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Flap Hinges: 4-Place A-Model - Hinge Plate Interference With Bearings

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  • Flap Hinges: 4-Place A-Model - Hinge Plate Interference With Bearings

    I've encountered a puzzle with my 4-place A-Model flap hinges.
    Background info: Kit was manufactured in 2006. The hinge plates (sheet metal parts that bolt up to the flap spar) were delivered cut, bent, and primed, but without any holes drilled in them.

    The plans call for MS21152-2 rod end bearings to act as the "hinge" between the hinge plates on the flap and the tube in the mounting bracket that extends aft from the rear spar of the wing. I have some old/crummy/unusable MS21152-2 rod end bearings on hand, and a full set of custom "made to spec" rod end bearings purchased directly from Mark Goldberg at Avipro last year. I want to use the Avipro bearings for flight.

    I've drilled the 1/4" hole for the rod end bearings in the first pair of mounting plates, in the location called for in the plans. The MS21152-2 rod end fits well, but the Avipro custom bearing binds up between the hinge plates.

    To me it appears that the hinge plates (only the outer ones, not the center one with the actuator arm) are much larger than called for in the drawings. The oversized hinge plates, with the MS bearings, works fine. And, the custom bearings, with "in spec" hinge plates should work fine too. But the combination of oversize plates with the custom bearings seems to be problematic. Maybe someone's seen this before, or it's just a corner case that's bitten me!

    think if I remove material from the plates to bring them into spec all will be good. I'd appreciated feedback before I start grinding though!

    Here are some photos of the problem, and my plan of attack:


    Here's the subtle difference in the bearings:

    Here's the hinge plate with the excess (I think) material:

    Comparison of sample "end" hinge plate with the middle plate which has the actuator arm.

    Rough outline of excess material I plan to remove:

    Any advice would be welcome - thanks!

    Attached Files

  • #2
    If you modify the supplied parts to match the plans you can’t go wrong. The only caveat is the larger parts give you a bit of leeway as to where you actually drill the holes. If possible, I would first drill the holes where the bearings line up the best and then modify the part, keeping the hole edge distance in mind.


    • Dpearson
      Dpearson commented
      Editing a comment
      Thanks! I hadn't considered the "bit of leeway" but after a bit of thought I can see that the two remaining degrees of freedom (up/down where the plates get bolted to the spare, and sliding the bearings in/out of the tubes) might not be enough to bring all 3 bearing points into alignment while having good fit between flap and wing. So maybe someone at the factor thought adding "extra" material to the outer hinges, while leaving the middle one "to spec" with the minimum edge distance per Bob's drawings, would mitigate that risk. I'll drill the middle hinge plates to spec (since I don't have any choice in hole location on that one) and then see where things line up.

  • #3
    That's a new one, it wasn't like that on the earlier A model kits.

    I would remove the minimum amount of material required to allow a reliable clearance, I can't see value in removing heaps of material (approaching the minimum edge distance) - it would be more work and I can't think of a benefit, only risks.
    Last edited by Battson; 05-15-2024, 04:31 PM.


    • Battson
      Battson commented
      Editing a comment
      Oh wow - that's a VERY early kit, unless the numbering changed in some way. My wings are about 247 and 248 or something like that.
      I had no idea some of the kids that old were still unfinished, it would have to be almost 20 years old?

    • kestrel
      kestrel commented
      Editing a comment
      I've seen quite a number of 20 year old kids that aren't yet finished. ;-)

    • Dpearson
      Dpearson commented
      Editing a comment
      Yup, this kit is old enough to vote. Delivered to the first owner in 2006. Thankfully it was well stored for all those years. It was quite a find!
      Last edited by Dpearson; 05-18-2024, 03:24 PM.

  • #4
    I have a BUNCH of parts that I made using the plans as templates that ended up in the scrap bin. I learned early on to leave the areas around the holes and places that fit around other tubes bigger and trimmed them to fit.


    • Bcone1381
      Bcone1381 commented
      Editing a comment
      excellant advice.