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Thread: Design and role of jury struts

  1. #1

    Join Date
    Nov 2017

    Design and role of jury struts

    I can't figure out completely how jury struts work.

    I clearly understand that jury struts can help and suppress buckling
    of struts in compression (with spar in tension in negative load).
    I've calculated deflexion of spar in compression (at +6G in positive load) and
    found it of few inches (with 2.5" OD 0.083" wall 6061T6 tube spar). Although nothing
    is wrong with that, I'm quite upset with flaps behind rear spar (my design
    is with plain flaps and not junkers avid kitfox style flaps) and would like
    to have your opinion about jury struts in this case.

    Does it alleviate spar deflexion and how much in this case ? (I can't
    imagine that jury struts report all their load and make the struts(in tension)
    only bend, but it could be the case (why not?)).
    If you can share an article, paper or proper explanation of this (I'd like to
    have figures for my design and not only (that would be however welcome)
    intuition about the phenomenon), it would be of great help.

    A definitive answer would be to test in reality loads of the wing but
    it's just at the design stage at this time.

    note: I made the deflexion calculus with plain spruce spar and it's
    much less, so the problem is only with aluminium round spar. Having
    greater inertia (bigger spar) isn't an option for me.

  2. #2
    Dana's Avatar
    Join Date
    Jul 2011
    Jury struts won't do anything for spar deflection, unless the strut was stronger (or rather stiffer) than the spar itself.

  3. #3
    Airmutt's Avatar
    Join Date
    Jan 2018
    NW. Atlanta GA
    Jury struts have two primary purposes. First they serve to stabilize the struts from resonance or vibration. Second, they aid in preventing the struts from buckling under negative loads. If the struts are sufficiently robust, jury struts are not required case in point the Piper Pacer, Colt, and TriPacer.
    Dave Shaw
    EAA 67180 Lifetime
    Learn to Build, Build to Fly, Fly for Fun

  4. #4

    Join Date
    Nov 2017
    Thanks for your answer. How to deal with aluminium spar deflexion and plain flaps
    and aileron elasticity ? With aluminium and same modulus of elasticity, it seems
    there are no other option. Wood would crack in my opinion.

    Example Just aircraft Escapade (outback kit here in France):
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    I'm not a big fan of replicating an existing design but I'm interested in
    foldable wings. Perhaps my choice will go to plain spruce spar and forget
    foldable wings.
    Have you a clue to get control surfaces elasticity with wood and aluminium round
    spar, I'd be interested in ?
    Last edited by JLS; 10-30-2022 at 03:52 AM.

  5. #5

    Join Date
    Nov 2017
    In these few weeks reviewing my goals, I finally found it more appealing with a single strut on each wing
    forgot foldable wings and aluminium round spar, so no worry about jury struts.

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    Last edited by JLS; 11-17-2022 at 02:46 PM.

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