Weeks 10-11: Right Wing / Fuel Tank

I didn't get an update done last week, but I have been busy working on the right fuel tank. As a part of prepping everything I got the level sender put together and attached to the mounting plate. The instructions where not extremely clear, but I figured out that I needed to disassemble the level sender from the original bracket and attach it to the smaller one provided with the kit. I then ben the arm per the manual and fit it in the tank. To get the full range of motion I had to rotate the arm so the ball is more in the center of the tank vs in line with the rest of the assembly.

To correct the issue with the hole for the fuel tank cap I market the correct hole size on the skin, then used a half-round file to enlarge it. It's not perfect, but I think you will have to look very close to notice. Overall, this was an easier process that I thought it was going to be.

The next step was to start sealing the tank. I followed Midwest Sky Sport's recommendation and used 1422-B2 sealant. Per the instructions I started with the ribs and front channel. This way the noes side of the front channel can be completely sealed before installing into the skin. I also sealed the level sender plate at the same time. Once this was done, the rib assembly was sealed into the skin. This allowed access to put extra sealant on the tank side of the rivets.

The last step was to seal the back channel onto the ribs and skin. There was no access to the inside of the tank, so I did my best to get all the rivets sealed from the outside in addition to the sealant on the flanges.

After allowing two days for the sealant to cure, I started leak testing. The instructions just say to pressurize the tank to 0.1 bar (about 1.5 psi) and use soap/leak check solution to find any leaks. The tank needs to hold pressure for at least one hour to pass the test.

Once I had the tank assembled, I figured out what I think is a good way to do the leak test. I ordered a couple of AN6 flare caps to seal the supply and return connections and a 1/4" NPT schrader valve to install in the drain fitting. The vent connection already had the 1/4 tubing installed, so I decided to use this to measure the pressure. I used a length of plastic tubing to create a homemade manometer. 1.5 psi is about 40" so the height of the tubing 'U' needed to be about 50". I then filled this about halfway with water (using the little funnels I had the foresight to order with the tubing and other parts).

As soon as I started the leak test I found a large hole in one of the corners of the back plate. This was a big enough leak that the tank wouldn't hold enough pressure to look for other leaks until it was fixed. I put more sealant on that corner, then after a couple days of curing time tested it again. This allowed me to find a couple of other leaks. After fixing those the pressure in the tank was still slowly dropping, so I re-checked all the seams again and found another small leak. I resealed that area, and am waiting on the sealant to completely cure before testing again. Fingers crossed that is all of them.

While waiting for things to cure, I also made and installed the bracket for the GMU 11 magnetometer. It needs to be installed within 3 degrees of level, but the wing has a 4.5 degree dihedral angle so the bracket has to accommodate that. After getting it installed, my digital level shows a relative angle between the bracket and the bottom wing skin of 4.1 degrees. To attach the GMU 11 to the bracket I am using aluminum riv-nuts. It is important to minimize magnetic material around it to prevent interference.

I also had a visit from an EAA technical councilor. It's definitely reassuring to have the project looked over by someone with his level of experience. Since the visit is done, now I can finish skinning the wing. I finished securing and cleaning up the wiring, and prepped the skins so they are ready to install. If the fuel tank passes the leak test, then I should be close to having the right wing finished up.