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  #31  
Old 05-31-2019, 10:50 AM
pecanflyboy pecanflyboy is offline
 
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Location: Granbury, Texas
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Not sure. Give them a call.
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  #32  
Old 05-31-2019, 10:57 AM
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Toobuilder Toobuilder is offline
 
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Quote:
Originally Posted by pecanflyboy View Post

...The Surefly is not competing with Pmag and other user adjustable EI's...

...I would argue that the curve is not aggressive...

...So, if you want an EI that you can be loaded with a curve that worked for someone else, and then test fly it to its optimum, PMag is the system for you. Great guys and a great product...
Just as a point of clarity, I don't consider the Pmag product to be "adjustable". You can shift the entire curve a bit, but you are still stuck with the slope that Brad and company locked down years ago. And there are some points on the Pmag curve that are more advanced than required for correct engine opperation. Surefly is similar in this respect. If the curve is more advanced than required, then the characterisation of " too aggressive" is accurate. The fact that Lycomings are not grenading as a result is good, but hardly lets either company off the hook. Too much advance adds heat and stress and reduces detonation margin, all for no benefit. And the degree of advance "required" varies significantly with engine configuration and basic architecture. Using a curve optimized for a low compression PV engine would be a disaster on a high compression AV - yet the locked down curve of the Pmag does not differentiate. This is exactly why there are 3rd party controllers available and the requirement to mechanically "spoof" the ignition to reduce the advance.

The reality is that when it comes to aircraft engines, one size does not fit all (ESPECIALLY in the EAB world) - and that includes magnetos. I will conceed that in context of a direct magneto replacement, Surefly might be a slight step up in some circumstances, but that will require analysis and test.
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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 : 05-31-2019 at 10:59 AM.
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  #33  
Old 05-31-2019, 11:10 AM
pecanflyboy pecanflyboy is offline
 
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Quote:
Originally Posted by Toobuilder View Post
Surefly might be a slight step up in some circumstances, but that will require analysis and test.
Errrrrr......that’s what they have been doing for the last three years in house and with FAA.

Last edited by pecanflyboy : 05-31-2019 at 11:41 AM.
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  #34  
Old 05-31-2019, 11:52 AM
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Toobuilder Toobuilder is offline
 
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I think you may be overestimating the scope of the FAA's testing. They will ensure that the Surefly will "do no harm" across a range of TC'd engines. I doubt very much they are going to explore the edge cases of the EAB world where we live. It would be foolish accept the testing on a 150 HP Skyhawk as applicable to a big bore, high compression Angle Valve that an RVer is going to hang on his new pride and joy.

FAA testing is worth something, but it's not the whole picture.
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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
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  #35  
Old 05-31-2019, 12:49 PM
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Toobuilder Toobuilder is offline
 
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Allow me to illustrate the "too aggressive" claim with some real world data.

I documented a series of flight test profiles with a timing sweep to determine "optimum". The flight was at 8500 and 23 inches MP. If I read the Surefly advance chart correctly I would have seen 35 degrees advance if using that product. Let's take a look at how the 35 degree value chosen by the Surefly developers stacks up in the real world:

My 50LOP optimum speed was 194 KTAS @ 33 degrees, but at 35 degrees the speed fell 4 knots to 190. Not the end of the world, but this speed loss came with additional CHT, oil temp and engine stress. None good things.

My peak EGT optimum speed was 199 @ 30 degrees. By 33 degrees the speed was down to 196, CHT, oil and stress was up. Didn't go to 35, but the trend is clear more advance woul be "no good"

Best power mixture is even worse. Highest speed was 201 @ only 27 degrees. (Keep in mind the Surefly would be forcing 35 down my throat). By 31 degrees my speed was down to 198. Clearly, the 35 degrees of the Surefly would be significantly over advanced here. Would it be destructive? Not in my low compression PV engine, but would CERTAINLY do no good. In this case, I'd be better off with a fixed magneto at the data plate value of 25. Would still be a bit slower than optimum, but would still be FASTER than the Surefly at a lot less heat and stress.

So without the benefit of comparative testing, the Surefly owner would likely accept the higher temps as "more power" and motor happily on.

...but now you know better. Hope you understand that my constant wailing about "correct" timing and "too aggressive" canned curves is based on real world test, not product bias.
__________________
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
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  #36  
Old 05-31-2019, 07:07 PM
cardinalflier cardinalflier is offline
 
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Toolbuilder: Please check your PM's. Thanks, Bruce Estes
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  #37  
Old 06-01-2019, 07:16 AM
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DanH DanH is offline
 
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Most folks in the airplane world have failed to note a great divergence. On one hand we have the LOP operating mantra promoted by GAMI/APS. It assumes fixed timing, typically magneto based. Going LOP with fixed timing pushes the point of peak pressure further after TDC. The result is lower CHT and a slight power loss. With a turbo, add another inch of MP to regain the power. With an NA engine, adding 100 RPM pretty much does the same.

On the other hand we have the mantra of LOP with ignition advance. The advance compensates for the slower combustion rate of the lean mixture (see charts, links below), returning peak pressure to a point closer to TDC. Early adopters tended to be the performance-at-any-cost type; Klaus would be a fair example with his hotrod EZs. As we've seen (refer to Nigel Speedy's recent data, for example), at altitude, the parallel valve engines respond to more and more advance with more and more speed, and no one seems to have found an absolute performance limit (the practical limit is CHT rise). The practical result was a trend toward more advance being incorporated into electronic ignitions.

Among consumers, the resulting CHT increases during ROP climb have become synonymous with EI, when in fact it is not EI, but the advance schedule dialed into that EI. It is entirely possible to run an EI with fixed timing, just like the GAMI/APS case. Or, one may select an EI with dual maps, and select less advance for ROP climb. Note the engine control computer in your automobile shifts the advance map in lockstep with fuel mixture; it's invisible to the operator. Unfortunately, none of the currently available ignitions for aircraft have that capability. The advance schedules are biased toward LOP operation, and are generally a little too advanced for ROP climb.

Both LOP mantras run cleaner, i.e fewer engine deposits and lower fuel burn. The GAMI approach (delayed peak pressure) results in lower cylinder pressures, i.e. less mechanical stress and lower CHT. The more advance method is equally clean and generally results in higher power at upper altitudes, at the expense of higher CHT.

Neither is wrong. I've simply suggested the Surefly's fixed timing capability allows an owner to use the GAMI approach, if desired.

Manifold pressure vs flame speed:

http://www.vansairforce.com/communit...8&postcount=45

Mixture vs flame speed:

http://www.vansairforce.com/communit...3&postcount=43
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  #38  
Old 06-01-2019, 08:05 AM
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rv6ejguy rv6ejguy is offline
 
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Quote:
Originally Posted by DanH View Post

Note the engine control computer in your automobile shifts the advance map in lockstep with fuel mixture; it's invisible to the operator. Unfortunately, none of the currently available ignitions for aircraft have that capability. The advance schedules are biased toward LOP operation, and are generally a little too advanced for ROP climb.
While this may be true of most other aircraft EIs, SDS EIs (CPI, CPI-2, EM-5) have LOP switches (which we pioneered in this market). This allows you to have the best of all worlds- speed/ efficiency, detonation margins and lowest CHTs. Though the feature is not automatic, unlike cars, aircraft engines have no emissions requirements and operate mainly under steady state conditions, so the automatic timing vs. mixture feature maybe wouldn't be worth the extra cost and complexity to implement. I'd suggest that this feature is in the realm of full engine management systems with integrated EFI and EI rather than a hybrid mechanical fuel and independent EI system.
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Ross Farnham, Calgary, Alberta
Turbo Subaru EJ22, SDS EFI, Marcotte M-300, IVO, Shorai- RV6A C-GVZX flying from CYBW since 2003- 445.2 hrs. on the Hobbs,
RV10 95% built- Sold 2016
http://www.sdsefi.com/aircraft.html
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Last edited by rv6ejguy : 06-01-2019 at 09:57 AM.
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  #39  
Old 06-01-2019, 08:50 AM
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rvator51 rvator51 is offline
 
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Surefly needs to do like Ross did, add a switch so you can use fixed timing during ROP climb, then flip the switch to take advantage of the Advance feature for cruise. Advance still can?t be optimized for your individual aircraft like the SDS though.
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  #40  
Old 06-01-2019, 09:07 AM
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Toobuilder Toobuilder is offline
 
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Quote:
Originally Posted by DanH View Post
...at altitude, the parallel valve engines respond to more and more advance with more and more speed, and no one seems to have found an absolute performance limit (the practical limit is CHT rise). The practical result was a trend toward more advance being incorporated into electronic ignitions...
Let's make sure the readership understands the proper context of "practical limit". I have demonstrated repeatedly that performance drops off very sharply with additional advance beyond optimum. So there very much is a "practical limit", and it is not constrained by CHT. Though CHT will continue to rise with additional advance, the real practical limit is clearly defined by maximum engine efficiency (peak speed). So just to be crystal clear: more advance does not = better performance.

If you are suggesting that the optimum advance value continues to increase with altitude, then the data seems to suggest that. I have not yet explored that regime yet because that's not my typical cruise altitude, but I'll bet Mr. Anders has reams of data near the Flight Levels But point taken: It's impossible to create a canned curve with enough breadth to handle every possible use case. And the larger the canned curve, the higher the probability that someone with an edge case is going to get stung by a dangerous condition.


.
Quote:
...Among consumers, the resulting CHT increases during ROP climb have become synonymous with EI....

Not anymore. Ross changed that a few years ago. And it is EXACTLY because of the advance (or specifically, the ability to manipulate the advance) that allows the SDS user to break free of the canned, arbitrarily derived curve forced on us by other manufacturer's and pull timing way out for those high power, rich mixture conditions. Rather than the straight line characteristic of other canned EI curves, the SDS user is free to alter any point to suit his mission. The SDS user can create a curve that looks like a sine waveform, perfectly flat emulating a magneto, or anything in between. One can even load the Pmag, Surefly, or LSI curve if that makes sense.

So no, one does not have to live with the compromise of high CHT on climb OR good high altitude performance. You can have it all. But you have to go to Ross to buy one.
__________________
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 : 06-01-2019 at 09:54 AM.
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