Maybe this sounds silly, but perhaps it’s the order of the boolean operation? Try slicing to have a solid piece first, then subtract out to make it hollow last. I’m going to go with that because I know Blender’s booleans seem to invert some things depending on which way the normals are facing, and a hollow object has surfaces with inward facing normals.
Thats an idea; I think with boolean operations nothing sounds sillly.
I managed to get one wing sliced in several pieces by trying this and that way until it worked out. But changing the dimension of the wing a little bit, I need to start fiddling aroudn anew; this is not practical for all day use… so I need to find a ‘stable’ approach.
Keep everything solid as long as possible seems sensibel, thanks for the hint!
I found the source of the problem: the wing’s outer edge was not closed -> it was only a hull, open at the wingtips. This leads to trying to subtract an infinitesimal hull from the cube which is obviously not sensible.
With a completely closed hull, the boolean difference works as expected: