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Thread: Fuel System Modification

  1. #1
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    Default Fuel System Modification

    I decided to eliminate the 90 degree fitting connecting line #2 to line #3 as it goes around the fuselage tube at the left rear corner of the extended baggage box. I merely extended the #2 line and swept it back a bit and rotated the T fitting just above the low point drain003.jpg.

    Checked this modification out with Mitch before I did it and he expressed a little concern that the line would perhaps have too much unsupported length so I built a standoff from the lower fuselage carbon fiber longeron tube.

    My experience has been that if you're going to have a leak it's likely to be at a fitting and this mod eliminates one - and it's one that would be almost impossible to get to after covering.

  2. #2
    Senior Member ceslaw's Avatar
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    Default Re: Fuel System Modification

    May need to wrap the bottom of the support with anti chafe tape. There may be a bump in the fabric on the bottom

  3. #3
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    Default Re: Fuel System Modification

    Quote Originally Posted by ceslaw View Post
    May need to wrap the bottom of the support with anti chafe tape. There may be a bump in the fabric on the bottom
    Right you are. My clever idea to make a standoff from the lower longeron to the fuel line was hatched before I had installed the elevator cables - which will indeed rub on the lower end of the standoff. Another lesson learned (again): whenever you think you have a better idea than the designer you need to look way ahead and be very, very careful.

    But I think I can salvage the basic idea. I'm going to make a new standoff - a flanged triangle of light aluminum riveted to the lower rear wall of the extended baggage. I'll post a picture when it's done.

    Good catch. Thanks.

  4. #4
    Senior Member ceslaw's Avatar
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    Default Re: Fuel System Modification

    Keep in mind that the ELT antenna mounts in proximity to where your triangular aluminum bracket will go. Consider whether it will interfere with your ability to reach the antenna for servicing through the bottom access hole. Also whether the bracket will interfere with the antenna's radiation and / or SWR.

    DSC_0003.jpg

    Given the plethora of connections in the fuel system, seems like a lot of thought and work to eliminate just one.

    Keep us posted on how it turns out.

  5. #5
    Administrator Pete D's Avatar
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    Default Re: Fuel System Modification

    Quote Originally Posted by ceslaw View Post
    This photo appears to show the antenna cable zip tied to the fuel line? Really not a good idea, here is why. I know that there isn't any power in that coax but that coax is bundled with wires that do carry power at other places in it's run. I have seen a couple of cases where there was a short which melted a wire bundle together and then put power into other wires that normally don't carry power. SOP is to not use a fuel line to support a wire bundle or vice versa. There are places in a cub air-frame where separation is very difficult, but actually securing wiring/fuel lines together is still not recommended.
    Pete Dougherty
    Customer Support Manager
    Cub Crafters Inc

  6. #6
    Senior Member ceslaw's Avatar
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    Default Re: Fuel System Modification

    Thank you Pete. Excellent suggestion. I will clip that wire tie and put some separation between the ELT coax and fuel line.

    Appreciate you pointing that out.

    Chuck

  7. #7
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    Default Re: Fuel System Modification

    Quote Originally Posted by jamiller View Post
    Right you are. My clever idea to make a standoff from the lower longeron to the fuel line was hatched before I had installed the elevator cables - which will indeed rub on the lower end of the standoff. Another lesson learned (again): whenever you think you have a better idea than the designer you need to look way ahead and be very, very careful.

    But I think I can salvage the basic idea. I'm going to make a new standoff - a flanged triangle of light aluminum riveted to the lower rear wall of the extended baggage. I'll post a picture when it's done.

    Good catch. Thanks.
    loath to abandon my perhaps not so brilliant idea, since it does eliminate an otherwise inaccessible fitting, I made a new support. Seems like there is still plenty of room to mount the ELT antenna. Hope I didn't paint myself into yet another unforeseen corner.
    Attached Images Attached Images

  8. #8
    Senior Member ceslaw's Avatar
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    Default Re: Fuel System Modification

    Looks good! Don't see any downside.

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