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  #61  
Old 04-01-2017, 11:04 AM
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Norcalrv7 Norcalrv7 is offline
 
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Without taking the cowling off, here is the best picture I have of the custom built intake tubes. They terminate right after their O-ring seal into the sump, instead of extending like the Lycoming diagram. I described the combination of sump and Cylinders I had to Clint at Veterman ( super nice guy) who built the exhaust and intake tubes together as a package deal. Probably a less than optimal design with the shorter length tubes, I wonder how much of a difference.


For what its worth, here is a graph of my fuel flow test from yesterday.

The fuel flows are close, but approximate. The leaning process was accomplished by leaning 1% at a time on the SDS mixture knob.


I might lean #4 another % or two. The slight hump in all the lines is probably due to operator error during the test.

Caleb
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Last edited by Norcalrv7 : 08-28-2017 at 09:47 AM.
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  #62  
Old 04-01-2017, 02:02 PM
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The SDS system should allow a bit of fairly easy experimentation with intake tube length. Once the engine is all dialed in and even across all cylinders, then any increase in volumetric efficiency will drive a leaner mixture. Suppose you are flying a cruise profile and 100 ROP: IF you could change the length of a single tube, then any improvement in VE would show up as a higher EGT for that cylinder. Continued adjustment of that tube should show a peak in EGT, indicating the highest VE for that condition. That length would be "optimum".

In my case, I intend to fabricate a single induction tube that can be adjusted for length in flight. If my theory holds, I will find my ideal length, and then go back and build 6 new tubes all of that length. In your case however, it seems like it would be easy to simply add a temporary trumpet to one of your tubes and fly it. Start long and cut it down inch by inch, graphing EGT for each change.
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  #63  
Old 04-02-2017, 06:47 AM
A-Ron A-Ron is offline
 
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Congrats Caleb! Very happy to hear your 7 is back in the air. Let me know if you need a copilot. I might need to borrow that crash helmet in about 6 months Cheers!
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  #64  
Old 04-03-2017, 10:16 AM
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Norcalrv7 Norcalrv7 is offline
 
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Quote:
Originally Posted by A-Ron View Post
Congrats Caleb! Very happy to hear your 7 is back in the air. Let me know if you need a copilot. I might need to borrow that crash helmet in about 6 months Cheers!
I'd love to take you along sometime! Still have my number?
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  #65  
Old 04-03-2017, 11:43 AM
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Quote:
Originally Posted by Toobuilder View Post
The SDS system should allow a bit of fairly easy experimentation with intake tube length. Once the engine is all dialed in and even across all cylinders, then any increase in volumetric efficiency will drive a leaner mixture. Suppose you are flying a cruise profile and 100 ROP: IF you could change the length of a single tube, then any improvement in VE would show up as a higher EGT for that cylinder. Continued adjustment of that tube should show a peak in EGT, indicating the highest VE for that condition. That length would be "optimum".
That's a very clever idea Mike.

One detail; as VE improves, the mixture will go leaner as you say (fuel supply, dictated by RPM, MP, and temperature, remains fixed, while cylinder actually ingests gets more air). However, peak EGT does not necessarily indicate best tube length. It merely indicates a tube length where air inducted into the cylinder is a stoich match (aprox) for the fuel supplied. If a further change in tube length continues the trend (improved VE, mixture gets leaner), the EGT will simply start to fall with each change past peak, same as with LOP operation. Best tube length will be found when a length change results in no EGT change (a flat spot, if EGT was graphed). Further length change should reverse the trend (effective mixture gets richer again) as VE gets worse.
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  #66  
Old 04-03-2017, 01:39 PM
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Duplicate Post
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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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1984 L39C

Last edited by Toobuilder : 04-03-2017 at 01:42 PM. Reason: Duplicate
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  #67  
Old 04-03-2017, 01:40 PM
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Good point Dan. I guess the problem is differentiating between the stoichiometric peak, and the max VE peak. Should be a simple matter to achieve a peak EGT (either one) with tube length adjustment, then richen that injector back up to the original 100ROP value and adjust length again. That should be an easy way to determine if it is a VE peak, or purely mixture. It?s a few more iterations that I had originally envisioned, but the injector trim of the SDS product should make it fairly painless.

This is assuming that the ?optimal? length is quite a ways off from what Lycoming came up with. Frankly, if I can move the EGT 100 degrees with tube length/VE alone, then I?ll be amazed. But who knows? It will be an interesting learning experience.

Thanks for the heading check.
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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 - SDS CPI
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1984 L39C
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  #68  
Old 04-03-2017, 02:23 PM
rv7charlie rv7charlie is offline
 
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You could just use the proper tool; an air/fuel ratio meter.

No, wait. you poor Lyc guys are afraid of using mogas, aren't you?

;-)

Charlie
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  #69  
Old 04-03-2017, 02:33 PM
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Another possibility Charlie. I will have a wideband O2 sensor, at least in the initial setup flights.

And I do intend to run auto fuel if testing proves it out.
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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 - SDS CPI
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1984 L39C
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  #70  
Old 04-03-2017, 04:07 PM
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Quote:
Originally Posted by rv7charlie View Post
You could just use the proper tool; an air/fuel ratio meter.

No, wait. you poor Lyc guys are afraid of using mogas, aren't you?

;-)

Charlie
Wait, I have one, don't we all
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