Dumd question, but being that none of the cars i have ever built had to be. I bought a Hanger 9 PTS and read the 60 plus posts and all in there it metioned Fuel Proofing. I know where and think that i know how, But what do i use?

Hi Skillet 92,

Epoxy thinned with alcohol, or dope straight out of the can work well. Make sure you proof the areas where fuel may leak from the tank, where residue may be forced by airflow as well as the obvious engine bay.

Cheers,

Colin

I use something called Balsarite because I have it around for covering planes also. A slow cure epoxy is best thinned by heating it a bit. Alcohol, while commonly recommended for thinning epoxy, occasionally causes curing problems, and also leaves the epoxy porous. If you want more information, do a google search on "west system epoxy thinning" (without the quotes). West Systems did extensive research to determine what works best.

Finishing resin is a low viscosity epoxy specially formulated for wetting fiberglass cloth. It should work pretty good as a fuel/oil proof paint. Be careful when heating uncured epoxy, especially a large amount of it. Heat accelerates the hardening of epoxy and epoxy gets hot on its own as it hardens. I have seen a couple of thermal runaways where the epoxy gets so hot that it starts to smoke and boil. Admittidly, this will not be a problem when you only mix a half ounce or so of it.

Paint

It's dead simple to apply.
You open the can and brush it on.
And it dries way faster than thinned epoxy.
(Some thinned epoxy NEVER cures or cures like rubber (if you use drugstore alcohol to thin it))

Where??????
On the firewall.
And inside the fuselage (behind the firewall) in the fueltank compartment and the areas immediately back from that tank compartment.

Why the firewall?
Because most ARFs aren't fuelproofed worth spit on their firewalls. There are often joints around the outside of the firewall that have poor coverage. The firewall often has an opening "through" it so the muffler can stay inside the cowl, and that's usually got incomplete fuelproofing along it's seams. Just because the front of the firewall looks like something has been painted on it for fuelproofing doesn't mean the something is adequate or has been adequately soaked into the seams. And if you make sure to paint in the hole through the firewall where the fuel lines come through, and you look to see your paint suck into that (often) raw plywood, or into that somewhat fuelproofed wood, you'll know why it's a good idea to follow up on the mfg's "fuelproofing".

Why inside the fuselage?
Someday the tank may leak.
For sure, the fuel line opening is going to allow oil/fuel into the fuselage if the firewall hole isn't sealed off. You're doing that with silicone seal, right?

Paint is good... Just make sure to use fuel-proof paint!

Thanks for the info. I knew to do in the engine bay but did not think of the tank area. I have good alcohal for cleaning my cars so i will go the the epoxy/achohal way. Never thought of paint, but that is a good idea for future projects.
P.S. Darock no i did the fuel line opening with the thinned apoxy and now realize that i can not easily remove them for repair LOL. That is why you said silicone. I have a C-160 Transall that i am building for the future when i learn how to fly so the things that i see on this one and read on here will only make that one better.(Don't know why i bought a twin when i have never flown anything, but i just love the look)