tank skin rivet spacing

[bransom]

I'm working on the tank skins on my second (left) wing and am embarrassed to
find that I missed something fairly important on the first wing and tank
skin. MAM (1994) says to put an extra hole between the prepunched holes on
Ribs 1 & 4 and the Main Spar. I got this on the ribs fine but missed it on
the main spar. Still can't believe I missed this, but glad I caught it now.

After careful double checking I see that the in-between holes to the Main
spar are called for on the bottom skin, but not on the top. (in-between
holes to ribs 1&4 on bottom and top, but to main skin on bottom only). Just
to help me believe all this, can someone confirm for me that rivet spacing
for the tank to main spar is about 5/8 inch on the bottom (1.25" before
drilling the in-between holes), and is about 1 inch spacing on the top tank
to main spar?

Also, I need to go back to the first wing, mark out and drill the in-between
holes I missed on the bottom, and proseal rivet these. This after that wing
is otherwise "done". I feel pretty sure that this is unlikely to introduce
any tank leaks, and the worst of it will be that I'll have to figure out how
to get drill chips out of the tank. Any thoughts on how to minimize chances
of making leaks in this process? I figure I may be able to vacuum and or
slosh the chips out instead of having to make a tank inspection port already.
Thanks all,
-Ben / 496R



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[Ken]

Hi Ben

I put the extra rivets in both top and bottom of the spar. If you ask
MAM, I suspect they will tell you this is a leak issue not a structural
issue as I don't believe they were used with the original plastic tanks.
So you might even consider leaving it as is since the proseal is already
"hardened". I'd bet you would not be the first to do that and at this
point I'm wondering if adding the extra rivets will really help prevent
future leaks??

One inspection hole and removing the baffles on the ribs would give you
access and it might be nice to apply extra proseal anyway. If I were to
try it without an inspection hole I'd drill and insert rivets from the
bottom to help chips fall out and to help proseal settle around the
rivet. I might also devise a method for injecting a bit of proseal into
each rivet hole. If you can drill slow most chips might clear out of the
hole before the drill bit even breaks through the proseal. Whats left is
going to get mostly trapped in the proseal I'd think.

Ken

bransom@dcsol.com wrote:

I'm working on the tank skins on my second (left) wing and am embarrassed to
find that I missed something fairly important on the first wing and tank
skin. MAM (1994) says to put an extra hole between the prepunched holes on
Ribs 1 & 4 and the Main Spar. I got this on the ribs fine but missed it on
the main spar. Still can't believe I missed this, but glad I caught it now.

After careful double checking I see that the in-between holes to the Main
spar are called for on the bottom skin, but not on the top. (in-between
holes to ribs 1&4 on bottom and top, but to main skin on bottom only). Just
to help me believe all this, can someone confirm for me that rivet spacing
for the tank to main spar is about 5/8 inch on the bottom (1.25" before
drilling the in-between holes), and is about 1 inch spacing on the top tank
to main spar?

Also, I need to go back to the first wing, mark out and drill the in-between
holes I missed on the bottom, and proseal rivet these. This after that wing
is otherwise "done". I feel pretty sure that this is unlikely to introduce
any tank leaks, and the worst of it will be that I'll have to figure out how
to get drill chips out of the tank. Any thoughts on how to minimize chances
of making leaks in this process? I figure I may be able to vacuum and or
slosh the chips out instead of having to make a tank inspection port already.
Thanks all,
-Ben / 496R

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[bransom]

Ken
Thanks for the quick reply. I guess I don't really need anyone to go
measuring rivet spacing now that I at least have another good soul confirming
what I had a hard time believing last night. Yes, I think drilling from
below will help, and I will probably set a drill stop to make the hole depth
just reach the inside proseal layer. Then make sure all is clean, poke thru
original cured proseal and inject some new and the rivet, still from below.
Picturing proseal dripping onto my face -- whoa that'll be fun. :)

I'd be a little curious too whether Murphy made the original without double
riveting there but that is too big a judgement call and departure from plans
for my blood (I'm definetly putting in the rivets).
Thanks again,
-Ben

On 11/4/2005 5:02 AM, klehman@albedo.net wrote to rebel-builders:

Hi Ben

I put the extra rivets in both top and bottom of the spar. If you ask
MAM, I suspect they will tell you this is a leak issue not a structural
issue as I don't believe they were used with the original plastic tanks.
So you might even consider leaving it as is since the proseal is already
"hardened". I'd bet you would not be the first to do that and at this
point I'm wondering if adding the extra rivets will really help prevent
future leaks??

One inspection hole and removing the baffles on the ribs would give you
access and it might be nice to apply extra proseal anyway. If I were to
try it without an inspection hole I'd drill and insert rivets from the
bottom to help chips fall out and to help proseal settle around the
rivet. I might also devise a method for injecting a bit of proseal into
each rivet hole. If you can drill slow most chips might clear out of the
hole before the drill bit even breaks through the proseal. Whats left is
going to get mostly trapped in the proseal I'd think.

Ken

bransom@dcsol.com wrote:

I'm working on the tank skins on my second (left) wing and am embarrassed

to

find that I missed something fairly important on the first wing and tank
skin. MAM (1994) says to put an extra hole between the prepunched holes

on

Ribs 1 & 4 and the Main Spar. I got this on the ribs fine but missed it

on

the main spar. Still can't believe I missed this, but glad I caught it

now.

After careful double checking I see that the in-between holes to the Main
spar are called for on the bottom skin, but not on the top. (in-between
holes to ribs 1&4 on bottom and top, but to main skin on bottom only).

Just

to help me believe all this, can someone confirm for me that rivet spacing
for the tank to main spar is about 5/8 inch on the bottom (1.25" before
drilling the in-between holes), and is about 1 inch spacing on the top

tank

to main spar?

Also, I need to go back to the first wing, mark out and drill the in-

between

holes I missed on the bottom, and proseal rivet these. This after that

wing

is otherwise "done". I feel pretty sure that this is unlikely to

introduce

any tank leaks, and the worst of it will be that I'll have to figure out

how

to get drill chips out of the tank. Any thoughts on how to minimize

chances

of making leaks in this process? I figure I may be able to vacuum and or
slosh the chips out instead of having to make a tank inspection port

already.

Thanks all,
-Ben / 496R

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[Ken]

Ben

I think I threw away my original wing manual but as I recall those extra
rivets only appeared when the wet tank construction was introduced.
AFAIK they never added the extra holes when they punch out the wing
skins but that makes some sense when you consider that not everyone uses
3 bays of tank. The wing upgrade mod to 1650 lbs was aftter the wet tank
mod appeared. (Both are now standard) If the extra rivets were required
for wing strength then they'd almost certainly be required on the top
and bottom of the wing and you say that is not the case. I haven't
talked to MAM for several years but last time I did they were pretty
good about answering this sort of question.

Doesn't matter anyway if you if want them in to be comfortable. I think
someone here has mentioned putting proseal in a syringe successfully
although I would have guessed it was too thick to squeeze out... Maybe
they drilled the opening out to #30.

Ken

bransom@dcsol.com wrote:

Ken
Thanks for the quick reply. I guess I don't really need anyone to go
measuring rivet spacing now that I at least have another good soul confirming
what I had a hard time believing last night. Yes, I think drilling from
below will help, and I will probably set a drill stop to make the hole depth
just reach the inside proseal layer. Then make sure all is clean, poke thru
original cured proseal and inject some new and the rivet, still from below.
Picturing proseal dripping onto my face -- whoa that'll be fun. :)

I'd be a little curious too whether Murphy made the original without double
riveting there but that is too big a judgement call and departure from plans
for my blood (I'm definetly putting in the rivets).
Thanks again,
-Ben

On 11/4/2005 5:02 AM, klehman@albedo.net wrote to rebel-builders:

Hi Ben

I put the extra rivets in both top and bottom of the spar. If you ask
MAM, I suspect they will tell you this is a leak issue not a structural
issue as I don't believe they were used with the original plastic tanks.
So you might even consider leaving it as is since the proseal is already
"hardened". I'd bet you would not be the first to do that and at this
point I'm wondering if adding the extra rivets will really help prevent
future leaks??

One inspection hole and removing the baffles on the ribs would give you
access and it might be nice to apply extra proseal anyway. If I were to
try it without an inspection hole I'd drill and insert rivets from the
bottom to help chips fall out and to help proseal settle around the
rivet. I might also devise a method for injecting a bit of proseal into
each rivet hole. If you can drill slow most chips might clear out of the
hole before the drill bit even breaks through the proseal. Whats left is
going to get mostly trapped in the proseal I'd think.

Ken

bransom@dcsol.com wrote:

I'm working on the tank skins on my second (left) wing and am embarrassed

to

find that I missed something fairly important on the first wing and tank
skin. MAM (1994) says to put an extra hole between the prepunched holes

on

Ribs 1 & 4 and the Main Spar. I got this on the ribs fine but missed it

on

the main spar. Still can't believe I missed this, but glad I caught it

now.

After careful double checking I see that the in-between holes to the Main
spar are called for on the bottom skin, but not on the top. (in-between
holes to ribs 1&4 on bottom and top, but to main skin on bottom only).

Just

to help me believe all this, can someone confirm for me that rivet spacing
for the tank to main spar is about 5/8 inch on the bottom (1.25" before
drilling the in-between holes), and is about 1 inch spacing on the top

tank

to main spar?

Also, I need to go back to the first wing, mark out and drill the in-

between

holes I missed on the bottom, and proseal rivet these. This after that

wing

is otherwise "done". I feel pretty sure that this is unlikely to

introduce

any tank leaks, and the worst of it will be that I'll have to figure out

how

to get drill chips out of the tank. Any thoughts on how to minimize

chances

of making leaks in this process? I figure I may be able to vacuum and or
slosh the chips out instead of having to make a tank inspection port

already.

Thanks all,
-Ben / 496R

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[Wayne G. O'Shea]

Mine is still flying...wings haven't buckled yet..I have 1" spacing on the
top tank skins at the spar. Don't think it's an issue....but yes indeed
confirm with MAM. Personally I wouldn't be drilling into that nicely sealed
tank...but that just me.

----- Original Message -----
From: "Ken" <klehman@albedo.net>
To: <rebel-builders@dcsol.com>
Sent: Friday, November 04, 2005 1:21 PM
Subject: Re: tank skin rivet spacing

Ben

I think I threw away my original wing manual but as I recall those extra
rivets only appeared when the wet tank construction was introduced.
AFAIK they never added the extra holes when they punch out the wing
skins but that makes some sense when you consider that not everyone uses
3 bays of tank. The wing upgrade mod to 1650 lbs was aftter the wet tank
mod appeared. (Both are now standard) If the extra rivets were required
for wing strength then they'd almost certainly be required on the top
and bottom of the wing and you say that is not the case. I haven't
talked to MAM for several years but last time I did they were pretty
good about answering this sort of question.

Doesn't matter anyway if you if want them in to be comfortable. I think
someone here has mentioned putting proseal in a syringe successfully
although I would have guessed it was too thick to squeeze out... Maybe
they drilled the opening out to #30.

Ken

bransom@dcsol.com wrote:

Ken
Thanks for the quick reply. I guess I don't really need anyone to go
measuring rivet spacing now that I at least have another good soul

confirming

what I had a hard time believing last night. Yes, I think drilling from
below will help, and I will probably set a drill stop to make the hole

depth

just reach the inside proseal layer. Then make sure all is clean, poke

thru

original cured proseal and inject some new and the rivet, still from

below.

Picturing proseal dripping onto my face -- whoa that'll be fun. :)

I'd be a little curious too whether Murphy made the original without

double

riveting there but that is too big a judgement call and departure from

plans

for my blood (I'm definetly putting in the rivets).
Thanks again,
-Ben

On 11/4/2005 5:02 AM, klehman@albedo.net wrote to rebel-builders:

Hi Ben

I put the extra rivets in both top and bottom of the spar. If you ask
MAM, I suspect they will tell you this is a leak issue not a structural
issue as I don't believe they were used with the original plastic tanks.
So you might even consider leaving it as is since the proseal is already
"hardened". I'd bet you would not be the first to do that and at this
point I'm wondering if adding the extra rivets will really help prevent
future leaks??

One inspection hole and removing the baffles on the ribs would give you
access and it might be nice to apply extra proseal anyway. If I were to
try it without an inspection hole I'd drill and insert rivets from the
bottom to help chips fall out and to help proseal settle around the
rivet. I might also devise a method for injecting a bit of proseal into
each rivet hole. If you can drill slow most chips might clear out of the
hole before the drill bit even breaks through the proseal. Whats left is
going to get mostly trapped in the proseal I'd think.

Ken

bransom@dcsol.com wrote:

embarrassed

to

tank

holes

on

it

on

now.

Main

(in-between

Just

spacing

tank

between

wing

introduce

out

how

chances

or

already.

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[bransom]

I took your suggestion (Ken and Wayne) and called MAM. Robyn surmised the
same logic as you, that the "in-between" holes on the bottom of the tank skin
into the main spar would likely be for sealing the tank and not structural.
But, to be sure, he said he'd check and call back. He did, and said that
Daryl said the same, and further that if the first wing proved leak proof
with just the prepunched holes/rivets, he'd leave it alone.

BTW, I was pretty impressed and pleased to get such thorough and prompt help
from the factory ...and even late on a Friday afternoon.
Ben/ 496R



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