Hi Rowland,
I would suggest (if you haven't already) making sure to soak the tank with
fuel for awhile, before fitting and glassing it, since it will expand
slightly. Otherwise, the tank would swell and create pressure points, and
small clearances might change. I should have the fluorinated tank (circa
Nov, 2001), but how can one know 100%? I believe the fluorinated tank will
swell slightly, anyway. After having the tank swell with fuel for a few
months (while doing other things, I don't think it needs to be that long),
it was apparent that the large flat, unsupported, rear faces of the tank
wanted to bulge outward, due to the weight of the fuel. Thus, once
installed, the tank will probably have a tendancy to want to push forward in
the module, but hopefully the spacers will tame it, and keep it at bay. Just
before installing the tank, I had to heat the rear tank faces and clamp them
down with a sheet of plywood and 2x4's on both sides, to get it to want to
revert back to its proper form, and allow proper tank placement in the
module, for glassing.
Upon draining the fuel, I had the tank glassed in within a day or two, to
stay ahead of the shrinkage curve.
The two most important alignment points (top and bottom, not side to side)
were the clearance of the wing spars at the top of the tank, and the fuel
outlets touching up against the pitch tube at the bottom of the tank.
I simply got the shelf of the tank to go as high as it would go in the
module (or as low as it would go, if the module is upside down), and then
tipped the tank to clear the tank outlets touching on the pitch tube, and
allow a little extra for the rubber hose. It seemed to work well. My tank
sits slightly tipped.
Once the fuel remnants dried out of the walls, the tank outlets (with the
rubber and clamps installed) were rubbing up against the pitch tube, just
slightly, especially when cold. I am confident that the addition of fuel
will regain the proper clearance. There is at least 3-4mm (guessing) of dead
air space between the very bottom brackets and the tank (not the saddle
plies, but next to the fuselage bottom, where the brackets hold the tank up
off the floor of the fuselage), due to tank shrinkage. That should
approximate the extra clearance regained between the tank outlets and the
pitch tube, when the fuel is put back in the tank. In the meantime, I placed
a tie wrap on the rubber and clamp, so that the pitch tube would wear on it,
instead of the rubber/clamp (it was mostly centered on the metal clamp).
Nowhere, did I allow the plies to stick to the tank (using benefits of
others experiences). This was done by placing plastic or plastic tape
wherever the plies contacted the tank.
This should cure the dreaded tank crack in the saddle area, that others have
experienced, especially when draining the tank for extended periods.
It will also allow for easy tank replacement later. There are measurements
in my journal as to where to cut the top of the module, to allow clearance
to pull the old tank straight up and out.
Also, on the tough, first bracket for the shelf of the tank (top side), I
make an aluminum spring to hold it to the module. It is simply a piece of
aluminum about 1 inch wide (which I covered in saran wrap) that is curved
into an arc. A hole was placed on either side of the spring, and the arc
part faced the ply, and the sides of the spring were pressed down to the
module, where the small screws held the spring in place. This held the ply
flat against the module, across its entire length, and made that part of the
job real easy. For grins and assurance to keep the ply from moving, I also
peeled back the ply (which still had its plastic backing to keep the glass
---From bending out of shape), right before putting on the spring, and dabbed
small amounts of 4-minute epoxy on the module side of the bracket. That
toughest-to-do ply was the straightest and neatest one of all the plies on
the gas tank. Too bad it is the one that is the least visible :( .
Regards,
Greg Fuchs, A050
Tigard, OR
P.S. I am sorry about your loss, recently.
>I recall that the tank needs to be as high as possible ( when
>viewed with the assembly in the "flying mode") This is to ensure that
>the wing spars do not conflict with the ledge of tank which runs across
>the width of the a/c.
Bob - thanks for that reminder. I think I can check it without
actually going to the bother of re-rigging the wings to the cockpit
module
>I don't understand your statement " flush with the bottom of the cockpit
>module"? Do you mean "bottom" to mean the area which sits on the floor
>of the fuselage
Yes, I meant the part that will at the bottom when everything is right way
up.
>the radius of
>the tank bottom does NOT sit on the fuselage it sits on more lay ups
>between it and the fuselage bottom
I don't see any references in the manual to any layups under the tank
(when it is right-way-up) apart from the t-section ones I've
mentioned. The drawing in the manual shows the bottom of the tank
fairly much in line with the bottom of the baggage bay and seat parts
of the cockpit module.
regards
Rowland
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