Gap behind #3

Just to chime in here a bit. While down at TEX 2006 a couple of people asked me about my SJ engine plenum and if my #3 cylinder was still the hottest. It is and always has been. My #1 is the coolest and the #3 the hottest. #2 and #4 have always been very close with each other. (I do have tape on the front of both #1/#2 cylinders.)

This past weekend, I pulled the plenum off and did two things. I put a washer between the cylinder and baffle on #3. (Baffle was right up against cylinder.) I also completely blocked off the 2" outlet for cabin heat. Don't need heat in the summer and I figured this was just wasted air blowing to nowhere when it could be cooling my cylinder.

After test flying my #2/3/4 cylinder temps were within 4 degrees of each other, right around 355. (Previously the #3 cylinder was runninng 380's) My #1 is still cooler at 335 but I could put a little more tape on it to bring it up inline with the rest.

When building, I was worried about the #4 cylinder since I have a 3" scat tube back there for the firewall mounted oil cooler. The majority of the 3" hole is behind the cylinder head with only a small amount showing above. I've never had problems with #4.

On a side note... I've never had problems with oil temperatures being to HIGH with my FW mounted oil cooler (with Van's install kit).. I've struggled to get the oil temp WARM enough. That firewall mounted oil cooler is working just fine! I'd read many didn't like Van's fw mounted oil cooler kit and oil temps would be 10-20 degree's warmer than a baffle mounted oil cooler. It's been in the 90's here in KS the last couple of weeks and I've had absolutely no problem at all with high oil temps, even on climb out.

Just my $.02.
 
A full-sized wind tunnel was not available to me. We were unable to duplicate the wind and air-movement effects on the ground and found it easier, cheaper, and more effective to flight test the concepts than to build an elaborate ground testing mechanism.

YMMV.

Walter
 
BruceMe said:
I wonder if anyone has head-to-head comparisons of a newer plenum systems vs. the classic rubber-seal systems in termps of real-world cooling improvements and drag?
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Bruce,
I know this is a little late. I found your question while searching for something else.

I have a database of temperatures posted on my website that show the head-to-head comparison you asked about. At peak EGT for each cylinder, CHTs are down as much as 55 deg F and TAS is up by 5 knots. The only change was removal of the classic seal and the installation of the plenum with sealed inlets.

Temperature Data Base - (you must allow Excel macros in your computer settings)
http://www.n91cz.com/cooling/Temperature-Regression_03-13-2007.xls

In the program you input EGT for cylinder #1 (the remaining three are computed), altitude and OAT and . The engine has a carb., so there is some EGT spread. All data point are WOT and about 2500 rpm

Before and after cooling drag reduction is shown in:
http://www.n91cz.com/Pressure/N91CZ_Cooling_Drag.htm
Cooling drag was reduced more than 50%.

Cooling Drag was computed after gathering the required data described in the following report:
http://www.n91cz.com/Pressure/PlenumPressure.pdf


It is indeed hard to find before and after data. Most build in mods right from the beginning and so the base line is not known.
 
Quote "I also completely blocked off the 2" outlet for cabin heat. Don't need heat in the summer and I figured this was just wasted air blowing to nowhere when it could be cooling my cylinder."


MATTHEW,
Won't that cause the heat muff to burn out? You should at least give it a little air to cool. I used 1 1/2 scat back there and have all the heat I need.
 
gasman said:
Quote "I also completely blocked off the 2" outlet for cabin heat. Don't need heat in the summer and I figured this was just wasted air blowing to nowhere when it could be cooling my cylinder."


MATTHEW,
Won't that cause the heat muff to burn out? You should at least give it a little air to cool. I used 1 1/2 scat back there and have all the heat I need.
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I use a 3/4" outlet at this location your talking about, but I do have a 321 stainless heat muff which will not burn out. The SCAT tube or Aluminum heat muff is what you don't want to melt or ?????? burn up.....Well you know. Some air flow in my opinion is needed in this area, but it doesn't take much. Be carefull with this area if anyone have Aluminum Heat muffs..... Some airflow needs to move and circulate. Just be carefull as we don't need RV's burning things up..... :eek: That makes my insurance go UP!!!!!!!!!!! :p
 
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This may sound far out but.....what if someone had an engine cowl formed from polycarbonate. Then internally tufted or set up w/ smoke streamer to show the airflow patterns in various flight conditions and videoed from a chase plane....I wonder.....could just be a brain fart!

Glenn Wilkinson
 
Sounds like a good way to make video easier. Don't know much about the price of polycarbonate, but it also sounds expensive.

Measuring pressure is a good way to gauge efficiency since pressure differential is the "cooling engine". It seemed the easiest route for me at least. I bought a dc voltmeter, made a 5 vdc regulator, a multi-position rotary switch, and bought a handful of solid state pressure transducers. I will be measuring the upper and lower plenum pressures for each side and during flight test will simply select and record each reading. All for less than $275.00 .
 
exhaust augmentation

RV8RIVETER said:
You asked for it! :)

Actually makes sense and could be considered an extension of Bob Axsoms speed mod idea post.

All of the poeple with 200hp cooling problems I have met or read about, used the stock set-up and Van's oil coolers. Van's cooling set-up is pretty much spam can stock and leaves alot of room for air to go all over the place.

It seems pretty logical that if you want to take air in, you want to take only the amount needed to do the job, hence you want to make sure all of the air is cooling something. You also want to smoothly flow and reaccellerate the "used" air back into the airstream. The NASA research seems to bear this out. Dave Anders 200hp RV-4 had (it may have changed) an inlet area of 34 sq inches and an outlet area of 24.7 sq in with exhaust augmentation, per CAFE. A Lancair pilot with has downsized his stock cooling 19.2 sq in of inlet area and his temps dropped 50deg. His website is very good reading and he took thorough plenum/cowl pressure measurements to boot! Here it is.

http://www.n91cz.com/cooling/webCowlrep.htm

Also very good reading is a varieze with inlet AND outlet plenum. he also uses exhaust ejctor pumping. Something I plan on doing.

http://www.ez.org/feature/F0502-1/F0502-1.htm

There is also a good NACA paper 1942 about exhaust ejector configurations for engine cooling, wich increased pressure drop 8 inches of water. Don't have the link, but I can email it to anybody who can't find it.
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Hi Wade,
I would really like to read the data you have on the NACA paper. I need to find more on the actual design and area ratios for a given exhaust. I'm planning on 500 cubic inches of high perf exhaust. How deep into the augmentor do you put the exhaust tubes? Are they increasing the area like a venturi as it exits? I used to fly a Curtiss C-46 with a nice augmentor that slightly inreased in diameter as it flowed aft.
Thanks Guys,
ThunderBee
 
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