Using a couple of 800mm long strips I did a little experimentation with the bend calculator and trial bends to establish bend lines that achieve the skin perimeter dimensions shown on the drawing. The bend lines established - starting at the top, inside flange - were:
18.5 - flange to top of web, 94.5 - bottom of web to bottom surface, 415.5 - to bottom portion of trailing edge
These get me pretty close to the 320mm bottom and 345mm top dimensions specified.
