Hy Stumble. I had forgotten about spadflyer.com. I had looked at their site about a year ago. Since you are building one of their planes I have a question. They show the wing leading edge having a rounded shape to it instead of the more angular shape that the Debonair wing has. Are the flutes cut on the inside of the top skin and sub ribs used in front of the spar to give it a rounded shape? That to me was the whole reason to use 2mm because it makes a better looking airfoil. The 2mm is only a little bit lighter in weight than 4mm because the only difference is the height of the middle spacing plastic ( i can't think of a good term for it) so not having to use 2mm would be a money saver for sure.

I had tried an experiment with 4mm and cut some of the flutes at the leading edge and then a couple more cuts between the leading edge and the spar and got a better looking airfoil. I just never built a full size wing with 4mm and sub ribs.