I remember Nigel Charles who refered some years ago to the augmentation
of the fuel capacity in the tank. In the beginning I toppled at 68
litres and now after 120 hours at 70 litres. Where will it end?
Karel Vranken.
----- Original Message -----
From: Karl Heindl
To: europa-list@matronics.com
Sent: Thursday, May 01, 2008 1:37 AM
Subject: RE: Europa-List: Fuel tank - bulges and leakage.
When I inspected my tank a couple of years ago I noticed that the back
wall had buckled inward, probably reducing its capacity somewhat. This
may well have happened on other Europas, but unless you have a large
opening at the top you would never see it. I have an opening for the
fuel level probe,
which allows me to get my whole arm into the tank. I was considering
constructing some sort of internal framing, but couldn't come up with a
good solution.
Karl
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>
>
> So, what you're saying is that the tank "grows" as it swells and
will do
> so inwardly if not allowed to, outwardly. Hmmmm, that's something I
> hadn't considered. I'll have to rethink my solution. Thanks for the
> information, Svein. Please keep us up to speed on any additional
> information you should get...
>
> Jeff - Baby Blue
>
> Sidsel & Svein Johnsen wrote:
> > <sidsel.svein@oslo.online.no>
> >
> > All,
> >
> > Preventing the tank from bulging too much forward will of course
prevent
> > it touching any of the controls or the wing spar (in which case
the
> > strap on the left spar might catch on the bulge during
> > withdrawal/installation).
> >
> > The inherent problem with high density polyetylene (HDPE) without
any
> > barrier layer (which automobile tanks have, and the newer Europa
tanks
> > may have - this is now being looked into) is that it is permeable
and
> > components of the fuel get into the material and causes it to
swell (and
> > some gets through the tak walls and gives the typical "Europa
smell").
> > Where the material is thick, as in the edges between the bottom
and
> > sides, sides and top, and sides to sides, the swelling is
apparently
> > negligible. This swelling cannot be stopped as such, so if the
tank is
> > prevented from buckling forward at all, it will bulge only
inwards.
> > This will probably not be one single large bulge in each panel,
but
> > smaller "wrinkles" that another contributor reported yesterday
---From his
> > findings along the top and the back (where outward bulging is
restricted).
> >
> > The best, given this undesired but unavoidable swelling, would be
if the
> > tank were of a simpler shape (say like a box without indentations
and
> > the saddle) and if we had no spacers to keep it away from the
controls.
> > Typical hard points as the saddle and the outlets at the bottom
appears
> > to be where cracks are developing in some cases. Even though the
fuel
> > components entering the permeable material also acts like
softeners,
> > local faults in the material may cause overstressing (e.g. thinner
than
> > intended material due to the fabrication process; maybe
insufficient
> > heating during the moulding).
> >
> > The spacers installed according to the Builders Manual could be
typical
> > danger areas as far as cracks. However, both on Arnold's tank and
mine
> > (which shows far less bulging - yet), the wave form of the bulging
> > across the width of the tank is such that there is an inward bulge
right
> > behind the spacers and a forward bulge on either side. It is easy
to
> > envisage the stress that would be introuced if a spacer were
installed
> > where the tank naturally wants to bulge forward.
> >
> > So, based on what I have observed and learned about the tank
material in
> > these last few days, I would carefully evaluate where to stop the
tank's
> > bulging. Newer tanks have a stiff rib or indentation running
across the
> > front, which should help (one such installation will be inspected
> > shortly by another owner).
> >
> > As for those still in the appropriate build stage, I would shape
the BM
> > spacers differently: Build the plate of thicker material, oval
instead
> > of rectangular (with long axis horizontal) and shape its thickness
> > markedly convex (thich in the center, thinning towards a well
rounded
> > circumference).
> >
> > I am in contact with a polymer expert at a central Norwegian
scientific
> > institute. His immediate comment is that HDPE does not "dry out"
if the
> > tank is left empty, but I am awaiting his further comments to a
host of
> > follow-up questions with relevance to our particular tanks and how
we
> > operate our airplanes. Temperature definitely plays a part in the
> > swelling. The hotter, the faster it swells, but I am still
awaiting to
> > hear from him whether HDPE swell more (higher maximum swell
elongation)
> > in hot weather than in cold. He also mentioned that the particular
fuel
> > used may play a role. When a major fuel supplier here introduced
> > unleaded 98 octane mogas several years ago, it was found to
"attack"
> > polymers more aggressively than the previously used auto fuel did
(we
> > use unleaded 95 octane mogas in our Europas here in Norway).
> >
> > What I really hate about this issue is not knowing whether I have
spent
> > 10% or 90% of my tank's safety margin with the present bulging,
and what
> > does say 5mm more bulging translate into as far as approaching a
crack
> > somewhere?
> >
> > Regards,
> > Svein
> > LN-SKJ
> >
> >
> >
> >
> >
> > =====================
>
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>
>
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