RV-4 Cowl cracks
 

I?ve chased this problem for years on my 20 year old RV-4 that I first flew in 1999. These early cowls were made with boat resin and gel coat and the older they get the crackier they get. The cracks are purely cosmetic but a real source of frustration.
A couple of years ago I wanted to repaint my custom flame job ( which had multiple cracks through them primarily around the spinner and air inlets ) so I pulled the cowl and sanded all back down to the gel coat and then kept going until the majority of the gel coat was gone. Latter We went so far and cut the front of the cowl off around the spinner and air inlets for our own performance up grades but now have new cracks at some of the transition areas. I haven?t been able to solve the problem so I?m resigned to the fact that Vans early cowl were just junk ! Walk the flight line at any RV gathering and all the 3?s and 4?s have the same cracking issues.
Permanent solution is an epoxy resin cowl in my opinion.

You'll want to grind out the old repairs, as they have cracked as well. Try to grind down to the base cowl material, then re-do the patch. Be sure the patch extends far enough from the crack to get good support. Given that this is a problem area, I would taper the patch so that it is gets thicker as it nears the crack area.

Larry

That makes sense. The polyester resins lose their liquid component over time and begin to crack, just like any plastic. Epoxy does not share this flaw and hence the go to material for longevity. An epoxy based patch should prevent future cracking, at least in the area of the patch. Future cracking could occur at the transition at the edge of the patch.

Larry

Crack me up...
 

Bruce,
As mentioned above, the vinyl-ester early cowls like the one I received in 1989 in my RV4 finishing kit are crack prone for certain. Thirty years later the battle continues.
Over the years I used several different types of glass including Kevlar and various resins for repairs only to see new fissures appear seemingly overnight in new areas. Argh is an understatement...

You could buy a new Pre-Preg cowling, install all the hardware, hinges etc and prime/paint to match, or.....keep fighting cracks.

Your call :)
V/R
Smokey

Polyester vs Vinylester
 

I?m pretty sure Vans early cowls were polyester resin same as most old boats. At least I?ve ground on both boats and Vans parts to make repairs and they sure smell the same. I have friends with Glasairs that use the vinylester resin system and it is far superior. I haven?t seen the cracking issues in their parts.

Gel-coat is hard colored resin they slather in the mold when they lay it up. This gives an even pinhole free surface. It is very hard and brittle and will crack over time. Heat, vibration, environmental conditions, age is the cause, but it is not a structural issue (unless you see cracks on the inner surface of the cowl).

Not even Van sells fiberglass parts with gel coat anymore. It is heavy and it cracks.... Yes 99% sure if it's an original RV-4 cowl is vinyl ester (or worse polyester but compatible with vinyl ester).

Cure = remove cowl and sand off ALL gel-coat, prime it, paint it. Enjoy crack free lighter cowl. (Sanding gel-coat by hand will take a long long time. Use power tools with care not to take off the glass plies. You don't have to get all of it off, just to where you start to see start to first ply though gel-coat. Thick gel coat which is what Van did was heavy and crack prone.)

Great advice guys! I have so much fiber glass terminology now that I didn't know before! One question: if you stand off all the gel coat, do you have to replace it with some other layer of something to retain the strength of the cowl? Or do you just apply primer and paint?