarified altitude. However, before going further, consider this question: Have you ever flown back to back tests with your EI fixed on a standard 25 BTDC (parallel valve), vs highly advanced?

Well, some of us have, and here's the bottom line. Optimized best power and best economy require two different advance schedules. If optimized operation is your cup of tea, your dual map EI choices are currently limited to SDS and EDIS/Megajolt.

If only one is available, install the less advanced best power timing, as any speed lost to insufficient advance at best economy can be recaptured simply by flying higher...and when there is no climb cooling problem, it is easy to get there quickly. It's also easier on the engine; lower peak cylinder pressures, lower temperatures.

[rv6ejguy]

Excellent post Dan.

Have done a lot of flight testing now on a PV 540 and see no gains in power ROP WOT at over 25 BTDC. 50-75 LOP up high WOT, MPG peaks with around 30 BTDC. Some other folks have reported best MPG at 30-33BTDC LOP. Maybe so, but I haven't seen needing more than 30.

You'd simply never want to run 38 under ANY circumstances on a PV Lycoming and especially so WOT, ROP and down low. CHTs will be through the roof, power will drop off noticeably and you seriously risk detonation damage.

I know for a fact that one EI manufacturer relies on Beta testers to supply them with optimal timing figures rather than doing their own flight testing. Not such a good plan in my view. Others want the curve kept secret. Again, why?

Surefly had the resources to get this right before any product was sold to customers but it seems from at least one post that they also don't have a clue about appropriate timing values. I hope that one post was in error.

Blunty, anyone advocating 38 BTDC ROP and at high MAP, is no expert and should bear responsibility for engine damage if that's what they are advocating with their EIs.

Proper ignition timing is important stuff for your engine to perform well and last a long time. Use science here, not guesses. The information has been out there for some time now.

[vlittle]

After all these years of debate on ignitions, the light bulb has gone on. operation at high DA/ROP, An electronic ignition optimized for LOP Operations may provide less HP than one optimized for ROP operations.

This explains a lot. Time to reinstall my arduino based variable timing controller for my Electroair. I've already seen TAS improvements with more advance when LOP. I can try best power mixture and less advance to see if TAS improves in that regime.

If this indeed the case, then it makes a lot more sense to use an integrated controller that controls both fuel and timing together. Automotive folks figured this out years ago. So have a few suppliers who advertise here.

V