Vans Cowling to Plenum

My 9A has the standard Vans Cowling and a plenum. There is a small air gap all the way around, between the two. How do others mate the two together so they can be detached easily? thanks Larry

Larry, are you talking about where the plenum meets the baffling? Do you have a picture?

The only baffling is on left right and rear. No baffling in the front. Have not figured out pictures. The fiberglass cowling does not touch the fiberglass plenum

Larry Parham said:

My 9A has the standard Vans Cowling and a plenum. There is a small air gap all the way around, between the two. How do others mate the two together so they can be detached easily? thanks Larry

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Here is one of the best examples I've seen:

Thread Title: "My attempt at a plenum"; Courtesy of Chris, VAF Screen name: CMW.

http://www.vansairforce.com/community/showthread.php?t=76759

CMW said:

Here's a few shots of my plenum. This has taken forever. I hope it works well.

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Baffel to Plenum

My plane does not have a forward transition piece across from left to right closing off the engine to the top of the plenum.
Wow that is a very extensive plenum arrangement. thanks for pictures It makes sense now

Us there any need to get a tight seal between thecowl and the intake to the carbie. I'me having high temps and wonder if that could be caused by high pressure air below the engine. I don't use a plenum, but the idea of making one appeals to me.

Larry Parham said:

My plane does not have a forward transition piece across from left to right closing off the engine to the top of the plenum.
Wow that is a very extensive plenum arrangement. thanks for pictures It makes sense now

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Larry, better put up some photos.

Yen said:

Us there any need to get a tight seal between the cowl and the intake to the carbie. I'me having high temps and wonder if that could be caused by high pressure air below the engine.

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Good question. Mass flow through the cylinder fins is driven by the pressure delta between the upper and lower cowl volumes. Anything that reduces that delta will reduce cooling capacity. it doesn't take much. Examine the 320 cooling chart below. A loss of just two inches H2O (0.07 psi!) drops mass flow from 2 lbs per second to 1.5 lbs per second, and given a Standard Day OAT, pushes CHT to the max allowable.

I've seen some really bad ideas which clearly pressurized the lower cowl. My favorite was a sport/bush plane with a rather large oil cooler located in an opening in the lower cowl face, below the prop flange, dumping its flow into the lower cowl volume. Not only was it large, but it wasn't very well sealed at its perimeter. Although there is certainly some pressure drop across the cooler fins and through perimeter gaps, I'm pretty sure it was raising lower cowl pressure. It would have been nice to know, but like the vast majority who ask advice for a cooling problem, this builder declined to actually measure anything.