Hello,
Just a note or two on torsion boxes.
They get their strength from the SKIN and the glue line TO THE SKIN. A torsion box without a skin is NOT a torsion box! And also not very strong, relatively speaking.
Next, if you ARE going to use a torsion box construction, do yourselves a favor and lighten it up! Using 1/2" inner parts and 1/4" skins (or even 1/4" for everything) will be about the same strength, but obviously MUCH lighter. FWIW, the only reason to use the thicker inner material is it makes them a bit easier to fasten together. (you DO want thicker material at fastening points; or waht an aircraft designer might call "hard points".)
The design shown uses eggcrate construction, which is fine. But NOT necessary for strength. You can build these things MUCH more easily using butt joints. Use long strips one direction and short squares/rectangles the other. No fancy joints necessary...
Ian Kirby first brought torsion box construction to the woodworking crowd through an article in Fine Woodworking magazine. You can look up his article if you want to hear what I'm saying from a "better" source. (FWIW I have used torsion box construction for years in furniture, and ALSO in my first CNC machine, back in '89...)
Modelers might realise that once they put the skins on their airplane wings, everything stiffens up. Same principle... (and think how thin those parts are!
Another example of torsion box construction we should all be familiar with is hollow core doors... Most of those use cardboard! for the inner parts, with 1/8" skins. Try and twist one! So you see, you don't need the thick, heavy materials to use torsion box design
Ballendo