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  #1  
Old 05-13-2014, 11:43 AM
hlangebro's Avatar
hlangebro hlangebro is offline
 
Join Date: Mar 2012
Location: San Diego, CA
Posts: 133
Default Modifying the Sam James plenum

I have had some cooling issues with the Sam James plenum. I do have a cowl flap, but still it was running high initially. I tried all the tricks in the book, sealed and everything. The inlet is big enough, the exit should be big enough...

The conclusion I came up with was that the plenum volume is too small. I modified the plenum by making it bigger and test flew it over the weekend. I was very gusty and I could only do a partial climb test. It seemed like cyl 1 and 2 were the same as before, but 3 dropped 7 degrees and 4 dropped 17 dregrees. I usually climb out at 115kias but this time I flew at 100kias, the highest temp, compensated for a 100F day was 403F on #2. This is ok, but it could be better. The lowest during the climb was 374 on #4. I still have some fixes to do, but it proved the concept that it needs more volume to slow down the air and to create a higher pressure differential across over the cylinders.

some initial pics of the mods...

https://scontent-b-lax.xx.fbcdn.net/...97656692_o.jpg


https://scontent-a-lax.xx.fbcdn.net/...48461015_o.jpg
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H?kan Langebro
San Diego, CA

RV-7A, slider
Lycoming O-320 D1A, 160hp C/S
First flight 6-11-13

Re-engineering a Lancair 320..!


http://www.youtube.com/watch?v=AJuQ68tccTQ
http://www.mykitlog.com/hlangebro/

Last edited by hlangebro : 05-13-2014 at 11:54 AM.
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  #2  
Old 05-13-2014, 02:19 PM
DanH's Avatar
DanH DanH is offline
 
Join Date: Oct 2005
Location: 08A
Posts: 10,358
Default

Quote:
Originally Posted by hlangebro View Post
The inlet is big enough...
Can you tell us the dimensions, please...inside diameter, and axially, the distance from the leading edge of the aluminum ring to the point where expansion begins?

Quote:
I still have some fixes to do, but it proved the concept that it needs more volume to slow down the air and to create a higher pressure differential across over the cylinders.
The desired goal is smooth expansion, which is not quite the same thing as adding plenum volume. Put another way, a large plenum volume tends to be a side effect of feeding the plenum with well-shaped inlets.

Based on the cylinder temperature change (..."1 and 2 were the same as before, but 3 dropped 7 degrees and 4 dropped 17 degrees."), it appears more likely the extra clearance in the pinch over #1 and #2 has allowed a high velocity jet to reach #3 and #4. When the jet (high dynamic pressure) impacts the rear baffle wall and rear cylinders, the result is a local static pressure increase and a good bit of turbulent flow in the upper fins. Cyl 2, being the more rearward of the front pair, now has a good bit of roof clearance, so #4 gets a more powerful jet.

There's no evidence that increasing plenum volume raised static pressure at the inlets. No surprise, as you didn't change the shape starting immediately aft of the aluminum rings. Let's look at that area in detail.
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RV-8 SS
Barrett IO-390

Last edited by DanH : 05-13-2014 at 02:21 PM.
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  #3  
Old 05-13-2014, 03:14 PM
Rupester Rupester is offline
 
Join Date: Dec 2005
Location: Mahomet, Illinois
Posts: 2,195
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I have the SJ plenum on an IO-320 and have not had significant cooling problems. In flight, my CHT's could hardly be better.
The only "side effect" of the plenum is during prolonged idle or taxi situations in hot weather. In those situations, the reduced motion-induced airflow thru the plenum causes a slight vaporization in the injector lines. ( I attribute this to the small volume of the plenum ... with low airflow it holds the heat in.) The symptom is what sounds like an occasional miss in the engine. It's not enough to affect dependable idling or low-RPM taxiing, but it is audible. Reducing the size of the injector nozzles, to increase back pressure in the lines, helped; but did not eliminate the problem completely.

In any event, I continue to be pleased with the performance of my cowl/plenum combination.
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RV-9A Tip-up; IO-320 D2A
S. James cowl/plenum
(Dues paid thru Nov '18)
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  #4  
Old 05-13-2014, 04:25 PM
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Don Jones Don Jones is offline
 
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Location: Snohomish, Washington
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Dan's analysis sounds right on as usual. In looking at my SJ Plenum and having very similar temps to yours I came to the same conclusion as Dan. The area particulary in the inlet on #1 needs to be worked over. It is on my list of things to do to rework the inlets on both sides when I find the time. Dans theory of high speed air hitting the rear baffel makes sense too. I have my oil cooler on the rear of #4 and mounted it as high as possible, I reworked the plenum in this area to allow the cooler to be almost entirely above the #4 cylinder to keep from putting hot air throught the cooler. My oil temps never go over 195 and cruise at altitude is in the low 180's, need to block some of that air through the cooler.
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  #5  
Old 05-13-2014, 10:08 PM
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hlangebro hlangebro is offline
 
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Location: San Diego, CA
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One cyl #1 the "new" expansion started a little bit ahead of where it was initially, no dimensions handy here. Same on #2. This is where my "smooth expansion started. Since I had an issue with 3 and 4, this provided more flow to the rear region of the plenum.

It has solved some of my issues. A while back I checked the baffle "openings" on the lower side of the cylinders. I seem to remember Sam recommends 1" and 2.25" openings. I need to go back and check this again. I also heard someone using deflectors inside the plenum for 1 and 2, but I had no real data nor proof that this would work. I still need to do my cruise test, with different cowl flap positions.

My oil temp is also constant at 190. I also have it right behind #4. I am a bit puzzled the #4 is running the coolest, but it could also be that the flow through the oil cooler also facilitates the flow around the backside of #4. I have tried various gaps behind 3 and 4 baffles, and also around 1 and 2. Still, I can't say that I have found a real good smoking gun..
As an experiment I taped over the cabin heat exit from cyl 3 and got the temps to drop a little but not a whole lot.


https://scontent-a-sjc.xx.fbcdn.net/...22453518_o.jpg
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H?kan Langebro
San Diego, CA

RV-7A, slider
Lycoming O-320 D1A, 160hp C/S
First flight 6-11-13

Re-engineering a Lancair 320..!


http://www.youtube.com/watch?v=AJuQ68tccTQ
http://www.mykitlog.com/hlangebro/

Last edited by hlangebro : 05-13-2014 at 10:38 PM.
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  #6  
Old 05-13-2014, 11:25 PM
Rupester Rupester is offline
 
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Location: Mahomet, Illinois
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Default Baffles on front cylinders

I did have to play with different size baffles in front of cyls 1 and 2, to better equalize temps across all four. I never saw a true overheating issue on 3 and 4, but they were 25 to 30 degrees hotter than 1 & 2. After some trimming iterations with the front cyl baffles, all cyl are within 10 to 12 degrees now.

My oil cooler is on the back of cyl 4, and installed down low due to the low height of the plenum. It actually works too well. On a long climb on a blistering summer day I saw my highest oil temp ever ... 191F. In winter months even 80% blockage of the oil cooler never lets oil temps go above 178F. Many winter days I have a tough time getting the OT above 170F.
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RV-9A Tip-up; IO-320 D2A
S. James cowl/plenum
(Dues paid thru Nov '18)
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  #7  
Old 05-13-2014, 11:31 PM
Rupester Rupester is offline
 
Join Date: Dec 2005
Location: Mahomet, Illinois
Posts: 2,195
Default Another thought ...

Are you running the SJ short cowl or the longer one? The pic looks like it might be the short cowl. My long cowl requires a 4" prop extension, and my plenum intake snouts look longer than what I see in the posted pic. I wonder if that might be the difference in the cooling performance we see ....
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Terry Ruprecht
RV-9A Tip-up; IO-320 D2A
S. James cowl/plenum
(Dues paid thru Nov '18)
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  #8  
Old 05-13-2014, 11:38 PM
Rupester Rupester is offline
 
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Location: Mahomet, Illinois
Posts: 2,195
Default Long cowl plenum pic ...

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Terry Ruprecht
RV-9A Tip-up; IO-320 D2A
S. James cowl/plenum
(Dues paid thru Nov '18)
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  #9  
Old 05-13-2014, 11:56 PM
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hlangebro hlangebro is offline
 
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Location: San Diego, CA
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I have the short cowl, and also a 4" extension. I also cut down the front baffle of #1 and it cooled much better. I am still baffled, no pun intended, as why the temp are higher than expected. As it is now, I can fly on a 100F day and still be ok, but I would like the climb temps to be about 30F lower... Ah well, more experimenting to do
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H?kan Langebro
San Diego, CA

RV-7A, slider
Lycoming O-320 D1A, 160hp C/S
First flight 6-11-13

Re-engineering a Lancair 320..!


http://www.youtube.com/watch?v=AJuQ68tccTQ
http://www.mykitlog.com/hlangebro/
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  #10  
Old 05-14-2014, 07:21 AM
William William is offline
 
Join Date: Nov 2006
Location: Tampa, Florida (KVDF)
Posts: 531
Default

Quote:
Originally Posted by Rupester View Post
I did have to play with different size baffles in front of cyls 1 and 2, to better equalize temps across all four. I never saw a true overheating issue on 3 and 4, but they were 25 to 30 degrees hotter than 1 & 2. After some trimming iterations with the front cyl baffles, all cyl are within 10 to 12 degrees now.
F.

Rupester can you let us know what part of the baffle you trimmed, got any pics of that? I have a Sam James cowl and plenum.

Thanks
Bill
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