Best material to join the cowl intake/plenum.

[Rbb469]

I’m curious what most are using to join the plenum/cowl intake? My -4 currently has some type of neoprene material thats weathered and needs replaced. TIA. Ricky

 

[Mark Wright]

I’m curious what most are using to join the plenum/cowl intake? My -4 currently has some type of neoprene material thats weathered and needs replaced. TIA. Ricky

PMC-780 DRY, add some black pigment.

 

[scsmith]

DanH has posted extensively about how he molds fiberglass-reinforced urethane for shapes like this. You would have to carve a mold out of a small block of foam for each side. As I recall, there are some urethanes that are oil-resistant but absorb water, and there are some that are water-resistant but not oil. I may have this wrong, and I don't remember which is preferred, so hopefully DanH will chime in here. But for sure search back in his archives for lots of guidance on the process he uses.

Another way to go would be to make a new neoprene foam "sock" to fit. An old mouse pad, or a leg or arm section cut out of an old wet suit will work. Or you can buy neoprene foam sheet from McMaster Carr. You can cut it to shape and cement the edges together with wet-suit repair cement. Then cement a reinforcing strip over the seam, just like your old one. Wet suits come in a range of thickness from 3mm to 7mm, and of course if you buy new, you can pick what you think would work.

 

[wirejock]

You can buy neoprene material on Amazon pretty much any thickness you want.
I like the Urethane idea. Need to search for that one.

 

[fixnflyguy]

I’m curious what most are using to join the plenum/cowl intake? My -4 currently has some type of neoprene material thats weathered and needs replaced. TIA. Ricky

I bonded an aluminum ring made of .063" 2024 with epoxy to the fiberglass intake of the cowl. It has about 1" of flange that the snorkle with a rubber wrap of baffle material fits up over. Nit a great description, but the aluminum flange ring doesn't wear like fiberglass. I don't have a handy picture of the cowl flange.

 

[Rbb469]

DanH has posted extensively about how he molds fiberglass-reinforced urethane for shapes like this. You would have to carve a mold out of a small block of foam for each side. As I recall, there are some urethanes that are oil-resistant but absorb water, and there are some that are water-resistant but not oil. I may have this wrong, and I don't remember which is preferred, so hopefully DanH will chime in here. But for sure search back in his archives for lots of guidance on the process he uses.

Another way to go would be to make a new neoprene foam "sock" to fit. An old mouse pad, or a leg or arm section cut out of an old wet suit will work. Or you can buy neoprene foam sheet from McMaster Carr. You can cut it to shape and cement the edges together with wet-suit repair cement. Then cement a reinforcing strip over the seam, just like your old one. Wet suits come in a range of thickness from 3mm to 7mm, and of course if you buy new, you can pick what you think would work.

Thank you for the great info! Much appreciated. That gets me in the correct direction! Thanks again.

 

[Rbb469]

PMC-780 DRY, add some black pigment.

Thank you!!!

 

[penguin]

Nothing? I was going to use DanH's method but tried with nothing and cooling is good. Plenum entry is very slightly larger than cowling inlet. The is a gap of around 1/4" between the two. Why go to all that trouble if it doesn't achieve much?

 

[HFS]

What I Did - Round Inlet HR II ...

I used 5mm wetsuit material (sourced from wetsuit mfg. as "rems). Made patterns (cooling & inlet) for the conical shape needed, then bonded them together with wetsuit material adhesive + stitching (cross link & straight) with Kevlar thread (can't break it), then sealed over the seam with clear silicone sealant to keep out any damaging residue.

Been using this system for 23+ years with no issues ...

HFS

 

[Rbb469]

What I Did - Round Inlet HR II ...

I used 5mm wetsuit material (sourced from wetsuit mfg. as "rems). Made patterns (cooling & inlet) for the conical shape needed, then bonded them together with wetsuit material adhesive + stitching (cross link & straight) with Kevlar thread (can't break it), then sealed over the seam with clear silicone sealant to keep out any damaging residue.

Been using this system for 23+ years with no issues ...

HFS

Oh wow! Those look amazing, I'm going to attempt to go that route. thanks for the info. Ricky

 

[Rbb469]

You can buy neoprene material on Amazon pretty much any thickness you want.
I like the Urethane idea. Need to search for that one.

Thanks for the info.

 

[Dugaru]

Nothing? I was going to use DanH's method but tried with nothing and cooling is good. Plenum entry is very slightly larger than cowling inlet. The is a gap of around 1/4" between the two. Why go to all that trouble if it doesn't achieve much?

+1. After the baffling material at the front of my FAB was damaged during reinstallation of the lower cowling, I just removed it. Zero effect.