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Fuel Tank Welding Tips

Cameron

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I'm installing a flop tube in the fuselage tank of my Skyote. Because of the way that the tank is shaped, the front sits a few inches lower than the rear, a using a flop tube as a fuel pickup will leave a little more than a gallon of unused fuel. The total fuel tank size is just a touch over 6 gallons so a gallon of unusable fuel is alot. So, I want to add a protrusion to the bottom of the tank to allow the bottom of the tank to be mostly level in the level flight attitude. This will keep all of the unusable fuel from collecting in the front of the tank at a point that is lower than the flop tube pickup. This also adds almost a gallon of fuel capacity. Note that there is also a 7 gallon wing tank in case you all are wondering. See below drawing. The new tank addition is circled in red. You can also see the original tank design. The fuel tank is shown in the level flight attitude in the drawing. There's also a higher resolution pdf attached as well.

10000-800-A8010.JPG

Anyway, I've never welded on a fuel tank and was wanting some tips on how to do this. Alot of practice on some scrap aluminum is obviously in my future. I already have a to plans fuel tank. Its made out of .040" 5052. My plan is to modify it by adding the triangular "sump" to the bottom of it. The material that I have for this is .050" 5052. I was planning on lap joints everywhere except the corners. My thought was to fit everything up with as little gap as possible everywhere and then to use a few 3/32" clecos to hold the new sump in place until I can get it tacked. I'd then have to fill those cleco holes up during the weld process. My biggest fear is that the tank will warp to a point where it doesn't sit flat on its mounting surface anymore. Is there anything I can do to mitigate that? Seems like I need some sort of heat sink? Any other tips and tricks that you guys have found while welding up a fuel tank?

And yes, I know full well that I may scrap the whole tank. That's ok. If that happens, I'll just have to make another one. I'm really more interested in learning how to do this than I am in having a finished part.
 

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