Eletronic Ignition STC

[Geo]

Hi!

I was looking at the AOPA website and found an article on "Frugral Flying" about electronic ignition by Electro Air. So I had a look at the website, and it all looks very interesting. Basically replace the right magneto with an electronic coil ignition (I hope I have that description right). The idea being that the spark timing can be adjusted as needed, and the spark is also run longer. Benefits are supposed to be reduced fuel consumption/increased horsepower, and smoother engine operation.

http://electroair.net/

Looking at Lycoming's website, I see they have a similar (but more expensive and complex) offering on rebuilds.
The theory looks plausible (to an engineer/private pilot with not many hours in aviation) but I thought I would ask here and see if anyone has any experience with this STC, or a similar system? On any engine or (preferably) a Lycoming O-360?

Also, is the FAA STC automatically valid in Canada? Or is a seperate certification required for such a retrofit?

Cheers
g

[CID]

The applicable policy states (in part):

FAA STCs applicable to Normal, Utility and Aerobatic Category airplanes, including VLA designs which were type certified on the basis of FAR 23 or equivalent standards, for which the U.S. is the State of Design are exempt from a type design examination, whether or not Canadian ATCs are implicated.

So if your airplane is small (not commuter or transport category) and made in the US, you're OK. Otherwise you need to get the STC validated by Transport Canada.

You can check here for more information:

http://www.tc.gc.ca/eng/civilaviation/o ... 03-968.htm

[Geo]

Well that's a little clearer than the CARs at least, thanks. (It's a PA-28-181, so this seems to be applicable).

I'm also querying the STC holder to see if they have Canadian clients yet. This particular mod is pretty new (a year or so for Certified AC)

Still curious if anyone here has used this particular mod, or has any input on the subject of electronic ignition in Aero Engines in general.

cheers
g

[azimuthaviation]

The two plugs are supposed to ignite simultaneously arent they? If the timing of the spark on the right plug is adjusted with MAP and it is retarded then the left will pre-ignite the mixture and the right, improved spark, will be doing nothing. If the right spark is leading then the left spark will be doing nothing. In both cases the engine loses the double spark. I dont see how there can be a benefit of having just one set of plugs with adjustable timing.. or am i missing something?

[Geo]

If the right spark is leading then the left spark will be doing nothing. In both cases the engine loses the double spark. I dont see how there can be a benefit of having just one set of plugs with adjustable timing.. or am i missing something?

My understanding is that the new coil with adjustable timing always fires before the remaining magneto (which fires at 25 degrees) and always fires for longer (around 20 degrees, as opposed to five degrees fixed for the mag). So the remaining magneto becomes redundant.

Which is good - since the adjustable timing runs off the aircraft electrical system - keeping the left mag means you still have backup if the electrical system or the new ignition system fails.

Overall they claim fuel savings, and a smoother running engine (which should improve TBO). But is it *real*? Theory is all well and good.

Corrections/expansions invited and appreciated.

g

[AirFrame]

Overall they claim fuel savings, and a smoother running engine (which should improve TBO). But is it *real*? Theory is all well and good.

I don't know how good the results would be in a PA-28, but in the amateur-built world (RV's specifically), people replacing one or two mags with electronic ignition have almost unanimously reported reduced fuel burn and smoother running after the upgrade. In the early days of EI, there were a lot of teething pains. But the technology seems rather stable now, and results seem pretty consistent between Elecro-Air, Lightspeed, eMag Innovations, etc. (not all of those products are STC'd for certified A/C). You get to choose whether you want the extra power or the better fuel burn... Just move the throttle in and out.

[Jungle Jim]

Guys,

Be carefull with this. The Thorp guys with O-320's, electonic ignition and C/S props have found that the increased hp has resulted in prop issues similar to what the O-360 find with C/S props. The O-320 and Hartzell prop does not have the AD, yet the same prop on the O-360 does. They suspect that the harder power pulses are the cause. No doubt that you get better power and fuel consumption but there may be a price for this.

Jim

[Jungle Jim]

Guys,

Be carefull with this. The Thorp guys with O-320's, electonic ignition and C/S props have found that the increased hp has resulted in prop issues similar to what the O-360 find with C/S props. The O-320 and Hartzell prop does not have the AD, yet the same prop on the O-360 does. They suspect that the harder power pulses are the cause. No doubt that you get better power and fuel consumption but there may be a price for this.

Jim

[Colonel Sanders]

IIRC the four-cyl Lycs do not have crankcase counterweights and as such can have real problems when you combine a pumped-up engine with (eg) a composite two-blade prop. This is a well-known issue in the aerobatic community. LyCon and Monte Barrett know all about this.

[Geo]

Thanks for the feedback! This is exactly the kind of "gotcha" I hope to avoid.

We are running a fixed pitch metal Sensenich prop - so no governor, but I don't know much about the need or use of crankcase counterweights (and if anyone knows a good introductory text on aeroengines, I'm all ears).

Is the amount of extra performance (which I assume can be expressed in fuel savings OR increased power) from replacing one mag really that much of a problem with a FP prop? I guess we're talking a 10-15% increase in power? (so going from 180 hp to, say 207)

Is it a question of too high a tip speed on the prop? Or too much force on the blades under full power?

cheers
g

[AirFrame]

15-20% may be a tad optimistic. The RV guys don't claim more than about 5HP for a single EI, or 7-8HP for both. The fuel economy benefit is greater, because the engine runs smoother you can lean more effectively and LOP operations become possible with more than guesswork.

With the smoother running in "normal" operation, id be very surprised if it would cause prop problems.

[Colonel Sanders]

For more information about crankshaft torsional oscillation:

http://en.wikipedia.org/wiki/Torsional_vibration

The problem is when an excitation torque (a cylinder firing)
excites a natural resonant frequency of the crankshaft and
propeller combination.

This was such a problem on the 6-cyl Lycs that they had
to install crankshaft counterweights. But the 4-cyl Lycs
don't have them, so some combinations of very powerful
engines and lighter propellers has not worked out well.

For more information about this:

http://www.sacskyranch.com/detune.htm

This explains why 4-cyl Lycomings have yellow arcs on
their tachometers.

[Geo]

Actually I thought I was being pessimistic with the HP increase - as I'm mostly enticed by the fuel economy/smoother engine operation (hopefully higher reliabilty as a result). But if the power is there, it will get used at some point, so the prop (and other components) better be able to handle it. 5 HP doesn't sound like it will put terribly greater stresses on the prop though. Hm.

Re: Torsional Oscillation...I see. Yup, I sure wouldn't have thought of *that* failure mode. Interesting, thanks!

I think I will write to both Lycoming and Sensenich (and the STC holder) and see if this particular prop/engine combo has been tested - and how and how much. I doubt if either of the first two will green light it (for liability reasons) - but I should at least hear back if they have problems.

On reflection, Lycoming *does* offer electronic ignition on their engines now (including the O-360) so maybe I will get some data on that after all. Can't hurt to ask!

thanks again everyone! If you're interested in what I dig up, PM me and I will share or post.
g

[cntrctr]

PA28-181 usually has an O360-E4M. The "M" designates a counterbalanced crank. Look in your engine log and if this is your engine then you have a counterbalanced crank. If that is the case I wouldn't worry about the crankshaft issue. I just finished working on an IO 360 (homebuilt) with the lightspeed mod and although not really familiar with this aircraft I am fairly impressed with the installation. I am a partner in a PA28-181 and if it was my aircraft alone I would be installing an electronic ignition. Car engines run just fine with one spark plug per cylinder. My opinion is that with the Magneto and Electonic ignition mix you get the best of both worlds.

[Colonel Sanders]

Back on topic .... I really doubt that a modern ignition system,
by itself, is going to increase your cylinder pressure enough to
cause torsional crankshaft oscillations with a Lyc 4-cyl crankshaft.

The guys that saw that were running high-compression pistons,
cold air intake, high performance exhaust, which add up to
considerably more torque - and thus crankshaft twist - at any
given RPM than merely a hotter spark.

[Geo]

With respect to the torsional vibration issue: My impression (and feel free to comment or correct) is that the electronic ignition would change the driving mode of crankshaft vibration by changing the shape of the driving frequency rather than just the amplitude. That is, a longer spark starting and ending in different places than the LH Mag. Area under the curve should be larger, corresponding to more energy release in the cylinder - but stretched out over a bit longer time, and not making as good a use of the mechanical advantage in the position of the position.

So the force distribution on the piston/crankshaft will be changed - and that could possibly hit close (or closer) to the natural frequency of the crankshat/prop assembly.

Any other factors that might affect the engine? Vibration might drop (assuming everything is working properly), Compression ratio shouldn't change - and peak RPM could be a little higher when the throttle is firewalled.


I did contact the STC holder, to their knowledge, this particular kit has only been installed in uncertified a/c in Canada (so far) but they believe the STC should be valid here. I should contact my AME and/or TC.


Sadly, this STC is becoming a bit more theoretical than I had hoped, as we just found we have to replace a cylinder (worn rings, heavy scoring, some surface corrosion). Oh and just to make it interesting, we may have a camshaft issue as well - so this "upgrade" will be waiting for a bit.
On the bright side - I just spent 7 hours looking over my AME's shoulder and getting a little oil on my hands. Mostly learning engine parts and assembly at close range. So I now have a *much* better mental picture of where this stuff would go.

g