On 8/12/2022 10:58 AM, svd via KRnet wrote:
After too long doing this - with leaks in 4 planes (longez, cavalier, osprey,
kr) one due to autogas softening and darkening in a seaplane tank when off in
the bush with no alternative, my advice would be to forget fiberglass tanks.
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Fiberglass tanks can be used successfully but require proper
construction and a great deal more caution in what fuel goes in to the
tanks. I built my tanks 27 years ago using Safety-poxy II and after
finding and repairing the initial leaks they have been trouble free.
The only exception was the sending unit to metal bracket cork gasket.
That had nothing to do with the glass tank. I burned a fair amount of
auto fuel in the early years but that was when ethanol free fuel was
easy to find and the purity could be trusted. I've only burnt 100LL in
recent years.
Given the problem I had with the fuel senders bolted to a 1/8" aluminum
plate, if I used aluminum tanks or aluminum plates in glass tanks
threaded to take a fitting, I would not thread anything thinner than
3/8" thick. Threads in aluminum plates, especially 1/8" stock, are very
weak and strip very easily. When the cork gaskets on my fuel sender
units started to weep fuel after 20 years I pulled the wings to replace
them. Several of the bolt threads stripped so easy that I couldn't even
feel the pressure when snugging them down. They just kept rotating
without getting tight. Given the situation, my easiest fix was to use an
overly generous amount of "pro-seal" in place of a gasket, use the
remaining bolts to hold it in place with a modest amount of mechanical
force and let the pro-seal cure. That seems sufficient to eliminate the
leak.
If doing it again I'd probably go with welded aluminum tanks to
eliminate having to "slosh" them internally and never having to hold a
tube of Pro-Seal. Only the Devil could have created the sticky crap I
used and the same stuff I had to work with on an RV10 fuel sender unit.
To me sloshing the tanks seems like building in another possible failure
point. Use the money you intended to spend on some spiffy interior and
leather seat covers and spend it on something beneficial.
Larry Flesner
P.S. I installed a 3/8" vent tube through each baffle near the top
surface of the wing to prevent airlock between baffles as the openings
in the baffles are quite small to prevent sloshing at lower fuel levels.
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