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Baffle Mod

...I suspect that there is an optimum gap width between the baffles, measured along the fins, that will result in the optimum airflow along the fins.....

'Twould make an interesting development project, if it has not already been researched.

See "Speed With Economy," Kent Paser, page 59. For the cylinder barrel baffle on his O-320, the optimum spacing was between 7/8 and 1 inch. For the cylinder head baffle, it was 2 1/4 inch. He said that he thought that these dimensions would be good for most Lycoming powered aircraft.

Dave
 
Silicone impregnable 9 oz cloth

Hi Dan
If I understand correctly, you are applying the silicone to the cloth, then using a roller to thoroughly impregnate it between layers of plastic on each side. How do you apply it to the cylinder fins? Trim to size with scissors then remove one side plastic? How are you left with enough silicone to stick to fins? Add a little more silicone? I have noticed significant improvement using silicone around the edges of my cylinder baffle parts. Planning on doing your wrap on the bottom side
Mark Wyss
 
Hi Dan
If I understand correctly, you are applying the silicone to the cloth, then using a roller to thoroughly impregnate it between layers of plastic on each side. How do you apply it to the cylinder fins? Trim to size with scissors then remove one side plastic? How are you left with enough silicone to stick to fins?

Measure the fin area you want to cover, draw the shape on the plastic, cut with scissors, peel one side, stick into place, peel the other plastic sheet. No additional silicone required, except for a bead here and there to make sure air can't escape between the "gasket" and the tin.

Sticks fine. None has ever moved, even where not trapped between fins and baffle tin. Here you can see it stuck to the front of the cylinder head and the cylinder barrel. The back side of the barrel (between 1 and 3) is wrapped the same way, without support except for a strip at the bottom under the edge of the inter-cylinder baffle.

The 598 is oil resistant. I may have cleaned the fin ends with MEK prior to bond.

P1010009.JPG
 
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This seems to be the best thread on the subject (ducts versus washers) so I thought I'd post here. I added a "washer" to space the baffles out on #3 this weekend. My "washer" was actually two pieces of 0.040" aluminum that I cut to about 1" wide in one direction and the width of the area that'd normally have to be silicone'd up in the other. I then drilled a hole where the screw goes through. I could have gotten away with no silicone, but ended up sealing it up with a tiny bit since I had it out anyway. That and removing and blocking off my heater air outlet seems to have sorted out my hot #3 issue. Not sure which did more, but I though my solution to the washer versus duct problem worked well (and was easy).
 
This seems to be the best thread on the subject (ducts versus washers) so I thought I'd post here. I added a "washer" to space the baffles out on #3 this weekend. My "washer" was actually two pieces of 0.040" aluminum that I cut to about 1" wide in one direction and the width of the area that'd normally have to be silicone'd up in the other. I then drilled a hole where the screw goes through. I could have gotten away with no silicone, but ended up sealing it up with a tiny bit since I had it out anyway. That and removing and blocking off my heater air outlet seems to have sorted out my hot #3 issue. Not sure which did more, but I though my solution to the washer versus duct problem worked well (and was easy).

Great Thread indeed! Your improvement was definitely the increased flow area on the head. It would be good to know just how much the temp dropped with your change - it is a good data point.

My #2 and #3 heads are the same. Pictures were posted earlier in the thread. The graph below is the result of measuring the flow areas for the first 8 (IIRC) fin channels from the base of the head. The area on the graph for the centerline is after working with a carbide die grinder to smooth the casting parting flash.

Note the maximum flow area between these same fins under he head. All the cooling is blocked with a tight fitting baffle and no grinder work. Look at the increase in flow area due to a .063" washer and .20" gap. Now, imagine where .040 would be. Better to be sure. If it works then it is good to know how little we really need. Right now I am adding .25" channel on #3 and .2" channel on #2. It is absolutely shocking that there is no "factory" attention to this and I wonder what the real world engine durability effects of loss of cooling due to those fins.
Head%2520Fin%2520Area.jpg
 
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Great Thread indeed! Your improvement was definitely the increased flow area on the head. It would be good to know just how much the temp dropped with your change - it is a good data point.

My #2 and #3 heads are the same. Pictures were posted earlier in the thread. The graph below is the result of measuring the flow areas for the first 8 (IIRC) fin channels from the base of the head. The area on the graph for the centerline is after working with a carbide die grinder to smooth the casting parting flash.

Note the maximum flow area between these same fins under he head. All the cooling is blocked with a tight fitting baffle and no grinder work. Look at the increase in flow area due to a .063" washer and .20" gap. Now, imagine where .040 would be. Better to be sure. If it works then it is good to know how little we really need. Right now I am adding .25" channel on #3 and .2" channel on #2. It is absolutely shocking that there is no "factory" attention to this and I wonder what the real world engine durability effects of loss of cooling due to those fins.
Head%2520Fin%2520Area.jpg

So I saw about a 25 degree drop, but I made several changes. I had 4 taps for blast tubes (mags, fuel pump, alternator) that were all 7/8", which seemed big, so I restricted them down to about 1/2". I also taped a little of the oil cooler off and took the heater muff completely off and blocked off that tap entirely. Who knows what helped more. I'm going to investigate my fuel flow a little as it might be just a touch low for takeoff. I know I have one small leak in the baffle seals where the rubber is kinked so there's a few other little things to fix.
 
Alternative to the washer - my solution

Well, #3 is pretty easy to make a chute, but #2 gave me a headache. I heated and pinched the end of some PCV to make a .2"x2" opening and used the vacuum blower to test it. An amazing about of airflow goes through that slow. Here are some pictures of the solution. Not much change, but it took a long time to create (I'm slow)

IMG_1288.JPG


IMG_1287.JPG

IMG_1286.JPG
 
How much gap for #3 .

Well said on previous threads. I measured the AREA ( gap x depth) between fully formed fins on the exhaust side . Count the spaces on the intakes side of #3 that are missing fins. Multiply the area X number of missing fins. Divide by the width of the missing fins. The answer = the gap for a " bypass baffle as noted in previous threads. Your mileage may vary depending on vintage etc.
 
You nailed it -

- Larry. The minimum depth on the exhaust side is about .500" This makes the gap across 8 fins, to be .25 inches. It does need to continue down lower ( 1.5" or so) then rejoin the fins to force the flow through the fins as they get longer.

The graph was to satisfy myself of the full schedule of area. .2" was all I could fit in on the front head.

Also, considering the engines are made this way, what is the real cooling need on the intake side anyway? Clearly it needs some, but how much is enough? I will find out when flying.
 
Is there any way to get DanH's photo to show up. They dont show up even using Google Chrom's "photobucket fix."
 
I suppose you could wait until I get back from S&F.

Photobucket is a dead issue. I may re-link the 1000 or so images, drawings, graphs, etc if we find a more-or-less permanent host.

9-3-18 Photos re-posted
 
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I suppose you could wait until I get back from S&F.

Photobucket is a dead issue. I may re-link the 1000 or so images, drawings, graphs, etc if we find a more-or-less permanent host.

I have also been searching and have great interest to see them, so when you are back, I would greatly appreciate it sharing them.

Hope you are enjoying Sun&FUN.
 
Photos and data

I have also been searching and have great interest to see them, so when you are back, I would greatly appreciate it sharing them.

Hope you are enjoying Sun&FUN.

+1 here. I would like to see the mods and data. This is such an awesome web site, it's a shame photos are so temporary. I started saving stuff I need to pdf files so I have a reference later. Some of it is linked on my blog. Anything I used is documented in the respective pages.
 
No before data, just after.

+1 here. I would like to see the mods and data. This is such an awesome web site, it's a shame photos are so temporary. I started saving stuff I need to pdf files so I have a reference later. Some of it is linked on my blog. Anything I used is documented in the respective pages.

I did the mods to #2 and #3, they and #1 are within a 10F degree band. #4 for me is a different animal. It is +25F. Maybe it is the flashing under the spark plug. I will let you know in a week.
 
I would also love to see some photos. The loss of photos on this site is problematic.

I am in Phase one with my RV8 and struggling with high CHT's on initial climb. They rise to 400 to 415 on 1 and three. 2 is also getting above 400 as the temps here in Ohio get out of the winter zone. My engine is a o-360 A1A with a carb. I have double checked the timing and tried the "washer trick on 3 and 2. I have 19 hrs on the plane so far. One I am in cruse they all settle down to 380 20 350. I am running high power during break in. 23" to 24" mp.

What is the consensus on how much to cut the Dams vans puts on the stock baffles. I have read that some recommend removing them entirely and finding the right size with aluminum tape.

Any help is appreciated
 
photos

I think if you post some photos or send a link to them, experienced people like Dan will be able to provide suggestions.
 
changing the dams

I got fed up with trying to figure out the right size for dams in trying to balance out my CHT's and finally made them removable so that I could experiment with different sizes etc. Just replaced the rivets with screws and locknuts, but during the build you could put nutplates instead.
Figs
 
metal forming baffle for #3

Dan
I'm looking at your post in 2008 about metal forming the baffle to make room for air to flow top to bottom for cylinder #3. Your photo shows a pretty small gap, maybe 1/8". Is that enough space to cool #3 or do I need about 1/4" inch of space?

I did first flight of my 7A with IO360 and CS. All went well except #3 ran hotter than the other cylinders. It was about 415 CHT and 1499 EGT at 24x24. More power and the temps would raise. All other cylinders were cool.

thanks
 
I?d like to know the experience of others too. Mine has been that with about 1/8th inch on the #3 and #2 cyls temps have been quite cool (low 300?s at similar power settings). The high egt would suggest to me a lean condition.
 
As many have written here many times, the “high” EGT doesn’t mean anything, other than that your probe is drilled a little closer to the exhaust flange than you might like. Absolute value of a single EGT means nothing - EGT is used to find peak for a cylinder, and to notice trends. A very small difference in probe to flange distance can make a noticeably difference in absolute values.
 
Tell us more Sam . . .

Dan
I'm looking at your post in 2008 about metal forming the baffle to make room for air to flow top to bottom for cylinder #3. Your photo shows a pretty small gap, maybe 1/8". Is that enough space to cool #3 or do I need about 1/4" inch of space?

I did first flight of my 7A with IO360 and CS. All went well except #3 ran hotter than the other cylinders. It was about 415 CHT and 1499 EGT at 24x24. More power and the temps would raise. All other cylinders were cool.

thanks

Sam, please tell us all the CHT's. Cooler could be 80 or 20F less. I ran .2 gap on #2 and .25" gap on #3. My #4 is actually a little higher (+20F) and nearly all conditions. I concluded #4 is due to the exit gap of the baffle opening at the bottom of the head. You can look back at my plot in post #56 for area. Lots more variables than area, though, so don't get hung up on a single variable. RE: Cutting out the fin flashing around the spark plug helped my CHTs about 15-20F.

EDIT: Sam, do you have any gap on the back of #3??
 
Steve, I later built a bypass for #3 with more area. #2 remains a 1/8" or so.

See post #24, this thread.
 
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#3 baffle mod

Lycoming cylinders have a classic baffle problem. I don't know if anyone else has taken this particular approach to solving it (lots of ways to skin a cat), but maybe the pictures will help the new guys understand the issue.

Here's the root of the problem. The intake side of the head has no fin depth in the area indicated by the pencil. but standard baffles for the left front and right rear cylinders place a plate directly against this area. There is plenty of air at "A", but there is no way for air to circulate down to area "B"

Intake%20Fin%20Depth.jpg


Details:

Fins.jpg


Here's the standard baffle (right rear) against the head. Flow to the lower fins and baffle wrap is blocked by the zero-depth fin area identified by the green tape. The standard "cure" is to place a washer or some other spacer between the head and the baffle, but that opens a gap along the entire length of the baffle plate.....in particular the area outlined in a black rectangle above. Any air sneaking past the area in the rectangle is pure leakage.

Intake%20Fin%20No%20Clearance.jpg


It is quite easy to hammerform a small duct of sorts in the baffle plate. The "duct" is nothing more than a fancy dent knocked in the sheet.

Intake%20Fin%20Hammered%20Duct.jpg


The result is a passage to bypass the no-depth fin area (arrow). Now air can flow down the back of the head and pass in between the lower fins where you have a baffle wrap. The reminder of the baffle plate is not spaced away from the head and cylinder, reducing undesired leakage. Any air not passing between fins is pure drag; it didn't do any cooling work.

Intake%20Fin%20Clearance.jpg


Not all builders have metal forming hammers, or may not want to try beating on an expensive baffle part as their first metal forming experience. I'll do the left front baffle using an alternate method and get it up here soon.

Have fun.

----->>>>POSTSCRIPT: See posts 24 and 25

So did this work well? If the dent in the baffle is made too large will that lower the pressure on upper side of engine and make all air flow worse?
 
So did this work well?

Pretty well, but I tend to experiment. I enlarged the bypass for #3 and got some further reduction. This photo was taken while making that mod; I've cut away the hammered duct:

Fins.jpg


A larger bypass was riveted on:

IMG_1233.jpg


If the dent in the baffle is made too large will that lower the pressure on upper side of engine and make all air flow worse?

No. The throttle is the lower fin wrap, just like the other cylinders.

This mod dates from summer of 2013: http://www.vansairforce.com/community/showpost.php?p=786133&postcount=24
 
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Pretty well, but I tend to experiment. I enlarged the bypass for #3 and got some further reduction. This photo was taken while making that mod; I've cut away the hammered duct:

Fins.jpg


A larger bypass was riveted on:

IMG_1233.jpg




No. The throttle is the lower fin wrap, just like the other cylinders.

Oh, great point about the throttle being by the fin wrap. Great. Thanks for your quick and helpful reply. My second test is tomorrow with slightly opened baffle slot. thanks
 
Intake side

The intake side of the head doesn't need as much cooling air flow as the exhaust due to the incoming air being cool. That's why the fins are shorter on the intake side but I think it needs more that it gets when the baffles are up tight against the head. Probably needs to be the same clearance as between the two cylinders. I wonder if too much cooling air going around the cold side would be a bad thing as in making the cylinder have a 'cool' spot or the head not being a more uniform temp all the way around? I guess the head needs several CHT probes around it to see what is really going on.
 
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The intake side of the head doesn't need as much cooling air flow as the exhaust due to the incoming air being cool. That's why the fins are shorter on the intake side but I think it needs more that it gets when the baffles are up tight against the head. Probably needs to be the same clearance as between the two cylinders. I wonder if too much cooling air going around the cold side would be a bad thing as in making the cylinder have a 'cool' spot or the head not being a more uniform temp all the way around? I guess the head needs several CHT probes around it to see what is really going on.

For the fins that wrap all the way around the head (all but the last two fins under Dan's black tape), they are dissipating heat from the crown of the combustion chamber. This crown/combustion chamber top has a fairly even temperature across it. The intake seats are pulling less heat from the valve, but is not significant in the grand scheme of the heads heat dissipation. Yes, they intake chamber area is cooler than the exhaust, but the bulk of the fins that are being dealt with here carry just as much heat away as their neighbors on the exhaust side.

Larry
 
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flying result of denting the aft baffle

Okay, I hammered a dent in the rear baffle to let a little air behind #3 cylinder. I kept the dent only on the top part of the cylinder where the fins go flush with the cylinder. Today's test showed it below temp of the other 3 cylinder. Others were about 325 and #3 was 315F. At first I thought it was too low but after awhile (30 minutes) it came up to match the others. I might plug the slot a little if it continues to be lower than the other three. Cylinders 1,2, 4 are all about the same. So making the dent to open up air flow definitely lowered the temperature. And it doesn't take much space. !/8" max.
 
Okay, I hammered a dent in the rear baffle to let a little air behind #3 cylinder. I kept the dent only on the top part of the cylinder where the fins go flush with the cylinder. Today's test showed it below temp of the other 3 cylinder. Others were about 325 and #3 was 315F. At first I thought it was too low but after awhile (30 minutes) it came up to match the others. I might plug the slot a little if it continues to be lower than the other three. Cylinders 1,2, 4 are all about the same. So making the dent to open up air flow definitely lowered the temperature. And it doesn't take much space. !/8" max.

Nice. Steve, those temperatures are quite low, which suggests some headroom for the more difficult cooling regimes, and the possibility of exit throttling for cruise.

"Difficult" usually means low dynamic pressure and high AOA. What do you get (1) in extended full power climb at some typical speed, and (2) when you slow down to 90 knots and hold it there in level flight for 20~30 minutes?

BTW, I'm never made a big effort to even out four CHT indications. Within practical limits, they are really four independent engines, and the order of warmest to coolest tends to change with different flight conditions.
 
Nice. Steve, those temperatures are quite low, which suggests some headroom for the more difficult cooling regimes, and the possibility of exit throttling for cruise.

"Difficult" usually means low dynamic pressure and high AOA. What do you get (1) in extended full power climb at some typical speed, and (2) when you slow down to 90 knots and hold it there in level flight for 20~30 minutes?

BTW, I'm never made a big effort to even out four CHT indications. Within practical limits, they are really four independent engines, and the order of warmest to coolest tends to change with different flight conditions.

Per your question:
Yesterday 25x25 climb; OAT=55F, Alt=4k. The CHTs = 404, 399, 380, 392.
Cruise 23x23 CHTs= 354, 352, 342, 343.
At idle after flying awhile CHTs = 342, 330, 342, 335.
Haven't done 90Kts test.

I have one high EGT (also #3) it runs about 200F higher. I just read it may be non-firing plug. I'll check that.
 
Naca Cylinder Cooling Report

The best (i.e. most recent) data for air cooled engine design is probably found with the SAE. I'm not a member and not curious enough to spend non-member money for SAE books.

Heat transfer from metal to air is governed by temperature delta. The air entering a full wrap baffle is at ambient temperature, so heat transfer from the hot metal is high. Further around the cylinder the air is now much warmer, and heat transfer is lower. The result is less and less cooling as the air proceeds further around the cylinder.

There's an early NACA work illustrating the issue. See Table 1 and Fig 2:

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20090014186_2009013404.pdf

It is interesting to note that our stock baffle scheme is something like Fig 2a; small exit radius, close entrance width, no exit duct...the worst configuration tested in terms of uneven cooling and energy loss.

To be fair the deformation of the cylinder from perfectly round to some unknown shape may be minimal. I don't know. It should also be noted that there is a difference between cooling cylinders and cooling cylinder heads. Obviously the fin area is shifted toward the exhaust side, and aluminum has a far higher ability to transfer heat by conduction as compared the steel barrels.

Like you I'm tempted to try full wraps. I have hesitated because of economics, not lack of curiosity; IO390 cylinders are very expensive. I've mostly concentrated on extreme sealing and a bit of airflow control to the regions left lacking. I do have partial wraps on the barrels between cylinders, thus each cylinder has symmetrical airflow.

Some of the EZ bunch have done radical cooling experiments. You might look there.




Wow ! Thanks for taking the time to post the NACA report. Real data is sweet, as opposed to what " your friend heard at Joe's hanger". I printed out the data spread sheet and highlighted the best numbers. I will try and post that tomorrow.

Thanks again,

Jonny o
 
Cht balance

People seem to want to balance cht’s between cylinders, but isnt it more important to balance temps across individual cylinders? For example, banging on the baffles on cy 3 lower the temps, but it still seems to me the part of the cylinder next to cy 1 still has much more air flow than the part that is next to the baffle. Wouldnt one wNt to have the same amount of airflow on all sides of a cylinder?
 
When I had my baffles off for some other work recently I came across this thread. I made the suggested modifications to my #2 and 3 baffles (using the riveted on bypass method), and also modified (lowered) the dam in front of #1, and came away with 15-20 degree cooler CHTs on those cylinders. Which might have been expected given the comments on the thread but still I was surprised that such a simple mod could make such a big difference. Thanks Dan and the VAF community!
 
Resurrecting this thread.
Mine is an IO-360-M1B. Exactly like this one. Photo.
Notice the area in red. That's basically where the cut out will land. I can't get the cut out hole exactly over the problem area without busting edge distances.
20220318_165234.jpg

I started the relief area. Notice the pointer. That corresponds to the spot on the cylinder where fins are flat. I haven't cut the hole yet but I don't see how I can get much closer without busting edge distances. Shim is .063" and chamfered to fit flush into the bend. Cover plate bend is designed to fit flush and close any leaks.
I don't see any way to get closer to the flat area. Any ideas?
20220318_165118.jpg
 
Resurrecting this thread.
Mine is an IO-360-M1B. Exactly like this one. Photo.
Notice the area in red. That's basically where the cut out will land. I can't get the cut out hole exactly over the problem area without busting edge distances.
View attachment 23529

I started the relief area. Notice the pointer. That corresponds to the spot on the cylinder where fins are flat. I haven't cut the hole yet but I don't see how I can get much closer without busting edge distances. Shim is .063" and chamfered to fit flush into the bend. Cover plate bend is designed to fit flush and close any leaks.
I don't see any way to get closer to the flat area. Any ideas?
View attachment 23530

Don't see how edge distance matters here. The cover piece is non structural and carries no load. On mine, I only put rivets on top and bottom and used RTV to seal the sides to the main baffle. Though I used bent .032 and not 063. I have a cover like this on the front baffle ramp of my 6 and it has only two pull rivets and the rest RTV. Has held on for many 100's of hours.

Larry
 
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Ditto on this being non-structural.

But rather than a flange on the inboard side, I'd eliminate it. You will still have upper, lower and outboard flanges. Here's the general concept, showing a cross-section. The green is the baffle, the other colors are the bump-out:

Baffle Mod.jpg

Dave
 
Baffle mod

Ditto on this being non-structural.

But rather than a flange on the inboard side, I'd eliminate it. You will still have upper, lower and outboard flanges. Here's the general concept, showing a cross-section. The green is the baffle, the other colors are the bump-out:

View attachment 23551

Dave

Sorry Dave, I'm lost again. I thought the idea was a path for air. The air needs to wrap around the cylinder. If it's non-structural, I can modify it inboard to capture a little more area.
 
Gap?

So how much gap did you add? Seems like onyl 032” or something?

Inwas thinking of making a bump so I get, like, 1/4” rightbat the cylinder mold line. Anything else I am not sure how much air will get by..JMHO
 
Baffle mod

So how much gap did you add? Seems like onyl 032” or something?

Inwas thinking of making a bump so I get, like, 1/4” rightbat the cylinder mold line. Anything else I am not sure how much air will get by..JMHO

.063" shim. It's hard to tell in the photos. Looking at it installed, there's definately a space. Dan's original post recommends .063-.080. That's what I had. Easy to drill rivets and add or change the shim.
 
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