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High CHT Temp

Was about to ask for the same. Pictures are worth a 1000 words, or so they say ;-)

Beach Bum said:
Some good input...do you mind taking pictures of your cooling improvements? Was looking the plane over again yestersday and we still have prtty big gaps in a number of places. Big holes at the front of the engine on both sides, cowling support channels are open on the under-side, etc. I'll take pictures and post to give a better idea of our problems.
Click to expand...
 
Good luck getting good pictures. I found that it's really hard to get good ones of something inside the cowling, especially when you paint them black...you can go to my picture gallery, all the ideas are there, the vane pictured was discarded quickly due to mounting, drawings would be clearer. There has been a lot published on this already, I'm getting tired of repeating myself so often, because this subject comes up again and again and again. I wish Piper had equipped the cub with just a few of the features in the cowl that ALMOST EVERY OTHER AIRPLANE cowl has.... but the search feature on this site isn't very good.
Instead, use Google as follows: Enter site:www.supercub.org CHT and you will get much better results. A vane used when you have an oil cooler behind the #4 cylinder would be problematic. The vane itself was made to increase air flow around the back of the #4 cylinder, but it did most of it's work by increasing air flow down between the #4 and #2 cylinders; the CHT of the #2 was reduced 20 deg F as well. Vane on the right side was discarded because it didn't do enough to justify it. The geometry is not the same between left and right sides. Vane on the left was mounted on that boss between the cylinders that is tapped for 1/4-20 (ugh)and the outer baffles. My advice would be to ignore the vane and just do all the other stuff, even though blocking the hole down the front is the most difficult, it's also the most effective.
 
I talked with a Westach representative today. I was told the spark plug ring probes do indicate a higher temperature than the bayonet probes. They will not give a estimate of how much hotter, they stated there were too many variables with different engines and airframes. That statement appears to make sense. They recommended when using these type probes they be placed on the top plugs. Mine have always been on the bottom. They do not make a recommendation whether or not to use both the plug washers and the probe, or to just use the probe as a single gasket. They say it is up to the user. I will change my probes to the top plugs today to see it that makes a difference.
 
fobjob said:
Good luck getting good pictures. I found that it's really hard to get good ones of something inside the cowling, especially when you paint them black...you can go to my picture gallery, all the ideas are there, the vane pictured was discarded quickly due to mounting, drawings would be clearer. There has been a lot published on this already, I'm getting tired of repeating myself so often, because this subject comes up again and again and again. I wish Piper had equipped the cub with just a few of the features in the cowl that ALMOST EVERY OTHER AIRPLANE cowl has.... but the search feature on this site isn't very good.
Instead, use Google as follows: Enter site:www.supercub.org CHT and you will get much better results. A vane used when you have an oil cooler behind the #4 cylinder would be problematic. The vane itself was made to increase air flow around the back of the #4 cylinder, but it did most of it's work by increasing air flow down between the #4 and #2 cylinders; the CHT of the #2 was reduced 20 deg F as well. Vane on the right side was discarded because it didn't do enough to justify it. The geometry is not the same between left and right sides. Vane on the left was mounted on that boss between the cylinders that is tapped for 1/4-20 (ugh)and the outer baffles. My advice would be to ignore the vane and just do all the other stuff, even though blocking the hole down the front is the most difficult, it's also the most effective.
Click to expand...


http://www.supercub.org/photopost/showphoto.php?photo=36072&title=75d066ff&cat=500
 
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lol yea makes for a much brighter and easier to see engine compartment. Also makes oil leaks more obvious.
4ed4d582.jpg
 
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I needed to hide the Farnsworth-Bussard fusion generator and anti-gravity unit from prying eyes....:-?
 
garrett490 said:
lol yea makes for a much brighter and easier to see engine compartment. Also makes oil leaks more obvious.
4ed4d582.jpg
Click to expand...
This rear cylinder might run cooler if the baffle were installed against the fins. It looks as though it has nearly an inch gap all the way down the back side so the cooling air is going around the cylinder and out the bottom rather than through the fins. Look at it from the air's perspective. The air is going to travel along the path of least resistance. You need to force it to go between the fins to do it's job of removing heat from the metal.
 
Bayonet probes run 50 degrees cooler than spark plug senders. Engine has been overhauled? What about magnetos and carburetor. It is easy to drillout a main jet but is that truly the problem? Look at a schematic of how the carburetor works. There is way more involved in fuel delivery than a main fuel meter size. Put a light in the back of the cowling and look through the front air inlets for light to see how tight the baffles are with the cowl doors closed.
 
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Seems like the hinge and upper cowl channels are contributing to cooling loss?


hinge.webp
 

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I understand. Between (2) upper channels and the (2) cowl door hinges, seems like a lot of air is escaping. May not help much but I'll do a test to measure the difference, if any, with these areas covered with high temp tape.

Steve Pierce said:
Normal on all Super Cubs.
Click to expand...
 
I posted earlier about the Westach Spark Plug senders. I just received this email from Westach. Thought some might be interested. Pete states their plug gaskets do read higher than bayonets, although now not sure about installing in the top or bottom plugs.

Hi
Yes the bayonet senders will run approximately 50 deg cooler then the ring type due to the fact the plug is the hot spot. I do not have any info on either the top or bottom plug.

I recommend leaving the gasket in place to make it easier to remove the plug without tearing the thermocouple ring. Some folks like to remove it to keep the same plug spacing etc.


Thank you
Pete
Westach / Westberg Mfg Inc
www.westach.com
707-938-2121
8am to 3:30pm




I blocked the front cylinders similar to a Cessna 150, lowered rear cylinders by 30 to 40 degrees, raised the fronts by only about 5 degrees. I then made up some curved aluminum facing forward and taped to the rear baffle behind both of the rear cylinders facing forward. I did this after reading on here that air does not like square corners. Cooled rear cylinders by another 20 degrees. This is of course on a experimental. Thanks fobjob for the ideas.
 
skywagon8a said:
This rear cylinder might run cooler if the baffle were installed against the fins. It looks as though it has nearly an inch gap all the way down the back side so the cooling air is going around the cylinder and out the bottom rather than through the fins. Look at it from the air's perspective. The air is going to travel along the path of least resistance. You need to force it to go between the fins to do it's job of removing heat from the metal.
Click to expand...

Yea I was thinking that also, but I didn't know if there was a purpose the builder had for making it like that. Guess not.
 
Never assume that a lot of engineering went into these planes. What they had in the back room probably had a lot more influence on their decisions. Air leaks out the top of the cowl to the outside world have no influence; leaks to the low pressure side, resulting in a rise of pressure and a decrease of differential pressure, have much influence. When I started this study, the low pressure side of the cowl had a +2.8 inches of water pressure at 100 mph indicated, (at 6000 ft MSL.) Measured with respect to static. Now, the pressure is maybe +0.2 in water. That's where you need to be. Buy a Magnehelic gage on Evil-bay 0-6 inches of water.
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Lycoming specs their engines at 4 inches of water for adequate cooling. We can only make that spec at 95mph and nothing else wrong.....i.e. low pressure side of the cowl=zero inches of water....
 
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Made some progress today finally. Installed the sacred "-32" carb with .10 main jet. OAT was 60-65 and CHT leveled out at 403 during climb out and 364 in cruise 2350-2400rpm. Defin
 
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Made some progress today finally. Installed the sacred "-32" carb with .10 main jet. OAT was 60-65 and CHT leveled out at 403 during climb out and 364 in cruise 2350-2400rpm. Definite improvement. 20-25 degrees cooler.
 
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