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In the photograph below, how are the lift pins structurally attached to the ribs and how far does its support structure run inside?

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Does the discontinuity in the torsional flow in the wing skins pose any specific problems in the wing design? Also, how much of the torsional load (lets say percentage) is taken by the spar?

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  • $\begingroup$ One question per post, please. $\endgroup$
    – Organic Marble
    Commented May 15, 2022 at 12:42
  • $\begingroup$ @OrganicMarble I thought it'd be rather annoying to post three closely related questions. $\endgroup$
    – Mridul
    Commented May 15, 2022 at 13:00
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    $\begingroup$ t's annoying if a person can answer "How deep do lift pins go inside the wing in gliders?" but cannot answer "how far does its support structure run inside?", "Does the discontinuity in the torsional flow in the wing skins pose any specific problems in the wing design? ", or "how much of the torsional load (lets say percentage) is taken by the spar?" When you ask four questions in one post, it breaks the Q&A model of this site, because "a correct answer" can't be posted and accepted. $\endgroup$
    – Organic Marble
    Commented May 15, 2022 at 16:22

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The lift pins sit in a block of plywood which in turn fills the gap between the rib and the face of the wing skin, as can be seen in the photo. They go almost all the way into that plywood, so they run inside for maybe 3 - 4 cm. Note that the structure of the lift pin inside the plywood has a larger diameter than the exposed part and is hollow on the inside.

The rib makes sure that the torsional and especially the lift load is well distributed. Since the area encircled by the wing skin is much larger than that of the spar, almost all torsion load is carried by the skin.

Loads go where the stiffness is. In the end, wing skin and spar will bend equally or the wing would disintegrate. Therefore, the strains are the same and the stresses are distributed according to the relative stiffness of the parts.

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  • $\begingroup$ I had to stare at the pic for a while to figure out what is going on. The glider has removable outer wing panels with a male/female spar socket and that big retention pin, and the "lift pins" are effectively dowel pins projecting from the inner panel's rib that plug into sockets in the rib in the removable section to transfer torsion loads from the outer panel to the inner panel? What kind of glider is that? I've never seen wings that break down at that location on a glider before. $\endgroup$
    – John K
    Commented May 16, 2022 at 0:35
  • $\begingroup$ @JohnK This is completely normal. I saw this first >30 years ago on an ASW-20 L, and this is common on all wings with more than 17 m wingspan. They need to be divided in three or four parts so they will fit in trailers and the single panels become not too heavy. $\endgroup$
    – Peter Kämpf
    Commented May 16, 2022 at 10:02
  • $\begingroup$ Ah that figures. I've never attended a competition and there weren't any 18m or open class gliders in the clubs I've been in. I've led a very sheltered life lol. $\endgroup$
    – John K
    Commented May 16, 2022 at 12:14

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