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Captain Avgas

Well Known Member
I have been told by some-one who has very extensive field experience with experimental electronic ignitions that the Lightspeed Plasma 111 has not proven to be as reliable or robust as the Plasma 11. As he puts it....the Plasma 111 is still more reliable than a magneto, but not as reliable as a Plasma 11. He considers that the crank sensor is also considerably more reliable than the Hall Effect sensor.

Has anyone out there had any experiences that would either substantiate or refute these claims.

Initially I fancied the Plasma 111 because I am interested in lean of peak operations and the Plasma 111s long hot spark would seem to be better for igniting very lean mixtures. But for me reliability is absolutely paramount because I intend to fly long distances over water so I'm now eyeing the Plasma 11.

Any comments.

Incidentally, I love the P-Mag concept..but it's just too early for me at this stage given the type of flying I plan. I need track record.
 
I run one of each Plasma II and Plasma III

I ran a LSII for 2 years and 500 hrs when I decided to add the second and dump the mag I went with a LSIII. I asked the same question but the answer I got was there is no difference in reliability. I stuck with the one of each concept though for a couple of reasons: the LSII has been around longer and has more of a proven track record than the LSIII and my LSII unit has been flawless since installing. The LSIII gives me the advantages of that unit with the higher output which is a good thing, but with higher output comes the associated electronics to drive it beyond what is in the LSII (higer output/higher parts count/higher current all mean lower MTBF in my book). No compatibility issues with running one of each so I kept my "proven" LSII and added the LSIII when I upgraded to dual EI. BTW, noticable improvement in smoothness with the second unit and I can run lean of peak now with no problem or roughness with my old fashioned bonehead reliable carb. I am all about reliability and only fly with components that have a proven track record, so when it came to electronic ignition Lightspeed was the obvious choice!
 
Walt said:
I ran a LSII for 2 years and 500 hrs when I decided to add the second and dump the mag I went with a LSIII.
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Walt, thank you very much for your considered and helpful comments. I spoke to Klaus at Oshkosh last year and he said the 111 was as reliable as the 11 (of course he would)...but that's not what some other people say. Your comments about the additional complexity of the the 111 makes sense to me.

Any other comments out there.
 
Hall vs. Crank

"He considers that the crank sensor is also considerably more reliable than the Hall Effect sensor."

I'd like to see some comments on this. I'll be using the LS system & have wondered what the differences were.

Thanks,
Sam
 
Question for Walt Aronow

Walt said:
BTW, noticable improvement in smoothness with the second unit and I can run lean of peak now with no problem or roughness with my old fashioned bonehead reliable carb.
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Walt, have you switched between the Plasma 11 and the Plasma 111 while you're running lean of peak. I am imagining that the Plasma 111 might run just a bit smoother due to its longer duration spark and perhaps superior ability to ignite the leaner mixture....but maybe not. You're the only person I know with a 11 on one side and a 111 on the other who runs LOP so your feedback would be very valued.

I know you said the engine runs better with EI on both sides (rather than one MAG) but can you now ascertain if one EI performs better than the other, particularly LOP.
 
I could do some testing next time I'm out between the II/III

to see if there is a difference LOP between the II and III. I do know that with the mag and the LSII running I could run LOP but it would not be as smooth as at peak. Now with both II and III running I can go LOP with no noticable change in engine smoothness. Overall engine operation seems a little smoother as well with dual LSI vs the single and a mag. In ref to the reliability of the crank pick up vs the hall effect, I ran the hall effect for a few hundred hours but started having trouble with oil seeping past the seal in the sensor which I could not get fixed so I switched over to the crank sensor, other than that it worked perfect. The hall effect was certainly easier to install than the crank sensor was though (thank you ECI for drilling and tapping the case for the crank seal retainer so the pickup bolted up with relatively little hassle).
 
I have two Plasma III's with direct crank pickup. I typically run fairly low power (~55%) LOP in cruise.

What is interesting, and seemingly pertinent to this thread, is that it could be difficult to notice if one ignition failed in flight. When running at the above conditions, there is a subtle change in the engine sound when one ignition is shut down, but if I were talking on the radio I'm not sure I would detect it. When running richer, it really is difficult to detect. I have the interconnect, which advances the remaining ignition 5 degrees should the other go off line or is switched off.

I believe that I need some sort of annunciator system to notify me that one ignition has failed. I haven't looked at the schematics, perhaps there is an output which could be used.
 
AlexPeterson said:
I believe that I need some sort of annunciator system to notify me that one ignition has failed. I haven't looked at the schematics, perhaps there is an output which could be used.
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Alex,

I'm sure you're like me in that you "know your EGTs." You get familiar with the range in which your EGTs end up running for a given condition & power setting.

If an ignition fails, expect to see those EGTs rise. That alone is a great indicator imho of an ignition failure.

Gotta love contemporary engine monitors.

For what it's worth...on my AF-2500 you can configure "yellow" and "red" limits for most parameters. On the EGT, I believe I set it up so that it goes into the yellow pretty close to where I typically see normal peak EGT.

The net result is...if an EGT goes on the rise due to some issue, the bar is likely to turn yellow, indicating the abnormal condition.
 
Dan, you are right on with regard to egt's. Once set up in LOP cruise, I will usually see about 1380 or so, and when I kill one ignition, it will rise to about 1460.
 
dan said:
If an ignition fails, expect to see those EGTs rise. That alone is a great indicator imho of an ignition failure.
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Dan, I believe that you have Plasma 11 on one side and a slick mag on the other.

Can you technically explain why turning off the mag in medium power cruise would result in an EGT increase.
 
Well, I'm not Dan, but he is probably still asleep out west ;)

The reason egt goes up with only one ignition running is that the effective timing is delayed when only one spark fires in a large bore engine. Less work is extracted from the burning charge (hp), and therefore the exhaust is hotter (more energy). One needs to remember that the burning process is not relatively fast compared to piston movement, so igniting only one side of the charge does change combustion dynamics considerably. This is true with mags also, that is why a noticable power drop occurs when shutting one down. You will see a egt rise when shutting down one mag also.

For those running one EI and one mag, shutting down the mag will probably increase egt's also, though not as much as the other way around. What that means is that the combustion front (ignited from the EI spark) has not yet reached the mag plug when it fires. Both plugs are contributing and igniting, just the timing is different.

Hotter exhaust = less work extracted in a general sense.
 
AlexPeterson said:
The reason egt goes up with only one ignition running is that the effective timing is delayed when only one spark fires in a large bore engine. .
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Alex, Thanks for your explanation. Of course as we both know, it's not exactly the variation in ignition timing that causes an increase in EGTs...it's the changing position of thetaPP (the angle theta beyond TDC at which peak combustion pressure occurs).

For instance in the case of switching off Dan's mag the timing stays the same. I would've thought that the mag (with it's weak spark and much later firing than the EI) wouldn't be adding much to the combustion process. It would be interesting to learn from Dan exactly how much his EGTs rise when he switches off his mag. People are always saying that "the mag is just along for the ride". But maybe not.

Your situation is a bit different. When you switch off one Plasma the timing does not change but as you say the flame front is probably slower due to only one plug firing...hence increasing thetaPP. BUT you also say that when you turn off one unit the other unit is supposed to advance by 5 degrees. You'd think that this feature was designed into the system to maintain thetaPP at roughly the same optimum angle (approx 15 degrees after TDC). It's therefore a bit strange that your EGTs rise. Presumably the 5 degree advance on one EI unit still does not compensate fully for the loss of the second spark.

Incidentally Alex how many hours do you have on the Plasma 111s and have you had ANY problems with them.
 
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Dang...just got down from a flight, otherwise I might have remembered to test the mag EGT rise thing, snarf the data, and post a graph of it. I'll add that to the growing list of like 50 things I want to test out and graph and publish.
 
Large cylinder

As I understand it, the reason Lycomings have two plugs is because the cylinders are so large. Ignition from only one side does not allow the flame front to propagate across the cylinder before the cycle has completed, hence the continued combustion on the way out of the cylinder resulting in EGT rise and of course RPM drop.

Now it was designed for mags, so things change a bit with EI. EI allows a longer and hotter (which usually means wider gap) which increases the area of the ignition front. It doesn't increase the speed of flame propagation, since that is governed by mixture ratio and pressure. It does seem to increase the speed because the initial area of ignition is larger increasing the "volume" of flame for the same given time period. So, it would seem the mag is probably doing less "work" but the physics of the cylinder area and flame propagation are the same, so it is not completely useless. Of course, there are probably mags which may be miss timed just enough so as not to be noticably doing anything.
 
Captain Avgas said:
Incidentally Alex how many hours do you have on the Plasma 111s and have you had ANY problems with them.
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I only have about 80 hours, no problems at all. I really like the "no moving parts" feature.
 
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