Older type (polyester resin/white gel coat) engine cowl

We bought a original, older type engine cowl with our RV-4 project. This cowl seems to be fabricated with polyester resin and has a white gel coat. It has no honeycomb core as the newer cowls.

We are currently in the process of fitting the cowl... and it is rather floppy , needs quite some trimming and glass work.

Aligning upper cowl with a laser.



What have builders, that have this older type cowl, used as a resin? Did you stay with polyester or did you use an epoxy system? I'm interested as well in the surface prep before painting: any specialities (products and techniques) that you used for the gel coat?

I have read as well, that some of those cowls show some deformation in flight: http://www.vansairforce.com/community/showthread.php?t=127490&highlight=polyester
Have some of you used some way to stiffen the cowl? Any experience on your modification?

Vinyl Esther!

Clouddancer said:

We bought a original, older type engine cowl with our RV-4 project. This cowl seems to be fabricated with polyester resin and has a white gel coat. It has no honeycomb core as the newer cowls.

We are currently in the process of fitting the cowl... and it is rather floppy , needs quite some trimming and glass work.

What have builders, that have this older type cowl, used as a resin? Did you stay with polyester or did you use an epoxy system? I'm interested as well in the surface prep before painting: any specialities (products and techniques) that you used for the gel coat?

I have read as well, that some of those cowls show some deformation in flight: http://www.vansairforce.com/community/showthread.php?t=127490&highlight=polyester
Have some of you used some way to stiffen the cowl? Any experience on your modification?

Click to expand...

Hi Andreas!
My 89' RV4 had the same vinylester cowl, wheel pants and wing tips from the factory. I used the West System epoxy, micro balloons for fill and Hy-Sol for cement. All can be purchased from Aircraft Spruce. I didn't beef up any places but I did reinforce the piano hinge attachments.
Lessons learned?
Back in the day many of us early builders had to use "bumpers" strategically placed to support the cowl underneath in places like the starter and near the flywheel ring as the cowls would sag down onto the starter ring.
The other issue is cracks. My VE cowl cracked around the intakes after about 200 hours and I noticed many other RV's back then with the same issue. It was disconcerting to say the least, especially after I spent months sanding, prepping and painting.
The cause I believe is heat stress. RV cowls, especially the upper get very hot when parked post flight. Opening the oil door when parked helps, but the heat is still there. The new PrePreg cowls are much less likely to crack with heat or stress.

Knowing what I know now I would be tempted to order a Pre-preg (pink) cowl from Van's. A much better option, lighter, stronger, easier to install with less time and cost to finish.
V/R
Smokey

All of the older gelcoat parts were made with polyester resin.

If proper surface prep is done, you can use epoxy, polyester, or vinyl-ester resin to add lay-ups.

Thank you for your valuable inputs!

I got a bit doubtful whether to proceed with old cowl or to order a new one... but my buddy and I decided to proceed with the original one. I'm familiar with gelcoat cracking from the gliders that I'm flying. But there, the cracking is not primary heat induced as it may be on the engine cowl.

I think we can manage without using "bumpers". We will decide wheter we stiffen the cowl in some places, when we finished fitting it. So we will see how floppy it will remain after the attachments to the fuselage are made.