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  #11  
Old 05-29-2019, 11:39 AM
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Quote:
Originally Posted by az_gila View Post
Yes, but what would be the gain in performance over just having one? Again, the KISS principle comes into play...
In the case of an angle valve, I suspect one Surefly would be just about right.

The stated advance is base plus 13. In the case of a dual Surefly install with base 20 timing, 33 BTDC would be too much. However, one mag at 20 and one Surefly would probably put effective timing in the sweet spot.
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  #12  
Old 05-29-2019, 11:57 AM
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Mark Dickens Mark Dickens is offline
 
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Quote:
Originally Posted by az_gila View Post
Yes, but what would be the gain in performance over just having one?

Again, the KISS principle comes into play...
I'm not advocating anything. I'm perfectly happy with my PMags. I was just trying to figure out what the differences were.
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  #13  
Old 05-29-2019, 12:37 PM
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Quote:
Originally Posted by DanH View Post
In the case of an angle valve, I suspect one Surefly would be just about right.

The stated advance is base plus 13. In the case of a dual Surefly install with base 20 timing, 33 BTDC would be too much. However, one mag at 20 and one Surefly would probably put effective timing in the sweet spot.
Maybe, but the mission, environment, and engine build also throw in variables.

Illustrating yet again the fallacy of a "one size fits all" curve.
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  #14  
Old 05-30-2019, 07:38 AM
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Originally Posted by Toobuilder View Post
Illustrating yet again the fallacy of a "one size fits all" curve.
Agreed.

Jimmy mentioned FAA approval. The FAA's sole interest is ensuring it won't fail the engine. They do not address optimum settings.

Quote:
Originally Posted by pecanflyboy View Post
Any electronic ignition system that burns the mixture more efficiently is going to highlight any deficiencies within your powerplant system. The CHT's will run slightly higher (10 degrees, below 25" MP) as you are extracting more BTU's from the fuel.
EI's tend to reduce cycle to cycle variation, i.e. they light less than optimum mixtures more consistently. Although consistency certainly contributes to overall efficiency, there is no combustion difference beyond the initial flame kernel, nor can increased spark energy extract more BTU's. The CHT increase is a function of spark timing and resulting point of peak pressure, not energy.

Flying a parallel valve engine, Nigel Speedy measured the CHT increase as 2.5 degrees F per degree of ignition advance when 100 ROP, and a little less than 1.6 degrees F per advance degree when 25 LOP. Given 13 degrees of advance (38-25), that would be a little over 30 F when ROP, and 20 F when LOP. The tests were flown with Pmags and an EI commander to vary the timing. At the same advance setting, the Surfly would deliver the same result. See the May 2017 issue of Kitplanes.

With the author's permission: https://www.danhorton.net/Misc/Nigel...Advance%20.pdf

Conceptually, I like the Surefly. Simple, self contained, with easy installation. That said, I could not accept the locked timing advance...not due to an inability to hot rod, as Jimmy put it, but rather because it's already too hot-rodded for my taste.
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Last edited by DanH : 06-10-2019 at 06:10 AM.
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  #15  
Old 05-30-2019, 09:13 AM
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Yes, "hot rod" gets thrown about a bunch in these threads. It's generally used as a disparaging term meant to scare builders away from developing a curve for their particular engine. Not sure I understand that. If you have spent several thousand hours building your dream airplane, why not spend 2 hours of flight test to make the ignition perfect?

But point taken- the Surefly fixed curve is "too aggressive" in some areas of the curve and "sub optimal" in others. That said, I'm sure that it can be mechanically "spoofed" like the Pmag to at least buy you some detonation margin. Of course, by the time you go through the testing to figure out how much to move it to keep the engine alive you could have developed your own curve.
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  #16  
Old 05-30-2019, 11:26 AM
YellowJacket RV9 YellowJacket RV9 is offline
 
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I had been considering going to one of these when my next mag overhaul is due. I am also concerned that it may be a bit too aggressive though.

That being said, I am not bothered by the fact that it is not “optimal”. It is still far and away superior to the old way, and not all of us have the inclination or desire to tinker for hours until we find the absolutely perfect setup for our engine. I would imagine gains from further optimization will be marginal compared to the initial gains from the stock system, at least as compared to traditional mags. I want plug and play, that will give improved economy and reliability compared to mags, with enough safety margin to not have to worry about reducing engine life.

I think I am more of the target audience than those who want complete control.

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  #17  
Old 05-30-2019, 12:24 PM
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Quote:
Originally Posted by YellowJacket RV9 View Post
I think I am more of the target audience than those who want complete control.
I think you're right...for every owner who wants optimization there has to be ten who just want reliable plug and play.

Please note that Mike and I are coming at this from two different directions. Mike would be an optimizer; best performance above all. If "best" includes a lot of advance, then "all" includes higher CHT and higher mechanical stress. It's a choice, and I'm not knocking it. I simply prefer low CHT and reduced mechanical stress, even if I accept slightly less power to get it.

Here's the thing; spark energy and spark timing are two different issues. They tend to get balled together, which is a shame. I really think the average owner would be better served with a fixed timing EI...all the energy, but no advance. It would provide the starting and lean operation advantages, but would not cripple climb due to CHT and oil temp concerns. If it's down a few knots, just climb an extra 2000 feet. Easy to do when your CHTs are low.
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  #18  
Old 05-30-2019, 01:12 PM
Bcone1381 Bcone1381 is offline
 
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Quote:
Originally Posted by DanH View Post
I really think the average owner would be better served with a fixed timing EI...all the energy, but no advance. It would provide the starting and lean operation advantages, but would not cripple climb due to CHT and oil temp concerns. If it's down a few knots, just climb an extra 2000 feet. Easy to do when your CHTs are low.
I think Surefly has a fixed timing mode. The installation instructions says (I cut and pasted below from the Surefly 4P installation instructions.)

To operate the SIM in advance timing mode, the engine onto which the SIM is installed must comply with the following requirements:
1. Normally aspirated,
2. Have Cylinder Head Temperature (CHT) monitoring capability,
3. Use minimum of 100-octane low lead aviation fuel.
If the installation does not have equipment to monitor cylinder head temperatures, if the engine is equipped with a turbo or super charger, or if the engine operates on any fuel other than 100LL, you must configure the SIM for fixed timing mode.
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  #19  
Old 05-30-2019, 03:04 PM
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Quote:
Originally Posted by DanH View Post
...Mike would be an optimizer; best performance above all. If "best" includes a lot of advance, then "all" includes higher CHT and higher mechanical stress. It's a choice, and I'm not knocking it. I simply prefer low CHT and reduced mechanical stress, even if I accept slightly less power to get it...
Not so fast. The engine is capable of 100% power indefinitely. It has the required strength, oiling and cooling capacity. At any altitude above sea level, the maximum power we can extract from "optimized" timing will be LESS than the engine is designed for. At altitude, an optimized advance is certainly going to result in higher temps than a magneto but it is well within the capability of the engine architecture. ALL of our NA engines give up power with altitude - an optimized ignition curve simply gives up the least.

Where people get in trouble is figuring if a "little is good, more is better". At high altitude and lean, the "optimum" advance is a very sharp peak, and one degree either side will make a difference in airspeed. And while the airspeed peak is easy to track, the temps keep going up with more advance, which leads some people to think that their higher CHT's of their newly installed EI are a sign of more power. Not necessarily. Often, the high CHT is the destructive byproduct of an overly aggressive "canned" advance curve.



Quote:
....Here's the thing; spark energy and spark timing are two different issues. They tend to get balled together, which is a shame. I really think the average owner would be better served with a fixed timing EI...all the energy, but no advance. It would provide the starting and lean operation advantages, but would not cripple climb due to CHT and oil temp concerns...
If we all flew below 1000 feet MSL I might be inclined to agree, but we don't, so I cant.

Fixed timing is a huge compromise. The data plate value HAS to accommodate the needs of lean, high altitude flight while also addressing the opposing requirements of low, rich, high power ops. So the fixed data plate value is as far advanced as the engineers can go for high altitude flight without grenading the engine at takeoff.

In other words, any fixed timing that provides acceptable flight when high and lean is going to be TOO advanced down low. Conversely, fix it so it works perfectly down low and the airplane will be a dog at altitude because the advance is not far enough. There is no way around this fact.

And contrary to your comments above, part of "my optimization" strategy includes a significant REDUCTION in timing at high power. I recognize the compromise of the data plate value and run LESS at takeoff power. I've done the testing and I know the power output is relatively insensitive to timing, but detonation sure isn't. I use the variable timing to "buy back" detonation margin to levels even Lycoming can't do. Do the timing right and you can have more detonation margin and cooler CHTs on takeoff and climb, as well as optimum performance when high and lean.

Easy to do, but it doesn't come in ANY canned curve from the EI manufacturer's.
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WARNING! Incorrect design and/or fabrication of aircraft and/or components may result in injury or death. Information presented in this post is based on my own experience - Reader has sole responsibility for determining accuracy or suitability for use.

Michael Robinson
______________
Harmon Rocket II -SDS EFI
RV-8 - SDS CPI
1940 Taylorcraft BL-65
1984 L39C

Last edited by Toobuilder : 05-30-2019 at 03:07 PM.
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  #20  
Old 05-30-2019, 03:24 PM
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DanH DanH is offline
 
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Quote:
Originally Posted by Bcone1381 View Post
I think Surefly has a fixed timing mode.
It does indeed. See page 8:

https://docs.wixstatic.com/ugd/712b8...3a67acf708.pdf

I think it's a marvelous development.

Noted a few other details. The system uses a Slick harness, thus massive aviation plugs...but apparently they can operate with much larger gaps.

Operating temperature range up to 250F; no need for blast tubes.

One suggestion; the Surfly unit is externally powered and grounds through the engine case. So, if installed dual (no magneto) the wise builder will run two braided ground straps, from separate points on the engine, to separate points on the airframe.
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