getting the cowl foil to stick

I have one little hotspot where my exhaust discolored the cowl (right at the bend on the #2 exhaust pipe). Got some of the cowl tape/sheet from Van's and tried everything to make it stick but couldn't.

How do you all get it to stick permanently?

I've flown about 11 hrs so far and the discoloration hasn't gotten any worse since first flight... so I don't know if I could just live with it as is?

Best,

Scott Will said:

.........Got some of the cowl tape/sheet from Van's and tried everything to make it stick but couldn't. How do you all get it to stick permanently?....................

Click to expand...

Scott,

During the build phase, everytime I worked with epoxy for one reason or another, there was always some material left over and rather than just throw it away, I would apply it to the inside of the cowl(s) to seal it.

Untreated, the cowl's natural porosity will trap all manner of grease and grime within its pores, and must be sealed so the adhesive backing on the foil has a smooth surface to adhere to.

A very effective way to keep exhaust pipe heat from damaging the cowl is to apply some thin aluminum (roof flashing works well, BUT, some of it is coated with plastic and shouldn't be used) to the appropriate areas. I used little chocolate chip sized blobs of RTV spaced about every inch, and gently pressed the aluminum sheet onto it. The goal is to leave a small air gap between the aluminum and the cowl. Clean the area with lacquer thinner first, and let it dry well. You may have quite a few little sheets of the aluminum, sort of fish scale like overlapping, to accomodate the compound curvature.

I agree with the last post as well, the inside of the cowl should be painted/sealed with something tough. Epoxy primer is probably best, but anything that doesn't dissolve in solvents will work.

The time effect of heat will catch up with you if you don't do something, so don't think that a lack of additional discoloration means all is well.

I Just Did This!

Scott,

I was just putting foil on the inside of my lower cowl the other night (so I can't give you a long-term result), but I also found that I had to do a very thorough cleaning - I used my current cleaner-of-choice, Coleman fuel....I know, it's flammable, but it works, and I used it in small quantities with good ventilation.

I put the foil on primarily to give me an oil-resistant finish, because unlike the smart builders, I didn't do a very good job of giving myself a smooth, hard, pore-free finish on the inside of the cowl. I painted it with a high-heat rattle-can finish, but should have done as suggested above, and sealed it with epoxy first.

I used a combination of the Van's sheet-foil and aluminum tape from Home Depot Aviation Supply to cover the entire interior - need to piece it in order to make it fit the curves.

One other trick is to use a burnishing tool of some sort to really, really press the stuff on tight - something that will put a lot of pressure on a small area. I used a piece of plastic like a Bondo spatula - worked really well, and you can tell the adhesive really is working.

Gotta get every molecule of oil off first though!

Paul

In a past RVator, there was a recommendation to use a mixture of 50% West epoxy and 50% acetone to make a water like mixture. (As someone said earlier, each time you mix up epoxy, you usually have some extra that you can use for this and paint at least some small area somewhere.) Paint this on over the inside of the cowl in the areas where you want to put the aluminum sheet.
I did this on my new RV8 cowling and the sheet has stayed put...at least for the last 92 hours.
I actually painted this over the entire cowling several times, lightly sanding between coats to make it smooth. Helps fill the pin holes!
If your mixture starts getting thick, as you use it, just add a little more acetone to keep it watery.

Before my latest concoction (sp?) I used houshold aluminum foil and 3M contact cement. That held for several years and a couple of hundred hours. Put the extra shiny side toward the engine.

I found the edges were peeling up

Even though I degreased well, or so I thought I still had adhesion issues.

I then took a strip of that very fine fiberglass weave and used that to stick it down around the edges..Seems to work OK.

Used the same stuff to bond down the foil Nav antenna as well.

Frank