Surefly electronic ignition

[lr172]

Originally Posted by 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.

My experience is similar with the new 540. I have my base curve set to give me around 32* at 21" of MAP. My megasquirt setup has both a second advance table that I use to up the timing 2* at lower MAPs and also have a 4* retard from the base table. I can set each of the two ignitions interdependently (important as total timing is a composite of the two spark events). As I play with the settings at cruise, I am only seeing only about a 2 knot variance as I play with timing in the 30-35* range. Not enough time and testing yet to correlate all of the variables to determine a best advance, but my gut is that it is right around 32* when LOP at 8000'. That said, we all fly at different levels of LOP and that will give us some variability in optimum advance.

I have my advance (both tables) set at 23* above 27" and have been playing with the 4* retard beyond that to experiment with CHTs. At 55 hours, I still haven't seen 400* CHTs (max that I have observed is 375) and that includes break in. Though that was done in ambients below 40*. That said, I did use a more agressive advance to raise my CHTs during the break in, as I was struggling to get CHTs above 340 and felt it was impeding my break in.

I had never given a lot of thought to these crazy canned timing curves, but after this thread, I really feel for the users taking off from high DA airport's. I just can't imagine someone stuck with a 38* advance at full rich. In my 6, I had some heat issues in the climb as the MAP came down (timing was still well less than 38) and the answer there was to use a 5* retard in order to accomodate ROP climbs.

We all know that the fixed timing of the mags is a limitation, but we need to recognize that many of the modern EIs are also fixed to a large degree, as they don't include enough variables to be optimal across our engines operating envelop. Kudos to SDS for creating options to real world requirements. I would never consider and EI that didn't have at least two discrete, user selected advance tables.

Larry

[lr172]

Originally Posted by 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

anxious to hear more about this. You should be able to incorporate fuel flow into the list of variables and this should be enough to set an appropriate timing level. That additional data point should allow you to determine an optimal timing level, when used in conjunction with MAP and RPM, assuming you have config details related to displacement and compression ratio. ambient temp input should also be incorporated, as IAT / MAT (derived from ambient) should drive a retard at certain levels to increase detonation margin.

Larry

[vlittle]

Originally Posted by lr172

anxious to hear more about this. You should be able to incorporate fuel flow into the list of variables and this should be enough to set an appropriate timing level. That additional data point should allow you to determine an optimal timing level, when used in conjunction with MAP and RPM, assuming you have config details related to displacement and compression ratio. ambient temp input should also be incorporated, as IAT / MAT (derived from ambient) should drive a retard at certain levels to increase detonation margin.

Larry

Turns out I have all the data I need in the serial stream from the SkyView, including timing advance, MAP, RPM, Altitudes, Fuel Flow, Leaning state and cylinder temps. I also have the pins I need on my OnSpeed display module to turn it into a control head for ignition timing. What I do is modify the MAP sensor output to force the Electroair timing advance.

I read the raw MAP sensor voltage, then add or subtract a bit to change the timing. Right now I do this manually, but with the proper testing, I can make it automatic. I need to gather a bunch of data and try not to blow up my engine.

#42 on my list of things to do. I should be done Tuesday.

V

[Bcone1381]

I wonder if an electronics whiz will engineer a LOP/ROP switch that we see in other systems for the Surefly to control the timing schedule that is done when installing the SIM.

[DanH]

Originally Posted by rv6ejguy

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.

Let's assume that data point was an outlier, a case of one misinformed individual, or a communication error. And arguably, every P-Mag owner flying without a jumper got the same instructions.

In Surefly's defense, remember the standard EAB versions allow the installer to easily set one of eight fixed timing choices, or one of eight more variable schedules. No laptop or expensive accessory needed, just set the switches. Put another way, if it doesn't get installed with reasonable timing, it's not really Surefly's fault. The installer has easy options.

[Carl Froehlich]

Just a side note, the new six cylinder pMag has a switch that locks the timing at 25 degrees (or whatever you set it at) or in the timing advance position (you set the max timing advance on install). The switch is operable at anytime - as in you can select in flight.

I?m told this was a requirement from the FAA for them to get this ignition approved for certified aircraft.

Carl

[Toobuilder]

Originally Posted by 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...

Absolutely spot on.

And to ask Dan for clarity - with your RV-8 side by side comparison, was the other ship an angle valve like yours? I just flew the RV cross country yesterday with the SDS system replacing the Pmags and can attest that the AV engine responds very differently than the PV (Rocket) I'm used to. My data is limited, but all indications point to the fact that aside from the name on the data plate, the PV and AV engines are very different breeds. If nothing else, the "one size fits all" approach of certain EI suppliers is incorrect and borderline irresponsible.

[lr172]

Originally Posted by Toobuilder

Absolutely spot on.

And to ask Dan for clarity - with your RV-8 side by side comparison, was the other ship an angle valve like yours? I just flew the RV cross country yesterday with the SDS system replacing the Pmags and can attest that the AV engine responds very differently than the PV (Rocket) I'm used to. My data is limited, but all indications point to the fact that aside from the name on the data plate, the PV and AV engines are very different breeds. If nothing else, the "one size fits all" approach of certain EI suppliers is incorrect and borderline irresponsible.

Not surprising. Don’t know much about AV engines, but do know that the shape of the cylinder head chamber and piston head can greatly impact the optimal timing required.

Larry

[rv6ejguy]

Originally Posted by DanH

Let's assume that data point was an outlier, a case of one misinformed individual, or a communication error. And arguably, every P-Mag owner flying without a jumper got the same instructions.

In Surefly's defense, remember the standard EAB versions allow the installer to easily set one of eight fixed timing choices, or one of eight more variable schedules. No laptop or expensive accessory needed, just set the switches. Put another way, if it doesn't get installed with reasonable timing, it's not really Surefly's fault. The installer has easy options.

I hope your first sentence turns out to be the case.

With regards to the 2nd paragraph, hopefully Surefly gives sound advice on making the timing options safe for their customers.

[Sam Buchanan]

The DIP switches in my SureFly are set for 25* fixed timing, the same as the Slick mag it replaced. SureFly recommends fixed timing for any engine that may use auto gas and I wanted to have that option. My mission profile is primarily short low-altitude flights so the greater economy that advanced timing might yield at higher altitudes and longer flights is not a priority for me. I also don't know how the advance curve is configured and have no desire or reason to explore it.

The SureFly so far is an excellent alternative for the impulse mag it replaced and was a quick and low-stress plug-n-play. I suspect this device was intended primarily as a mag replacement. Other more 'experimental' ignitions may be a better choice for those who wish to explore the corners of the ignition envelope. But maybe SureFly will be forthcoming in the future with more details about the advance curves.