Rear Tank baffle leaking- need advice

[bkthomps]

Well I leak tested the tank today, and I'm thinking now I did something incorrect when sealing the rear baffle- there are no less than 5 or 6 leaks on each side. I put a bead of sealant 3/16" from the rivet holes forward, set it down nicely and riveted away

So anyway, now what to do, it has been 48hrs, should I drill all of the rivets out and remove it? should I just drill the baffle->skin rivets out and spread sealant down in there, re-rivet

I'm thinking if drilling all the rivets out, z brackets have to come off too....I'm not really wanting to put up that much of a fight, and I can't find decent instructions on how to properly drill an access hole, do you use scrap metal to make a cover? which exact blind rivet do you use?? help!

Also, I don't think I squeezed the shop heads enough on the rear baffle, is it too late to go and do that now? This is what you get for working tired/late

Pics because some are visual:

[mototopo]

Hi,
I'm unable to see the pictures so I don't know where the leaks are. If they are all in the same bay, the best fix is to cut an access hole to seal them. If the leaks are all along the skin/baffle joint...well, I really don't know which is the best way (more than one access hole?).

To fabricate a cover you can use some scrap aluminium sheet; as rivet I think you can use the same kind used to rivet the z-brackets (I don't remember the correct part number).

By the way, to seal my tank baffle, I spread the sealant forward of the rivet line but just in touch with the edge of the holes. Once dropped the baffle onto the tank I had a good fillet all along the contact zone between the skin and the baffle. Maybe you used not enough sealant or you spread it too forward...

Good luck.

[bruceh]

I think you should have put the sealant bead right in front on the rivet line for the baffles, not 3/16" forward. When you push the baffle into place it should squeeze the sealant forward and create a solid bead. It also helps to butter up the baffle flanges and rib flanges with sealant so you know that there will be a good solid sealant coverage all along the baffle to tank skin contact areas.

If the sealant hasn't completely set up, any drilling of rivets will create one heck of a mess with all of the metal shavings. If it has set up, trying to pry the baffle off may be difficult.

[bkthomps]

Originally Posted by bruceh

I think you should have put the sealant bead right in front on the rivet line for the baffles, not 3/16" forward. When you push the baffle into place it should squeeze the sealant forward and create a solid bead. It also helps to butter up the baffle flanges and rib flanges with sealant so you know that there will be a good solid sealant coverage all along the baffle to tank skin contact areas.

If the sealant hasn't completely set up, any drilling of rivets will create one heck of a mess with all of the metal shavings. If it has set up, trying to pry the baffle off may be difficult.

yeah I think a series of access holes are in my future, I tried the MEK thinning/vaccum method, but i didn't see any movement on the thinned proseal, it sorta sat there mocking me, so when that dries up maybe tomorrow or sunday, i'll try again....assuming it will not fix it I will start to figure out how to do my access holes

I saw another builder who tried removing the rear baffle and well, i'm not really wanting to walk a mile in his shoes

[terrye]

It would be helpful if you could post some pictures to show exactly where the leaks are.
If the leaks are at the factory heads of the countersunk AN426 rivets between the skin and the baffle, then you probably didn't drive the rivets wet and you may have to drill them out and reseal them.
If the leaks are along the aft seam between the baffle and the skin, or around the shop heads of the AN426 rivets between the baffle and the skin, it doesn't look like you have sealed these seams after driving the rivets. I used a veterinary syringe with a homemade nozzle (3/8" aluminum 3003-0 tubing with a tip filed to the bead contour) to run a crescent shaped bead about 1/4" wide x 1/8" high (use a guide to get a straight bead) centered on the baffle flange to skin seam. Then I used another syringe to encapsulate each rivet shop head with about a 5/16" dia x 3/16" high blob.
No, I haven't yet done a leak test but I am pretty confident I won't have any.
See also Rick6a's post "Tip:Proseal...The fact and the fiction". Shows these beads and blobs.
Also:
http://www.bergdahl.com/NeatStuff.htm
and click on Thickness and Contours of Sealant

[Steve Barnes]

A friend of mine put an access hole on the baffel, between each rib. Use the same access flange and covers that you did on the end baffel. This may sound like a lot of work, but if you get future leaks you'll be glad you did. If you suspect more leaks after you start flying, you might think about not painting the tanks until after phase one, and the leaks have been fixed.

Steve Barnes "The Builders Coach"

[Wayne Gillispie]

you may end up cutting the access holes to fix properly. I would not recommend baffle removal. Only use toluene(max. 15% by weight) to thin sealant not mek. Mek for cleaning surfaces before/after applying sealant. Also if you have not built second tank yet, allow at least 4 or 5 days cure time. Higher temp/humidity=quicker cure.

[bkthomps]

Originally Posted by terrye

It would be helpful if you could post some pictures to show exactly where the leaks are.
If the leaks are at the factory heads of the countersunk AN426 rivets between the skin and the baffle, then you probably didn't drive the rivets wet and you may have to drill them out and reseal them.
If the leaks are along the aft seam between the baffle and the skin, or around the shop heads of the AN426 rivets between the baffle and the skin, it doesn't look like you have sealed these seams after driving the rivets. I used a veterinary syringe with a homemade nozzle (3/8" aluminum 3003-0 tubing with a tip filed to the bead contour) to run a crescent shaped bead about 1/4" wide x 1/8" high (use a guide to get a straight bead) centered on the baffle flange to skin seam. Then I used another syringe to encapsulate each rivet shop head with about a 5/16" dia x 3/16" high blob.
No, I haven't yet done a leak test but I am pretty confident I won't have any.
See also Rick6a's post "Tip:Proseal...The fact and the fiction". Shows these beads and blobs.
Also:
http://www.bergdahl.com/NeatStuff.htm
and click on Thickness and Contours of Sealant

I will get some pictures, it is mostly along the skin to baffle seam, I'm guessing there isn't enough pressure held in yet to stress the rivet holes enough to determine if they are leaking, the balloon will not even inflate!

[DanH]

It's not hard to access the inside of an assembled tank. An ordinary fly cutter does fine, IF you turn it with a very slow (60 RPM or less), very high torque drill motor.



Think of it as an opportunity to seal your tanks really well, per the Bergdahl link Terry supplied.

[miyu1975]

lots of good advice already...as usual, I was curious as to where the z brackets are?