Tank skin overlap

[Jesse Jenks]

I am confused about the area where the tank skins overlap onto the main
skins, and the tank bulkheads. On the bottom of the wing does the mian skin
go between the tank bulkheads and the tank skin, or is it trimmed short of
the bulkheads?
Thanks
Jesse





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[mbetti]

I seen the same confusion in my build. I took advice from group and the tank skin whether top or bottom goes on last, not in between anything. Search the arcives for wing building a couple months ago. The tank skin will overlap the main skin by 2 rows of rivets. The tank skin should have 3 rows of rivets at bottom and side of each, with 2 rows overlaping the main skin and one row for attaching to tank bulkheads. The main skin is short of the bulkheads. The idea is that you can put the main skin on after the tank has been finished and you can check for leaks on the sides. Put some scraps of sheet in between the tank skin and ribs or spar where it overlaps to prevent sealant from filling in. Put some wax on them so they don't stick to proseal. You can rivet the main skin and tank skin on the first one but leave main skin off on the other. It was either Al or Ralph that wrote me pretty lengthy on the procedure. I'm at work and going by memory here. If you still have issues let !
me know and I will put my remembering hat on for a while.
Mike Betti

On Fri, 08 Jul 2005 12:29:28 -0700, rebel-builders@dcsol.com said:

I am confused about the area where the tank skins overlap onto the main
skins, and the tank bulkheads. On the bottom of the wing does the mian skin
go between the tank bulkheads and the tank skin, or is it trimmed short of
the bulkheads?
Thanks
Jesse





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[Jesse Jenks]

Another question: If you rivet the top tank skin on before the main skin and
LE skin in order to pressure test, what happens at the mail spar where the
LE skin is supposed to overlap on top of the tank skin? I am obviously
missing something here.
Thanks
Jesse





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[Mike Betti]

Put proseal down on the main spar, put tank lid on, put more proseal on tank
lid, put LE skin over tank, rivet in across tank area, just cleco remainder
of LE skin. Put a piece of waxed sheet metal (2"X2" piece) under the tank
skin corner where the main skin needs to sneak under later. You are going to
have to put several more of these pieces in at each stringer and also at a
couple ribs, anywhere where you can see the main skin needs to go under
later. Also the stringers will go on with the tank lid. I don't remember if
you put the bottom or top skins on first, I followed the manual on that one.
I believe it was the bottom. I think what I did was put the bottom tank
lid/main skin on with proseal, just riveted the tank area, rest in clecos.
Then flipped wing over as soon as done riveting tank and worked on getting
the stinger seal plates riveted and brushed with proseal. Although you
should get those plates in right away, usually you can reach under neath to
get them in place. That's also a better position for proseal drying to help
keep it in the joint. I used the B-product to assemble and then after it set
somewhat, I mixed up some A-product and painted all joints from bottom side.
I used about a 2" paint roller to apply B-product and used a flux brush to
smoothen out. With the roller, when you are rolling if you don't seen any
sticking after going over a piece, you know it's contaminated. Then after a
week I finished riveting the main skin on and started on the top closing.
The first half of the closing is easy, the other half is harder, trying to
sneak that main skin in after is a real pain!
Look at my website at the wing pictures www.mikeselite.com
Let me know if you need more.
Mike Betti
771E


----- Original Message -----
From: "Jesse Jenks" <jessejenks@hotmail.com>
To: <rebel-builders@dcsol.com>
Sent: Friday, July 08, 2005 3:01 PM
Subject: Tank skin overlap

Another question: If you rivet the top tank skin on before the main skin
and
LE skin in order to pressure test, what happens at the mail spar where the
LE skin is supposed to overlap on top of the tank skin? I am obviously
missing something here.
Thanks
Jesse





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[Jesse Jenks]

Thanks Mike,
Thats all very helpfull information. I was having trouble visualizing how it
all goes together, but your dscription has clarified it I think. I have been
looking at your website already.
Thanks again
Jesse

From: "Mike Betti" <mbetti@up.net>
Reply-To: <rebel-builders@dcsol.com>
To: <rebel-builders@dcsol.com>
Subject: Re: Tank skin overlap
Date: Fri, 8 Jul 2005 18:51:06 -0500

Put proseal down on the main spar, put tank lid on, put more proseal on
tank
lid, put LE skin over tank, rivet in across tank area, just cleco remainder
of LE skin. Put a piece of waxed sheet metal (2"X2" piece) under the tank
skin corner where the main skin needs to sneak under later. You are going
to
have to put several more of these pieces in at each stringer and also at a
couple ribs, anywhere where you can see the main skin needs to go under
later. Also the stringers will go on with the tank lid. I don't remember if
you put the bottom or top skins on first, I followed the manual on that
one.
I believe it was the bottom. I think what I did was put the bottom tank
lid/main skin on with proseal, just riveted the tank area, rest in clecos.
Then flipped wing over as soon as done riveting tank and worked on getting
the stinger seal plates riveted and brushed with proseal. Although you
should get those plates in right away, usually you can reach under neath to
get them in place. That's also a better position for proseal drying to help
keep it in the joint. I used the B-product to assemble and then after it
set
somewhat, I mixed up some A-product and painted all joints from bottom
side.
I used about a 2" paint roller to apply B-product and used a flux brush to
smoothen out. With the roller, when you are rolling if you don't seen any
sticking after going over a piece, you know it's contaminated. Then after a
week I finished riveting the main skin on and started on the top closing.
The first half of the closing is easy, the other half is harder, trying to
sneak that main skin in after is a real pain!
Look at my website at the wing pictures www.mikeselite.com
Let me know if you need more.
Mike Betti
771E


----- Original Message -----
From: "Jesse Jenks" <jessejenks@hotmail.com>
To: <rebel-builders@dcsol.com>
Sent: Friday, July 08, 2005 3:01 PM
Subject: Tank skin overlap

Another question: If you rivet the top tank skin on before the main skin
and
LE skin in order to pressure test, what happens at the mail spar where

the

LE skin is supposed to overlap on top of the tank skin? I am obviously
missing something here.
Thanks
Jesse





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[Jesse Jenks]

I have all the skins clecoed on my first wing. Last night I drilled the
extra rows of holes around the bottom tank skin. I drilled one extra row of
holes between the stringer and tank bulkheads. I have about 1" of the tank
skin overlapping beyond the stringer. There is a picture on the archives
that shows the tank skin overlapping aft of the stringer with an additional
row of rivets, but the manual does not show this. Is it common to do it that
way, or should I just trim the tank skin up to the stringer as the manual
shows?
On the outboard edge of the bottom tank I seem to have minimal overlap. I
ended up with about 11/32" between the two extra rows after allowing 5/16"
edge distance from the tank skin, and the estimated trim line of the main
skin which has not been cut yet, but will have to be trimmed so as not to
interfere with the tank rib, and also have enough edge distance for the skin
overlap rivets. I was considering staggering the two rows if they got too
close. I may have to on the top of the wing as I think I have even less
overlap in that area. Has anyone had this concern?
I have 4 bay tanks, and so at the outboard solid rib on the bottom of the
wing where the tank skin, leading edge skin, and main skin all overlap on
the main spar I also have a corner of the skin doubler for the strut attach
area overlapping. This seems like a lot of layers (5 including the spar) I
was thinking of trimming the doubler to go around the corner of the tank
skin instead of over it. Can someone with 4 bay tanks comment on this?
Thanks.
Jesse





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[Ken]

Jesse Jenks wrote:

I have all the skins clecoed on my first wing. Last night I drilled the
extra rows of holes around the bottom tank skin. I drilled one extra row of
holes between the stringer and tank bulkheads. I have about 1" of the tank
skin overlapping beyond the stringer. There is a picture on the archives
that shows the tank skin overlapping aft of the stringer with an additional
row of rivets, but the manual does not show this. Is it common to do it that
way, or should I just trim the tank skin up to the stringer as the manual
shows?

It seems that every Rebel I see has a slightly different tank skin. As
long as you have two rows of rivets with the correct edge and pitch
spacing you should be fine. Ideally you'd want to be able to cut the
main skin back far enough so that it doesn't interfere with a good
fillet of proseal along the tank exterior. As it happens I joined the
two skins at the stringer line and with one more row of rivets behind
the stringer line but I don't believe that is common.

On the outboard edge of the bottom tank I seem to have minimal overlap. I
ended up with about 11/32" between the two extra rows after allowing 5/16"
edge distance from the tank skin, and the estimated trim line of the main
skin which has not been cut yet, but will have to be trimmed so as not to
interfere with the tank rib, and also have enough edge distance for the skin
overlap rivets. I was considering staggering the two rows if they got too
close. I may have to on the top of the wing as I think I have even less
overlap in that area. Has anyone had this concern?

Yes. I gave up and made up new larger tank skins. Larger in both
directions. Perhaps extreme but it sure made me more comfortable and
gave more room to assemble everything. IIRC you want at least 1/2" of
rivet to rivet spacing. 11/32 of row spacing doesn't allow very many
extra rivets compared to one row.

I have 4 bay tanks, and so at the outboard solid rib on the bottom of the
wing where the tank skin, leading edge skin, and main skin all overlap on
the main spar I also have a corner of the skin doubler for the strut attach
area overlapping. This seems like a lot of layers (5 including the spar) I
was thinking of trimming the doubler to go around the corner of the tank
skin instead of over it. Can someone with 4 bay tanks comment on this?
Thanks.
Jesse

Perhaps you could put the strut doubler on the exterior (mine is) if it
isn't already and butt it up against the tank skin? If you have to make
the doubler narrower along one side you can always compensate by making
it out of thicker stock. I have not seen a Rebel with 4 fuel bays yet.
With the Subaru I actually dropped to only two bays on the left side.

Ken




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[Jesse Jenks]

Thanks Ken,

Your comments are much appreciated.
I am having trouble understanding exactly what you mean here though:

Yes. I gave up and made up new larger tank skins. Larger in both
directions. Perhaps extreme but it sure made me more comfortable and
gave more room to assemble everything. IIRC you want at least 1/2" of
rivet to rivet spacing. 11/32 of row spacing doesn't allow very many
extra rivets compared to one row.

What do you mean by "extra rivets"?
Thanks
Jesse





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[Rick Harper]

G'day from COLD Australia, guys !

Our Rebel has 4 bays on each side for fuel ( she holds 230 Litres )
..... and has NEVER leaked a single drop !

I custom made the larger skins out of .040" 6061-T6 and there are two
rows of rivets on all sides - with plenty of gap to each edge

We used 3 full cans (about 3 litres) of Proseal in total - 1 can for
each tank bottom & sides & the 3rd tank was used to seal the 2 lids ....
You'll never see the proseal after the wings are closed - so don't be
shy with the stuff - put LOTS of it at every joint, stringer opening etc
- FILLET ON BOTH SIDES TOO ! ( and clean every joint with M.E.K. before
you seal )

I read all the old "Rebel Rouser" magazines before we started building -
and there were articles in just about every one of them about fuel tank
leaks - even after they redesigned the tank system - that's why we
decided to got to town with the proseal - and it worked !

I can't remember the 5 layers of skins you are talking about ( we
finished our Rebel 5 years ago) - so I don't want to comment on that one
- sorry

Rick & Wendy Harper
541R - Flying fabulously
----- Original Message -----
From: Ken
To: rebel-builders@dcsol.com
Sent: Monday, July 18, 2005 3:01 AM
Subject: Re: Tank skin overlap


Jesse Jenks wrote:

I have all the skins clecoed on my first wing. Last night I drilled

the

extra rows of holes around the bottom tank skin. I drilled one extra

row of

holes between the stringer and tank bulkheads. I have about 1" of the

tank

skin overlapping beyond the stringer. There is a picture on the

archives

that shows the tank skin overlapping aft of the stringer with an

additional

row of rivets, but the manual does not show this. Is it common to do

it that

way, or should I just trim the tank skin up to the stringer as the

manual

shows?

It seems that every Rebel I see has a slightly different tank skin. As

long as you have two rows of rivets with the correct edge and pitch
spacing you should be fine. Ideally you'd want to be able to cut the
main skin back far enough so that it doesn't interfere with a good
fillet of proseal along the tank exterior. As it happens I joined the
two skins at the stringer line and with one more row of rivets behind
the stringer line but I don't believe that is common.

On the outboard edge of the bottom tank I seem to have minimal

overlap. I

ended up with about 11/32" between the two extra rows after allowing

5/16"

edge distance from the tank skin, and the estimated trim line of the

main

skin which has not been cut yet, but will have to be trimmed so as

not to

interfere with the tank rib, and also have enough edge distance for

the skin

overlap rivets. I was considering staggering the two rows if they got

too

close. I may have to on the top of the wing as I think I have even

less

overlap in that area. Has anyone had this concern?

Yes. I gave up and made up new larger tank skins. Larger in both
directions. Perhaps extreme but it sure made me more comfortable and
gave more room to assemble everything. IIRC you want at least 1/2" of
rivet to rivet spacing. 11/32 of row spacing doesn't allow very many
extra rivets compared to one row.

I have 4 bay tanks, and so at the outboard solid rib on the bottom of

the

wing where the tank skin, leading edge skin, and main skin all

overlap on

the main spar I also have a corner of the skin doubler for the strut

attach

area overlapping. This seems like a lot of layers (5 including the

spar) I

was thinking of trimming the doubler to go around the corner of the

tank

skin instead of over it. Can someone with 4 bay tanks comment on

this?

Thanks.
Jesse

Perhaps you could put the strut doubler on the exterior (mine is) if
it
isn't already and butt it up against the tank skin? If you have to
make
the doubler narrower along one side you can always compensate by
making
it out of thicker stock. I have not seen a Rebel with 4 fuel bays yet.

With the Subaru I actually dropped to only two bays on the left side.

Ken




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[Ken]

Jesse

I just meant that usually you put the second row of rivets in because
you need more rivets than will fit into a single row with acceptable
minimum spacing. If the second row is more than about 1/2" from the
first row then you can put a whole new row in and have twice as many
rivets and about twice the strength. You may or may not choose to
stagger them.

However if the second row is only 11/32 away from the first row then you
must stagger the rivets to keep minimum spacing as 11/32 is too close to
just put another identical row. You may end up with only one or two
extra rivets per linear foot instead of double the number that you could
put in with the rows 1/2" apart. The 1/2" number is from memory but I
think that is the minimum allowable spacing between 1/8" rivets. I don't
recall the actual spacing specified by MAM in the manual but I do
remember going through this when I built my wing...

Ken

Jesse Jenks wrote:

Thanks Ken,

Your comments are much appreciated.
I am having trouble understanding exactly what you mean here though:

Yes. I gave up and made up new larger tank skins. Larger in both
directions. Perhaps extreme but it sure made me more comfortable and
gave more room to assemble everything. IIRC you want at least 1/2" of
rivet to rivet spacing. 11/32 of row spacing doesn't allow very many
extra rivets compared to one row.

What do you mean by "extra rivets"?
Thanks
Jesse

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[Jesse Jenks]

Thanks Ken,
I gave the wrong measurement. I have 11/16" not 11/32" between the two rows.
Sorry about the confusion. Thanks for the spacing info anyway though. So I
guess I have enough spacing after all? Did you just go with the standard rib
rivet pitch (about 1 1/4" between rivets) for the extra rows, or add another
rivet between each. I am still a bit worried about how the edge of the main
skin will fit up next to the tank rib flange under the tank skin with dry
proseal in there. For the bottom skin it should not be an issue because if
I understand correctly you put everything together in one shot so I should
be OK with minimal clearance between the main skin edge and the rib flange
(right wing, flanges facing outboard) I can even do the external proseal
fillet after riveting all the bottom skins in place. For the top skins
though I guess I should cut the main skin back a bit further to allow enough
room for a cured proseal fillet before sliding the main skin under the tank.
Since I havn't drilled the extra rivet rows in the top tank erea yet, heres
what I have to work with: about 1 3/4" of tank skin outboard of the tank rib
rivet holes. Can you suggest a minimum distance to the first row of extra
rivets that will allow enough working room for the skin edge?
Thanks
Jesse

From: Ken <klehman@albedo.net>
Reply-To: <rebel-builders@dcsol.com>
To: rebel-builders@dcsol.com
Subject: Re: Tank skin overlap
Date: Sun, 17 Jul 2005 18:44:53 -0400

Jesse

I just meant that usually you put the second row of rivets in because
you need more rivets than will fit into a single row with acceptable
minimum spacing. If the second row is more than about 1/2" from the
first row then you can put a whole new row in and have twice as many
rivets and about twice the strength. You may or may not choose to
stagger them.

However if the second row is only 11/32 away from the first row then you
must stagger the rivets to keep minimum spacing as 11/32 is too close to
just put another identical row. You may end up with only one or two
extra rivets per linear foot instead of double the number that you could
put in with the rows 1/2" apart. The 1/2" number is from memory but I
think that is the minimum allowable spacing between 1/8" rivets. I don't
recall the actual spacing specified by MAM in the manual but I do
remember going through this when I built my wing...

Ken

Jesse Jenks wrote:

Thanks Ken,

Your comments are much appreciated.
I am having trouble understanding exactly what you mean here though:

Yes. I gave up and made up new larger tank skins. Larger in both
directions. Perhaps extreme but it sure made me more comfortable and
gave more room to assemble everything. IIRC you want at least 1/2" of
rivet to rivet spacing. 11/32 of row spacing doesn't allow very many
extra rivets compared to one row.

What do you mean by "extra rivets"?
Thanks
Jesse

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[Jesse Jenks]

Thanks for the proseal tips Rick,
I will order some extra so I am not trying to skimp on it.
Jesse

From: "Rick Harper" <rjwh@optusnet.com.au>
Reply-To: <rebel-builders@dcsol.com>
To: <rebel-builders@dcsol.com>
Subject: Re: Tank skin overlap
Date: Mon, 18 Jul 2005 07:46:58 +1000

G'day from COLD Australia, guys !

Our Rebel has 4 bays on each side for fuel ( she holds 230 Litres )
..... and has NEVER leaked a single drop !

I custom made the larger skins out of .040" 6061-T6 and there are two
rows of rivets on all sides - with plenty of gap to each edge

We used 3 full cans (about 3 litres) of Proseal in total - 1 can for
each tank bottom & sides & the 3rd tank was used to seal the 2 lids ....
You'll never see the proseal after the wings are closed - so don't be
shy with the stuff - put LOTS of it at every joint, stringer opening etc
- FILLET ON BOTH SIDES TOO ! ( and clean every joint with M.E.K. before
you seal )

I read all the old "Rebel Rouser" magazines before we started building -
and there were articles in just about every one of them about fuel tank
leaks - even after they redesigned the tank system - that's why we
decided to got to town with the proseal - and it worked !

I can't remember the 5 layers of skins you are talking about ( we
finished our Rebel 5 years ago) - so I don't want to comment on that one
- sorry

Rick & Wendy Harper
541R - Flying fabulously
----- Original Message -----
From: Ken
To: rebel-builders@dcsol.com
Sent: Monday, July 18, 2005 3:01 AM
Subject: Re: Tank skin overlap


Jesse Jenks wrote:

I have all the skins clecoed on my first wing. Last night I drilled

the

extra rows of holes around the bottom tank skin. I drilled one extra

row of

holes between the stringer and tank bulkheads. I have about 1" of the

tank

skin overlapping beyond the stringer. There is a picture on the

archives

that shows the tank skin overlapping aft of the stringer with an

additional

row of rivets, but the manual does not show this. Is it common to do

it that

way, or should I just trim the tank skin up to the stringer as the

manual

shows?

It seems that every Rebel I see has a slightly different tank skin. As

long as you have two rows of rivets with the correct edge and pitch
spacing you should be fine. Ideally you'd want to be able to cut the
main skin back far enough so that it doesn't interfere with a good
fillet of proseal along the tank exterior. As it happens I joined the
two skins at the stringer line and with one more row of rivets behind
the stringer line but I don't believe that is common.

On the outboard edge of the bottom tank I seem to have minimal

overlap. I

ended up with about 11/32" between the two extra rows after allowing

5/16"

edge distance from the tank skin, and the estimated trim line of the

main

skin which has not been cut yet, but will have to be trimmed so as

not to

interfere with the tank rib, and also have enough edge distance for

the skin

overlap rivets. I was considering staggering the two rows if they got

too

close. I may have to on the top of the wing as I think I have even

less

overlap in that area. Has anyone had this concern?

Yes. I gave up and made up new larger tank skins. Larger in both
directions. Perhaps extreme but it sure made me more comfortable and
gave more room to assemble everything. IIRC you want at least 1/2" of
rivet to rivet spacing. 11/32 of row spacing doesn't allow very many
extra rivets compared to one row.

I have 4 bay tanks, and so at the outboard solid rib on the bottom of

the

wing where the tank skin, leading edge skin, and main skin all

overlap on

the main spar I also have a corner of the skin doubler for the strut

attach

area overlapping. This seems like a lot of layers (5 including the

spar) I

was thinking of trimming the doubler to go around the corner of the

tank

skin instead of over it. Can someone with 4 bay tanks comment on

this?

Thanks.
Jesse

Perhaps you could put the strut doubler on the exterior (mine is) if
it
isn't already and butt it up against the tank skin? If you have to
make
the doubler narrower along one side you can always compensate by
making
it out of thicker stock. I have not seen a Rebel with 4 fuel bays yet.

With the Subaru I actually dropped to only two bays on the left side.

Ken




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[Ken]

Jesse Jenks wrote:

Thanks Ken,
I gave the wrong measurement. I have 11/16" not 11/32" between the two rows.
Sorry about the confusion. Thanks for the spacing info anyway though. So I
guess I have enough spacing after all? Did you just go with the standard rib
rivet pitch (about 1 1/4" between rivets) for the extra rows, or add another
rivet between each. I am still a bit worried about how the edge of the main
skin will fit up next to the tank rib flange under the tank skin with dry
proseal in there.

That pitch sounds about right. I think my outboard rivet line has half
as many rivets as the inboard one. I believe AC 43-13 has a section that
explains why it is slightly better to use the spacing that MAM
recomends. It has to do with how much material is removed by the actual
rivet hole.

I wasn't going to mention it as it would get tricky in the corner but I
believe some guys have rolled (bent) the edge of the skin up to provide
a little more room beside the tank. Prosealing from the tank to the main
skin won't help anything as the fuel could then go between the tank skin
and the main skin. You will feel better if you can get the fillet around
the outside of the tank but it is certainly is not essential.

For the bottom skin it should not be an issue because if
I understand correctly you put everything together in one shot so I should
be OK with minimal clearance between the main skin edge and the rib flange
(right wing, flanges facing outboard) I can even do the external proseal
fillet after riveting all the bottom skins in place. For the top skins
though I guess I should cut the main skin back a bit further to allow enough
room for a cured proseal fillet before sliding the main skin under the tank.
Since I havn't drilled the extra rivet rows in the top tank erea yet, heres
what I have to work with: about 1 3/4" of tank skin outboard of the tank rib
rivet holes. Can you suggest a minimum distance to the first row of extra
rivets that will allow enough working room for the skin edge?
Thanks
Jesse

I'd keep it as large as you can but I'd be comfortable with 1/4 or more
which it sounds like you can easily do.
5/16 edge plus 11/16 row (or whatever the manual says) plus 5/16 edge
leaves 7/16. This is sounding much better ;)
Ken




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[Jesse Jenks]

Ken,
Very helpfull. Thanks a bunch.
One more question, the last one, I promise: Along the main spar in the tank
area should I add aditional rivets between the existing ones? The manual
doesn't seem to show a picture of that area, but does show twice the
existing number of holes put along both the inboard and outboard tank ribs,
and the spacing on the tank bulkheads is pretty close also.
Jesse





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[Ken]

Jesse this is the place to ask if you can't figure it out from the
manual! I recall my manual saying to go back and drill another hole
between the existing ones on the main spar for the tank skin on my
standard Rebel. I just measured and my spacing is about 5/8" on the
bottom of the tank and about 1/2 on the top.
Ken

Jesse Jenks wrote:

Ken,
Very helpfull. Thanks a bunch.
One more question, the last one, I promise: Along the main spar in the tank
area should I add aditional rivets between the existing ones? The manual
doesn't seem to show a picture of that area, but does show twice the
existing number of holes put along both the inboard and outboard tank ribs,
and the spacing on the tank bulkheads is pretty close also.
Jesse

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