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Thread: bracket for stab flying wire

  1. #1

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    Default bracket for stab flying wire

    Looking at my tail post area tonight.(Pa22/20) Had read of a SB about the wire bracket being welded to the longeron tubes.....(Pa-12) Visually checked to see that it wasn't that way. (OK) Looked at the bracket its self--- noticed that on the top side where it meets the longeron tube-- there are some good sized rust pits.
    Looks like maybe dirt or mud may have lain in that vertex. Tube OK but plate has pits. Since it is only
    welded at the edges to the square spreader tube-- should be easy to cut off and put a new one on.....

    Here is the question---

    The material it is made of is .100 inches. However--- the little interconnect tabs on the other ends of the flying wires are .125 inches thick. Has some used the incorrect thickness when they did the tailwheel conversion ? I tried to find this part on the drawing CD. Found views showing it-- but didn't find specs for
    dimensions. Would it seem obvious to make a new one out of 1/8 Cro-Mo ? Looks like there must be quite a bit of stress on this part over time in view of the previous SB where its welded to the tubing.

    am I looking on the correct drawing ? Looked on one for fuse and one for fittings--

    Tim

  2. #2
    Administrator Steve Pierce's Avatar
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    Default Re: bracket for stab flying wire

    I will have to measure one because I don't remember. The issue with welding along the longeron was the bending moment causing the fitting to crack outside of the heat effected zone of the weld. Univair sells that fitting by itself.

  3. #3
    andya's Avatar
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    Default Re: bracket for stab flying wire

    could help if you would post pictures......
    "Progress is our most important problem"

  4. #4

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    Default Re: bracket for stab flying wire

    I remember reading about the problem with the weld between the tube and ear. After I went out and looked at it- it was obvious what they meant when they described the
    weld situation.

    Andy--- the ears are inclined slightly up-hill to point to the attach point on the underside of the stab. I think maybe dirt may have accumulated there and kept the ear wet
    over time and rusted some deep pits in the ear near the edge of the longeron. There is a square tube welded in between the bottom longerons and the ear is a single one piece strip and it is welded to the square tube and not to the longeron tubes. Appairently they were once welded to the longeron too- but it was found that the ear was
    breaking just outboard the weld in whats called the heat affected zone-- (this is an area that runs along the edge of a weld where the steel's properties transition between
    the area heated and the area mostly not heated. If you are testing a weld-- it should break in this HAZ area and not through the weld. I believe it is expected that the
    HAZ area is the weakest area in the vicinity of the weld---)

    It wasn't clear from the descriptions if the HAZ was cracking -- or if the tube just rotted away from the tab. I should think it must have been the former. even if the tube released the tab on one side--- if the tab was still intact-- it should be still connected to the square tube and to the other flying wire. So if the tab was cracking--- that gives me inclination to make it 1/8 instead of .100 inches.

    Just read about an SB about finding cracks in the engine mounts where the tubes weld to the bushings. Not surprised since the whole mount probably weighs 3 lbs.....
    I hope there may be an aftermarket STC's one a little beefyier…...

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