Sorry guys, missed a picture in the original post
Begin forwarded message:
From: Robert Borger <rlborger@mac.com>
Subject: Re: Europa-List: XS Fuel Tank Kiwi Mod
Date: March 30, 2014 at 5:13:40 PM CDT
Hi Fred,
I used Bud=92s instructions for the fuel tank replacement.
Andrew Sarangan and I sent our tanks out for heavy-duty fluoridation.
No, I did not make cuts before fluoridation.
Yes, to the stress concentrations caused by the fiberglass =93shelf."
My tank cracked right at the corners of one of those fiberglass layups:
In this view the top of the tank is off and you are looking down into
the port side of the tank. The crack is pretty well defined in blue and
is right on the corner of the outside, forward corner of the =93shelf.=94
Right at the 45=BA predicted by stress analysis.
Kinda/sorta, the fix is to provide support under the tank. The rear
=93shelf=94 is still there attached to the rear bulkhead which carries
most of the load supported on a layer of cork. There is also support
built under the forward part of the bottom of the tank. This is a thick
micro applied in lines upon which the tank was set (plastic wrap used as
a parting agent) and the micro allowed to cure. The micro was also
covered with cork. The micro is not to provide primary support only
secondary support should the gas soften the tank and allow some sag.
The micro would support the sag rather than sagging over the shelf
causing another stress riser.
The aluminum T shelf on the front bulkhead had a layer of urethane foam
bonded on top to support the ledge of the tank. This was also covered
with cork.
=46rom my (very limited) research on this issue it appears that tank
cracking is a combination of things. First, of tank softening due to
the absorption of fuel or solvents in the fuel. Second, softening
causing sagging. Third, stresses induced by sagging over a corner of
the fiberglass used to support the tank on the aft bulkhead. Fourth,
perhaps the tank becoming brittle and more susceptible to cracking by
removal of the fuel and subsequent evaporation of the fuel or solvent
---From the softened fuel tank material. I=92ve seen pictures of a crack
virtually identical to mine only on the starboard side. I also saw a
picture of a crack on the starboard side corner of the fiberglass
support in the tunnel area.
Some sort of support is needed under the tank to prevent the sagging
causing stress risers on the corners of the fiberglass. I=92m providing
support as suggested by Bud in his fuel tank replacement guide.
Bud has his fuel tank replacement instructions available on his company
website.
Being fulla questions isn=92t a problem. I just hope you can get
satisfactory answers for them.
Blue skies & tailwinds,
Bob Borger
Europa XS Tri, Rotax 914, Airmaster C/S Prop (50 hrs).
Little Toot Sport Biplane, Lycoming Thunderbolt AEIO-320 EXP
3705 Lynchburg Dr.
Corinth, TX 76208-5331
Cel: 817-992-1117
rlborger@mac.com
On Mar 30, 2014, at 1:39 PM, Fred Klein <fklein@orcasonline.com> wrote:
On Mar 30, 2014, at 10:53 AM, Robert Borger <rlborger@mac.com> wrote:
> Gentlemen,
>
> Having just replaced my fuel tank, I can speak to this issue. I did
the replacement with doors on & wings off. There is one issue in
fitting the new tank. The door sill on one side must be cut out to
allow the new tank to go in:
Bob=85sorry to hear that you=92ve had to go this, but grateful for your
insights into and photos of the process. When installing the new tank,
were you following any explicit instructions (from where/who?) as to how
best to support and secure the tank?
Did you consider having your tank treated w/ additional fluoridation
treatment? If so, did you make all cuts into the tank before sending it
off for treatment?
(It=92s been my understanding that the cracks were the result of stress
concentrations caused by the fiberglass shelf and supports bonding to
the tank; consequently I=92ve presumed that the =93fix=94, in addition
to the new tank itself, was to ensure there was a bond break or slip
sheet between the new tank and it=92s supports=85but perhaps I=92m
mistaken, and the brittleness and subsequent cracking is a consequence
of fuel interacting w/ the tank material alone, irrespective of
potential stress concentrations caused by portions of the tank being
unable to expand and contract=85?=85)
=85jus fulla questions, but tryin to get my head around this...
Fred
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