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  #1  
Old 03-01-2013, 05:11 PM
Don Jones's Avatar
Don Jones Don Jones is offline
 
Join Date: Nov 2005
Location: Las Cruces, New Mexico
Posts: 591
Default Carburetor mixture distribution

I am early in Phase 1 testing on the RV9A with 17 hours on it so far. It has performed extremely well and has only had a few minor glitches to deal with. The engine is running strong and oil consumption stabilized in the first 4 hours. Early on I noticed I had the typical fuel distribution issues common to carbureted Lycoming engines. Wide open throttle produced very uneven EGT’s as well as causing cylinder head temps to be 50 to 60 degrees apart. (Forget lean of peak ops all together) Simply closing the throttle slightly brought everything inline. Not the best situation, so I started doing lots of research on correcting the issue. I found several articles from sources like NASA, Navion, etc. pertaining to uneven fuel distribution caused by turbulence entering the carburetor from poor air box design. Since I fabricated my own air box I became convinced this was the source of my distribution issues. I found over the years several manufacturers had to include air straightening devices in their air box to correct similar issues. Most consisted of a few well-placed blades to help straighten the air and direct it through the carb. I didn’t want to go that route, so enter 21st century materials. Cars today use a honeycomb airflow straightener in front of the airflow sensor to straighten the air and prevent inaccurate readings caused by turbulent flow. The material they used appeared a little restrictive to me for use in a 320 cubic inch engine, so after some searching I found someone who sold a replacement with 1/8” honeycomb cells made from aircraft grade aluminum and 1/4" thick. I took the material, sandwiched it between two pieces of aluminum, potted the thing together with epoxy with spacers in the bolt locations and mounted it between the air box and carburetor.




I now have 4 hours on it since the mod and the results so far are impressive. I gained 50 RPM in static run up. The engine is smoother and more responsive. The really amazing part is, it will now run 20-30 degrees lean of peak with fuel flow under 7 GPH . I feel more could be had if I had electronic ignition to help light the lean mixture as anything over 30 degrees LOP causes an intermittent slight miss. I have more testing to do before I call it a complete success, but at this point I am convinced it’s a win.

Disclaimer: I am not an engineer and I didn't stay at a Holiday Inn last night. Do your own research and choose wisely
We are talking about a powerplant modification. It's in early testing and I make no claims as to it's safety. If you choose to
make a modification like this you do so at your own risk.
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RV9-A
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First Flight 1-13-2013!

Last edited by Don Jones : 03-02-2013 at 11:46 PM.
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  #2  
Old 03-01-2013, 05:55 PM
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AJ85WA AJ85WA is offline
 
Join Date: Sep 2011
Location: Perth, Australia
Posts: 188
Default Very interesting

Very Interesting, thanks for sharing!

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  #3  
Old 03-02-2013, 09:00 AM
Fred.Stucklen Fred.Stucklen is offline
 
Join Date: Oct 2006
Location: E Windsor CT
Posts: 184
Default Air Straightener

So where can we purchase this material? I've been looking for this type of solution for a long time.....


Quote:
Originally Posted by Don Jones View Post
I am early in Phase 1 testing on the RV9A with 17 hours on it so far. It has performed extremely well and has only had a few minor glitches to deal with. The engine is running strong and oil consumption stabilized in the first 4 hours. Early on I noticed I had the typical fuel distribution issues common to carbureted Lycoming engines. Wide open throttle produced very uneven EGTís as well as causing cylinder head temps to be 50 to 60 degrees apart. (Forget lean of peak ops all together) Simply closing the throttle slightly brought everything inline. Not the best situation, so I started doing lots of research on correcting the issue. I found several articles from sources like NASA, Navion, etc. pertaining to uneven fuel distribution caused by turbulence entering the carburetor from poor air box design. Since I fabricated my own air box I became convinced this was the source of my distribution issues. I found over the years several manufacturers had to include air straightening devices in their air box to correct similar issues. Most consisted of a few well-placed blades to help straighten the air and direct it through the carb. I didnít want to go that route, so enter 21st century materials. Cars today use a honeycomb airflow straightener in front of the airflow sensor to straighten the air and prevent inaccurate readings caused by turbulent flow. The material they used appeared a little restrictive to me for use in a 320 cubic inch engine, so after some searching I found someone who sold a replacement with 1/8Ē honeycomb cells made from aircraft grade aluminum and 1/4" thick. I took the material, sandwiched it between two pieces of aluminum, potted the thing together with epoxy with spacers in the bolt locations and mounted it between the air box and carburetor.




I now have 4 hours on it since the mod and the results so far are impressive. I gained 50 RPM in static run up. The engine is smoother and more responsive. The really amazing part is, it will now run 20-30 degrees lean of peak with fuel flow under 7 GPH . I feel more could be had if I had electronic ignition to help light the lean mixture as anything over 30 degrees LOP causes an intermittent slight miss. I have more testing to do before I call it a complete success, but at this point I am convinced itís a win.
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  #4  
Old 03-02-2013, 09:21 AM
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GrayHawk GrayHawk is offline
 
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Location: TexaRado
Posts: 756
Default

Also since this is on the carburetor side of the air filter, what type of epoxy was used?
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  #5  
Old 03-02-2013, 10:38 AM
David Paule David Paule is offline
 
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Location: Boulder, CO
Posts: 1,852
Default

When the honeycomb finally fatigues and starts coming apart, what keeps it out of the engine?

Other than that -- nice.

Dave
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  #6  
Old 03-02-2013, 01:22 PM
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GrayHawk GrayHawk is offline
 
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Location: TexaRado
Posts: 756
Default

Change it every condition inspection?
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  #7  
Old 03-02-2013, 02:46 PM
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billnaz billnaz is offline
 
Join Date: Jan 2005
Posts: 205
Default down stream fuel distribution

You may have a game changer here if your results are repeatable. I'd given up on anything close to lean of peak with my carb'd 0360. I'd understood that the problem with fuel distribution in carbs was uneven fuel mixing down stream from the venturi. How does this straightener effect that? Any expert opinions?
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  #8  
Old 03-02-2013, 02:53 PM
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Location: lake charles, La.
Posts: 673
Default

This is very interesting, seems effective. We do maintenance and inspections any way so a check on the condition periodically should be no problem. It makes sense to me and if we can get the cylinder flows a little closer to each other that is good and should help some.

Bird
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  #9  
Old 03-02-2013, 03:46 PM
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LifeofReiley LifeofReiley is offline
 
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Location: Round Rock, TX
Posts: 3,405
Default

Been working for a while...

http://www.shortwingpipers.org/forum...hp/t-5018.html

http://aviacompinternational.com/carbheatboxes.html

http://www.aircraftspruce.eu/Engine-...LISON-TBI.html
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Last edited by LifeofReiley : 03-02-2013 at 04:04 PM.
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  #10  
Old 03-02-2013, 06:44 PM
jrs14855 jrs14855 is offline
 
Join Date: Apr 2008
Location: Gallup, NM
Posts: 1,139
Default mixture distribution

A couple days ago I posted this somewhere else on the forum. Bart at Aero Sport??? in Canada has some alternative ways of dealing with this. Superior has a sump that improves mixture distribution and Bart makes some further improvements to the Superior sump. If I were to make a flow divider for the top of the air box it would be made of steel. I think the openings can be much larger than 1/8".
Another thing that allegedly works is wrapping the leanest intake pipes with insulation-cooler mixture equals richer mixture.
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