Hmmm maybe, but if you calculate out a gap 1/16 inch over that 40 inches that could be a pretty good sized leak.
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Photos: Really good baffle seals
- Thread starter DanH
- Start date
Hmmm maybe, but if you calculate out a gap 1/16 inch over that 40 inches that could be a pretty good sized leak.
Yes, I agree the area of the gap seems big, but my experience - which may not match yours, is that even without all the silicone I have great cooling.
Tankerpilot75
Well Known Member
The “ramps” that you’re referring to were put there to direct more air towards cylinders 3&4. Say what you want but they seem to be working because the CHT difference between 1&2 and 3&4 is now around 10+ degrees which is much better than what I experienced before adding the “ramps.” Before the re-baffling my temps were reaching 415-420+ in the climb and 400+ cruise. After rebaffling and adding the ramps I’m seeing 370-380 in the climb (Oklahoma spring/summer temperatures) and around 330-335 cruise. I consider this a win!Nice looking baffling seals! BUT: what is with the ramps on the front cylinders? Blocking for cold weather.....?
Roadjunkie1
Well Known Member
I was admiring them; just wondering what they were for! I am impressed something so simple could make such a difference!
Nice job! How did you determine placement? Was it trial-and-error? Yes: I would definitely consider that a WIN! Better temps on climb and cruise: how can you beat THAT?? 
Tankerpilot75
Well Known Member
Can’t claim anything like intelligent design or engineering. Just made them based upon a picture I saw that Walt had posted on a thread a while back discussing my CHT issue . I kinda copied his picture and put them where I thought his were. All I can say is I try to imitate smarter people than myself.I was admiring them; just wondering what they were for! I am impressed something so simple could make such a difference!
My perspective of Baffle Seals is one of no experience, with curiosity and questions. My q's are one issue. The second I'll mention as one installing these right now, is I wish we had photos of the earlier posts. Today that database of photos is not available to us. Unfortunate. Do the moderators have a fix going forward for that?
My Q's:
Q1: Every overlap of baffle material creates a small air leak. I can prevent overlaps between seals by careful attention to detail when I fit them together. Was this an acceptable factory practice to improve productivity? Why is the leak creating overlap the industry best practice? Does silicone baffle material blow out unless its overlapped? Does the superior McFarlane Cowl Saver material that has a stiff UHMW coating allow us skillfully mate two pieces edge to edge to prevent these air leaks? Or will my seals contract when its 70F colder outside and leak then?
Q2: Why dont we stitch this juction of two mating seals with a needle and lacing cord (basball stich) and a leather hole punching tool to prep the material for each stitch?
Q3: I tested seal material to determine an optimal length that should rise above the cowl. 1.25" to 1.5" allows it to curl over when the cowl is installed and maximizes pressure between its edge and the cowl surface. When I see excess seal material bending around and beyond 90 degrees I cant envision and I have tested in my shop the pressure placed on this seal to cowl interface is weaker. Am I discovering something or missing something?
Q4: I suspect a seamstress or upholstry professional could give us good criticism. Is anyone here have background in that area?
I dont know if I am on to something or misunderstanding. Help me understand.
My Q's:
Q1: Every overlap of baffle material creates a small air leak. I can prevent overlaps between seals by careful attention to detail when I fit them together. Was this an acceptable factory practice to improve productivity? Why is the leak creating overlap the industry best practice? Does silicone baffle material blow out unless its overlapped? Does the superior McFarlane Cowl Saver material that has a stiff UHMW coating allow us skillfully mate two pieces edge to edge to prevent these air leaks? Or will my seals contract when its 70F colder outside and leak then?
Q2: Why dont we stitch this juction of two mating seals with a needle and lacing cord (basball stich) and a leather hole punching tool to prep the material for each stitch?
Q3: I tested seal material to determine an optimal length that should rise above the cowl. 1.25" to 1.5" allows it to curl over when the cowl is installed and maximizes pressure between its edge and the cowl surface. When I see excess seal material bending around and beyond 90 degrees I cant envision and I have tested in my shop the pressure placed on this seal to cowl interface is weaker. Am I discovering something or missing something?
Q4: I suspect a seamstress or upholstry professional could give us good criticism. Is anyone here have background in that area?
I dont know if I am on to something or misunderstanding. Help me understand.
airplane up-skirt pervert
Its a condition that is highly contagious.
Kyle Boatright
Well Known Member
If you're going with traditional baffle seals, the overlap gives you the fewest leaks, particularly on curved sections. If you did those sections in one piece, they would be likely to pucker when compressed by the cowl, resulting in gaps. If you try butt joints, you'll find that it is incredibly difficult to create joints that don't leak when the seals are deformed by the cowling top. Are there better ways to reduce cooling leaks? Sure... A properly installed plenum. But overlapping baffle seals are the proven "next best thing".
Roadjunkie1
Well Known Member
This is exactly what I did. There were gaps I was not happy with. I got out my leather sewing awl and put stitches in multiple places on the baffling which REALLY helped with holding the baffling in place. I put several 'helper' tabs behind places I thought might want to move. End result: the black pattern on my upper cowl made by the baffling shows very good sealing. Engine/CHT temperatures are actually sometimes lower than I would like. Oil cooler inlet needs to be blocked to let the oil heat up more than if it is left completely open. I'll see if I can send some picture. Busy with OOT guests right now.....
Q1 The overlaps (on RV's at least) are typically done for two different reasons.
1 They coincide with a joint in the baffle section to allow for easy removal of a section for engine maintenance and repairs
2 The are used to allow for installing small sections of seal where it would be otherwise very difficult to do with a continuous piece and get a good deal.
Overlaps, if done properly, can have a very minimal leak.
If desired, the typical small leak can be dealt with by careful trimming of one piece to match tightly with the other (requires close inspection of the shape they take when the top cowl is in place).
They can also be dealt with by applying a small amount of RTV in select locations and then putting the top cowl in place so they take proper shape while the RTV cures. If the baffle section ever has to be removed, you just cut the RTV. This has to be done carefully though because once you make an intersection immobile, it can actually make a leak worse in flight with the plenum pressurized since the pieces can no longer move and conform as they could otherwise.
Q2 Because it is often times difficult to determine what the actual position of each piece is relative to each other when the top cowl is in place and they take their natural positions relative to each other. It sometimes works, but you can also cause a bigger leak that
exists if you do nothing.
Q3 The gaps between the baffles and cowl, and the width of the seal sections, can play into how tightly they seal against the cowl but working to get the highest contact pressure is unnecessary from my experience, and can induce other undesirable issues such as more vibration transfer between the engine and cowl (air-frame).
People are often ignorant about how much the engine actually moves relative to the cowl. Particularly during start-up and shut-down.
Too small of a gap can result in baffle contact and / or more vibration transfer. Too large of a gap can result in seals that blow through to the opposite side. Particularly at very high speed from increased plenum pressure (this is most common along the back).
I believe best practice is an installation that allows for some movement, and when reading the transfer marks on the inner surface of the top cowl, there is indication that the seals are sealing well everywhere. If they are not, then do whatever it takes to correct it. If that is done, I believe actual contact pressure of the seals to the inner cowl surface are not important (the internal plenum pressure in flight will take care of that).
Q4 Seamstress I am not, so I can't help much with that one.
Plenum was built, and discarded. My Bearhawk cowl uses doors like a Supercub. Due to lack of creativity and expertise I am unable to design and fabricate a suitable plenum for me. Its a different animal than your one piece cowl which is well suited for a plenum.
Roadjunkie, you give me inspiration and confidence that I'm ok thinking outside the box. Thanks
Rvb2002, Thanks, I've considered the RTV to fill gaps. I'll use that in some other areas! Re; vibration....McFarlane would agree with you 100%. There baffle seal material is very expensive, but its surface that touches the cowl has a UHMW coating to improve the vibration transmission. I am one of the ignorant ones re: engine vibration. Wish I had concrete data.
I am experimenting. Baseball Stitch and then creating a cruved edge using darts and stitching on the edge.
My aft baffle cannot be done in one piece using the McFarlane material. In contrast to Kyle's report in post #109, it was very easy to fabricate this dart. I just closed up the doors, observed the overlap and marked it with a super fine sharpie, and removed a bit of material. 60 seconds.
So, I closed the doors and was able to see and fabricate an exact dart. When I closed it up I felt this joint needed some support. I like what I see now
Roadjunkie, you give me inspiration and confidence that I'm ok thinking outside the box. Thanks
Rvb2002, Thanks, I've considered the RTV to fill gaps. I'll use that in some other areas! Re; vibration....McFarlane would agree with you 100%. There baffle seal material is very expensive, but its surface that touches the cowl has a UHMW coating to improve the vibration transmission. I am one of the ignorant ones re: engine vibration. Wish I had concrete data.
I am experimenting. Baseball Stitch and then creating a cruved edge using darts and stitching on the edge.
My aft baffle cannot be done in one piece using the McFarlane material. In contrast to Kyle's report in post #109, it was very easy to fabricate this dart. I just closed up the doors, observed the overlap and marked it with a super fine sharpie, and removed a bit of material. 60 seconds.
So, I closed the doors and was able to see and fabricate an exact dart. When I closed it up I felt this joint needed some support. I like what I see now
WingnutWick
Well Known Member
Dan,Considering all RV fabrication tasks, the thing I most often see done badly is baffle sealing rubber. Flap seals arranged so they blow open, seals that seal against nothing, puckers, gaps, overlaps, you name it...the list of sins appears to be endless.
However, I have seen some installations that were beautiful. Believe me, I look; I'm the nut case who walks around fly-ins while peering into cowl openings like some kind of airplane up-skirt pervert
Builders need to see some really good seals. Who has pictures? Who can show us how it's done? Post those photos please. You'll help a whole generation of RV builders enjoy lower CHT and oil temperature, while going faster due to reduced cooling drag.
What are your thoughts on plenums? It seems you could create one with some well designed curves to optimize airflow while solving the problems you get with baffles.
WN
Just asking - has anyone done a comparison with measurements of cooling and performance (drag) between a properly installed baffle systems and a plenum? Asking because I installed the baffles just like Van's designed, using a slightly different rubber material, and it just works fantastically, was easy to install, and is easy to inspect and maintain. Plenums look cool, gotta give them that.
A plenum is simply a lid, same as an upper cowl with flap seals. A good one seals better than typical rubber strips. Airflow quantity ( usually expressed in pounds per second) has very little to do with choice of lid. Mass flow (quantity) is generally a function of exit area, unless the engine wraps are very tight. That typically requires extensive silicone/ glass wrapping.
Our goal is to convert a high percentage (~85%) of available dynamic pressure to increased static pressure above the engine. Low percentage is usually a matter of poor inlet ducting. The key design challenge is good ducting between inlet opening and the plenum space. With a high velocity inlet (think small diameter), duct shape is very important. Low velocity inlets can use any shape allowing good sealing. Shape is not critical.
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chrispratt
Well Known Member
Here are some photos of different angles on the baffling for my O-360-A1A (carbureted) in my RV-8. It has worked great for 19 years and counting. I have 950 hours on the engine now.
For installation, I just followed the diagrams in the instructions. This was a slow process to trim the baffles, but well worth the time spent. I’m in Texas and yet I rarely see oil temps above 180 F and never above 190 F. A cool engine is a happy engine as the Lycoming guys say. My highest cylinder temp is rarely above 320.
As a side note, a friend of mine two hangars down from me, just bought an RV-7A and I noticed the cowling off a couple of weeks ago. He said he was chasing high oil temps – like close to 300 degrees F. I thought I was going to fall over. Seriously.
He said he thought it might be a clogged oil cooler or a bad temperature gauge. I took one look at the engine and noticed a large gap in the baffling on each of the left and right sides toward the front of the engine, about 5-6 inches in length where they were about half-height of the rest of the baffling. I wish I had taken a picture to share, but look at images 2 and 3 above toward the front of the baffling and image those baffles with a big chunk missing out of each.
Instead, I went to my hangar, got a roll of baffle material, handed it to him and said, “Before you do anything else, try making those gaps level with the rest of the baffling. It’s an easy and cheap solution and just may solve your problem.” I saw him again a week later, he said that solved the problem. All temps are normal now.
I can’t think of a better example of how something as seemingly simple as baffling is so important to the performance and health of your engine.
For my part, I have to admit that I was more excited than he was that a simple observation led to fixing his problem and it didn’t cost him a dime. It also made me realize how much I’ve learned by building an airplane. RVs rock, especially with proper baffles.
Chris
For installation, I just followed the diagrams in the instructions. This was a slow process to trim the baffles, but well worth the time spent. I’m in Texas and yet I rarely see oil temps above 180 F and never above 190 F. A cool engine is a happy engine as the Lycoming guys say. My highest cylinder temp is rarely above 320.
As a side note, a friend of mine two hangars down from me, just bought an RV-7A and I noticed the cowling off a couple of weeks ago. He said he was chasing high oil temps – like close to 300 degrees F. I thought I was going to fall over. Seriously.
He said he thought it might be a clogged oil cooler or a bad temperature gauge. I took one look at the engine and noticed a large gap in the baffling on each of the left and right sides toward the front of the engine, about 5-6 inches in length where they were about half-height of the rest of the baffling. I wish I had taken a picture to share, but look at images 2 and 3 above toward the front of the baffling and image those baffles with a big chunk missing out of each.
Instead, I went to my hangar, got a roll of baffle material, handed it to him and said, “Before you do anything else, try making those gaps level with the rest of the baffling. It’s an easy and cheap solution and just may solve your problem.” I saw him again a week later, he said that solved the problem. All temps are normal now.
I can’t think of a better example of how something as seemingly simple as baffling is so important to the performance and health of your engine.
For my part, I have to admit that I was more excited than he was that a simple observation led to fixing his problem and it didn’t cost him a dime. It also made me realize how much I’ve learned by building an airplane. RVs rock, especially with proper baffles.
Chris
Ingo Weise
Active Member
Do you think that Mooney-like baffles would work on RVs? The 201 has an IO360-A3B6D in a very tight cowling. The intake is constructed like the snorkle, with or since 1990 without RAM-air. There are really big holes around the alternator and the starter. The alternator is cooled this way. There is no RTV anywhere.
I don’t really need the cowl flaps in a typical German summer, even in climb. Only with OAT in the 40th °C, CHT and oil temperature will reach the upper green arc in prolonged climbs.
This installation is much simpler, and with no baffles around the cowl inlet, installation of the lower cowl is easy.
How much speed would I loose with this modification? 201s are fast and efficient.
I don’t really need the cowl flaps in a typical German summer, even in climb. Only with OAT in the 40th °C, CHT and oil temperature will reach the upper green arc in prolonged climbs.
This installation is much simpler, and with no baffles around the cowl inlet, installation of the lower cowl is easy.
How much speed would I loose with this modification? 201s are fast and efficient.
Theres some research here across a few different articles. Like DanH has alluded to is that the design of the lid is important as well. Sealing the top by itself can be detrimental if the air is turbulent. Ramping the air to a slower speed increases the pressure above the cylinders.
The other aircraft to look at is Dave Anders RV4. He has some really good articles in Kitplanes.
