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Left Tank Leak - Looking like a new tank

Saville

Well Known Member
Well this was the year for the prop inspection and as that was going to take several weeks I decided to so the annual 4 months early - lousy flying weather in January and February anyway.

But the other reason I downed the plane was that I had developed a small leak in the left hand tank. You'd wipe the underside of the wing clean and the next day there would be a track a few inches long. Nothing major but enough to bother me.

So the prop came off and and the annual completed (few minor adjustments to be made), and the tank came off.

The leak is in the lower seam about 3/4's the way outboard:

Leak_track.png


Turns out that someone had buttered up the entire outside of the seam with Pro Seal but...the sealant never cured - you can wipe it off with your finger:

Uncured.png


So then it was observed that just about every fastener hole along the top spanwise edge had a small crack on the underside. The conjecture is that maybe the screws were turned too tightly or that the dimples were not created squarely - or maybe both.

Anyway this tank has been a problem from the start. Firstly the tank vent B-nut on the inside was never tightened down so I had to remove the access plate, reach in there and tighten it. And the pass-through the rib for the vent was sloppily put on and leaked so I also removed it, put new fittings in Pro Sealed it and it was good from that point on. There was also Pro Seal on the tip of the vent near the fuel filler cap partly blocking the vent.

So it looks like a new tank. I suppose one could try to remove the skin and reskin the structure but the time taken to drill out all those rivets must be close to just constructing a new tank. And this one I can inspect as it's being built.

Well that's the fun of EAB and buying someone else's airplane. I'm not complaining...these things happen: Only if you build it yourself do you reduce the chances for surprises. But the prop might be back on before the tank is built and installed.
 
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Gregg,

Cut access ports in the rear wall, re-seal as necessary, live happily ever after.

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Well that's the fun of EAB and buying someone else's airplane. I'm not complaining...these things happen: Only if you build it yourself do you reduce the chances for surprises. But the prop might be back on before the tank is built and installed.

If you don't want to build tanks, I think Evan Johnson is still building tanks. Evan took over the tank building business from Don London who built RV tanks for many years. I might be able to dig up his contact info if you are interested.
 
Turns out that someone had buttered up the entire outside of the seam with Pro Seal but...the sealant never cured - you can wipe it off with your finger...

Probably because there were fuel fumes/residue weeping into the proseal as it "cured".

Your tank is definitely repairable....do as DanH suggested, open up the tank in the bays where the leak is located and seal inside the tank after is it completely dry and free of fuel. You should then be good to go. :)
 
Gregg,

Cut access ports in the rear wall, re-seal as necessary, live happily ever after.

P8080002.JPG


P8080003.JPG


P1220002.JPG
Take the advice from one who has experience with this (7 times worth of experience, go ahead and do a quick search to see some of my posts), this is the only way you are going to successfully seal leaks in a leaking fuel tank.
 
Cut access ports in the rear wall, re-seal as necessary, live happily ever after.

Dan,
Are these tanks you built that developed leaks later in life ? Or??. ?

Reason I ask, I have new 2005 vintage QB tanks that have never flown that I don't trust the Philippine builders Vans had at the time.
I was thinking to re-seal just as you have here before paint & fly.

J.

~
 
Seal Tanks

As one of the early guys that got bit by leaking QB tanks, around 2006 / 2007 era, I would urge everyone to open the rear wall and reseal tanks properly. The work performed inside tanks by the QB personnel that I have witnessed was performed by obviously untrained labor. I repaired mine in 2009 and never another problem. At the time I had several friends in the flying and building stage that had me do a reseal on their tanks without a future problem. Do not paint tank installation screws so they can be removed with minimal damage to paint if needed. Also install flushing washers under screws to help protect paint. Save yourself time and labor later by doing this during the build.
YMMV
 
Dan,
Are these tanks you built that developed leaks later in life ? Or??. ?

Reason I ask, I have new 2005 vintage QB tanks that have never flown that I don't trust the Philippine builders Vans had at the time.
I was thinking to re-seal just as you have here before paint & fly.

J.

~

I'm aware of a local 8 builder with QB tanks around the vintage you mentioned that developed leaks. He basically did what Dan prescribed. The leaks developed shortly after his first flight but before it was painted. No problems since.
 
Dan,
Are these tanks you built that developed leaks later in life ? Or……. ?
Reason I ask, I have new 2005 vintage QB tanks that have never flown that I don't trust the Philippine builders Vans had at the time.
I was thinking to re-seal just as you have here before paint & fly.

Those were brand new QB tanks, vintage 2005. They were indeed a mess, but that's another story.

Closed end pop rivets, installed wet.

Closed%20End%20Rivets.JPG


Perhaps not strictly required, but I recommend a sealant joggle around the perimeter of the cover plate. It guarantees structural loads cannot shear the sealant line.

Joggle%20Seal.jpg
 
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Probably because there were fuel fumes/residue weeping into the proseal as it "cured".

Your tank is definitely repairable....do as DanH suggested, open up the tank in the bays where the leak is located and seal inside the tank after is it completely dry and free of fuel. You should then be good to go. :)

Well - referring back to my OP - there's the cracks in the screw holes along the top of the wing that the mechanic mentioned. I need to see those for myself. If there are as many have cracks as he says then the tank skin is no good.

If the skin is no good then at that point it's either a re-skin or a new tank. I think I'd opt for a new tank.
 
I had weeping rivets first year after the built. Opened the tank and resealed. Used wheel hub covers to close the access holes. Non event if you have a hangar :)





 
Here is an idea. The back baffle should come from the factory with the holes prepunched out. It's a convenient way to chase fuel leaks in the future. If I were building now, I would just do them from the beginning.
 
I just built a rank and am building the 2nd one. No way in **** could you remove a skin that was riveted and prosealed without destroying the ribs. Proseal sticks like you know what to a blanket if the prep was done right. At least I can?t imagine how. The ribs are cheap. Just build a new one if the skin is cracked.

If you are going to build a new tank or two, do yourself a huge favour and buy, borrow or steal a pneumatic proseal gun. It really makes that whole process pretty easy. You use the tubes that vans sells, you mix them with a cordless drill, pop the tube in the gun and go. When it starts to get a bit stiff a bit of heat makes it easier to work.

My tanks were done with skin from flat stock. Nothing predrilled - old school. And it wasn?t too difficult. With the new kits where everything is drilled for you it would be so much easier.
 
So then it was observed that just about every fastener hole along the top spanwise edge had a small crack on the underside. The conjecture is that maybe the screws were turned too tightly or that the dimples were not created squarely - or maybe both.

Regarding the cracked dimples, this is quite a well known issue and apparently they very rarely propagate any further. It seems to happen during dimpling so it is likely they have been present since the tanks were built. I suggest doing some research but here is at least one thread to get you started :http://www.vansairforce.com/community/showthread.php?t=13696&highlight=cracked+dimples

There are many more threads if you search. Good luck!
 
Regarding the cracked dimples, this is quite a well known issue and apparently they very rarely propagate any further. It seems to happen during dimpling so it is likely they have been present since the tanks were built. I suggest doing some research but here is at least one thread to get you started :http://www.vansairforce.com/community/showthread.php?t=13696&highlight=cracked+dimples

There are many more threads if you search. Good luck!

To be honest I'm not worried so much that they migrate forward, but that the cracks cause the screw hole to open AFT of the screw and the tank to fall off.
I realize there are other things holding the tank on but so are these screws
 
Hi Dan,
Is there a source for the cover plates with a joggle?

Mitch, it's not strictly required, just one of those "a little better" details.

I have a bead roller, for which I machine whatever roll forms are needed. This picture is an early test of a setup with some skateboard bearings as guide rollers. The scrap disc is a cutout from the tank. Rolling a bead in the smaller diameter scrap says I can definitely roll a joggle in a larger cover plate.

Bead%20Experiment%20Jig.jpg
 
Update

Ok so I pulled the trigger on getting a new tank built.

Question:

On the RV-8, the distance from the inboard tank rib and the Fuselage is only about a couple of inches. The fuel line from that inboard rib is also just a couple inches long. It connects to a "banjo" 90 degree angle which then attaches to the Andair fuel selector via another 90 degree angle. The selector is mounted very close to the fuselage skin - one 90 degree Andair fitting away

Everything has to line up PERFECTLY in order to start the b-nuts and get it all tightened down.

I'm wondering what people use for that fuel line.

Is it better to move that selector inboard an inch? Or forward an inch or two and use a longer line? Maybe a line with a right angle bend in it?

Gathering ideas....

Thanks
 
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Those were brand new QB tanks, vintage 2005. They were indeed a mess, but that's another story.

Closed end pop rivets, installed wet.

Closed%20End%20Rivets.JPG


Perhaps not strictly required, but I recommend a sealant joggle around the perimeter of the cover plate. It guarantees structural loads cannot shear the sealant line.

Joggle%20Seal.jpg

Hi Dan,
Just curious as why pop rivet instead of screw which it would mean more work if this has to be opened again?
 
New Tank require a fly-off?

Does replacing a tank with one made strictly by the plans with all SB's require a Phase 1-like flyoff?
 
Saville, I would not think you need to go into phase 1. You are making a repair, although it is a large job, it is not a "major change" as defined by the op lims or the FAA. However, after finishing the job, I would certainly be very conservative and do do some hours of local flights, checking for leaks and movements and such. The weight difference between your new tank and old will probably be insignificant to the overall W&B.
 
Saville, I would not think you need to go into phase 1. You are making a repair, although it is a large job, it is not a "major change" as defined by the op lims or the FAA. However, after finishing the job, I would certainly be very conservative and do do some hours of local flights, checking for leaks and movements and such. The weight difference between your new tank and old will probably be insignificant to the overall W&B.

I share your sense of being conservative and would be doing a few hours of flight test first before venturing off on an XC. The tests would eventually include some acro.
 
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