Gidday,
I am hoping someone has a more definitive way of preserving the tanks we
have, those that have only built as per the manual. I get in trouble
---From my Europa Dad for not following the manual, and in fact I often
don=92t know where it is, but in this case it seems like it was a
mistake to not perceive a threat of the tank splitting over time. Mine
is in, and whilst I know of low expansion foam squirted in underneath
the tank in situ, I am hoping someone may have come up with another,
better and less messy solution.
Even with the Expanding foams, I am hoping to get a suggestion of the
best type to use, which of itself probably creates for me a problem
because I=92ll have to get it out of the US no doubt, or UK, and get it
home to Aussie somehow. We seem to have a very limited range of
expanding foams, down under. So, any advice much appreciated, as always.
Regards
Tony Renshaw
On 31 Mar 2014, at 9:13 am, Robert Borger <rlborger@mac.com> wrote:
> 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:
>
> <IMG_6973_em_s.jpg>
> 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.
>
> <IMG_7231_em_s.jpg>
>
>
> =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
|