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  #21  
Old 01-16-2018, 09:13 AM
Carl Froehlich's Avatar
Carl Froehlich Carl Froehlich is offline
 
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Default Is there any data to provide a vector on all this?

Iíve looked at the various options for electronic engine management. I would appreciate anyone who has data that can shed light on this simple comparison:
- Engine #1; Precision or AFP fuel injection and dual pMags. The fuel injectors have been balanced.
- Engine #2; Any electronic engine fuel and ignition management system.

Assume both engines are identical except for the above. Is there any data that shows:
- Either engine will produce more take off power?
- Either engine will be have a higher efficiency LOP cruise performance (fuel flow for same TAS)?

Everything Iíve read tells me that either set up, if properly operated, will have close to identical performance. If that is the case, then any reason to choose one over the other falls down the list of builder priorities (cost, must have the latest shiny bobble, etc.).

Iíd like to hear if my analysis is wrong - and if so why.

Carl
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  #22  
Old 01-16-2018, 10:01 AM
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Toobuilder Toobuilder is offline
 
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Quote:
Originally Posted by Carl Froehlich View Post
...Assume both engines are identical except for the above. Is there any data that shows:
- Either engine will produce more take off power?
- Either engine will be have a higher efficiency LOP cruise performance (fuel flow for same TAS)?

Everything I’ve read tells me that either set up, if properly operated, will have close to identical performance...
First, think about Magnetos vs Pmags. Magnetos, by virtue of a locked down timing will be a compromise at virtually any flight condition but one. It will be too advanced for takeoff, and too retarded for LOP. The Pmag, is a vastly superior ignition in that it adjusts to open this envelope up significantly.

That said, the Pmag has a pretty restricted curve that has been well documented on this and other sites, so if you are going to compare the Pmag to "any" other product, and that product has a completely adjustable program, then yes, there is performance to be had. The SDS products for example will allow a significant retard for takeoff power (even more so than the "too advanced" magneto's) as well as proper RPM/MP curves for best power up and away, AND additional advance setting when high and LOP. The envelope is simply bigger on the SDS products, and that shows up as "better" performance.

Edit to add the following observations about the fuel side.

Mechanical injection, even when balanced does fall on its face at really low fuel flows. I'm sure anyone who flies traditional FI LOP has seen this. This is a function of the nozzle itself being a regulation element of the system. If you pinch down the nozzle size to provide stable, balanced flow at low flow, then at takeoff power you would need something like 900 PSI to deliver enough fuel. EFI, on the other hand provides regulation by opening and closing a pintle within the injector. The rail pressure is always high, so the spray is atomized regardless of fuel flow. the only difference is how long the injector is open. So instead of the dribble you get with mechanical injection, you always get a nice pattern. Will this translate to more power on a test stand? I doubt it, but it most certainly will improve LOP and idle performance. I hope to be collecting data as soon as the Rocket gets in the air. Will let you know what's truth and whats hype.
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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
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RV-8 - Flying
1940 Taylorcraft BL-65 -flying

Last edited by Toobuilder : 01-16-2018 at 10:18 AM.
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  #23  
Old 01-16-2018, 10:03 AM
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rv6ejguy rv6ejguy is offline
 
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Originally Posted by rmartingt View Post
I'm going to play Devil's Advocate for a moment and suggest that one should not discount human error, either.


[DA]To wit, how many good airplanes have been put in the dirt because the pilot mismanaged some aspect of that "simple" mechanical system? One of the two C150s I trained in met its end a month after my checkride (in that airplane) because the student and instructor forgot the carb heat. How many other "loss of power" accidents over the past decades could we attribute to lack of carb heat or an improper mixture setting?

And beyond that, how many good engines have been doomed to early overhauls, how many millions of gallons of gas have been wasted, because the crude mixture adjustment was set incorrectly?
One of the main reasons people tell us they want EFI instead of a carb is the carb ice issue. Mechanical FI also gets rid of that concern of course.

Certainly human factors account for more problems than the injection hardware does, both from an installation and operational standpoint.
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Last edited by rv6ejguy : 01-16-2018 at 10:05 AM.
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  #24  
Old 01-16-2018, 10:24 AM
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Quote:
Originally Posted by Carl Froehlich View Post
I’ve looked at the various options for electronic engine management. I would appreciate anyone who has data that can shed light on this simple comparison:
- Engine #1; Precision or AFP fuel injection and dual pMags. The fuel injectors have been balanced.
- Engine #2; Any electronic engine fuel and ignition management system.

Assume both engines are identical except for the above. Is there any data that shows:
- Either engine will produce more take off power?
- Either engine will be have a higher efficiency LOP cruise performance (fuel flow for same TAS)?
A lot depends on how you fly and what mods are done to the engine. If you're low, ROP, there is little difference between Bendix setups and EFI. I haven't seen more than a 3.5% difference in power between Bendix and EFI setups on a decently balanced engine (airflow wise).

If you fly high, LOP and especially at low power settings, like Dave Anders often does to catch the big tail winds, the EFI is clearly better. Bendix type FI can't meter accurately at low fuel flows. Dave dumped his AFP setup because it didn't meet his needs under these conditions where the EFI was still easily balanced below 4 gph. How many people fly like this? I really don't know. http://www.vansairforce.com/communit....php?p=1110419 Page 7, post #64

We've seen some sizable airflow imbalances with various induction and cylinder setups. The EFI allows you get equal AFRs in each cylinder at ANY power setting. Tailoring nozzles on Bendix types only gets it close within a narrower cruise range and that can work well enough for many people as we've seen. No screwing around changing out nozzles with EFI, it's all done from the cockpit in a few seconds.

"Canned" ignition curves are not optimal for higher CR engines or when running LOP as Michael points out.

EFI cures all the hot start and funny idle issues with mechanical FI.

I think it all comes down to preference as has been suggested. Those tired of carb heat/ ice and Bendix hot start/ idle issues will probably consider EFI. Those who don't care so much about this and who don't trust an electrically dependent engine, will probably stay with the legacy hardware.

No one solution is best or right for everyone. Luckily we have a number of choices in the area of fuel and spark delivery.
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Turbo Subaru EJ22, Marcotte M-300, IVO, RV6A C-GVZX flying from CYBW since 2003- 420 hrs. on the Hobbs,
RV10 95% built- Sold 2016
http://www.sdsefi.com/aircraft.html
http://sdsefi.com/cpi.htm



Last edited by rv6ejguy : 01-16-2018 at 02:11 PM.
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  #25  
Old 01-16-2018, 11:00 AM
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Carl Froehlich Carl Froehlich is offline
 
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Originally Posted by rv6ejguy View Post
A lot depends on how you fly and what mods are done to the engine. If you're low, ROP, there is little difference between Bendix setups and EFI. I haven't seen more than a 3.5% difference in power between Bendix and EFI setups on a decently balanced engine (airflow wise).

If you fly high, LOP and especially at low power settings, like Dave Anders often does to catch the big tail winds, the EFI is clearly better. Bendix type FI can't meter accurately at low fuel flows. Dave dumped his AFP setup because it didn't meet his needs under these conditions where the EFI was still easily balanced below 4 gph. How many people fly like this? I really don't know. SNIP
Yep - familiar with such outlier special cases as well as the advertising logic - but again Iím looking for actual data, not theory or opinion.

So to my orginal question, and assuming operation like 99% of us fly, is there any measurable performace difference between these two engines?

Side notes - there have been several ďyou will have hot start problemsĒ offered. I have a lot of hours behind an IO-360 and dual pMags and not once have I ever had a hot start problem - or for that matter any start problem. This same engine runs smooth LOP well below any practical fuel flow - so my personal data on mechanical fuel injection running at low fuel flow does not support the previous comments. No - never operated down at 4gph, but a lot of time at 7gph which for most people is a reasonable speed vs fuel flow operation spot for high efficiently LOP cruise.

Carl
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  #26  
Old 01-16-2018, 11:34 AM
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Toobuilder Toobuilder is offline
 
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Originally Posted by Carl Froehlich View Post
...So to my orginal question, and assuming operation like 99% of us fly, is there any measurable performace difference between these two engines...?
Ignoring the "99%" hyperbole, the answer is yes. There is a measurable difference between an advance setting optimized for LOP and one for ROP. I have demonstrated a 3 knot TAS difference between my optimized advance number for a typical 8500 cruise when ROP and when LOP. This is repeatable and documented well on this forum. A Pmag set to be optimized for LOP will be too advanced for ROP, while a Pmag set for ROP will not have enough advance for LOP. Period. Dot.


As to your FF point, 7GPH is right around the area where my IO-360 experience shows them to start falling off a cliff. This is good for a reasonable LOP cruise at 9500 feet, and I don't think that's an "outlier" case. Out west, that's barely above MEA in some areas, so higher is better. That means leaner. Its a major PITA to have the EGT's split as the Bendix system falls apart because you are trying for better altitude. I think it is a performance benefit to have solid fuel metering at any altitude I wish to fly.
__________________
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 instalation in work
RV-8 - Flying
1940 Taylorcraft BL-65 -flying

Last edited by Toobuilder : 01-16-2018 at 11:37 AM.
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  #27  
Old 01-16-2018, 12:14 PM
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airguy airguy is offline
 
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Quote:
Originally Posted by Carl Froehlich View Post
Side notes - there have been several “you will have hot start problems” offered. I have a lot of hours behind an IO-360 and dual pMags and not once have I ever had a hot start problem - or for that matter any start problem.
You obviously don't run MOGAS. Go try it about once.

Quote:
Originally Posted by Toobuilder View Post
As to your FF point, 7GPH is right around the area where my IO-360 experience shows them to start falling off a cliff. This is good for a reasonable LOP cruise at 9500 feet, and I don't think that's an "outlier" case. Out west, that's barely above MEA in some areas, so higher is better. That means leaner. Its a major PITA to have the EGT's split as the Bendix system falls apart because you are trying for better altitude. I think it is a performance benefit to have solid fuel metering at any altitude I wish to fly.
I see better than that on mine, IO360 with Bendix injection. I routinely cruise at 16,500 and 17,500 WOTLOP and my "cliff" seems to start at about 5.8 gph. I also have .024 orifices and a 4-pound divider spring if that makes any difference, and I suspect it may.
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Last edited by airguy : 01-16-2018 at 12:18 PM.
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  #28  
Old 01-16-2018, 12:16 PM
Kyle Boatright Kyle Boatright is online now
 
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Originally Posted by airguy View Post
You obviously don't run MOGAS. Go try it about once.
Isn't that an outlier? ;-)
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  #29  
Old 01-16-2018, 01:24 PM
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Originally Posted by airguy View Post
I see better than that on mine, IO360 with Bendix injection. I routinely cruise at 16,500 and 17,500 WOTLOP and my "cliff" seems to start at about 5.8 gph. I also have .024 orifices and a 4-pound divider spring if that makes any difference, and I suspect it may.
It would make a difference.
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  #30  
Old 01-16-2018, 02:20 PM
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rv6ejguy rv6ejguy is offline
 
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Quote:
Originally Posted by Carl Froehlich View Post
Yep - familiar with such outlier special cases as well as the advertising logic - but again I’m looking for actual data, not theory or opinion.

So to my orginal question, and assuming operation like 99% of us fly, is there any measurable performace difference between these two engines?

Side notes - there have been several “you will have hot start problems” offered. I have a lot of hours behind an IO-360 and dual pMags and not once have I ever had a hot start problem - or for that matter any start problem. This same engine runs smooth LOP well below any practical fuel flow - so my personal data on mechanical fuel injection running at low fuel flow does not support the previous comments. No - never operated down at 4gph, but a lot of time at 7gph which for most people is a reasonable speed vs fuel flow operation spot for high efficiently LOP cruise.

Carl
Unfortunately I can't provide dyno data due to NDAs with some of our partners.

I'm not sure how 99% of people fly but if you frequently fly between 12,500 and 18,000 feet on O2, you'll see some small benefits in power and fuel economy with EFI. I can only offer the numbers that Rusty Crawford and Dave Anders have provided. These two frequently fly high and long legs and pile on lots of hours.

Lots of folks are tired of the Bendix hot start "grind". One of the top 3 reasons they want to buy EFI from us. If you don't have that problem, EFI won't be of any aid there.

It sounds like you're happy with your setup. In that case, if I were you, I'd have a hard time parting with a bunch of $ for minimal benefits.

Some people are plain uncomfortable with EIs and EFI and they never phone us. Today, I quoted 2 people.
One had timed out mags and a tired carb. He didn't want to deal with carb heat any more. He wasn't looking for uber efficiency, just solid, reliable running. Since he was going to have to spend a bunch to fix up the legacy parts, he's seriously considering EFI/EI. I'd say a good 60% fit in this category. The other guy was most interested in a bit more power and the best economy possible LOP. He likes the individual cylinder trim and the adjustable timing, LOP switch.

Other's just want to turn the key, hot or cold and go. They want it to run more like their car.

Lots of different reasons why people choose EFI-or don't.
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Ross Farnham, Calgary, Alberta
Turbo Subaru EJ22, Marcotte M-300, IVO, RV6A C-GVZX flying from CYBW since 2003- 420 hrs. on the Hobbs,
RV10 95% built- Sold 2016
http://www.sdsefi.com/aircraft.html
http://sdsefi.com/cpi.htm



Last edited by rv6ejguy : 04-29-2018 at 01:26 PM.
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