Fred,
We all learned the hard way that the tank really bonds well to the
glass. Your advise is sound.
The point that the floor is not strong enough to hold the whole tank is
important!
The method I use has a shelf that glasses the tank aft support to the
floor and the back wall.
I do not glass the saddle but only up the sides a bit to assist in side
to side motion.
The front of the tank must be supported also, but not solely by a wedge
of foam or filler, it must be a glass beam.
Typically the tank will set 1/2 to 3/4 inch off the floor. That area is
filled in most cases with expand cell, smoothed and then glassed over to
provide a beam support.
Of course the forward ledge is a good support for the top of the tank as
is.
As you all know I use a thin cork or similar (one of my clients used
felt) to allow the tank to move as it expands and contracts with fuel to
try to prevent stress risers.
Also it is imperative that the tank be wedged in with the forward tank
supports, as well as foam on the sides, front and top to keep it firmly
in place.
Should one have followed the assembly manual (as one would think we
should) and the tank sag becomes apparent, I have filled the area
between the tank and the floor with foam to spread the load out a bit.
It is only a band-aide and not a cure. Someone asked if the forward
wedge could be glassed to the tank, and I don't believe that is sound as
it would become another stress riser now on the forward side.
Bottom line, Do not just let the tank rest on the floor.
Andrew,
The wrap around the tank only holds it from fore and aft movement as you
said but foam will do that also. Something has to hold that 120 lbs of
fuel and tank at 6+ gs. The glass aft bulkhead and T in the front will
do it, but not without a sag on that front edge. I thought about a
floor pan under the tank and a uni strap diagonally from the top rear
bulkhead to the pan to hold the front of the tank early on, but a simple
glassed beam on the floor is all that should be necessary. Make your
forward T on the bench and let it cure (make a mold) then Redux to the
front. On the aft saddle and bulkhead, put a layer of thin release
plastic on the tank ( I put cork on the tank also) and make your bracket
tapes per the book. Put the cockpit module in (I have the advantage of
a ceiling hoist so it is easy for me to say) and check the position and
mark the tank outline. Remove the tank and make a aft bulkhead to belly
support as well as a line under the front of the tank about 2 inches
wide of expand cell or similar and cover with release plastic. (You
noticed the flexibility of the module, so a strap of glass to hold the
bulkheads vertical is fairly smart.) Set the module in place and allow
the expand cell to cure. Pull the module again (repetitive isn't it)
and check, fill voids and smooth in preparation for 2 layers of glass
over the expand cell or filler. Set the module in again and once
assured it is all comfy, you are ready for bonding. In the 5 years 12AY
has had its tank, it has been left full of fuel, empty, and every sort
of load between and the support I have has left the tank still looking
like new, no sags in the floor or belly and has served me well. My tank
is the new style tank which is a bit thicker, reinforced and holds just
a bit more fuel somehow. The top is nice and flat for a change. Older
tanks are thinner and do bulge as many have commented on.
Just my two cents.
Regards,
Bud Yerly
----- Original Message -----
From: Fred Klein<mailto:fklein@orcasonline.com>
To: europa-list@matronics.com<mailto:europa-list@matronics.com>
Sent: Friday, December 06, 2013 2:02 AM
Subject: Re: Europa-List: Alternative fuel tank mounting?
On Dec 5, 2013, at 10:36 PM, Andrew Sarangan wrote:
No, the straps will not be bonded to the tank, just to the baggage
bay
wall. The side of the strap facing the tank will have a neoprene
pad,
so there will be some 'give' to accommodate small expansions.
Andrew...if I had it to do over again, I would attempt to ensure that
the underside (including the "ledge") is fully supported yet free to
expand and contract...I would install all the tapes to the CM which are
called for, but I would provide a cushioned bond-break between the tape
and the tank. In my attached build-photo, the FG tape was regrettably
bonded to the tank.
Fred
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