Torsional stiffness - drag spars
Josh and Tim,
After more thought, I've realised that the tube spars for drag spars and LE control surface spars will have much
more torsional stiffness than flat ones! Obvious to me now. I guess I just have to think about such things more thoroughly.
I have some nice little threaded plugs to fill the air injection holes. See picture (not very good) in post #411.