# Torsion box question



## DonnyBahama (Jun 21, 2011)

Torsion boxes never seem to be made with full length+full width cross members that use overlapping half notches. Is there a reason for that? It seems like it would be a much better way.


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## BlasterStumps (Mar 13, 2017)

?? I wouldn't go all the way to "never".


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## therealSteveN (Oct 29, 2016)

I agree.

Just looking at images on a duck search many of them are half lap, some are stringers and blocking.

Both end up with similar support, just the blocking ones may leave the top a little helter skelter, if not done well.


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## splintergroup (Jan 20, 2015)

Lap joints "help" but mechanical engineering speaking virtually all the bending loads are carried in the skins. The cross members carry the shear loads. If the attachment between the cross members and skins is good and complete, there is only a marginal gain in bending strength with half laps


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## wapakfred (Jul 29, 2011)

I've built 2, and made both of them using 1/2 laps (or whatever you want to call those joints. It was easier (for me) and simplified construction.


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## bondogaposis (Dec 18, 2011)

Torsion boxes are like 3D I-beams. The stiffness comes from the distance of separation between the skins. How that separation is achieved doesn't matter so much.


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## DonnyBahama (Jun 21, 2011)

Thanks everyone! I'm glad to know that half lap notch joints work just as well. They sure do seem a lot quicker/easier to make and assemble. Thanks for the photo, @Fred Hargis! The little bit of OCD in me really prefers the way that looks! I know that no one will ever see it once it's assembled But I particularly like the idea that each compartment has a known, repeatable dead center because I'm planning to put a hole in each one to accommodate these clamps (for glue-ups)…


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