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Kitplanes May 2017 - The "Effects of Ignition Advance

Chkaharyer99

Well Known Member
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on Cylinder Head Temperature, Speed, and Efficiency"

The May 2017 article in Kitplanes written by Nigel Speedy is outstanding.

Nigel does an fantastic job of explaining the effects of varying EI timing over a range of conditions. I found the context of the article to be clear, concise and objective. The illustrations are easy to understand, even for me, a novice in this arena.

It would be really interesting to see this same test conducted using other EI systems on this specific aircraft by this writer. Apples to apples.

Once again, the folks at Kitplanes raised the bar. This is experimental aviation at its best.

Thank you Nigel. Great job!
 
Darn

Well now i just have to subscribe to the mag. Too many good articles i am missing out on. Going broke just reading about building.....
 
agree

on Cylinder Head Temperature, Speed, and Efficiency"
Nigel does an fantastic job of explaining the effects of varying EI timing over a range of conditions.

Totally agree. I didn't have an understanding of how timing worked in relation to altitude and mixture, this article fixed that! Bravo Nigel
 
on Cylinder Head Temperature, Speed, and Efficiency"

....
It would be really interesting to see this same test conducted using other EI systems on this specific aircraft by this writer. Apples to apples.

Once again, the folks at Kitplanes raised the bar. This is experimental aviation at its best.

Thank you Nigel. Great job!

I agree, it was a very well written article.

Different EI's should give the same results. If not, then they are not firing at the same time.

What differs between the different EI's is where they fire the plugs based on MAP and RPM and even this is should be manageable.

Don't take Nigal's results as absolute numbers. Remember, he has high compression pistons. However, focus on the impact each timing change had on CHT, EGT, fuel flow, etc.
 
Thanks Bill. Maybe I should go back a re-read the article, but how did Nigel manage to manipulate/change the timing in flight? or did he?

I thought the Pmag and EI Commander were set it before flight then don't touch it.
 
Thanks Bill. Maybe I should go back a re-read the article, but how did Nigel manage to manipulate/change the timing in flight? or did he?

I thought the Pmag and EI Commander were set it before flight then don't touch it.
With the EICommander, you can change the timing in flight, if you want. However, it is best to play with your timing while sitting on the ground.

There are two ways to change the timing in flight with the EIC, one is to send the ignitions a predefined configuration and the other is to bump the timing one 1.4 degree step at a time. It is up to you as to how you do it.

Nigel experienced an occasional issue with one or possibly both of his P-mags getting messed up when he sent them a new configuration. However, all he had to do was send them a different (standard?) configuration in flight and all was well. We are not sure why he had an issue, but feel free to call me to discuss it.
 
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Nigel has promised more articles like this one on different flight tests he's performing on his RV-8. Personally, while I like the specific tests he's doing, the real value is in learning how an experienced test pilot goes about planning test missions and then executing them - and then evaluating the data. We are very pleased to be able to bring this kind of experience to our readers.
 
Dont get it

So after seeing this thread about the article, i bought a subscription to kit planes and read the article.

But i dont get why the horespower went up and fuel flow went down with electronic ignition as compared to a mag set at 25 BTDC, but range didnt show the same improvement? Please explain.

Anybody? Bueller?
 
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But i dont get why the horespower went up and fuel flow went down with electronic ignition as compared to a mag set at 25 BTDC, but range didnt show the same improvement?

Nigel flew each test altitude twice, once ROP, then again LOP. Both were flown with MP, RPM, and mixture fixed, varying only timing, thus fuel flow did not change for each series of advance values checked at that altitude. Fuel flow only decreased when the test pilot changed from ROP to LOP, or changed altitude.
 
It's also interesting to note that at each altitude, the LOP specific range increased by about the same percentage as the TAS with increasing advance. (~5%) The ROP didn't have the same results. Bob
 
Change in TAS same as SR

Each test series was done with constant fuel flow and just varying the timing. Any change in power resulted in a change in TAS with constant fuel flow. Specific Range is TAS/Fuel Flow. As every series was done with constant fuel flow a change in TAS resulted in exactly the same change in SR. The increase in TAS and SR was larger when LOP compared to ROP.

For those with PMags here is how the timing change they generate with change in MAP compares to what my specific engine desires. I did not include it in the article as I didn't want the issue of equipment brand to cloud the issue of how timing changes affected performance. As you can see at 2500 RPM the PMag starts to increase advance at around 24.5" MAP and adds an additional 8 degrees all in by 22" MAP. For my engine this is too much advance at too high a MAP but not enough advance at the low MAP associated with high altitude flying. For other engines it might work better or worse. I have spoken with Brad at PMag and there seems little probability of having this advance v MAP slope changed.

Operationally how I get around this excess timing at high MAP, which just generates higher than optimal CHT, is to use the target EGT method of leaning. My home airport is at 4000' so I normally only see high MAP in the climb for a short time. If the CHT get to 375F I delay the next leaning a bit, or richen slightly. If I am cruising at low altitude I pull the throttle back so I only have 22" and make sure I am LOP.

If I was to build again I would probably look seriously at electronic fuel injection and ignition where there is more control.

Ignition%20Timing_zpspm5lli2b.png
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Cheers

Nigel
 
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Nigel, I'm sorry, somewhere in the fog I forgot....is your IO360 a parallel valve or angle valve?

If I was to build again I would probably look seriously at electronic fuel injection and ignition where there is more control.

In the context of ignition timing control, let's do a little survey. As noted in the article (and in the graph above), the optimum timing for ROP and LOP are very different. Which systems will allow building two independent maps (red and blue above), and selecting between them with a switch?

If I understand correctly, a P-mag with EI Commander will only create a compromise map (above, in green)....at least until Bill gets busy (rumor mongering at its worst ;)).

The EDIS/MegajoltE will store two independent maps (like red and blue), created on a laptop. Inflight switching is seamless.
 
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Nigel,

Your graph seems to indicate that the "optimum" timing when rich and high MP (near 100% power) is 25 degrees. Is this value the result of testing, or simply using the data plate value as a baseline? I ask because my own testing at 100% was unable to establish a distinct peak in performance within a wide range of timing values both retarded and advanced from that 25 degree data plate baseline. My testing with the CPI system agrees with your results in general, but my results with retarded timing lead me to theorize that the factory setting is in fact a compromise and too far advanced for high power operation.

If you want to explore this further I agree that you need an adjustable system like CPI. Considering the cost difference between the two systems, I imagine that you could sell your Pmags and buy a CPI system with little to no out of pocket cost.

I'm just over the hill if you want to discuss.
 
Nigel, I'm sorry, somewhere in the fog I forgot....is your IO360 a parallel valve or angle valve?

In the context of ignition timing control, let's do a little survey. As noted in the article (and in the graph above), the optimum timing for ROP and LOP are very different. Which systems will allow building two independent maps (red and blue above), and selecting between them with a switch?

If I understand correctly, a P-mag with EI Commander will only create a compromise map (above, in green)....at least until Bill gets busy (rumor mongering at its worst ;)).

The EDIS/MegajoltE will store two independent maps (like red and blue), created on a laptop. Inflight switching is seamless.
Dan, I just re-read Nigel's article when responding to an EIC customer, I do know Nigel has 10:1 pistons but I'm not sure if his engine is a parallel or angle valve.

We would love to set the EIC up so it can manage the P-mag curve rather than just picking a starting and ending point along the existing curve. That would allow people to tune their ignitions to their engine configuration.

I do know the P-mags have an X-Y matrix that they pull the timing advance from; one axis is the RPM and the other is the MAP.

It would be great if we could have access to that table and provide an interface that allows the customer to tune them. The challenge with that is, how many customers have the equipment and understanding to adjust such a table?

I have done this with a car, sitting on a chassis dyno and it was challenge. Then again, we were adjusting both fueling and timing. To do it properly, an airplane engine should be in a chamber where the tuner can reduce the atmospheric pressure while tuning the ignition.
 
...I have done this with a car, sitting on a chassis dyno and it was challenge. Then again, we were adjusting both fueling and timing. To do it properly, an airplane engine should be in a chamber where the tuner can reduce the atmospheric pressure while tuning the ignition...

I would argue that tuning in a dyno is a starting point. It's convenient and quick and safe, but is subject to correction factors that may not represent reality. In my mind, flying the airplane and finding the peak performance through real time, but responsible iterative testing is far more valuable. You might be able to add correction factors to approximate my Rocket at 8500 feet and 200 knots on a dyno, but I KNOW those factors are accounted for when I tune in situ.
 
I would argue that tuning in a dyno is a starting point....I KNOW those factors are accounted for when I tune in situ.

Either way would be better than what most folks are flying. Nigel and I talked to one ignition manufacturer at S&F who cheerfully admitted the curve in their system is a best guess, and I suspect that's common.

It's not crazy, or improper. Remember, even in the case of a certified ignition, the FAA's only interest is "Will it fail the engine?", not optimum performance.
 
Either way would be better than what most folks are flying. Nigel and I talked to one ignition manufacturer at S&F who cheerfully admitted the curve in their system is a best guess, and I suspect that's common.

It's not crazy, or improper. Remember, even in the case of a certified ignition, the FAA's only interest is "Will it fail the engine?", not optimum performance.

I guess I find it interesting that in their attempt to remain solidly in the "conservative" camp (which I fully understand), some of those "best guesses" are actually too aggressive.
 
Parallel Valve

Hi Dan,

My engine is a parallel valve IO-380 (a stroked IO-360 0.200") with 10:1.

Toolbuilder,

The curves in the graph in this thread are the peaks from the individual curves at a range of altitudes. At each condition I swept the timing from as little as 20 degrees to as much as 40 degrees. Short answer is that yes the graph is based on test. The curves for any one altitude and mixture condition were pretty flat and the difference between 20 degrees advance and say 30 degrees advance when ROP were pretty small, as in just a couple of knots. The original graphs are in the KitPlanes article if you want to see them.

The limitation of the PMag for someone looking to highly optimize their timing is the fact that the slope of timing as a function of MAP and RPM is locked. You can limit the maximum timing, but setting it at 40 degrees doesn't mean that a condition exists where you will ever get that much. Also if you think you have too much advance at high MAP and you use the advance shift function it slides the whole matrix so what you take off at high MAP you also take off at low MAP.

I also agree that curves from popular vendors all probably have too much advance at high MAP and they ramp in the extra timing quite aggressively as well. My test showed that you were much better off having a bit less advance than optimal rather than more than optimal. The gain was cooler CHT and better detonation margin, the cost was a very small speed and efficiency loss.

Sure would be nice to be able to set the MAP where extra advance is added and the rate at which it is added up to some maximum at a set MAP.

Cheers

Nigel
 
Hi Nigel,
As a result of this testing, how do you have your pmags set for normal operations? My engine is a virtual clone of yours, and I will need a starting point when we begin test flying later this year.
Thanks again for sharing all of your work with us.

William
 
How I set my PMags

Hi William,

My set up is equivalent to timed at TDC with jumper in. Via the EICommander I also set the rev limit at 3072, max 35 deg advance and zero advance shift. I know putting in a negative shift will lower my CHT a little but I hate to loose efficiency in the cruise.

If you want to be conservative during the break in period when you are likely running at high power and ROP you could just use a lower max advance, say 25 degrees, to stop excessive advance increasing CHT. If you don't have an EICommander remember you can also change these settings with a laptop.

Cheers

Nige
 
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