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Thread: Thermal Shock

  1. #1
    Senior Member TroyBranch's Avatar
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    Default Thermal Shock

    When I bring the plane in after flying on a cold day, the wingtips near the hinge seam to be the only place that shows a visual of the slacker covering from thermal shock. This happens on both wing tips in the same place top and bottom. Is this typical on a cub wing? I know many don't fly in -20c but those days are quite often the nicest up here in the winter for flying. Not sure at what temp it doesn't do it. My guess is 0c.

    It must be the geometry of that area Maybe? Maybe the way the fabric stretches more in that area during flight? Can't figure it out.

    Curious if any have seen this?

    After about 5 minutes everything goes back to normal.

    As soon as I bring it in and crank the heat.


    Five minutes later.




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  2. #2
    Senior Member Dan L's Avatar
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    Default Re: Thermal Shock

    I've never seen that on my EX and I flown in a lot of 0 F and colder temps. The coldest in this plane was probably -20 F.

    I wonder if it could be the top coat? You've got a nice polyurethane and mine is Polytone.
    Flying Carbon Cub EX #11 since 2011

  3. #3
    Senior Member TroyBranch's Avatar
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    Default Re: Thermal Shock

    It could be. A friend did a test with just fabric on a tail surface and put it in the freezer. When he took it out at room temperature it went right slack. Than went back to normal in a short amount of time.

    Is your hanger room temperature?


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  4. #4
    Senior Member Dan L's Avatar
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    Default Re: Thermal Shock

    I have heat in the hangar but don't turn it on unless I'm working in it. So when I push the Cub back in following a cold flight the hangar temperature is probably 20 degrees or so warmer than the outside temp.
    Flying Carbon Cub EX #11 since 2011

  5. #5
    Senior Member TroyBranch's Avatar
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    Default Re: Thermal Shock

    Ok, if you don't hit it with heat right away you will have no change as the fabric is slowly changing temp. I go into a warm hanger and the radiant heat is cranking on it. The perfect test condition... a 40 degree temp change on occasion. I do believe that the thick polyurethane, when really cold, stiffens the fabric which likely plays a roll.

  6. #6
    Senior Member Californiacubs's Avatar
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    Default Re: Thermal Shock

    Someone with more expertise can chime in, but here is understanding. The internal wing structure heats up much slower than the fabric. Applying the warm heat of the hangar warms the static temp of the fabric and it slackens until the internal structure of the wing gets up to the same temperature. Make sense?


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    Ben Hodges
    California Cubs
    www.californiacubs.com

  7. #7
    Senior Member TroyBranch's Avatar
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    Default Re: Thermal Shock

    Here is from AC43.13

    NOTE: Temporary wrinkles will developin any fabric coated and finishedwith dope, when moisture fromrain, heavy fog, or dew is absorbedinto a poor-quality dope film, causingthe film to expand. Temporary wrinklesmay also develop with any type ofthick coatings, on any type of fabric,when an aircraft is moved from a coldstorage area to a warm hangar orparked in the warming sunshine,causing rapid thermal expansion ofthe coating.

  8. #8
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    Default Re: Thermal Shock

    If i remember correctly, poly fiber said this is normal when going from a warm dry climate to a cold damp, and not to worry. Ive seen a pacer a few years ago, covered with dope, after sitting outside all week, the owner had to turn it around to sit in the sun to get rid of the wrinkles before flying home. He said it was that way sense he covered it some 20+ years ago.

    Tom

  9. #9
    Senior Member Clay Hammond's Avatar
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    Default Re: Thermal Shock

    Some do it and some don't. All depends on who did the covering and the process/coatings that was used. And the ambient conditions. Your mileage may vary. On the Sport Cub and Carbon Cub I usually see it at the roots, not at the tip...and I've seen it a lot.
    Last edited by Clay Hammond; 02-07-2017 at 03:30 PM.
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  10. #10
    Senior Member David H's Avatar
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    Default Re: Thermal Shock

    Troy,

    I am starting covering. Check this link starting at 18:18. He talks about critical adherence to iron temperature when shrinking in regards to cold weather wrinkles

    https://www.youtube.com/watch?v=iu3g...ZMdJUn&index=7

    So under and over temperature, or too loose fabric requiring maximum shrinkage could be the culprit here.

    David

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