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  • #16
    I’d be interested in knowing whether the original AN490’s that failed were tig or O&A welded. If tig welded whether the thread portion was stress relieved??

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    • jaredyates
      jaredyates commented
      Editing a comment
      OA welded in this case.

  • #17
    Been rolling this thing around in my head..... gotta think this is vibration induced some how. Either from the air across the tube or some vibration from the horizonal.
    seems like it wouldn't be too hard to put a small transducer on the strut and record the vibration present.

    A thought-- though this might be some effort---- might be to make a small socket on one end with a completely captured polyurethane core. Like a mini- lord engine mount.
    Make the thing like a cup and piston such that if the rubber failed and came out- the unit could not separate. The rubber could be replaced at annual.
    I guess it would be good to know if the vibration is coming from the fuselage or horizonal so you would know which end to mount it on. (or the strut its self---)
    It might be able to be incorporated into the fixed bracket on the horizonal--- so the strut could be plain with no special ends.
    Maybe such a device all ready exists-- like a small damper in a helicopter rotor head.

    Though--- I guess until you know if the vibration is longitudinal or transverse- that would change how a damper would look and how it would be located and mounted. Maybe pouring the tube full of visco -elastic rubber might kill the vibrations too (?) Just thinking out loud here-----
    Last edited by fairchild; 03-29-2019, 03:19 AM.

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    • #18
      I remember years ago while recovering a J-3 seeing welding rod bridging between the top of the rudder spar and the fwd edge of the top rudder rib. This to absorb vibration. Don't remember if the horizontal or elevator had them. Might help but I'm not really qualified to comment on a fix. Can't see how it would hurt.
      Gerry
      Patrol #30

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      • #19
        The vibration back there doesn't need fine measurement, the tail plane shakes like crazy during a full power take-off.

        Our tail strut broke after a comparable number of flight hours, in flight. Same location for the breakage.

        It was not a huge deal, the plane pitched up somewhat sharply and I needed to re-trim. It does load up the flying wires.

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