Taper Pins or Bolts for spar connection?

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by DaveD, Nov 6, 2012.

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  1. Nov 6, 2012 #1

    DaveD

    DaveD

    DaveD

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    The glider guys seem to have a preference for taper pins over bolts (or a straight pin?) when it comes to joining spars. Is there anything about a taper pin attachment that would make it inherently 'better' than a bolted connection? I'm guessing you'd need close tolerances either way, i.e. reamed holes even if using bolts?

    Cheers

    Dave
     
  2. Nov 6, 2012 #2

    pwood66889

    pwood66889

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    I'll hazard an answer, Dave, using my current ride as an example.
    * Taper pins are used to secure the control yoke to the steering mechanism.
    * Bolts (big, honkin' ones!) are used to attach the outer wing panels.
    How long does one live after one or the other fails?
    I believe it may have to do with frequency of disassembly. More often = taper pins.
    Over to the mechanical engineers!
    Percy in SE Bama
     
  3. Nov 6, 2012 #3

    DaveD

    DaveD

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    Percy, I think you're right. I was mentally looking for a strength or tolerance explanation but it probably just comes down to ease of assembly. Especially for something as hard to manoeuvre as a wing, getting a taper pin installed would be much easier than the precise alignment required for a tight fitting bolt, not to mention wear on the parts...

    Thanks

    Dave
     
  4. Nov 8, 2012 #4

    DaveK

    DaveK

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    The reason is pretty simple. For high load connections you need a nice tight connection which means very tight tolerances so that you don't have slop in the joint that leads to wear and other issues. You can do this with bolts but you end up with a connection that is hard to assemble due to the near interference fit that is required for something like a wing attachment. Taper pins on the other hand are inherently tight tolerance as the pin gets pulled into the joint by the end nut aligning everything and creating nice intimate contact between the pin and the joint. So for pure shear connections taper pins are a perfect solution in many cases.
     
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  5. Nov 9, 2012 #5

    pwood66889

    pwood66889

    pwood66889

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    Thanks for the insight, DaveK.
    Percy in SE Bama
     
  6. Nov 9, 2012 #6

    autoreply

    autoreply

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    Another reason is the way many sailplanes join their spars. Some have two pins, joining the overlapping spars and bending moment (shear) is carried over by those two pins, lift is carried to the fuselage by 4 pins on the inner rib. Many others simply have a pin at the end of the spar stub, sticking into the root rib of the other wing. That way, the pin doesn't carry any load, apart from keeping the wings together. Because of thermal elongation etc, it's essential to press both wings together with a lot of force, hence the taper.
     

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