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Thread: High wing taildragger fuel system

  1. #1

    High wing taildragger fuel system

    I'm trying to figure out the fuel system for my Wag 2+2/ PA14 scratch build. Two wing tanks, each with front and rear ports. Plans call for a header tank with simple on/off valve. Does anyone have a good diagram for a system that works with either the header tank or without? I'm concerned about unporting during climbing or descending. If fuel lines are run along wing root than forward as the plans show, the rear port would be below the flow of the fuel. Wondering how others have solved this issue. My tanks differ from the diagram as they have a forward port and a rear port on each tank.
    Thanks,
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  2. #2
    Dana's Avatar
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    With the header tank you shouldn't have to worry about the wing tank(s) briefly unporting during descent. During a climb, since the line between the wing and header tanks is full of fuel, it will continue to siphon even though portions of the line may be above the fuel level in the tank.

  3. #3
    FlyingRon's Avatar
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    Siphon? It looks like a straight gravity feed to me. In fact, many high wings get by without an accumulator tank at all. Your typical Cessna just runs the lines to the fuel selector.

  4. #4
    Dana's Avatar
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    Quote Originally Posted by FlyingRon View Post
    Siphon? It looks like a straight gravity feed to me.
    It is, but he was talking about climb, when it's possible that the fuel line running forward from the rear of the tank could be above the level of fuel in the tank itself at high pitch angles if the tank itself is nearly empty. It that case it would be siphoning that (hopefully) keeps the fuel flowing.

  5. #5

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    There is no law of physics that requires use of both forward and aft fuel tank ports. You could cap the front port of each tank and install the plumbing as shown in the drawing in post #1 and stop worrying.

    Best of luck,

    Wes

  6. #6
    bigdog's Avatar
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    My L-2's have the forward port go down the front door post and the aft port down the rear door post. They join in a Tee fitting near the floor then go up to the header tank. The right and left rear lines have a crossover under the rear floor with a quick drain. I suppose you could do the same without the header tank but why? What's your objection to the header tank that's already in a proven design?
    Regards,
    Greg Young
    1950 Navion N5221K
    RV-6 N6GY - first flight 5/16/2021
    1940 Rearwin Cloudster in work
    4 L-2 projects on deck

  7. #7
    FlyingRon's Avatar
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    Quote Originally Posted by Dana View Post
    With the header tank you shouldn't have to worry about the wing tank(s) briefly unporting during descent. During a climb, since the line between the wing and header tanks is full of fuel, it will continue to siphon even though portions of the line may be above the fuel level in the tank.
    You've still lost me. What siphoning? If you have two ports and one is open and the other is in fuel in the gravity system, the fuel will flow through the one that has fuel. No siphoning is required.

  8. #8
    Dana's Avatar
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    Quote Originally Posted by FlyingRon View Post
    You've still lost me. What siphoning? If you have two ports and one is open and the other is in fuel in the gravity system, the fuel will flow through the one that has fuel. No siphoning is required.
    In the illustration in the first post, there is only one port, in the rear of the tank; the front port is a vent. The line from that rear port runs forward along the lower edge of the tank. If the tank is nearly empty to the point that the fuel level in the tank is below the 45 elbow at the front of the tank, fuel will not flow unless the line is already full and siphoning.

  9. #9
    FlyingRon's Avatar
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    Ah, hadn't thought about the tube not being a continual downward slant.

  10. #10
    MPerkins's Avatar
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    At some point, most of us find benefit from having installed two additional shutoff valves, one each for tank. Agreed that they're superfluous 99.9% of the time, but:
    1) if the airplane is parked one wing-down, fuel will crossfeed and overflow the low tank's vent, and
    2) calibrating the sight gauges with crossfeeding is difficult, and
    3) maintenance of one tank requires de-fueling both tanks (plus, one tank can be used for temp storage of fuel from the other if there are shutoff valves),
    4) roll trim can be provided by unbalancing the tanks (but this violates redundancy, so I'm not cray about the idea except in special cases), and
    5) you can get home even with one leaking tank.

    Note that I am a proponent of feeding from both tanks all the time in flight for lots of reasons and only turning them off in unusual cases. A header tank is also marvelous.

    My Kitfox fuel system is not pretty, but fuel always goes downhill (except where it travels along the floorboard but is still guaranteed to be pressurized by the header tank).

    I also used nylon fittings, but after about 15 years, they'd shrunk to the point that the only thing keeping fuel from leaking was the (very excellent) Dow 730 sealant. No credit goes to me for missing this issue for at least a year or two.

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