Leaking Fuel Tank - pictures

After filling my fuel tanks for the first time a few days ago to calibrate my fuel level senders, my tanks have been sitting with about 18 gallons of fuel in each side. Yesterday afternoon, while crawling under the right wing to make an adjustment to the aileron linkage, I saw this...

Uh Oh!!! So I looked a little closer, and found that there were several rivets that had bulging paint blisters. Probably more weeping rivets under the paint!

Well, after talking to a couple of friends and searching out VAF forums, I decided that I couldn't allow the situation to stand. After de-fueling and removing the fuel tank (about 45 minutes), I took the tank home and marked the offending rivets - just in case I needed future reference.

Looking at the plans, I reminded myself that I would not be able to reach through any lightening holes to pro-seal the rivets, since the baffles/ribs don't have any lightening holes!

Looks like I'm going to have to cut an access hole in each bay to get some pro-seal in there. I measured my hand and determined that I could reach through a 3 1/2" access hole, so out came the fly-cutter.

I had to cut into three bays. Mix up a batch of pro-seal - no reason to scrimp on this stuff - I'm only adding a couple of ounces and I REALLY don't ever want to open this up again. I used a round tip applicator to force about a 3/8" fillet of pro-seal along the joint. The rivets are on the exterior of the tank, and there's no fixing the rivets after the fact. So the joint is gooped up. I used a little MEK on my gloved finger to really force the pro-seal into the joint and smooth it out.

Next step is to make some 4" cover plates and install nutplates in the fuel tank.

After lots of vacuuming and cleaning pro-seal, it's almost ready to pro-seal the cover plates and screw them in place.

I'll give the pro-seal a couple of days to completely cure, then fill the tank up with av-gas while it's still on the bench. I'll let it sit for a couple of days to see if there's any more leakage before bolting it back onto the wing.

In the meantime, first engine start is scheduled for tomorrow and I don't see any reason to postpone that event!

Scott,

I can think of a good reason to postpone the event. Van's does not recommend running the engine without the wings attached, for structural reasons. Having a wing attached without it's tank-attach fittings securing the wing could cause problems. I'd wait, or at least consult with Van's before doing this.

Bummer about the tank leak though. Been there, done that, all better now but it took some work.

I am not sure new Pro-Seal can just be added on top of old Pro-seal. Good luck with your attempt. I re-sealed Mooney tanks once and it was a mess. Had to remove all factory sealant before the new stuff could be added. Wear a mask.

DakotaHawk said:

I'll give the pro-seal a couple of days to completely cure, then fill the tank up with av-gas while it's still on the bench. I'll let it sit for a couple of days to see if there's any more leakage before bolting it back onto the wing.

Click to expand...

Are your tanks slow build or factory made QB.

A few notes.

I used a little MEK on my gloved finger to really force the pro-seal into the joint and smooth it out.[QUOTE/]

No surprise, but the manufacturer has specific proceedures and guidance for finger tooling:

Do not use lubrication such as soap, detergent, oil, etc; however, use plain water, or preferably, a 50/50 solution of Isopropanol alcohol and water for smoothing purposes.

I'll give the pro-seal a couple of days to completely cure, then fill the tank up with av-gas while it's still on the bench.[QUOTE/]

For CS3204-B-2, cure time under standard conditions (77F +- 2, 50%RH +-5) is 72 hours to Shore 35A. That's not fully cured, but it is considered cured enough for service. Full cure is about 50A. Cure is accelerated with increased temperature and RH, and extended with lower temperatures and RH. Point is, "a couple days" is not something we want to get in our heads as good proceedure. Cure time can vary a lot, so carefuly monitor temperature and humidity if you intend to push a return to service. The only sure indicator is a durometer. If a firm thumbnail push leaves no mark you're generally good to go. When in doubt let it cure more.

Click to expand...

Click to expand...

While at it, I would replace those cork gaskets with just proseal. Proseal does such a better job.

On related subject:
I may have to deal with this fuel leakage at some point in the feature as I found very little blue stain below my root fairing about a month ago, the thing I had feared the most, leaking fuel tanks. After taking the root fairing off, it seemed the leakage was thru either one screw that holds the fuel gauge unit or its gasket. I tighten the screw a bit and so far have not seen any more stain but this would be a relatively easy fix if I have to deal with it.

Good luck
Mehrdad
RV7A - IO360M1B

Bavafa said:

While at it, I would replace those cork gaskets with just proseal. Proseal does such a better job.

On related subject:
I may have to deal with this fuel leakage at some point in the feature as I found very little blue stain below my root fairing about a month ago, the thing I had feared the most, leaking fuel tanks. After taking the root fairing off, it seemed the leakage was thru either one screw that holds the fuel gauge unit or its gasket. I tighten the screw a bit and so far have not seen any more stain but this would be a relatively easy fix if I have to deal with it.

Good luck
Mehrdad
RV7A - IO360M1B

Click to expand...

Mehrdad,

Two things to think about, one dip your screws in proseal when replacing them. This will form a good seal. Second, use cap screws so you can remove them with an allen wrench/key. That makes life a lot easier than useing a screwdriver.

That's a real bummer Scott. Did your tanks pass the overnight ballon test?
I only ask because it seems some leak and some don't regardless of the test.
I passed but am still nervous.

boom3 said:

Did your tanks pass the overnight ballon test? I only ask because it seems some leak and some don't regardless of the test. I passed but am still nervous.

Click to expand...

The balloon test tells you the tank doesn't leak under static conditions. It indicates nothing about how it will seal following dynamic flight loads. Sorry.

There is no such thing as a perfectly rigid aircraft structure. Think of your tank as a flexible envelope expected to contain many times its own weight in sloshing liquid at up to 6 G's. In addition to fuel, consider that the tank must bend and twist along with the rest of the wing.

Repairs complete

OK, it's been two days since this mess started. Yesterday, I prosealed the lower aft joint on the inside of the right tank. This morning, I installed covers on the three access holes that were cut into the tank yesterday. The tank will be left in a heated shop over the weekend to allow the proseal to completely cure. Next week, I'll run a balloon test again, and if that passes, then let fuel sit in it (on the bench) for a couple of days.

On a side note, after weighing the pros and cons, I decided that I would go ahead with first engine start today. After a minor glitch, the engine caught on the second blade and ran beautifully. My engine guy helped get idle and mixture set and we cycled the prop several times to get oil to all of the systems.

Scott, are your tanks QB. There seems to have been more leakage reported from QB tanks.

Hope you did both the TOP and the bottom flanges. If there were leaks on the bottom, there probably were on top as well. And you said 18 gallons...so you most likely didn't have fuel in contact with the entire top baffle flange. Anyway, that'd be my advice!

The tank was a slow build, so I can only blame myself for any mistakes made in the construction.

What did I learn from this? Use lots of pro-seal the first time around. When you attach the rear wall of the fuel tank, you're doing it blind. You can't see what's going on inside the tank. You're using blind pop rivets to close out the tank. You have no idea how good your seal is until it is too late to make an easy fix. So goop up lots of pro-seal, scuff the surfaces well for good adhesion, put a smear of pro-seal on both mating surfaces, and don't worry about a few extra ounces of pro-seal! As long as you're not blocking the fuel from flowing between the baffles, you're ok with using a little extra and ensuring a good seal.

DakotaHawk said:

The tank was a slow build, so I can only blame myself for any mistakes made in the construction.

What did I learn from this? Use lots of pro-seal the first time around. When you attach the rear wall of the fuel tank, you're doing it blind. You can't see what's going on inside the tank. You're using blind pop rivets to close out the tank. You have no idea how good your seal is until it is too late to make an easy fix. So goop up lots of pro-seal, scuff the surfaces well for good adhesion, put a smear of pro-seal on both mating surfaces, and don't worry about a few extra ounces of pro-seal! As long as you're not blocking the fuel from flowing between the baffles, you're ok with using a little extra and ensuring a good seal.

Click to expand...

Thanks for posting the pictures and all the info concerning the experience.

I am considering building new tanks to replace the blistering QB units and need lots of input to make sure the effort is not a huge waste of time.