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In aircraft like the Pipistrel Virus, there's a single spar in each wing which is held with steel pins inside the fuselage.

Are these spars offset along the chord line or are they bent at an angle for assembly?

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2 Answers 2

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If you look closely at the view from below, you can see that they are built with matching tapers, thin at the end and normal thickness at the root. The left wing's spar tapers toward the front, and the right tapers toward the back. When the tapered sections are overlapped together, they form a uniform thickness across.

So the spars in each wing are at the same location chordwise. It's just that they taper across the cabin in different directions so they mate together in a constant thickness beam with a diagonal axis-wise seam, like a scarf joint connecting two wood planks, but without the glue. Once you are beyond the overlapping middle section, they are the same.

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Single spars are generally located at the thickest part of the wing airfoil (both sides the same); if they disconnect inside the fuselage or cabin for wing removal (as in the video example), they'll either taper, one on the forward side and the other on the aft side, or one will slide inside the other before they are locked together by pins or bolts.

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  • $\begingroup$ In the video and other picture I found, It seems the combined thickness of tapered section is more than of a single spar. Might they be slightly offset? $\endgroup$
    – Mridul
    May 12 at 16:02
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    $\begingroup$ It's possible, but it would cost more to make and be inferior to a spar that isn't offset due to stress risers and such -- or heavier to add material offsetting that. $\endgroup$
    – Zeiss Ikon
    May 12 at 16:51
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    $\begingroup$ @Mridul Yes, each tapered section needs to be wrapped in shear layers which will combine to more thickness than a single spar. Now consider this: If the spars were at different chord in each wing, each wing would twist differently when bending. You really want to avoid such behavior. Clearly, they must be at the same chord position on each side. $\endgroup$ May 14 at 20:32

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