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Thread: Oops, darn it...

  1. #1881
    BC12D-4-85's Avatar
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    Stress cracks next to welds....there must be some guidance to reduce that (?). I wonder if failure is gradual or sudden? If gradual any cracking might be hard to see under the fabric. But the metal is exposed at the hinge due to typical fabric application methods so external corrosion focused there is a possibility. The NTSB's metal analysis mentioned will be revealing. If the rudder's shaking some I'd think the pins and bushings would reflect that. Maybe once they get loose it gets worse - the vibration.

    Gary
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  2. #1882
    Crash, Jr.'s Avatar
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    Interesting that 2/3 are bent in the same direction-to the left. Would make sense if it was a stress issue to bend that way as you normally use more right rudder than left. Over a long enough period of time maybe?

    The balance tab forward rib seems to be the place where it breaks. Possible that the weld was too hot or not enough filler was used and pulled material from the tube. That would account for a loss of material in roughly 40% of the tube circumference at that point.
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  3. #1883
    RVBottomly's Avatar
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    Quote Originally Posted by Crash, Jr. View Post
    Interesting that 2/3 are bent in the same direction-to the left. Would make sense if it was a stress issue to bend that way as you normally use more right rudder than left. Over a long enough period of time maybe?

    The balance tab forward rib seems to be the place where it breaks. Possible that the weld was too hot or not enough filler was used and pulled material from the tube. That would account for a loss of material in roughly 40% of the tube circumference at that point.
    It's kind of sobering. I'm looking hard at a rudder I welded up a couple of years ago.

  4. #1884
    BC12D-4-85's Avatar
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    How would a fabricator/welder know if the weld compromised the rudder tube?

    Gary
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  5. #1885
    RVBottomly's Avatar
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    Quote Originally Posted by BC12D-4-85 View Post
    How would a fabricator/welder know if the weld compromised the rudder tube?

    Gary
    Not really sure except to check for good penetration and maybe warping. I actually tested an earlier version of mine by twisting the top. The ribs buckled first.

  6. #1886
    SuperCub MD's Avatar
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    So all 3 rudders were on 12's from the same area. Two have the same sort of paint scheme... I ain't sherlock holmes but I would be looking for a connection and the origin of the rudders.

  7. #1887
    Crash, Jr.'s Avatar
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    Quote Originally Posted by BC12D-4-85 View Post
    How would a fabricator/welder know if the weld compromised the rudder tube?

    Gary
    Normally you can just tell by the color of the weld and checking for undercutting at the sides of the weld bead. Once you get paint or other coating on it's much harder to tell without running a bore scope into the tube to see if there is deformation on the interior of the tube wall.
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  8. #1888
    Crash, Jr.'s Avatar
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    After going over those pictures again, I have to take that back. The break point seems to be just up from the upper hinge point, not the rib facing forward. Interesting that it breaks there as there is really no weld to speak of at that point but it is the last point supported by the hinge line going upwards so structural fatigue may be the issue.

  9. #1889

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    Quote Originally Posted by BC12D-4-85 View Post
    How would a fabricator/welder know if the weld compromised the rudder tube?

    Gary
    Being a skilled fabricator, one has learned just what a good weld is while you are doing it. In a nutshell looking at a weld from the outside, many of the prettiest welds might well have insufficient penetration. There are welders that can not for the life of them properly join .028 wall to .065 tube. Something that comes easy to some but not others.
    Inspection by visual means, general shape of the fillet, clean edges, under cutting or a step or sharp edges. Caricaturist tell tails that a skilled welder and inspector can determine if something is good, or needs to be looked into.
    If the area is painted or god forbid powder coated it is all but impossible to see the surface texture of the material to judge what temperature the metal had been brought to during the weld process.
    Regards, Charlie
    Super Coupe E-AB build in process
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  10. #1890
    www.SkupTech.com mike mcs repair's Avatar
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    Tig welds. Usually more likely to crack tube next to weld on thin tube like this. As penetration is very abrupt compared to oxy welds.....

    Never seen what shown. But all 3 at lake hood I assume???? Windy place. I like stewarts assumption of gust lock up top most of year.....


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  11. #1891

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    My rudder top hinge is higher up than those shown. I never thought much about it but a Cub rudder appears set up to fail faster with that top hinge location than it would be if the hinge was up as high as practical to the top of the fin.
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  12. #1892
    RVBottomly's Avatar
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    Quote Originally Posted by stewartb View Post
    My rudder top hinge is higher up than those shown. I never thought much about it but a Cub rudder appears set up to fail faster with that top hinge location than it would be if the hinge was up as high as practical to the top of the fin.
    That observation makes sense to me. Reduces the lever arm of whatever is pushing on these. Is there any downside? I can't think of one.
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  13. #1893
    BC12D-4-85's Avatar
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    So what next for Cub rudders? Another expensive SAIB or AD based upon a small % of fleet? Something unique was wrong with those rudders.

    Gary
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  14. #1894

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    little heavier walled rudder post, maybe along with a little longer hinge??

  15. #1895
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    Quote Originally Posted by tempdoug View Post
    little heavier walled rudder post, maybe along with a little longer hinge??
    Don't jump towards requiring alterations or repairs to thousands of rudders when there have been only three failures with undocumented histories in question. This FAA inquiry is a fishing expedition looking for something to do.

  16. #1896

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    Maybe, but I bet a lot of guys have wiggled their rudders and looked closely at the top hinges as a result. That's not a bad thing.

    I thought it interesting that in the picture two failed to one side and one failed opposite. What factors played into that?

    Backcountry used unusual rudder and elevator hinges on my plane. I wasn't a fan but it wasn't worth changing. Maybe it has an advantage with big tailfeathers, a heavy Cub, and lots of horsepower? Can't say. A preflight item, for sure.
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  17. #1897
    skywagon8a's Avatar
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    Quote Originally Posted by stewartb View Post
    Maybe, but I bet a lot of guys have wiggled their rudders and looked closely at the top hinges as a result. That's not a bad thing.

    I thought it interesting that in the picture two failed to one side and one failed opposite. What factors played into that?

    Backcountry used unusual rudder and elevator hinges on my plane. I wasn't a fan but it wasn't worth changing. Maybe it has an advantage with big tailfeathers, a heavy Cub, and lots of horsepower? Can't say. A preflight item, for sure.
    That style hinge was common back in the 1920s and 30s. Useful for minimizing the gap.
    N1PA
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  18. #1898

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    Strap hinges are very good, especially when lined with a low friction material, which few Have. Yours are drilled for lubrication which is also lacking on many planes.
    Regards, Charlie
    Super Coupe E-AB build in process
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  19. #1899
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    What should the right and left deflection of the rudder be on a PA12?

  20. #1900
    Gordon Misch's Avatar
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    20 deg per TCDS A-780
    Gordon

    N4328M KTDO
    My SPOT: tinyurl.com/N4328M (case sensitive)

  21. #1901

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    To answer post 1892, Piper seems interested in putting the hinge next to the wires, Backcountry, not so much. So the concern is not for the tail post but the possible binding of the longer Piper hinges .
    What's a go-around?
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  22. #1902
    www.SkupTech.com mike mcs repair's Avatar
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    not much information yet, any update or new links??


    https://www.alaskasnewssource.com/20...o-naknek-lake/

  23. #1903
    www.SkupTech.com mike mcs repair's Avatar
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    Quote Originally Posted by mike mcs repair View Post
    not much information yet, any update or new links??


    https://www.alaskasnewssource.com/20...o-naknek-lake/
    Katmai air

    “Some sort of emergency then landed Naknek lake, broke spreader between floats still there”



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