I scale up to the 32" cubed that would be required to accommodate the propellers of the same length (real, Jim, and not as we know fascia-board) and can see straightway that the requisite stiffness is going to be more bother than it's worth. Fortunately this exercise has only cost me a couple of quid for pop-rivets, and as Edison said, I didn't fail a thousand times, but discovered a thousand ways it wouldn't work. Answers deliberations of recent days, to the extent underslung propellers remain the way to go.
