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I'm quite a newbie of these systems and I am designing the wing box of a drone. I know where I want my shear centre. However, I have been trying to determine the shear centre of my idealized airfoil. My airfoil is the NACA6412 and it's highly unsymmetrical.

I know this subject have been touched in this forum before and I have read T.H.G Megson a lot, but I think I am missing something. I have been stuck in this problem for 3 months now and if someone can provide some light on it, it would be great. My goal is to implement this determination in a script or in excel for future situations.

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    $\begingroup$ The shear center depends on the structural construction, e.g. where the spar, shear box, etc. are located. $\endgroup$
    – JZYL
    Commented Oct 25, 2021 at 22:12
  • $\begingroup$ This is not enough for a response because I don't know the exact method to find the shear center, but I think assuming a constant thickness shell you could come up with a reasonable numeric approximation by dividing the airfoil shell into a number of short straight segments? $\endgroup$
    – Raketenolli
    Commented Feb 22, 2022 at 20:59
  • $\begingroup$ This is actually a not bad question, as shear center can change if ailerons or flaps are applied. The main force on the wing is bending from G forces. As long as AR is not too high and airspeed not excessive, a good strong box spar structure should be adequate. Existing designs may save some time. Reverse engineer them. $\endgroup$
    – Robert DiGiovanni
    Commented Jun 23, 2022 at 14:21

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Plot the airfoil on a piece of paper, glue that to a piece of cardboard and cut it out. The shear center is where the center of gravity of that cutout airfoil is when balanced horizontally on a pin.

This is a valid method if the wing skin has the same thickness over the full chord. If you intend to use more material in some corner (say, a torsion box forward of the spar), increase the thickness of the cardboard proportionally to the relative shear stiffness of the corresponding section of the airfoil.

If a section does not contribute to shear stiffness (say, an aileron or a flap), leave this section away.

Background: The resistance to torsion of a hollow structural member is proportional to the circumscribed area and the stiffness of the skin of this structural member.

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The best way is to assume the airfoil symmetric (since the location of the shear center in the chord is more important) for a preliminary phase; It will help a lot. Also, don't forget that idealization is a very rough estimate of the stress analysis of a wing structure or fuselage. It helps, however, with initial pre-sizing.

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