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Homebuilt Fuel Tank ("Cell") Design and Fabrication

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Vigilant1

Well-Known Member
Supporting Member
Joined
Jan 24, 2011
Messages
10,596
Location
US
I'm interested in designing and building a fuel cell that provides a measure of protection about the same as the commercially available models for amateur racing. I've looked at the off-the-shelf designs and they don't seem to fit the bill on at least two counts: They'll never exactly fit the very limited, precious "good spots" in the airplane (every cu inch not used is a bit of fuel left on the ground, and it adds up), and these things are pricey (I can only imagine what these companies pay for lawyers and insurance, and it's all reflected in the prices).
I'd also like the tank to be resistant to current and likely future fuels/fuel additives. That's a tall order, since no one quite knows what good idea the government will mandate next.
Current thoughts:
- Tank:
-- Inner layer: A welded AL inner tank (more fuelproof than any plastic, rubber, etc. Light, reasonably tough).
-- A hand-built elastomeric layer on the >>outside<< of the tank. Maybe fairly thick sheet rubberized compound heat-glued at the seams, or a liquid product that will form a sheet but remain flexible, perhaps with fibers included to improve tear resistance. This is to provide a backup flexible fuel containment "bag" if the rigid tanks are compromised by crushing, and the flexible nature of the material may reduce the amount of leakage if there's a piecing intrusion of the tank. Also, the flexible layer provides some mechanical isolation between the rigid layers so a break/crack in one isn't propagated to the other.
-- A composite "toughbox" on the outside. Probably Kevlar composite with whatever epoxy matrix seems to have the best chance of surviving the most likely fuels, if needed.
- Fittings: self-closing breakaway hose fittings (vent and supply, return also if using EFI) and a robust filler port.
- Other:
-- "Safety foam" in the tank. I'm on the fence on this--I'm not sure any of it is 100% compatible with real fuels and additives, and a fuel filter clogged with "foam goo" doesn't make for safe flying. I'd go with expanded AL "foam" if I thought I'd be taking hostile gunfire, but I don't.
-- Fuel bladder: Putting the flexible, collapsing "bag" inside the inner tank has many advantages (reducing flammable vapors, etc). But successful home-fabrication and fitting of such a bladder seems unlikely, and the questions of resistance to present and future fuels would remain. The constant flexing/folding of these bladders increases the likelihood of eventual (undetected) failure with potential trapped/unusable fuel issues, etc. So, in a perfect world I'd like bladders, but as far as I can tell their negatives outweigh positives in this application.

Thoughts, criticisms, open laughter?

Mark
 
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