RE: Rib Scale up and Re-Sizing Problem
I am not sure if I am missing something but surely if you are scaling it up to twice the size then if the original is 10.5" chord with 2.312" thickness the scaled up version would equate to 21"chord with a 4.624" thickness which would be about right?
Like Bruce said, it is a little much (more like 3.5" thickness would be ample) but it would keep the original design characteristics in proportion.
I dont know what way you are going to cut the ribs but to make them from sheet would be rather costly at that thickness. I would prefer building the ribs up from balsa strips and strapping them with 1/64th ply cossets.