FP404 fusellage main spar replace

Discussion in 'Wood Construction' started by Orsovolante, Nov 30, 2019.

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  1. Nov 30, 2019 #1

    Orsovolante

    Orsovolante

    Orsovolante

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    Good morning.
    I'm putting my hand to a Fisher FP404 returning from a heavy landing and a clumsy attempt at repair.
    At the moment I am rebuilding the firewall but the most serious problem concerns the main fuselage spar.
    Someone tried to repair it even screwing on another piece of wood :-(. They saw the screw holes and one of them caused the complete breakage of the upper element.
    Normally this element is built separately and then the sides of the fuselage are closed around it.
    Now I believe that the only way is to demolish the damaged one with ease, remove the two longitudinal elements that close the seat, and insert a rebuilt side member from scratch.
    My doubt is on how to get a good bond in those areas where the new piece should inevitably enter by sliding, crawling, and the impossibility of compressing all the parts already in position against it.
    Do you think it might be a good idea to make the piece just a little narrower, and use glue with additivated structural cotton fibers (Flock?)

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  2. Nov 30, 2019 #2

    don january

    don january

    don january

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    If it was me I'd take all usable components you have and start over. If your wings are good that would be a plus. With the damage shown who knows what other cracks and damage is hidden. IMO
     
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  3. Nov 30, 2019 #3

    Orsovolante

    Orsovolante

    Orsovolante

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    The damage was done mainly by those who tried to drive screws. the plywood has been broken by me to show the longitudinal member. the wings are stelate and have a few broken ribs. the other damages were related to the
    firewall and its structure that I am reconstructing.
     
  4. Nov 30, 2019 #4

    poormansairforce

    poormansairforce

    poormansairforce

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    If it was me I would cut out all the old pieces with a Fein saw and rebuild it in place one piece at a time.
     
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  5. Nov 30, 2019 #5

    proppastie

    proppastie

    proppastie

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    without plans hard for the list (or perhaps just me)to understand what is going on. Looks like a "Box Spar" for the wing. Is it a one piece wing or does the wing bolt onto this section?....Perhaps cut it all out, and make a one piece wing on the bench and put the fuselage back onto it. Perhaps cut it out and re-build the "carry through" on the bench and re-install into the fuselage. Probably will have to fiddle with the fuselage to make it fit either way......I would not make the wing weaker to make it fit.
     
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  6. Nov 30, 2019 #6

    TFF

    TFF

    TFF

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    You will need to cut it out at a the glue lines. Two choices I see. Cut the rest back. the longerons may need cut back and scarf in fresh woods. Alternatively you may be able to make the cross through thicker. That way you can cut the wood joints on the fuselage back about 1/16 for good glue bond. I would probably do it with thicker ply faces. You should be able to rout out where the wing attaches to the original dimension.
     
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  7. Nov 30, 2019 #7

    Dana

    Dana

    Dana

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    You definitely don't want to reduce the size of the spar. Like others have said above, cut it out and build a new spar. Then glue the new spar in with additional gussets, blocks, and scarf plates as necessary to tie it into the existing structure.

    What's with the aluminum strap on the rear carrythrough? I don't remember anything like that. And you have a few broken geodetic strips, too...

    Trying to remember what mine looked like, the drawings went with the plane when I sold it... though mine was a little different, the builder ran the elevator linkage through a cutout in the spar web, instead of running it under the fuselage on the outside.
     
  8. Nov 30, 2019 #8

    TFF

    TFF

    TFF

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    The strap from the back might be from someone who had built a Flybaby. Straps were added to those as an update.
     
  9. Dec 1, 2019 #9

    Orsovolante

    Orsovolante

    Orsovolante

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    I'm waiting for a new set of drawings because with this cell I received only a few faded sheets. I didn't intend to reduce the cross-section of the side members but shorten it a little, 1mm the "bos spare" to get the glue better on the sides. however basically I will follow your advice to add some elements to improve the connection with the cell. I don't know if the aluminum strap is a modification to the original design. the rear side member also has a small plywood delamination that should not be difficult to repair. I think the geodetic strips have been broken in the various movements that the plane suffered. for now I have postponed their repair.
     

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