The last step in building the fuel tanks is to test them for leaks. This is done by pressurizing them to about 1psi and making sure they are airtight.
The tanks have a total of four openings:
1. Fuel Cap
2. Fuel drain
3. Fuel pickup tube
4. Vent Line
I installed the fuel cap with a latex glove to make sure it was airtight. I also capped the main fuel pickup line, and installed a bicycle-style stem on the fuel drain. I left the fuel drain line open.
There are two ways to pressure test the tank. One is to hook up a balloon to the fuel vent line, and inflate it through the fuel drain. You then make sure the balloon doesn’t deflate after a few days. The problem here is that you have to compensate the expected diameter of the balloon for any temperature changes. This sounded difficult.
The other way to do this test is to connect a clear plastic hose to the fuel vent line, and pour some water in it to form a water column (making sure the water doesn’t go into the tank!). This also requires compensating for temperature changes, but I figured it’d be a lot easier to accurately measure the distance between two water levels than a balloon diameter. So, I got me some clear hose from Home Depot (they have them in the plumbing section) and used food coloring to dye some water for my test. I then mounted the tank up high on two special platforms and used my little bicycle pump to get about 27″ of water (~1psi). I installed an old thermostat nearby, and I would check the temperature two or three times a day, as well as the water level.
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This is one of the tanks access plate ready to get drilled. The tube is the fuel intake. Notice the 90 degree bracket has ‘teeth’ to keep the nut from rotating. This was a service bulletin for people with an older revision of the tanks. They had to pry their tanks open, drill a hole through the nut, and use safety wire to secure it. This little bracket eliminates all that work.
This was one of the last steps in sealing the tank. Sorry for the lack of pictures. The tank sealant gets EVERYWHERE, and I didn’t feel like cleaning sealant off my camera. 🙂
Here is a close up of one of the fuel tank vent lines. This is just a tube that goes along the entire length of the tank, and it terminates open on the inside near the fuel tank. It goes to a fitting on the last rib (shown removed in the picture), and eventually goes to a drain on the belly of the plane. This is so that pressure (or vacuum) doesn’t build up in the tank and causes it to burst. When I get ready to install the inboard rib, I will flare the end and hook it up to a threaded fitting. You can see the blue nut near the rib in the picture below.
This was my first time using a pipe-bender, and it wasn’t bad at all. Of course, the aluminum tube is very soft, so it is very easy to work with.
I’ve spent the last several weeks working on sealing and riveting the fuel tanks. The tank sealant gets on EVERYTHING, so I have not taken very many pictures. We took a few when we first started, and then the rest are after the tanks are mostly done…
Here is my usual setup — Respirator and safety glasses. The tank sealant is not too bad, but the MEK I was using to clean up is scary stuff. The label says it will give you a headache and as long as there is plenty of ventilation (notice open garage door) it is not dangerous, but one whiff of the stuff and you know it can’t be good to be breathing it. Also, it will melt almost everything, including your gloves, your eyes, and probably your neurons if you breathe too much of it..
Here is me applying tank sealant to an internal rib.
Here here is Fabiola decked out in her respirator and glasses too..
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Chugging along. I am in the process of fitting the capacitive senders, modifying the end rib, etc…
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The last step before starting work on the right fuel tank is the fuel cap. The cap flange has a slight bend in it to conform to the shape of the leading edge. It took a while to get it to line up. Once I had a good match, I used some C-clamps to hold it in place while I drilled the holes.
Then, on the bottom side, I made a little bracket that will hold the vent tube when it is finally fitted in.
And that’s it for now….I’ll start work on the right tank, which will hopefully be just a boring repeat of the left tank. So, no pictures for a while.
The end rib of the tank (the rib closest to the fuselage) needs some holes for the vent and fuel lines, as well as the BNC connector and the reinforcement plate where the inspection plate attaches.
I started by drilling the vent line and BNC holes. Note that the vent line is a 7/16″ hole, which I drilled to 9/16″. I wasn’t ready to get a new rib and start over, so I made a washer out of 0.032″ aluminum that will sit between the rib and the fitting, on the outside of the tank. I emailed Van’s about it, and they said it’s OK as long as I seal it well enough so it doesn’t leak.
After dealing with this screwup, I lined up and drilled the holes for the reinforcement plate. I found that the best way to do this was to place the reinforcement plate on the outside web of the rib, making sure the rib hole and the reinforcement plate hole match up. I then drew the outline of the reinforcement plate with a marker, and placed the access plate in the same spot. This guarantees when I drill the access plate to the rib, it will be centered in the hole.
After drilling the screw holes, I clecoed in the reinforcement plate and drilled the platenut holes.
This is the fitting that allows your to drain water from the tank. The fitting actually goes on the outside of the tank (the other side from where I have it). It’s just easier to drill it from the top and then just flip it. Note the two blue marks to make sure I can line it up later.
After a long break due to some work travel, I’m back in business. The fuel tank rib at the end of the tank has an access plate, where the fuel pickup is located. The hole for this plate has to be drilled out. The hardest part of this was just finding the center of the hole. Once I lined things up in the drill press, it was just a matter of holding on, clenching my teeth, and letting the fly-cutter do its thing.
The result is a nice clean hole…
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The bottom of the fuel tank has two rows of stiffeners to keep the skin from sagging. These come in long rows which have to be cut, trimmed, etc.
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