OK,
I have fuel proofed before using Fiberglass resin, but that included sealing the tank into the firewall. On my 4*, the tank sits behind the firewall and I want to run 3 lines through the firewall. I want to seal the firewall though, and still be able to pull the lines through the wall. Any ideas?
Here is what I was thinking of doing: Take three lines and spread some vaseline or aquaphor around the outside and slip them into the holes in the firewall. Next, pour the resin in and let it harden around the tubes, then I can pull the tubes in or oout and let the vaseline make a grease seal to keep the fuel in the engine compartment.
What do you think?
Thanks,
Curtis

You drill the holes in the fire wall just big enough for the fuel lines first then mix epoxy with alcohol to thin it then use it to fuel proof the fire wall. You can also use finishing epoxy if you want. Then you pull your lines through A nice tight fit. If that still isn't good enough you can use silicone to go around your fuel line at the fire wall.

Gray Beard,
So you suggest not applying the epoxy or surfacing resin while the lines are installed in the holes? That makes sense, I guess I was just worried that the resin would build up in the holes in the wall and not allow me to pull the lines through. Maybe while the resin is setting up, I can run a few Q-tips around in the hole to wick up any residual liquid.
Thanks,
Curtis

You're making it too hard.

Drill the holes. Run the fuel lines through. Seal the firewall. Done.

So you get some epoxy on the fuel lines............... so?

You planning to take the tank out every weekend? You don't like epoxy on the first 1/4" of fuel line sticking out through the holes? Is that going to ruin the model?

By the time you need to take that tank and fuel lines out........... you'll want to replace the lines anyway. You trying to save that 6" of fuel line for the 2nd tank you put in this model 5yrs from now?

Get er dun!!

I just whack some silicone around the hole if I am worried. But to be honest, if you choose the right drill bit and get a snugg (but not tight) fit than simply sealing the firewall with whatever product you use should be enough. Never had anyproblems with the latter.

Maybe I'm just an odd ball but I fuel proof my tank area, inside the fire wall and any holes that fuel or fuel vapor can seep into?? I also have some very old airplanes that are still flying and get rebuilt and recovered every now and then. Anal may be another term used?? I even fuel proof the outside sheeting behind the fire wall about an inch or two. Yep, maybe anal is the correct term.

Yeah, that is my concern, I want to be able to put the tank in and make sure that if any raw fuel runs around in the engine compartment, it doesn't leach into the area where the tank is and weaken the wood there. I don't want to put it in and take it out all of the time, but I need to pull it in from the back(4* 40) and I expect it to be pretty tricky if the fit is tight. I forgot that Ii could just use a little silicone around the lines.
Thanks for the responses,
Curtis

Shoot, I go a good inch back on the outside, the whole tank bay, around landing gear mounts and a good bit of the wing bay if not all of it. Anywhere oil will seep in gett a once over. I thin mine down pretty good to make the coat pretty light, as I get near the end of the mix and most of the alcohol has flashed off I go back over the main spots I want protected.
The planes seem to last longer when I do all of this.[8D]

I'm not saying you shouldn't seal it up. I seal up inside the fuse as well. I seal the back of the firewall and the entire tank compartment. Seal the chin area to keep exhaust oil from leaking into the wood.

Standard glow fuel line fits perfectly snug through a 1/4" hole (or was it 3/16" ?). Drill the holes. Run the lines out and slap some epoxy on with an acid brush. Done. Takes 15 minutes.

I use water based polyurethane for the firewall exterior and the fuel tank area's interior. Easy clean up, no stink and it is fuel proof enough for me. Just slather it on, spread it around to thin it a bit and then wait a day or two and do it all over again. Done. No hurry because of the time limit with epoxy, no ruined shirts or pants and no additional exposure to epoxy which will eventually sensitize you to it and make it impossible to use unless you like visiting the hospital's emergency room. This applies to everyone. Everyone has a limit to how much epoxy that they can use in their life time. Why use it up on non structural construction chores? Ditto CA.


Ed Cregger

Before fuelproofing... I mark prop-shaft centerlines (both vertical and horizontal) on the firewall. Then I write (fine point sharpie) the motor thrust angles on the firewall as well. Careful not to write where drill holes are.

Then.. mix up 30 minute epoxy. With a heat gun the epoxy mix thins to water consistency, and spreads very well. It dries nearly clear, leaving all the marks/writing I made earlier permanent.

Even if you spread the expoxy into the fuel line holes, and it builds up too much to get a fuel line through... you can always run a drill through it again to clear it out enough... Even though the heating/thinning may weaken the strength of the epoxy, you're using as a sealing agent, not as a structural enhancement..


I tried fuel-proof paint on my first plane... yuck... wouldn't cover, needed several coats... Not worth it... The near clear epoxy looks way better.. IMHO....

Picture: Even though I built this STM for electric power, I fuel proofed the firewall and engine bay. I really think making center lines, and writing down thrust angles is a good idea.. Even if I do say so myself...

I just dip the entire model in a huge tub of epoxy.







Nah, just kidding!

On the subject of fuelproofing I offer a warning that came in my SIG Sumthi' Extra kit. "Don't fuelproof anywhere that will be covered on the other side before covering." In other words, do the covering job then fuelproof the other side of the strusture. They claim that the covering won't adhere to an area thet has had its other side coated with a sealer like epoxy or any other fuel proofing product. The reason is that the balsa needs to breath through to the other side and cannot do that if the other side is sealed. So cover first, then fuelproof.