Installing brass hardware into composite fuel bays

[Greg Reid]

I'm looking for tips on a proven, lightweight, leak-free, and
long-life installation of threaded brass fittings into my composite
fuel tanks. I have the typical fuel finger strainers, fuel sump, and
other threaded hardware to install. The strainer and sump may need to
be removed and reinstalled on occasion.

The obvious way is to use 1/4-inch or thicker phenolic, drilled and
tapped for the hardware. Scuffed phenolic would certainly give a nice
permanent bond with the epoxy, but I've heard that some folks who have
gone this route have had trouble later with the threads stripping in
the phenolic.

Another builder suggested that I use a 1/4-inch brass strip. I'm not
sure how well brass will bond with epoxy, and it's awfully heavy.

Aluminum is another possibility and certainly lighter, but another
recent thread in this newsgroup cautions about the difficulty of
getting a permanent epoxy bond with aluminum.

Titanium, magnesium, other? Of course if metal, it has to be
compatible with brass.

Thanks,
Greg

[Sean Trost]

Greg,
How about a phenol plate bonded in to the tank. Then turn a bung with a
flange sufficient to seal and bolt to the plate. Tap the bung, install
the fitting. If it should ever stip out replace the bung and retap.

Did this as a repair on a poly tank in my jeep. Trouble free for two
years now. (without the phenol panel tho).


All the best
Sean Trost

Greg Reid wrote:
> I'm looking for tips on a proven, lightweight, leak-free, and
> long-life installation of threaded brass fittings into my composite
> fuel tanks. I have the typical fuel finger strainers, fuel sump, and
> other threaded hardware to install. The strainer and sump may need to
> be removed and reinstalled on occasion.
>
> The obvious way is to use 1/4-inch or thicker phenolic, drilled and
> tapped for the hardware. Scuffed phenolic would certainly give a nice
> permanent bond with the epoxy, but I've heard that some folks who have
> gone this route have had trouble later with the threads stripping in
> the phenolic.
>
> Another builder suggested that I use a 1/4-inch brass strip. I'm not
> sure how well brass will bond with epoxy, and it's awfully heavy.
>
> Aluminum is another possibility and certainly lighter, but another
> recent thread in this newsgroup cautions about the difficulty of
> getting a permanent epoxy bond with aluminum.
>
> Titanium, magnesium, other? Of course if metal, it has to be
> compatible with brass.
>
> Thanks,
> Greg

[Marc J. Zeitlin]

Greg Reid asks;

> Aluminum is another possibility and certainly lighter, but another
> recent thread in this newsgroup cautions about the difficulty of
> getting a permanent epoxy bond with aluminum.

Every composite canard aircraft out there uses aluminum hardpoints for
NPT threaded attachments into the tank, for the wing bolts, etc. I've
never heard of any of these (2000+ aircraft) leaking or failing.
Corroding, maybe, on one or two Vari-EZ's that live near the ocean, but
that's about it. The aluminum used for the tank drain mount points is
completely buried - only the threads get exposed, and only until the
fitting is screwed in.

Data's worth more than theory.

--
Marc J. Zeitlin
http://marc.zeitlin.home.comcast.net/
http://www.cozybuilders.org/
Copyright (c) 2004

[Don Hammer]

Greg,

I've made some repairs to German built gliders in the past. One
installation I have seen from the factory is to take a section of
brass rod approx 3/8" in diameter and drill and tap it. Knurl the
outside with a lathe and bond it in with the same epoxy as the
structure. No way will it pull out. If the threads happen to strip,
insert a helicoil.

All this is predicated on having thick enough material to make it
work.

[Leon McAtee]

(Greg Reid) wrote in message >...
> I'm looking for tips on a proven, lightweight, leak-free,
>
> Aluminum is another possibility and certainly lighter, but another
> recent thread in this newsgroup cautions about the difficulty of
> getting a permanent epoxy bond with aluminum.
>
> Thanks,
> Greg

While it's true that yo can't get a reliable structural bond to
aluminum without proper etching there are lots of planes flying with
many hours, and years, using aluminum "welding flanges" for fuel tank
fittings. Just drill several holes in the flanges and use plenty of
flox to bed them in.

Unless you plan to be bending on the fittings on a regular basis they
should remain leak free as they have proven to do for others.
============================
Leon McAtee

[Greg Reid]

Thanks very much for all of the helpful responses, folks. OK, I'll go
with 3/8 aluminum -- drilled and etched and bonded in place ASAP after
the etching.

Regards,
Greg

[Dan Thomas]

(Greg Reid) wrote in message >...
> Thanks very much for all of the helpful responses, folks. OK, I'll go
> with 3/8 aluminum -- drilled and etched and bonded in place ASAP after
> the etching.
>
> Regards,
> Greg

For my glass tank I brazed brass pipe fittings to a 2" x 4" steel
plate (20 gauge) that had a few holes punched in it, and bead blasted
the plate before bonding it it, glassing all around it. Hasn't leaked
in 8 years.

Dan