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Thread: Leaking airspeed line

  1. #1

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    Leaking airspeed line

    Indicated airspeed has dropped a bit from normal. Investigation discovered the aluminum tube from wing root to jury strut has a leak somewhere. This cub has pitot tube built in front jury strut, so tube runs in front of forward spar. No inspection holes in the leading edge. Anyone have a suggestion to fix? It's not time for new fabric.
    Owned same cub for 26 years!!!

  2. #2
    www.SkupTech.com mike mcs repair's Avatar
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    use GOOD contact cement like 3M Fastbond 10 and add some inspection grommets, round or rectangle and then cut out.... very simple...

  3. #3

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    Mike, how is that airspeed tube secured to the nose ribs or spar? Is it taped to ribs? Is there a local source for the aluminum tube?
    Owned same cub for 26 years!!!

  4. #4
    www.SkupTech.com mike mcs repair's Avatar
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    Quote Originally Posted by Webfoot View Post
    Mike, how is that airspeed tube secured to the nose ribs or spar? Is it taped to ribs? Is there a local source for the aluminum tube?
    cloth friction tape, and not up in nose rib area usually ???? ... behind front spar, taped to rib braces...

  5. #5
    www.SkupTech.com mike mcs repair's Avatar
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    are you SURE you have a LEAK, and not a BLOCKAGE like WATER in it?? my first solo flight after signed off turned out to be with a unresponsive Airspeed indicator... not fun...

  6. #6

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    IMG_2204.jpgIt's a leak, not a blockage. Appears tube is in the nose bay, ahead of the spar so any inspection hole cut will be in leading edge skins. Photo is one I took before last wing re-cover.
    Last edited by Webfoot; 10-01-2017 at 11:53 PM.
    Owned same cub for 26 years!!!
    Thanks LVDS3 thanked for this post

  7. #7
    BC12D-4-85's Avatar
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    Tell them it's an early model with the pitot on the front jury strut and aluminum line through the D-bay (?). I sent you a mail about threading twisted stove wire through the wing from the cockpit

    Gary

  8. #8
    coxcub's Avatar
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    If you have any flexible hose connections - have they perished or are any of the clips slightly loose?

    I had the loose clip (several) problem when picking up my SC from rebuild out of a very very short strip - V1 did not exist! - Plane was ready to fly so brought it home with very little speed showing - seat of the pants and RPM.
    Thanks LVDS3 thanked for this post

  9. #9
    Eddie Foy's Avatar
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    Abandon the old line and run a new one behind the spar. Use poly tubing.
    http://www.aircraftspruce.com/catalo...?clickkey=3505
    Eddie Foy
    "Put out my hand and touched the face of God"

  10. #10
    wireweinie's Avatar
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    If this is still the stock set up, the lines are connected with 3/16 rubber hose at the wing root and at the jury strut. Were there any more 'non stock' connections between those points?

    If you verify that the tubing has no other hose connections that need replacing, you can replace the aluminum tubing. Get access to the connections at the top of the jury strut (like Mike said) and open the wing root fairings. If you use soft, 3/16" aluminum tub, you can route it from the strut to the root. If you need, you can fish it with a string or feed a nylon tube in first and push the aluminum tube through it. Takes patience but it's doable.

    Then re connect the new lines to existing, with rubber hose. If all is correct, there should be no noticeable leaks in the pitot lines over about a one minute interval.

    Web
    Life's tough . . . wear a cup.

  11. #11

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    Without cutting a hole in the leading edge skins, I could push replacement aluminum tubing through (about 4 feet) but it would be only secured at butt rib and at jury strutt opening. Would this be acceptable or would it be better to use rubber or plastic tubing? Anybody know a source for 3/16 tubing around Fairbanks or Anchorage?
    Owned same cub for 26 years!!!

  12. #12
    wireweinie's Avatar
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    The factory just used friction tape to tape it to the ribs. If you want, just leave it in the nylon tube used to snake it into place. That will provide mechanical protection for the tube and any ribs it touches.

    Call Glacier for the tubing. 907-745-7100 and tell them you need 3/16", soft, aluminum tube.

    The old tube lasted this many years, replace it with the same. Rubber hose dries and cracks. Nylon (Tyvek) leaks like a sieve at the fittings. And both are bulky compared to aluminum.

    Web
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  13. #13
    www.SkupTech.com mike mcs repair's Avatar
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    Quote Originally Posted by Webfoot View Post
    IMG_2204.jpgIt's a leak, not a blockage. Appears tube is in the nose bay, ahead of the spar so any inspection hole cut will be in leading edge skins. Photo is one I took before last wing re-cover.
    thats fine, you can cut an inspection hole(s) in leading edge, glue ring on first then use a hole saw, carefully.... we do that allot to install Atlee tie downs, or to get inside and pound out sins... like when you fly through trees

  14. #14

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    Problem solved temporarily. Leak was found where the tube was bent at butt rib. I cut the bend off and attached the flexible tubing, then confirmed no more leak. Found a local source for the aluminum tubing and plan to replace the old stuff sometime during warm weather or access to a hangar. Thanks for the tips!
    Owned same cub for 26 years!!!
    Thanks wireweinie thanked for this post

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