Okay, I'm the king of cowl rings.

I first tried it on my GP Patty Wagstaff Extra 300S ARF. I built about four of those each with a cowl ring. Next was the GP Christen Eagle ARF and we encorporated the cowl ring into the kit.

I've now built four GP 27% Extra 330S ARFs of my own, each using a cowl ring and finally my GP 27% Edge 540 ARF also using a cowl ring.

All have fiberglass cowls, but I'm not certain what resin they were "laid up" with (epoxy or polyester). I would bet they were made with polyester resin.

First, attach the cowl ring without the cowl to the fuselage. For my first Extra I used 6-32 socket-head cap screws, but now I use 4-40 and those are fine for up to (and over?) 50cc planes. Use blind nuts on the back of the former that you are bolting the cowl ring to. And you'll need an extended ball-end Allen wrench to get to the screws once the cowl is glued on. You can make an extended Allen wrench first by using a Dremel with a cutoff wheel to cut a regular Allen wrench in half. Then, using silver solder, splice a piece of 4-40 pushrod wire between the two halves using 1/8" (or is it the next size larger?) brass tubes to "sleeve" them together.

Also, once you have your cowl ring bolted to the fuselage, drill a 1/8" hole through the cowl ring and into the former on each side. Insert 1/8" wood dowels into the holes and glue the dowls to the ring, but not to the fuse. This will perfectly align the ring with the fuse when installing the cowl later on.

Mount your engine. This is when I "rough-cut" the hole in the cowl for the head of the engine (if it sticks out). Just cut the hole where you think it should be, starting extra small. Test fit the cowl and mark, then cut where necessary to get the cowl on.

Once you can get the cowl over the engine, roughen the inside of the cowl where the ring will go with coarse sandpaper. Fit the cowl over the fuse and ring, mount your spinner (and prop if necessary), then somehow "clamp" the cowl to the ring and fuse. You can use masking tape, but what I found works best is to hook five or six #64 rubber bands together and put them around the cowl over the cowl ring as though it is one large rubber band. Now you can adjust the position of the cowl and it will stay put without glue.

Okay, your cowl is lined up (be sure to look it for a wile from all angles), so time to glue. All you need to do is tack it in a few spots so it won't move when you take off the cowl so you can securely glue it later.

This can be the hardest part, so work carefully. What I do is drip medium CA down into the cowl in a few spots trying to get it to land on the ring and cowl where they touch. You don't want to use too much otherwise it may leak onto the fuse gluing the ring to the fuse. I usually have the model upside-down and can drip glue down through the opening in the bottom of the cowl for the air outlet. You can always follow up with accelerator so the CA doesn't wick past the ring onto the fuse.

Once the ring is tacked to the cowl, use your extended Allen wrench to un do the scews and remove the cowl. Now securely glue the ring to the cowl. I used to use epoxy, but I have found that CA adheres better - at least to the kind of fiberglass used on GP ARFs.

Now that the ring is permenantly glued to the cowl, you can perfect the cutout for the engine head and any other holes needed (for the muffler, needle valves, etc.).

Notes:
In some cases you will not be able to get to all the screws through the front of the cowl. Then, you will have to cut slots in the cowl to accommodate your wrench.

If you use the correct-size drill to drill the holes in the ring for the screws, they won't fall out when you take off the cowl. I forget the exact size, maybe I will post size later.

When it's all done, fuelproof with epoxy thinned with alcohol.

Here are a few verious pics from my recent Edge build and my Extra;