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  #1  
Old 11-11-2016, 07:15 AM
JDA_BTR JDA_BTR is offline
 
Join Date: Dec 2013
Location: Baton Rouge, LA
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Default Ignition - Mag/Electronic/Both?

Can we discuss ignition systems? My Arrow has 2 mags. A friend with an RV-10 has mag/electronic. What are the risks/benefits of 2 mags vs mag/electronic vs all-electronic? Does the engine care? I'll be putting in an IO-390.....
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  #2  
Old 11-11-2016, 07:46 AM
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N941WR N941WR is offline
 
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While it is "best" to have identical ignitions, having dissimilar ignitions will work just fine.

To discuss the advantages and disadvantages of mags vs. EI would take a few pages of writing and that is without getting into the differences between the various ignition options.

Basically the EI's allow the timing to advance when the MAP drops off. This allows your engine to ignite the fuel-air charge at closer to the optimum time before Top Dead Center (TDC), which will maximize the chemical energy converted to mechanical energy within the cylinder and not blown out the exhaust pipe. This will reduce your GPH burn on long cross country flights.

If you stay in the pattern and do an hours worth of TOL's, then your fuel burn with an EI will probably be identical to a mag because the EI will set the advance at or close to what your standard mag should be.

Check your PM's.
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  #3  
Old 11-11-2016, 08:34 PM
tim2542 tim2542 is offline
 
Join Date: Aug 2009
Location: Redding,Ca
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Im suprised there haven't been more replies to this thread.
On the same plane I have flown with:
1 Jeff Rose-ElectroAir/1 Slick
1 Pmag/1 Slick
2 Pmags
Now Im moving to 1 CPI system and my old friend Slick, who has never let me down. Feel free to read between the lines.

Unless you're a very good test pilot or have access to a Dyno, you will not be able to measure the difference with a second EI, at least I couldn't. And I'm talking about measured fuel burn and performance, not subjective "It feels smoother" or being impressed by the RPM delta when doing a mag test vs EI. (That's more about the timing advance delta between the two systems at idle than a hotter/longer spark).

IMO, the first EI is very much worthwhile, but for me the second ignition system has to be simple and reliable. A single well maintained magneto does that with no loss of performance or fuel economy, nor added weight from standby batteries or alternators.
Just one guys opinion
Tim Andres
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  #4  
Old 11-11-2016, 08:58 PM
Canadian_JOY Canadian_JOY is offline
 
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Location: Ontario, Canada
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Quote:
Originally Posted by tim2542 View Post
IMO, the first EI is very much worthwhile, but for me the second ignition system has to be simple and reliable. A single well maintained magneto does that with no loss of performance or fuel economy, nor added weight from standby batteries or alternators.
Just one guys opinion
Tim Andres
The key element in this discussion, for me, is highlighted by Tim in his reply above. The words "well maintained magneto" are of significance. Particularly, the COST of maintaining that magneto. While our aircraft currently has one impulse-coupled Slick and one P-Mag, I am dreading the cost of keeping that Slick running. When it comes up to the 500 hour mark I may very well dump it in favour of another P-Mag or similar, simply to get away from the regular maintenance required with this highly mechanical device.

There's more to the decision-making equation than just engine performance. Economics and long-term reliability are also factors which need to be considered.
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  #5  
Old 11-11-2016, 09:42 PM
Chkaharyer99 Chkaharyer99 is offline
 
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Location: Pilot Hill, CA
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Quote:
Originally Posted by tim2542 View Post
Im suprised there haven't been more replies to this thread.

Im moving to 1 CPI system and my old friend Slick, who has never let me down. Feel free to read between the lines.

IMO, the first EI is very much worthwhile, but for me, the second ignition system has to be simple and reliable. A single well maintained magneto does that with no loss of performance or fuel economy, nor added weight from standby batteries or alternators.
Just one guys opinion
Tim Andres
I value and appreciate your opinion Tim. Looks like you have had an opportunity to test a variety of ignitions and have a good understanding of what works and why.

In your newest configuration is the Slick a backup to the CPI in case the electrons stop flowing for some reason or do you have second battery, second alternator or something else?
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  #6  
Old 11-11-2016, 10:46 PM
tim2542 tim2542 is offline
 
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Quote:
Originally Posted by Chkaharyer99 View Post
I value and appreciate your opinion Tim. Looks like you have had an opportunity to test a variety of ignitions and have a good understanding of what works and why.

In your newest configuration is the Slick a backup to the CPI in case the electrons stop flowing for some reason or do you have second battery, second alternator or something else?
The Slick would be a backup yes, but it does contribute to ignition even when the EI is advanced beyond *25, you can tell that by doing an inflight mag test.
IMO, if you lose D.C. power it's time to land anyway and find out why, no matter what ignition system you have.
Tim Andres
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  #7  
Old 11-12-2016, 08:14 AM
KeithB KeithB is offline
 
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A friend of mine has a 2-year old RV-8. He installed a P-mag and a Slick. The Slick failed catastrophically at 300+ hours requiring an engine tear down. He is replacing the Slick with a second P-mag. Anecdotal, yes - but one can't assume that the old faithful mechanical system is the most reliable. Also, P-Mags are electronic but no more dependent on battery/alternator (once running) than a magneto due to their internal power generation.

My Rv-14 has dual P-mags.
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  #8  
Old 11-12-2016, 08:30 AM
Aggie78 Aggie78 is offline
 
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Quote:
Originally Posted by KeithB View Post
A friend of mine has a 2-year old RV-8. He installed a P-mag and a Slick. The Slick failed catastrophically at 300+ hours requiring an engine tear down. He is replacing the Slick with a second P-mag. Anecdotal, yes - but one can't assume that the old faithful mechanical system is the most reliable. Also, P-Mags are electronic but no more dependent on battery/alternator (once running) than a magneto due to their internal power generation.

My Rv-14 has dual P-mags.

When considering which mag to replace on my recent P-mag install, I decided to dump the Slick impulse mag on the left side, partially because it was starting to give me problems, but also because of concerns of the impulse mechanism coming apart and ruining the engine internals...which sounded as if what happened to your buddy.

I was told one "downside" to doing so was the loss of being able to hand-prop the aircraft if the battery was dead...which wasn't a downside to me as I don't ever plan on hand-propping it...I will either charge or replace the battery. (There's also a way to get the P-mag to fire with a 9v battery if you REALLY want to hand-prop it..)

Only ~20 hours on the P-mag so far (Slick on the RH side) and I am very happy with it so far. Once the other Slick croaks, I will probably go dual P-mag too...
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  #9  
Old 11-12-2016, 09:07 AM
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Toobuilder Toobuilder is offline
 
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Quote:
Originally Posted by tim2542 View Post
Im suprised there haven't been more replies to this thread...

...Unless you're a very good test pilot or have access to a Dyno, you will not be able to measure the difference with a second EI, at least I couldn't. And I'm talking about measured fuel burn and performance, not subjective "It feels smoother" or being impressed by the RPM delta when doing a mag test vs EI...
This subject has been discussed in great detail recently, so that might be the reason for the lackluster response.

As for not being able to measure the difference with a second EI - that has not been my experience. I have a couple of threads documenting my single and dual CPI performance. The second unit will most certainly show a gain if you are running high and lean. The higher and leaner you go, the more important the second unit becomes. That said, this is less true of the CPI in particular due to the ability to taylor the curve to your mission. If your single EI has the adjustability (like CPI) you should be able to get the single plug to initiate the combustion event to create an optimal ICP. At this point, the magneto is just along for the ride.

I was in the planning stages of testing the "optimum" single plug operation when I took the airplane down for the SDS EFI installation. The experiment will have to wait, but it looks promising.

And Tim, since you are going CPI, I would highly recommend installing the dual hall sensor now. Its not much of a cost/weight difference and if you ever decide to add the second system, the "hard" part is done. Or think of it as a "spare".
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Last edited by Toobuilder : 11-12-2016 at 09:23 AM.
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  #10  
Old 11-12-2016, 10:12 AM
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rv6ejguy rv6ejguy is offline
 
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I'll step in an mention that there is no scheduled maintenance with the CPI/SDS ignition systems- no drive gears or shaft bearings to inspect or fail. You can toss the $3 plugs every annual when you do a compression check and maybe replace the plug wires every 5 years/1000 hours if you like- about $150 for an all new harness with the recommended MSD parts on all 8 plugs.
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