The Murphy Builders Site

Wayne

I saw the comment below in your discussion about re-sealing tanks and it

a question about the treatment of the top edges of the "bathtub".

When you do the bathtub, you say you should carefully prepare the top

how do you go about this? Do you put on an excess of Proseal in the

up over spilling onto the top edges and trim it down to the level of the
rib/bulkhead where the top skin will fit once it it has cured (or become
workable) so it is a nice continuous plane as you transition from the top
surfaces of the rib to the bulkhead?

Any concerns about adhesion of the next layer of Proseal (top skin)?

creating a filet against a substitute top surface make sense? I'm

one of the plastics which is very hard to bond to like automotive body

spreader material (polyethelyne or polypropylene).

In our case we intend to do the bathtub of both wings and call in the

for a (first) pre-closing inspection then close. Any thoughts about this
relative to adhesion of sealer to itself some time later (considering how

it took us to get this far on the first wing....

Still teetering on the edge of doing the first tank........

Thanks,

Dave R
Francine D.
Elite583.jcb.net

"Wayne G. O'Shea" wrote:

SNIPPED!

These bulkhead corners are the most common leakage area due to guys/gals

to put the top skin down and fill these areas in one process. It is very
important to have a cured (to semi-cured) "bath tub" created before

the top skin.

SNIPPED!
--
David A. Ricker P. Eng.
Fall River, Nova Scotia
Canada

Dave, that's what I said in the next part of the message....

""Build it up in the open corners between the rib and the bulkhead flange so
that the Proseal
sits proud at all corners and goes onto the top of the flanges and ribs.
Then when it has hardened somewhat use an exacto knife to trim JUST ABOVE
the bulkhead/rib flanges feathering to bare aluminum about 1/2" to 1" in on
the flange. This way you'll have a skim of proseal that is bonded to the top
of the flange and a solid platform for the proseal to squeeze against in the
area between the rib and bulkhead flange when you put the top skin down, so
there will be no pin holes or leakage from the rear bulkhead. You should
also need to take a drill bit to clean out the first hole or two on each
bulkhead flange for the rivets before putting down the top skin, as it will
be filled in with Proseal if you did the corner filling sufficiently.""

If you are building "new" you should have a fillet inside and outside on
this rib to bulkhead junction (and your outboard rib flanges at the main
spar, as well as the lower perimeter of all ribs and bulkheads) as that way
if you missed a pin hole inside it shouldn't be able to get further than
under the flange and the outside dyke will stop the leak. The important
thing before starting is that you have to have WELL scotchbrited areas on
all sides of the junctions for adhesion to the bare aluminum, otherwise it
will just leach by between the proseal and the smooth dirty aluminum. The
above "Build it up...." instructions are referring to the open corner at one
end of each bulkhead, where there is a gap between the flange and the back
side of the rib, that you need to keep coming back to while your working the
fillets around the tank until it is staying "proud" of the flange and you
have built a "bridge between the rib and the flange. The other important
area is a good coat of proseal BEFORE you slip the bulkhead flange into
place under the rib flange at the other end of each tank rear bulkhead. This
is a MUCH neglected area as well and you should get a gob in there while
putting the rear bulkheads in at the early stages of construction and this
is also why the Super Rebel tanks are MUCH easier to build and seal than the
little Rebel/Elite tanks, as they just use the rear spar for the back of the
tank.

I haven't had any trouble with adhesion or leaks in any tank since my very
first one (and it even has normal RV1410 rivets in it - not tank rivets!)
and that wasn't an adhesion problem, just missed a "slump away" from my top
forward stringer on the outboard rib.

I have left the top skin un-sealed for as much as a year and a half (cleco'd
in place to keep the dirt out) and then made sure everything was
scotchbrited and clean and then sealed down with no problems. This includes
a very light rub on the proseal areas to get rid of the shine to allow the
next coat to bite into it.

My concern with using a "dummy" lid would be that you would get a perfectly
smooth surface when you removed it, making it even harder for the new
Proseal to bond to it. It is also liable to pull the proseal somewhat when
you remove it and this might cause your "bridge" to lift away from the top
surfaces of the bulkhead flanges slightly and if you miss this it will end
up being a leaching area.

If I get some time today I will look through some of my 2 or 3 thousand
pictures of these things going together and see if there is a clear one of
the "bridge" I refer to. In the mean time I have to get my ass outside
(-21*C and gusting 45Knots), see if the tractor/snowblower or the backhoe
will run and remove another foot of snow from the laneway. I'd sure like to
get ahold of the "idiot" that built this house 1400 feet from the concession
road (Oh yah, that was me!!). I took a foot and a half out yesterday
afternoon and another 6" the day before. Ron if you are looking for some
deep snow to test those skis out in just head West for 2 hours!! I've had
enough of winter already and think it's time to head back to Grenada. It
didn't snow there at Christmas (mind you it did pour all day Xmas day 'till
the roof's leaked!!)

Cheers,
Wayne G. O'Shea
www.irishfield.on.ca

----- Original Message -----
From: "Dave Ricker" <ricker@dbis.ns.ca>
To: <murphy-rebel@dcsol.com>
Sent: Sunday, January 12, 2003 10:00 AM
Subject: Re: Repairing leaking fuel tanks <after> removing top skin

Wayne

I saw the comment below in your discussion about re-sealing tanks and it

brings

a question about the treatment of the top edges of the "bathtub".

When you do the bathtub, you say you should carefully prepare the top

corners,

how do you go about this? Do you put on an excess of Proseal in the

corners and

up over spilling onto the top edges and trim it down to the level of the
rib/bulkhead where the top skin will fit once it it has cured (or become
workable) so it is a nice continuous plane as you transition from the top
surfaces of the rib to the bulkhead?

Any concerns about adhesion of the next layer of Proseal (top skin)?

Would

creating a filet against a substitute top surface make sense? I'm

thinking of

one of the plastics which is very hard to bond to like automotive body

fill

spreader material (polyethelyne or polypropylene).

In our case we intend to do the bathtub of both wings and call in the

inspector

for a (first) pre-closing inspection then close. Any thoughts about this
relative to adhesion of sealer to itself some time later (considering how

long

it took us to get this far on the first wing....

Still teetering on the edge of doing the first tank........

Thanks,

Dave R
Francine D.
Elite583.jcb.net

"Wayne G. O'Shea" wrote:

SNIPPED!

These bulkhead corners are the most common leakage area due to guys/gals

trying

to put the top skin down and fill these areas in one process. It is very
important to have a cured (to semi-cured) "bath tub" created before

putting down

the top skin.

SNIPPED!
--
David A. Ricker P. Eng.
Fall River, Nova Scotia
Canada

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