More information about Surefly SIM electronic ignition

[Battson]

Hi everyone,

I wanted to share some more information about the Surefly "SIM" mags. I am looking at installing this product, and found the internet left me wanting more information. Their website has a lot of detailed information and it takes time to dig deep enough - but there are a few natural questions which were left unanswered, even after consulting other forums.

I won't post everything about them here, just stuff I couldn't find without calling their staff. Hopefully this helps anyone looking to install this product.

• Their wiring diagram shows the first ignition powered directly by the ship's battery. This means there's no way of switching it off completely. I am told the current draw by the SIM when shutdown is just a few milliamps. This mean the ignition would flatten the main battery after about half a year or so, if the plane wasn't flown.

• Some people have been saying that electronic ignition causes excessive interference (RFI), including the SIM. The testing conducted by Surefly team demonstrates that no additional noise is created by their install, no additional shielding is required.

• They talk about their system operating better with a larger spark plug gap, 0.034 for instance. The typical gap is 0.018. They said that a smaller gap leads to a longer dwell, lower voltage, cooler spark. The larger gap delays the spark very slightly while the voltage builds, and the spark is higher voltage (proportional to gap size), hotter, and shorter dwell. The same volume of energy is delivered in about half the time. Their testing has found that engines run slightly smoother with the shorter, hotter spark. They recommend allowing the plugs to burn out the gap from 0.018 to 0.034 naturally over a couple of hundred hours, rather than opening out the plugs by hand.

• Their system sets the advance to 0 degrees BTDC below 400 RPM, for starting. There is also a timeout feature, so if the engine is cranking really slowly the spark can fire before reaching TDC causing a weak kickback. They also increase the spark dwell and spark energy to 50mJ, which is about 50% more energy than normal. They tested this higher energy spark in the normal operating range, and there were no obvious benefits over the normal 35mJ spark. It's only beneficial for starting.

• I am installing two 6 cylinder engine SIM mag units, which means a small backup battery is required. Per their wiring diagram, this backup battery is basically charged by the master bus in normal operation. Throwing a DPDT switch isolates the second SIM mag and the battery from the rest of the aircraft's electrical system. This allows one SIM to continue running while drawing down that battery, in case everything else fails. With a 75% voltage factor of safety, that allows for over 3 hours flying in the event the ship's battery fails totally and the alternator fails too.

• All EI systems seem to claim a fuel savings benefit. For instance, Pmag claims about 10% savings. Surefly shoots straight on this one, saying fuel savings are totally at the pilot's discretion. Installing their EI system (or any other EI) will not save you fuel unless you set the red knob differently. It is certainly possible to save up to 8 to 10% fuel burn, but you have to run the engine a lot leaner, certainly lean of peak. Of course, running leaner with EI will not cost much power or airspeed. The engine is developing more power relative to given RPM / MAP setting, below 25 inHg MAP or below 75% power. This is because of the increased advance and hotter spark. This increased power also results in the engine CHTs running hotter when lean, about 20*F.

• Because their system returns to 25 or 20 degrees BTDC (depending on your engine model) when the MAP gets above 25 inHg, those running extreme oversquare power settings many need to reconsider how the operate their engine to see any cruise flight benefits from this system.

• Their system is not designed to run on pure autogas alone, such as 94. They have done testing with autogas, and at full power there is very little margin over detonation. Although that being said, at full power their system has the same timing advance as normal mags. That is food for thought... Their testing also revealed that, when running 100LL / AVGAS, below 75% power there is almost no way to induce detonation.

• The EI system shines the most at higher altitudes. Above 6,000ft where normally aspirated engines suffer from the lack of ambient air pressure. As the MAP drops off and the amount of available Oxygen reduces, the hotter spark and greater timing advance pays dividends by delivering more engine power relative to normal magnetos. This is where pilots will see the greatest benefit from EI in terms of material changes to their aircraft's performance and fuel efficiency, cruising at high altitude.

So that's what I've learnt so far, in addition to their extensive documentation.

I know this won't benefit many on this forum, but it's good to have a Google searchable resource online either way.

[whee]

Very good. Thanks Battson!

[Bcone1381]

Whee, What ignition are you installing? How is your engine coming along?

[Bdflies]

Couple of thoughts about electronic ignitions; My first, was an Electroair system on a Continental IO-520. Now, a P-mag on a Lycoming O-360.
The electronic ignitions have created no RF interference. My Patrol has the P-mag and a Bendix mag. At low speeds, a barely detectable popping is present. Grounding the Bendix eliminates the noise. The P-mag is silent. The Electroaire system never made a sound.
It's my impression that the bigger gap/hotter spark promotes more complete combustion of the air/fuel mixture. This is confirmed by the higher CHT's and lower EGT's. I'm seeing EGT's nearly 200 degrees lower than my previous plane (which had 2 mags.). More complete combustion should equate to more fuel efficiency. How much is hard to say. Being a hot-rodder since the '70's I fully understand the concept of fuel savings being up to the pilot. I've never put an improved induction, free flow exhaust and hotter ignition on an engine, to get better fuel mileage. If it makes more power, you use it, right?
I'm running auto plugs at .032" gap, on the P-mag. My previous Electroaire ran Aviation plugs at .032". I'm at a loss as to why the Surefly folks would suggest letting plugs wear from .018" to .034" over a couple hundred hours. If the efficiency gain is a result of the wider gap, why wait a couple hundred hours?
Battson's description of the power to the SIM being direct from the battery, got me thinking. Looking at the Surefly site confirmed Battson's description. I guess they want to be sure the ignition is powered, even if the pilot needs to turn off the battery master switch. I understand that part, but I think I'd want to have that power lead switched.
Having flown mags and electronic systems, I see no reason to fly just magnetos. The electronic systems just run SO MUCH BETTER, it's hard to justify mags.

Bill

[Battson]

One further note,

If the ships battery is quite flat and the prop only cranks very slowly, then the SIM will almost certainly cause kickback.

The cause of the kickback is as follows:
The SIM pre-charges in anticipation of the engine reaching firing position. Once the charge is completed then the engine needs to pass firing position (TDC during start) within 10-20ms, or else the SIMs internal over-current protection will operate, causing discharge and the ignition to fire early.

Apparently hand propping can still be accomplished with this short time delay. A very flat battery whereby the blade stalls on the compression stroke will lead to a guaranteed kickback.'

Normally with a very flat battery, if the engine would still turn over at all then I could start it using the starter. Because it only needs to fire once and then it would go every time. However, with SIM the battery will become more of a dependency than I had originally thought. Otherwise we will need to hand-swing on a low battery, which is possible but of course comes with a higher level of risk. An "interesting" development.

[svyolo]

I have been looking at all the EI options over the last year. I love the idea of Pmags, and they are very popular. I think I have a slight preference for ones that you can program yourself. Autogas is more volatile than 100LL, and risks detonation if running an aggressive advance taylored for 100LL. A couple of the EFI manufacters recommend running 5 deg less advance at higher power setting with autogas.

[bergy]

The potential weight-savings of EFI have recently tweaked my interest in replacing the old mags in my Patrol. I know really nothing about what aircraft builders are now using. I do know that spark-plugs, gap, and subtle timing changes can really affect performance.

I played around a lot in the 1960s with the first snowmobiles on the market. In many ways the little single-cylinder engine sitting right there against my belt-buckle was an ideal testing platform; any roughness in the combustion process was obvious, there was a mixture-control for the carburetor right at ones finger-tips. It was routine to constantly tweak the mixture as the engine warmed up or driving conditions change. I even experimented with tuning the length of the intake ducting to see if I could improve performance.

What amazed me most in my experimenting was the engine performance changes caused by spark-plug changes. For a while I used multiple-electrode plugs, which gave much better low-rpm performance. The two-cycle Rotax engine would typically run 4-cycle at low rpm, But when using the Bosch double electrode plugs I could tune the engine to purr along really nice and smooth with moderate loads at little more than and idle.

In the 60s mo-gas was filled with lead. It was not uncommon to go through a spark-plug every weekend (just a few hours of running time). I carried a 5-gal can with me and when I went flying; I would often bring a can of 100LL home with me for my snowmobile. It did wonders for my spark-plug bill.

For the most part, I found that the smallest spark-plug gap possible worked best in the long-run. Of course this might be due to the small voltage/amperage available from the small flywheel-type magnet and coil set up.

I do wonder, however ... if my chainsaw can be started with the energy from a single pull on a rope, run at several thousand rpm at temperatures between -30F to +90F, and burn oil-laden mogas reliably and fairly cleanly, all with an ignition module about the size of my fore-finger, just why do I need 16# of Bendix mags hanging on the back of my Lycoming?

[schu]

Battson,

Thanks for posting. I've looked at a lot of this too and have some thoughts below:

Hi everyone,
Their wiring diagram shows the first ignition powered directly by the ship's battery. This means there's no way of switching it off completely. I am told the current draw by the SIM when shutdown is just a few milliamps. This mean the ignition would flatten the main battery after about half a year or so, if the plane wasn't flown.

This is poor design in my opinion, I'd feed it with the master switch normally, and through an emergency buss feed which is becoming more common with all of the glass panels. Should you loose your master contactor, or battery, or whatever, you flip on the emergency buss and you get some stuff back.

They talk about their system operating better with a larger spark plug gap, 0.034 for instance. The typical gap is 0.018. They said that a smaller gap leads to a longer dwell, lower voltage, cooler spark. The larger gap delays the spark very slightly while the voltage builds, and the spark is higher voltage (proportional to gap size), hotter, and shorter dwell. The same volume of energy is delivered in about half the time. Their testing has found that engines run slightly smoother with the shorter, hotter spark. They recommend allowing the plugs to burn out the gap from 0.018 to 0.034 naturally over a couple of hundred hours, rather than opening out the plugs by hand.

That sounds really odd to me. I would think you would set the gap to whatever their system is designed for.

I am installing two 6 cylinder engine SIM mag units, which means a small backup battery is required. Per their wiring diagram, this backup battery is basically charged by the master bus in normal operation. Throwing a DPDT switch isolates the second SIM mag and the battery from the rest of the aircraft's electrical system. This allows one SIM to continue running while drawing down that battery, in case everything else fails. With a 75% voltage factor of safety, that allows for over 3 hours flying in the event the ship's battery fails totally and the alternator fails too.

That's not a bad way to go, but how do you qualify the condition of the second battery? It could be 5 years old and barely hold a charge, and you wouldn't know it unless you needed it. I would add testing the second battery under load (ideally finding the internal resistance) during annual.

Even better, ditch the second battery and get one of these: http://www.bandc.aero/alternator8ampshomebuilt.aspx

All EI systems seem to claim a fuel savings benefit. For instance, Pmag claims about 10% savings. Surefly shoots straight on this one, saying fuel savings are totally at the pilot's discretion. Installing their EI system (or any other EI) will not save you fuel unless you set the red knob differently. It is certainly possible to save up to 8 to 10% fuel burn, but you have to run the engine a lot leaner, certainly lean of peak. Of course, running leaner with EI will not cost much power or airspeed. The engine is developing more power relative to given RPM / MAP setting, below 25 inHg MAP or below 75% power. This is because of the increased advance and hotter spark. This increased power also results in the engine CHTs running hotter when lean, about 20*F.

Super cool to see them be honest here. I'm not sure EI makes sense unless you are planning on running lean of peak. I guess it's a little smoother, and more reliable, but also more dependent on the electrical system.

Their system is not designed to run on pure autogas alone, such as 94. They have done testing with autogas, and at full power there is very little margin over detonation. Although that being said, at full power their system has the same timing advance as normal mags. That is food for thought... Their testing also revealed that, when running 100LL / AVGAS, below 75% power there is almost no way to induce detonation.

This is a little odd. If their system is the same advance as normal mags, then the detonation margin shouldn't change. Hotter spark does nothing for detonation as you want the fire lit anyway. Below 65-75% power (depending on the engine) you pretty much can't hurt it at any mixture setting. I wonder what engine they were testing with to see the detonation margin, it doesn't sound like a super low compression engine to me.

The price is super reasonable.

If one wanted more control over their ignition this also looks like a reasonable way to go: http://sdsefi.com/cpi.htm You aren't stuck with fixed timing, you can configure it to do whatever you want.

schu

[whee]

Super cool to see them be honest here. I'm not sure EI makes sense unless you are planning on running lean of peak. I guess it's a little smoother, and more reliable, but also more dependent on the electrical system.

Great discussion. I strongly agree with this point.

I'm installing the SDS CPI system on my plane and am pretty excited about it. SDS is working on their CPI2 which they are hoping to have available this spring and will have a better form factor to fit the instrument panel. Mogas and LOP was my main motivation for EI. The CPI didn't cost any more than new mags so that was a plus. A dual CPI draws 3.4A (1.7A each) during max power so with a single PC680 you could keep the engine running for 5hrs after the alternator fails. I'm a chicken and I want to keep my EFIS running so I installed dual 680s.

[Battson]

Battson,

Thanks for posting. I've looked at a lot of this too and have some thoughts below:

This is poor design in my opinion, I'd feed it with the master switch normally, and through an emergency buss feed which is becoming more common with all of the glass panels. Should you loose your master contactor, or battery, or whatever, you flip on the emergency buss and you get some stuff back.

schu

I thought hard about this too.

The way they've done it is a compromise, but I feel they have chosen the more conservative option. In the litigious environment of the USA they probably have no choice.

The way Surefly recommend wiring it, the pilot cannot accidentally or inadvertently kill the engine. I like that.
The only downside is a very small draw on the battery while at rest, also an unwary builder might give themselves a minor electric shock once in a while....

[Battson]

Further notes about the ignition:

- Running the ignition, it proves to be smoother and better starting than magnetos which is really no surprise.
- CHTs are hotter during ground running, about 10*C more than mags
- Electronic RF interference is much reduced compared to mags, my radio is a lot cleaner (it was already fairly clean). So much so, that I was able to remove the P-lead filters.

[schu]

Battson,

How is the EI testing going? Have you tried to hand prop it? With all of your back country stuff, seems like having options with a dead starter or mostly dead battery would be nice.

How much faster is your BH using EI over mags while running LOP?

thanks,
schu

[Battson]

We are still breaking in new piston rings, so we can't do a wide range of testing right now. Our only focus is keeping the CHTs and oil temp down, and we're having a hot summer. Of course the temps will settle once the rings have broken in.

We also have the new Hartzell Trailblazer prop installed plus the new wing tips, so I can't say how much airspeed difference each individual change makes.

Speaking to Jason at Surefly, they can hand prop them no worries. I am chicken so I won't be trying it unless I need to.

[schu]

hmmm, why breaking in new rings? Something happen to your engine?

[Battson]

hmmm, why breaking in new rings? Something happen to your engine?

Took it apart after a prop strike, nothing wrong with it though. Installed all new hardware, new rings, repainted etc. so it's looking good as new right now.