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Make a fiberglass cowl by Edwin Smith

Caution! You should make a few practice cowls first before the real thing.

To begin, I tack glue a styrofoam block to the firewall. Sand to shape with what ever means seems practical. I normally sand even with the fuse side so that the cowl will fit over the fuse like a plug.

Next, Paint a coat of white Elmers glue thinned with water onto the styrofoam. This will seal it so that you don't get a bunch of little spikes on the inside of your cowl. When dry, fill in the voids with spackling like Dap. I apply it with water on my finger so it will fill all the voids. Sand again when dry. Paint another coat of thinned white elmers glue and let dry. If you make the cowl to plug onto the fuse you need to protect the fuselage, I use a clear mylar packing tape. I overlap the fuse with glass by about 3/4". This leave me enough to trim the edge.

I use 6oz fiberglass cloth to make cowls. From West Marine or any other boat repair shop. Its a heavy weave that goes around corners pretty good. Spray a light dusting of 3M77 spray adhesive on the plug, this will hold the cloth in place while you apply the epoxy or finishing resin. Lay a piece of cloth on. I apply layers in pieces. You can use 30 min epoxy THINNED A LITTLE, you don't want it too runny. Or you can use Finishing Resin from the hobby shop. Finishing Resin cures a little stiffer than epoxy and is good when making wheel well doors. Epoxy does fine for cowls. I use disposable hobby brushes (also from the hobby shop) to paint on the resin. I let a coat cure till its a little tacky then apply another layer of cloth and resin. I do this till I have 3 layers on. Let cure till pretty hard. Usually over night is enough.

You can sand with the plug still on the fuse or just break the tack glued plug off and you can wet sand. If I have some really bad surfaces, I will sand it on my bench sander and then move onto wet sanding up to 400 grit. Sometimes you might want to use spackling to help get a finer finish. You might want to wait until the foam is removed. I normally end up sanding off about 1 layer of cloth by the time I'm done.

To remove the foam, just pour a little gasoline onto the styrofoam. It will dissolve it. Do this until its all dissolved and just scrape out the messy goo left inside. I use a narrow paint scraper. To get into the tight spots I use a dremal with a small (~1" dia) wire wheel and a crown type of wire brush. You will also be scraping out that last coat of elmers glue. That helps to give a smooth finish on the inside.

I used luster coat to paint it, but I guess you could use just about anything thats fuel proof.

One improvement I will do next time is to imbed a piece of 1/16" ply in the areas that the screw holes will be. Bad vibration will damage it in the area of the screw holes. You can also use what ever weight glass is available.

Last updated on Monday, September 11, 2017