Here is a photo of a cowl I recieved off of someone. Do you guys have any ideas of how to repair this fiberglass cowl? Any help is appreciated. The cowl is going to get a new paint job anyway. The cracks are visible inside and out. Help, please! I do not want to have to buy another cowl. This plane is a Sig Cap 231 that I recieved after the past owner dumped it into a field. He never used this cowl and said he got it that way. I have stripped the covering off of the plane and I am starting to rebuild it. Thanks guys!

Probably a coat of resin and 3/4 oz fiberglass followed by Bondo and lots of sanding. Or... some of those Amish body shops might do the rough work and leave the finish work for you.

The proper way to repair fibreglass is to add a fibreglass backing to the inside of the cowl under each crack and after it has cured remove the crack with abrasives down to the backing.
Then make the proper amount of lay ups to replace the fibreglass that has been removed.
Proper technique doesn't require any bondo.

Zpat,
Normally I would defer to your expertise. However, careful observation of the photos indicate that the entire surface of the cowl is cracked. What you suggest would result in an totally new surface requiring some kind of surface finishing. And, the end result could be a smaller cowl that no longer fits...maybe?

It would be a heck of a lot easier to start with a new cowl if you can get one. Otherwise I would say it's a write-off and not bother with it. It would be easier to make your own mold from foam and lay up a new cowl than try to repair that one.

I'm sorry, I didn't realize is was stress cracks.
The only way to alleviate the problem would be to lay up the interior of the cowl, media blast the exterior of the cowl and perform at least 2 lay ups with a light cloth and a good epoxy resin on the cowl exterior.
I would suggest finishing with a catalized primer surfacer.

I like all of your suggestions so far. What would be the easiest way to make a foam mold? It would have only one use, right! Could I use this cowl to get the foam mold? I am curious. I really appreciate your help guys.

I'm not versed enough in mold making to tell you how you could use that cowl to make a mold. What I do for one-off parts is get some green florist's foam, glue the blocks together until they're big enough, draw my front, back and side views and have at it with a carving knife and sanding blocks.

First layer is light cloth to make the inside smooth. Then a couple layers of heavy cloth diagonally opposed, followed by a layer of light cloth. How many heavy layers you use depends on how big the cowl is and how stiff you make it.

You can get florist's foam at craft shops (Ben Franklin, Michael's, etc).