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Fuel line connections at fuselage

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  • Fuel line connections at fuselage

    I had decided I did not want to use a hose connection between wing and fuselage fuel lines, mainly because I didn't have a beading tool. I installed bulkhead fittings in the wing root and planned to run the fuselage lines to connect there. A consequence of that is that the fuel lines out of the tank to the bulkhead fittings are only 8" long. With everything plumbed up it is a very rigid setup. My concern now is that if the fuel tank moves much at all it could crack that short piece of line. Would be a terrible place to have a leak. Using hose connections allows those lines to move a little. Would like to hear others thoughts on this.

  • #2
    Some STC'd fuel systems REQUIRE short runs of rubber hose for just that reason. CubCrafter and Dakota Cub both use sections of mil spec hose to mitigate vibration in their upgraded Super Cub fuel systems. They were designed and tested that way. A beading tool is pretty cheap, Earl's plumbing.


    • #3
      I am using hose connections.


      • #4
        The tanks do move around ever so slightly. There's a lot of weight and g-force involved, and the thin flexible tank straps will allow for some slight movement. But it's almost nothing.

        I don't think it's enough to cause a problem, the aluminium line will move slightly. The weak point will be the AN fittings, which can leak if they move around much. But personally I doubt it would cause an issue.

        Several planes are flying with hard-lines at the wing root. I don't think anyone has reported back though.

        The line beading tool is widely available in the USA and very cheap. You can buy online. Flexible hose is what Bob called for in the plans. Provided there's a large enough gap between the line in the wing and the line in the fuse, to allow the hose to be worked into place, the hose is very easy to use.
        Last edited by Battson; 03-14-2018, 09:56 PM.


        • #5
          I had a similar concern with the 6ā€ fuel line between my electric fuel pump and the firewall bulkhead fitting. Iā€™m replacing the aluminum tube with a pre-made AN6 Jose from Summit Racing. You could do the same from the tank to a bulkhead fitting at the wing root.

          Or you could buy the 3/8ā€ Earls bead roller for $40 and sell it to me for $30šŸ˜ I have to buy a 1/2ā€ bead roller too.
          I'm a Tapatalk user so I can't see your "comment"


          • #6
            Like Jon said it probably would be okay. I called around and a builder locally has both an Earls bead roller and a homemade one that he says makes a better bead. I'm going to be using hose attachments, will be one less thing to worry about. Would have taken you up on your suggestion Whee if I hadn't found one to borrow.


            • #7
              I riveted my Patrol's gas-tanks together last year and just now got around to the welding. A friend of mine has welded one of them now, so I plugged up all the bungs and pressurized the tank until some bulging between bulkheads is evident. I screwed a 0-30 psi gauge into one of the bungs but the needle still shows 0-spi. The tank made a couple of little popping sounds but so far I detect no bubbles when I checkng all the seams and rivets with soap-water. Need I do anything more in the line of testing?


              • #8
                I found the bubbles were not a great tell-tale, it takes a lot of air to fill a bubble... provided the soap has film over exactly that spot. It is not reliable.

                Air bubbles in soap failed to show about a dozen small leaks in my fuel lines.

                I prefer to put a coloured liquid inside and pressurise that with air on top. Much safer than making an air-bomb, and you see the colour leaking out almost immediately. You can leave it overnight and even the smallest hole will leave a huge stain below - white paper underneath helps to show any drips.


                • #9
                  Leak check process, on a previous build, involved securely plugging all but 2 outlets. Screw a ball valve into one and affix a good, helium grade balloon onto the other. Pressurize the tank to inflate the balloon. This doesn't take much pressure. Close the valve and plug it securely. If the balloon stays inflated till the next morning, the tank is presummed good. You have to use a good balloon, though. Cheap balloons probably won't hold overnight, no matter how tight the tank is.