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Dual electronic ignition vs. Single + Magneto

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David Z said:
I have looked at those, the SD-20 as well. But they are an alternator and require something to excite the windings. That's why I am thinking of a generator. So regardless of what's going on with any myriad of electrical system malfunctions, it can always be counted on to start making power.
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They are not the same beast as the typical primary alternator - they are a permanent magnet alternator. Im sure i remember from the Aeroelectric List forum that there is a simple mod you can do to make them self exciting. Check in the drawings available on the AeroElectric Connection website or if that fails, subscribe to the forum and do an archive search or just post an inquiry.

erich
 
erich weaver said:
They are not the same beast as the typical primary alternator - they are a permanent magnet alternator. Im sure i remember from the Aeroelectric List forum that there is a simple mod you can do to make them self exciting. Check in the drawings available on the AeroElectric Connection website or if that fails, subscribe to the forum and do an archive search or just post an inquiry.
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Follow up to my previous post:
Schematic for wiring of the B&C permanent magnet alternator with self-excitement feature (sounds kind of dirty doesn't it? :)) is here:

http://www.aeroelectric.com/PPS/Adobe_Architecture_Pdfs/Z25L.pdf

Erich
 
I have a 30-amp B&C permanent magnet alternator on my Continental engine. It definitely does not need external excitement. Wire per B&C's wiring diagram, including their over-voltage module and you'll have no troubles. I just wish I could get a high-capacity alternator (60amp) that would run off my Lycoming vacuum drive pad. Hate alternator belts with a passion...
 
I tried one of those permanent magnet alternators on my Lycoming, like Ross links in post 151.
I have the flywheel with the small diameter belt pulley, about 7" diameter. I think the standard diameter is about 9".
Anyway, that little alternator and it's regulator seemed an ideal solution for a lightweight aircraft that doesn't have a big electrical load, but it didn't work out.
The pulley diameter ratio ended up with the alternator RPM too great. The voltage regulator works by sinking excess current to ground, and it couldn't control the voltage when I was doing full static RPM ground testing. It was just starting to break out into overvoltage, and the alternator light was flickering.
It would happen at a lower RPM if the larger (standard) belt pulley flywheel were used. The Corvair applications use a smaller drive pulley.
My son Peter has the 12 amp vacuum pad PM alternator on his Pitts S1E. It does fine as the sole power source, but then, he has 2 mags.
You can see a picture of the PM alternator on my RV-8 just before I removed it, check the link in my signature below.
 
Has anybody considered the dual CDI ignition from Champion Aerospace? This is the system that comes on Lycoming's O-233 LSA engine. It is self generating like the P-mag at higher RPMs. Don't know if there is any spark advance involved (don't think there is). Also, have no idea about cost. But, ATSM approval since it's LSA.
 
Is there much difference in efficiency between 2 EI systems and a single system? My understanding is that guys with 2 EI systems don't see any "mag drop" on runup. If that is true, then that tells me that there is no efficiency or power advantage to 1 EI vs 2.

Anytime you have dis-similar or un-related systems to perform a specific function I think the reliability goes up. Having dis-similar ignition sources (i.e. a mag and an EI) would be a more conservative approach. One would have to run the numbers, using failures at the aircraft level, system level and the individual component level, which is how we do it in industry, but I would expect the numbers to favor 1 conventional mag and one EI. And with one EI you still get the advantages of a hotter spark, variable timing and lack of moving parts.

Another opinion.....
 
sblack said:
Is there much difference in efficiency between 2 EI systems and a single system? My understanding is that guys with 2 EI systems don't see any "mag drop" on runup. If that is true, then that tells me that there is no efficiency or power advantage to 1 EI vs 2.

Anytime you have dis-similar or un-related systems to perform a specific function I think the reliability goes up. Having dis-similar ignition sources (i.e. a mag and an EI) would be a more conservative approach. One would have to run the numbers, using failures at the aircraft level, system level and the individual component level, which is how we do it in industry, but I would expect the numbers to favor 1 conventional mag and one EI. And with one EI you still get the advantages of a hotter spark, variable timing and lack of moving parts.

Another opinion.....
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Scott,

Your base assumption is correct. The thumb rule is you get ~85% of the gain with one EI.

I do not agree however with your conclusion that a one mag and one EI will enhance reliability. Reliability is still tied to the weak link in the chain. If you believe the EI you are installing is less reliable than a mag, do not install it.

Now looking beyond the 85% performance gain with one EI, you still have all the PITA stuff associated with a mag and overpriced aviation plugs.

The only situation I can see for one EI and one Mag is if the owner has a new mag to run out and wants to save a few bucks.

Bottom line:
- Find an EI that you believe is more reliable than a mag.
- Install on both sides.
- Fly on.

Carl
Dual pMags on my old RV-8A with 700 trouble free hours
Still flying behind these !#%* mags on my RV-10 waiting for the six cylinder pMags
 
Carl Froehlich said:
...Your base assumption is correct. The thumb rule is you get ~85% of the gain with one EI...
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This is an oft quoted sentiment, and one I have experienced personally.

But why is this so?

We know that ignition timing itself does not make power. The ignition event starts a chain of events which hopefully results in the maximum cylinder pressure possible at the best possible crank angle. So ignition timing is a derived value that results in the thing that does the work. So the question then becomes: can a single plug in an aircraft engine be timed sufficiently so that the same maximum cylinder pressure occurs at the same optimum crank angle? If so, then a single, properly timed ignition will do just as well as dual from a performance standpoint.

My experiments show that the timing needs between a single and a dual system are quite different. The aircraft cylinder is large and getting the flame front from one side to the other will take longer than starting at two sides and meeting in the middle. But what I have not tried is to see if I can get a single system to get me the same power output as a dual.

Time to experiment, I think. It would be very easy for me to record performance in cruise on two ignitions, shut one down, then crank timing in to the remaining ignition to see where the speed peaks. I can do this easily with the CPI in real time. The results should tell the tale conclusively.
 
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"Expensive" aviation plugs? I'm just not seeing it. Our fine wire plugs look like and test like they day they were new, many, many, many years ago.
 
Carl Froehlich said:
Scott,

I do not agree however with your conclusion that a one mag and one EI will enhance reliability. Reliability is still tied to the weak link in the chain.
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That's not really the case unless you need both ignitions to run the engine. In this case if either fails you can still fly. Having a lightspeed or efii or other non-self-powered system now makes the ship's electrical system a potential weak link.

Your case is a bit different because you are running pmags that don't depend on the ship's power. For me, for the other systems which do require power from the bus there is no question that having one ignition not requiring ship's power is a safer way to go. I think the accident history has shown that, based on what was stated earlier in the thread (i have not researched it myself). Also my point was purely concerning reliability, not cost or the maintenance requirements, which are all valid considerations.
 
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sblack said:
That's not really the case unless you need both ignitions to run the engine. In this case if either fails you can still fly. Having a lightspeed or efii or other non-self-powered system now makes the ship's electrical system a potential weak link.

Your case is a bit different because you are running pmags that don't depend on the ship's power. For me, for the other systems which do require power from the bus there is no question that having one ignition not requiring ship's power is a safer way to go. I think the accident history has shown that, based on what was stated earlier in the thread (i have not researched it myself). Also my point was purely concerning reliability, not cost or the maintenance requirements, which are all valid considerations.
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As I said, if you think the EI you are putting on your engine is less reliable than a mag, don't put it on your engine.

Carl
 
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