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Thread: Fuel Line

  1. #1

    Fuel Line

    I am rebuilding a Kitfox II which was badly damaged in an accident. The remains had no fuel lines installed anywhere, except for a short piece from the wing tank. I assume it may have been connected to aluminum fuel line, but there is no evidence to support that assumption. I have installed a new header tank, located behind the seat. I will be installing a Facet pump between the header tank and the gascolator, or perhaps between the gascolator and the pulse pump, which is located on the firewall. I am trying to decide if there is any problem with use of flexible fuel line such as the Bing blue line between the wing tank and the header tank, and between the header tank and the firewall, as well as in the engine compartment. The line has a temperature rating of 250 deg F, and a pressure rating of 80 lbs/sq in. The pressure rating is fine for this installation, as the maximum pressure is on the order of 2-3 lbs/sq in. I know certified aircraft use solid fuel line prior to the firewall, but given a number of considerations, I would prefer using the flexible line. If need be, I can protect the line from getting pinched prior to the firewall by careful routing, or by using a short section of solid line in areas where this might be a significant risk.

    I am looking for ideas and opinions before I make a decision. Thanks in advance.

  2. #2

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    I'm not a fan of flexible lines in the cabin, especially when you add a fuel pump to the mix. It might be a little harder to figure out and route a hard line now, but what are you going to do in a couple of years when you need to replace that flex line? Why not install hard line now and not have to worry about it?

  3. #3

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    Flexible fuel lines have a limited life. Thus any permanent installation that does not require flexibility should be done with solid aluminum lines. This minimizes future maintenance and protects against fuel line leaks or failures as the flexibly hose ages.

    The fuel line from the gascolator to the engine needs to be flexible to allow for engine movement, but it it very important to have that line protected with a product like Aeroquip Fire Sleeve.

  4. #4

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    If a fire in the cockpit started, for whatever reason, what stops the plastic line from melting and adding fuel to the fire right underneath you?

  5. #5
    steveinindy's Avatar
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    I'm not a fan of flexible lines in the cabin
    There's no good justification for routing a fuel line of any variety through the cockpit.

    If a fire in the cockpit started, for whatever reason, what stops the plastic line from melting and adding fuel to the fire right underneath you?
    Which is why a few extra dollars for a fire-resistant fuel line is a good idea along with fuel shut-off valves between the tank and the cockpit. Also, there are very few in-cockpit fires (that aren't fueled by spilled gasoline, etc in the post crash environment) that can't be controlled by isolating the electrical components. This is one of the major reasons why being a little cautious about your choice of materials (structural and insulation as well as things like fuel and electrical lines), the layout of systems, etc can make a huge difference in whether a crash is survivable or not.

    Thus any permanent installation that does not require flexibility should be done with solid aluminum lines
    Or something more resilient than a simple plastic line. Aluminum lines tend to increase the forces applied to the tank if a wing is sheared off and can actually cause more problems from a fire safety perspective than they solve. There are plenty of better options in any aircraft supply catalog such as Aircraft Spruce.
    Unfortunately in science what you believe is irrelevant.

    "I'm an old-fashioned Southern Gentleman. Which means I can be a cast-iron son-of-a-***** when I want to be."- Robert A. Heinlein.



  6. #6

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    Hmmm, I was thinking copper....
    The opinions and statements of this poster are largely based on facts and portray a possible version of the actual events.

  7. #7

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    Not sure with wing tanks or a behind the seat header you could avoid fuel lines routing through the cockpit?????? Anyhow stainless braided fuel line with an fittings is a much better choice than the blue bing line although that is exactly what I had in my first experimental and it was not a problem, I think alot of the avid's/kitfoxes use that line with no issues just route it to protect from pinching and chaffing.

  8. #8
    steveinindy's Avatar
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    Not sure with wing tanks or a behind the seat header you could avoid fuel lines routing through the cockpit??????
    Just my two cents (based largely off of the US Army crash survival research related to fuel tanks for light aircraft and helicopters) but the only thing dumber than a fuel line through the cockpit is a fuel tank in the cockpit.

    With wing tanks, keeping the fuel lines out of the cockpit is pretty easy if you're willing to put some effort into the design. Sadly, with a lot of the kit and plans built designs out there it seems like once the designer(s) got past the aerodynamics phase they took the path of least resistance and didn't give much thought to any of the subsystems beyond "Eh....that'll work".
    Unfortunately in science what you believe is irrelevant.

    "I'm an old-fashioned Southern Gentleman. Which means I can be a cast-iron son-of-a-***** when I want to be."- Robert A. Heinlein.



  9. #9

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    Well every piper cub and aeronca champ and tens of other designs have header tanks right there to smash into you if you crash, so I guess i just won't crash with any fuel left. I see the logic, but small aircraft have little other choice. So just for conversation sake what small tractor engine design doesn't have at least fuel lines through or under the cockpit?

  10. #10
    steveinindy's Avatar
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    So just for conversation sake what small tractor engine design doesn't have at least fuel lines through or under the cockpit?
    Under isn't so much of a problem if you properly shield the fuel lines. It's yet another use for thick-walled aluminum tubing or something similar In my LSA design, the fuel tanks inside the structural protection of the wing box (which is design to stay intact up to a 40 g vertical impact and roughly 90 g longitudinal impact because the seats are attached to it and because it protects the fuel lines along with providing a large part of the structural integrity to the cockpit roll cage) and then forward of the firewall. There are four self-sealing quick disconnect valves on each line: one at the tank, one at the junction of the wing and fuselage, one at the posterior side of the firewall and then one right before the fuel line enters the engine. The one at the posterior firewall can also be triggered by the pilot to seal off fuel flow to the engine compartment in the event of a fire.

    I see the logic, but small aircraft have little other choice
    Honestly, especially in the homebuilt community, there are plenty of better choices but so many of us get hung up on the idea of expediency (read as: "wet wings") or tradition (read as: header tanks and plastic fuel lines)

    Well every piper cub and aeronca champ and tens of other designs have header tanks right there to smash into you if you crash, so I guess i just won't crash with any fuel left.
    Touche, but just because a design is a classic and sold well doesn't mean it is something to be emulated in every detail. All designs have room for improvement. That said, I'm looking forward to getting my taildragger endorsement this summer in an Aeronca.

    The one advantage of a partially full aluminum header tank is that the grade of material many of them are made out of is one of the best metals to use to form an energy absorbing impact surface for one's face. (No, I'm not kidding but I'm also not actually suggesting a cockpit mounted fuel tank as a safety measure either).
    Unfortunately in science what you believe is irrelevant.

    "I'm an old-fashioned Southern Gentleman. Which means I can be a cast-iron son-of-a-***** when I want to be."- Robert A. Heinlein.



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