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As Oscar states below, a common practice many many years ago to make fiberglass
unusual shaped items such as air intake?boxes,?cabin air boxes,?fuel tanks etc
guys including myself used Dow Styrofom as the core or shape needed,
fiberglassed over it? and after cured? poured gasoline inside of it to dissolve
the foam out of it leaving a hollow tank or whatever. I never made a fuel tank
this way but I guess it would work ok as long as there weren't some weird
contaminates left in there to get into your fuel system. I would have to try
this on a very small scale before I would use this myself for a fuel tank. I
have used 3/16" pieces of klegicell foam to build fuel tanks. they are
fiberglassed on the inside as well as the outside. these are really good fuel
tanks but may weigh more than aluminum tanks.
Common practice in composite fuel tanks is to take a square 1/4" thick 1 1/2" X
1 1/2?piece of aluminum, hog out the foam tank bottom foam core a little larger
than these dimensions put wet?flox?into? the area around the edges of it,
fiberglass over it inside the tank and outside,?drill and tap for a fuel quick
drain to screw into it.? I like building? the top on last. this way you can
paint extra layers of epoxy or vinylester resin on the inside surfaces? of the
bottom and sides to make sure there are no pinholes to cause a leak. Then have
the top glassed and tacky wet, apply really wet flox to the top edges of the
tank and baffles if any are inside put the top on then put light weights around
to hold the top?in place until the resin has cured. Once cured sand edges
slighty rounded so the fiberglass exterior cloth can wrap over easily and lay
down flat. If my memory serves me I don't think fuel affects klegicell foam if
you were to get a tiny
leak. ?Some do this in reverse putting the bottom on last and have success but
I feel top last is more structural for holding the fuel weight and maybe or
maybe not more leak proof. It just seems to me it would be more leak proof.
.Larry Howell
Oscar said
As others have noted (or have discovered the hard way), the main caveat when
working with extruded polystyrene board is to keep any hydrocarbons, solvents,
or fuels away from it.? If you want to see a disappearing act, just get some
gasoline, MEK, or even spray paint near the foam board and *presto*!- it's
gone. In fact, this can be used to advantage when forming a fiberglass part
over a foam form.? When the layup is cured, just slosh a little gasoline around
inside it and the foam will dissolve away.
My M-19 is being constructed using the pink board and AeroPoxy laminating
resin, but the wet cell wing fuel tanks will use vinylester for fuel resistance.
Oscar Zuniga
Medford, OR
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