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Fuel Tank Follies

mulde35d

Well Known Member
Friend
Since I am about 24 hours from closing up my right and left fuel tank with the Tank Baffle, I figure I would poll the group to see if their is anything you wish you had done before sealing it up. Your past follies may help me and everyone else coming to this point prevent the fun of re-doing a fuel tank seal.

While I am asking, I was curious just how one would replace / seal a leaking solid rivet once the tank is all sealed up. Seems it would be exceptionally hard to reach on the back side through the fuel cap and disassembling the tank baffle would be exceptionally labor intensive.

18-6-2.jpg
 
How

I pressure tested prior to permanently securing the rear baffle.

I have to ask, how did you manage to pressure test it before securing the tank baffle? I would think you would at least have needed to install the blind rivets to get a seal.
 
I would proseal the rear baffle in place and test without rivets if I had to. It’s no fun to find and fix after the plane is assembled.
 
I'm assuming you have dry fit/aligned the fuel sender floats. This was a bear on our QB tanks - peering into the tiny fuel line hole(s) and following the misleading float wire bending dimensions on the dwgs.
 
I'm assuming you have dry fit/aligned the fuel sender floats. This was a bear on our QB tanks - peering into the tiny fuel line hole(s) and following the misleading float wire bending dimensions on the dwgs.
Good point to do it at this point and certainly more accurate but there are other ways that is not as painful when it is closed.
 
Since I am about 24 hours from closing up my right and left fuel tank with the Tank Baffle, I figure I would poll the group to see if their is anything you wish you had done before sealing it up. Your past follies may help me and everyone else coming to this point prevent the fun of re-doing a fuel tank seal.

While I am asking, I was curious just how one would replace / seal a leaking solid rivet once the tank is all sealed up. Seems it would be exceptionally hard to reach on the back side through the fuel cap and disassembling the tank baffle would be exceptionally labor intensive.

18-6-2.jpg

From memory I had only one leaking rivet on one of the fuel drains. I used Loctite "Wicking" thread locker (can't remember the number). I was greatly relieved when it worked and still no problem 21/2 years later.
There are plenty of threads on VAF about tank leaks.
 
Almost there

Fuel level sender lines are bent and installed, fuel drain hooked up / sealed / torqued. Left wing is pictured below.

I can't imagine trying to bend the fuel level sender in a quickbuild with the rear tank baffle installed.

I am going to wait till this evening to attach the tank baffle in case any amazing ideas pop up on the thread. Otherwise I will clean the interior real well with denatured alcohol and seal it up.

Interestingly, I haven't even used 1 full quart of tank sealant. The rear baffle will probably force me to break into the second can, but just slightly. Should leave plenty available for other tasks later on in the build.

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In the last picture, I see that you have installed the fitting and B-nut on the fuel vent line. Make sure it is tight (I?m sure it is). QB wings come with the tanks built and sealed and you install the cover and plate on the inboard tank rib. This is your (my) chance to take a look inside the tank and make sure everything looks OK. Well, a finger tight (barely) B-nut looks just like a tight one. I didn?t put a wrench on it and I got to remove the tank, inboard cover plate, and tighten that nut. Pressure test didn?t catch it because the vent line fitting is capped on the outside for the test. A loose B-nut will leak fuel through the vent line anytime there is more than about 12 gallons in the tank. So far there have been 4 QB tanks on our field (KHAO) with loose B-nuts and fuel leaking through the vent line from the inside of that fitting. That was my right tank. My left tank isn?t leaking, so I assume it is tight. Reaching in that cover plate hole and reaching forward with a wrench would have saved a lot of aggravation. For those with QB parts, don?t assume anything.
 
appreciated

In the last picture, I see that you have installed the fitting and B-nut on the fuel vent line. Make sure it is tight (I?m sure it is). QB wings come with the tanks built and sealed and you install the cover and plate on the inboard tank rib. This is your (my) chance to take a look inside the tank and make sure everything looks OK. Well, a finger tight (barely) B-nut looks just like a tight one. I didn?t put a wrench on it and I got to remove the tank, inboard cover plate, and tighten that nut. Pressure test didn?t catch it because the vent line fitting is capped on the outside for the test. A loose B-nut will leak fuel through the vent line anytime there is more than about 12 gallons in the tank. So far there have been 4 QB tanks on our field (KHAO) with loose B-nuts and fuel leaking through the vent line from the inside of that fitting. That was my right tank. My left tank isn?t leaking, so I assume it is tight. Reaching in that cover plate hole and reaching forward with a wrench would have saved a lot of aggravation. For those with QB parts, don?t assume anything.

I appreciate that insight. I torqued the nut to 60 inch/pounds (45-65 recommended) and also applied Loctite 567 to the threads before installing. Fingers crossed.
 
Tank repair - outer bay

I had to do this recently due to a slow leak that was getting worse. Purchase the parts that are normally used on the inboard end of the tank and create a new access panel. Mine was leaking at a seam, not a rivet, but the fix would be the same. An air nibbler from HF made doing the hole cut out quite easy.

Finally, no leak after 2 years of not being able to fill the tank past 13 gallons.

ZFb3Nivl.jpg


iCWD5tQl.jpg
 
fuel level sending unit setup

The float should be ALMOST touching the floor of the tank when empty, and touch the top when full (about 1/8"). Adjust until you get that right!

The tanks on my plane are almost 8' long, so the sender says FULL until I burn off about 10 gal. Your setup is likely to have a bit of that also.

I would add to put a dab of the Black Death stuff where the float might touch the skin (top and bottom) so it won't wear a hole in the skin.

The workmanship looks good - carry on!
 
Here are a couple images from a tank sealing document that I came across. They might be helpful. You can see that this says to cover all the edges of surfaces that could possibly leak.

I bought some type A sealant from skygeek.com for the overlay. This is a thinner, honey-like consistency. I applied it to the seams and rivets with a hobby syringe. Didn't take long.

Mu8Ju6b.jpg


and

2psygWr.jpg


There's also another handy tank sealant, access hatch sealant, which is intended for removable panels.

Dave
 
I agree with the last post. Your tank does not come close to the illustrations. I would almost say it is guaranteed to have a leak. I am sorry to say this to you. Better someone says something now than later, though.

I would strongly recommend looking at the illustrations closely and comparing. I would say you need almost 2x to 3x more proseal.

My 2c.
 
Don I put tank in cradle then taped up the rear baffle in place. Put a fair bit of weight along the rear baffle. Hooked up the balloon.
Did soap test and found a leak which was easily fixed.
 
Success

With both fuel tanks all closed up, and a slight adjustment to the fuel tank cap tightness, the balloon has remained inflated for about 30 minutes. I will put about 5 gallons of 100LL in the tank and let it sit in different orientations for a while to verify, but for now I am calling this success. I plan to close up the right tank next.

In all it took about 2/3rds a can of tank sealant per side with good taping and about ten 60 ml syringes with catheter tips to get a clean look and reduce total weight from excess sealant. The catheter tip was great since it fit over the back side of the rivets to seal them up. I met one gentlemen who used 5 quarts of sealant on his fuel tanks and for the life of me I can't figure out how. As long as the rivets are sealed on the skin and a large filet is placed on the end ribs to seal the edges, the tank holds liquid. I simply followed the directions and focused on sealing the backside and front side of each rivet.

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