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Enclosed pressure cowl vice baffles

Is anybody using an enclosed pressure plenum above the air cooled engine cylinders so that the air pressure and velocity flowing past the cylinders is handled without “silicone baffles”?
 
Plenum

Is anybody using an enclosed pressure plenum above the air cooled engine cylinders so that the air pressure and velocity flowing past the cylinders is handled without “silicone baffles”?

Lots of them. To be clear, the baffles don't get replaced. Traditional baffles are aluminum with a strip of material used ti seal the space against the top cowl. The plenum is basically a sealed cover attached to the baffles. I just finished fitting mine. Still needs some tweaks and final carbon fiber layer to make it purdy. Mine was a pretty big modification. The inlets are part of the bottom cowl. Top cowl is more like a cover. Plenum has inlets matching the cowl and will be sealed with neoprene sleeves.
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I can't help wondering if there isn't a middle ground between the standard baffle arrangement and the completely enclosed plenum? Presumably, the flaws of the standard baffle is the imperfect sealing of the silicone baffles "Flaps" against the top cowling. On the other hand, a plenum seals perfectly, but at the loss of access to the engine.
Suppose the top cowl had attached to it aluminum strips which would knife inside of the lower cowl baffles? Wouldn't the pressure inside the enclosed top area seal the top and bottom "Baffles" against each other? Yet, if the top cowl were removed, there would be no further layer to remove to gain access to the engine. Checking the oil wouldn't be harder, either.
This seems too obvious. Someone must have tried this and it failed, right?
 
Oil

I can't help wondering if there isn't a middle ground between the standard baffle arrangement and the completely enclosed plenum? Presumably, the flaws of the standard baffle is the imperfect sealing of the silicone baffles "Flaps" against the top cowling. On the other hand, a plenum seals perfectly, but at the loss of access to the engine.
Suppose the top cowl had attached to it aluminum strips which would knife inside of the lower cowl baffles? Wouldn't the pressure inside the enclosed top area seal the top and bottom "Baffles" against each other? Yet, if the top cowl were removed, there would be no further layer to remove to gain access to the engine. Checking the oil wouldn't be harder, either.
This seems too obvious. Someone must have tried this and it failed, right?

Pretty cool idea. It is experimental. Go for it.
By the way, oil door and tube is outside the plenum.
 
I can't help wondering if there isn't a middle ground between the standard baffle arrangement and the completely enclosed plenum? Presumably, the flaws of the standard baffle is the imperfect sealing of the silicone baffles "Flaps" against the top cowling. On the other hand, a plenum seals perfectly, but at the loss of access to the engine.
Suppose the top cowl had attached to it aluminum strips which would knife inside of the lower cowl baffles? Wouldn't the pressure inside the enclosed top area seal the top and bottom "Baffles" against each other? Yet, if the top cowl were removed, there would be no further layer to remove to gain access to the engine. Checking the oil wouldn't be harder, either.
This seems too obvious. Someone must have tried this and it failed, right?


Hold on there a second….Lycomings move around a lot relative to their cowlings - that’s what those big rubber LORD mounts are for. The reason that flexible baffle seals are used to seal the baffle area to the cowl is because of that movement - you have to allow for quite a bit of rotation of the engine, so I’m thinking your idea is going to leave bits of cracked cowl an aluminum bits everywhere….
 
Am I correct in assuming that the sealing between the top cowling and the flexible parts of the baffle is the root of the inefficiency of standard baffling? Might the problem simply be the large volume of the space above an engine? Perhaps the intake air gets turbulent with all that space to play in? If that were the case, might it be possible to add a lowered "ceiling" above the engine which was part of the upper cowl to direct the cooling air? And, how is it that some oil dipsticks are accessible with plenums, and some are not?
 
Leaks

Am I correct in assuming that the sealing between the top cowling and the flexible parts of the baffle is the root of the inefficiency of standard baffling? Might the problem simply be the large volume of the space above an engine? Perhaps the intake air gets turbulent with all that space to play in? If that were the case, might it be possible to add a lowered "ceiling" above the engine which was part of the upper cowl to direct the cooling air? And, how is it that some oil dipsticks are accessible with plenums, and some are not?

Most problems are due to leakage. Anywhere cooling air leaks is a loss of cooling. That includes the baffle seals to the top cowl. Turn off the lights. Shine a light from the bottom and look for light. There's gaps everywhere. Seal with black RTV. The air should only pass through the fins. Oil cooler, frankensnorkel, carb heat and cabin heat muffs all have holes too but they are necessary. It's all about pressure above vs pressure below. That's all I got. Lots of experts here with serious data way smarter than me. You might try running a search.
I know the standard Vans Lyco 320 and 360 have the oil tube behind the #3 cylinder. Oil door is Starboard side top cowl near the firewall well outside the baffles.
 
540s & 550s I've played around with had the dip stick on top of the engine. The 540 had a plenum I fabricated for it which involved putting a bowl around the dipstick housing up to the plenum skin. It was a pain but functioned well.
The 550 guy wanted a plenum but I talked him out of it. Instead, I fixed his baffle seals...
 
Is there anyway to quantify the amount of "Jiggle" one needs to allow for between engine and cowl? I saw a You Tube video about baffles, and there was a photo of the baffle on a Cessna 206. The fixed portion of the baffles extended vertically higher than I expected, and were capped off with a horizontal metal rim. The baffling was attached to the top cowl. Interesting take on this problem.
If the major problem is leakage in the flexible portion of the baffle, it seems to me one should have an idea who much room to leave for flex, and how much should be fixed. Too much flexible portion will allow leaks. Too little flex, and the baffle might impact the cowl.
So, how much is just right? Any intrepid Go-Pro guys put a camera in there during start to see?
 
John Thorp's intake on N18JT (Lyc O-360 updraft) is attached to the carburetor and sealed conventionally with baffle strips. He allowed about 1-1/4" and at 1100 hrs, no sign of contact between the filter intake and cowl.
 
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