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alpinelakespilot2000

Well Known Member
I've heard of some people spreading a skim layer of epoxy on the inside of their cowl halves to facilitate keeping it clean later. However, on my cowl, the honeycomb portion on the inside seems to be covered with a layer of dacron or similar fabric. Don't want to sand or rough that up in prep for epoxy.

Is it useful to do something on the inside of the cowl? Or unnecessary altogether?

Thanks.
 
alpinelakespilot2000 said:
However, on my cowl, the honeycomb portion on the inside seems to be covered with a layer of dacron or similar fabric.
Click to expand...

Sounds like you are describing a layer of peel ply.

Any chance of a photo???

Vans sells a heat reflective foil, adhesive backed, that I covered the entire inner lower cowl with. I figured besides the heat reflective quality, it will make oily mess cleanup easier.
 
Hi Steve,

I used a 50/50 epoxy/acetone mix on the inside of my cowl. It really was a good idea. Sure makes cleaning easy. I also lined the lower portion with some aluminum tape.

The "dacron" fabric you are talking about is most likely just fiberglass cloth that is not entirely resin saturated. I am still working on filling the pin holes on the exterior of the cowl. That is a whole lot more work!

(P.S. I went to High School in Yakima!)
 
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Yes, it does look very much like a couple big sheets of peel-ply (as I understand it, peel ply is essentially dacron). The picture below is about the best I can show. You can see what appears to be the overlap running down the center. It doesn't appear to be fiberglass b/c when I went to rough it up in preparation for epoxy it didn't sand at all like fiberglass cloth. The only other thing I can think is that maybe the mold had a fabric like texture and my cowl just picked up that same very fine weave texture making me think it's fabric. Still it really does seem like fabric.



So how's the Midwest for a Yakima native, Tony? About 7 years ago I lived in Ohio but finally made it back to the NW where I grew up (Spokane). Ellensburg is like Yakima except a bit prettier b/c it's right next to the mountains, but also a lot windier! Sometimes that wind drives me crazy. Still, can't complain though. As you may remember from YKM, there are very few days in the year that are not VFR.
 
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It looks to me they forgot to pull up that peelply sheet. If it was me and I was putting a little thinned epoxy down, I'd peel that off first.
 
Steve,
If it's peel ply, it will pull off easily. I think it just appears to be peel ply. You would notice the edges especially. I had the "pink" cowl so it's probably a different construction. I think you can epoxy right over that. It almost looks like they used a different type of adhesive other than epoxy resin. Perhaps Aerobond or another bonding agent for the honeycomb. Others will reply who know more about your cowl than do I.

P.S. I started out here in the midwest, moved to Yakima (Naches) in middle school. We used to float the Yakima river through the gorge. We'd go almost to Ellensburg to start. I moved to Seattle and spent a few years there. Did a tour of duty at Boeing and then left WA an really haven't been back. My father and brother are still out there (Selah). My wife is from OR and we'd like to move back that way someday.
 
A good idea I read somewhere (probably on this list) is to use the leftover epoxy from working on other pieces/parts of fiberglas over time to eventually coat the entire inside of the cowl...
 
Steve,

I did a finish coat of epoxy on the inside of my cowl to prevent oil stains etc. In addition, I put a bunch of strips of reflective tape inside where the epoxy started to brown after a few hours. I use the 2-inch stuff and just overlapped it about a quarter inch. Using the tape makes it relatively easy to deal with the curves.

greg
 
I finished the inside of my cowling on my Midget Mustang and I am REALLY happy I took the time to do it. Oil drips are very easy to spot and it cleans up with a little Stoddard Solvent or mineral spirits or whatever.

The Midget Mustang cowling is a wet layup with no honeycomb so it took a bit of filling, sanding, and priming to get the result you see here. It was completely worth it IMHO.

cowling.jpg
 
Buy a three inch paint roller, three heavy knap rollers, a wallpaper seam roller, and roll or two of black electrical tape from your local hardware store. Order some cowl heat shield, it comes 30? wide and I ordered 9 feet of the stuff. (This is more than you will need but I would rather have too much than not enough.) Finally, get a big tube

Sand the inside of the cowl with heavy grit sandpaper. All you are trying to do is knock down the big bumps. Blow off the dust and wipe it clean with some acetone.

Mix your epoxy with 50% acetone. This will make it like water. Roll it on and let it harden. Repeat three times. That will fill the pin holes and keep the oil out of the cowl weave.

Put the heat shield on using a wall paper seam roller.
IMG_1209.JPG
IMG_1212.JPG


When all the heat shield is down and secure, outline the foil on either side of the edge with the electrical tape. Then smooth a bead of RTV over the edge of the foil to seal the foil to the fiberglass. (This will keep oil and such from getting under the foil and cause it to peal up.) Before the RTV hardens, remove the tape and let it cure.
 
Cowl paint

Just a data point, I prepped and painted the inside of the cowl on my '8' with epoxy and the same paint as the exterior and no added heat shields, or aluminum foil. At 400+ hours and 5 years, there is no sign of blistering or discoloration in the paint. And yes it is super easy to keep clean.

John Clark ATP, CFI
FAA FAAST Team Member
EAA Flight Advisor
RV8 N18U "Sunshine"
KSBA
 
DanH said:
...Do epoxy coat and then paint inside your cowl.

Never thin epoxy:

http://www.seqair.com/skunkworks/Glues/WestSystem/Thinning/Thinning.html
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Dan,

The last line states the reason why.
Gougeon Brothers AKA West System said:
Adding solvent is a quick, simple method of thinning epoxy, but the strength and moisture resistance of the cured epoxy are signiflcantly reduced.
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Since we are not using the epoxy for strength or moisture resistance when sealing the inside of the cowl, there should be no issue. However, using it full strength won't be an issue.
 
Is it useful to do something on the inside of the cowl? Or unnecessary altogether?
Click to expand...

Yes is is necessary to seal the inside of the cowl with epoxy or paint.
Gas and oil will eat into the honeycomb if you don't. Like others said it makes clean up a breeze.
 
Oh contraire....

Bill,
"Since we are not using the epoxy for ... moisture resistance when sealing the inside of the cowl"

Is not oil moist.........:rolleyes: ?

If it weakens the epoxy (which acetone thinning does) it will soon crack and let liquids in where you don't want them. Just not a good practice and is a common misconception (that it's OK) among non-composite folks.....
Best to follow the manufacturers' instructions.
;)
 
Flyingguido said:
...Best to follow the manufacturers' instructions.
;)
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I agree 100% and had I seen that before I sealed the inside of my cowl, I would have used it straight.

However, by "moisture", I was assuming water, not oil.

Three coats of thinned epoxy seems to have done a good job of sealing the inside of the cowl. However, one coat of pure epoxy would probably do the same job in a lot less time.
 
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