hi
i have two foam wings and tail feathers for a gaint shoestring racer and a gaint prime cut i dont like using foam on big birds i would like a build up wing so i can make them into two piece wings for transporting to the feild and i going with the dle 35 on both 80" wings ,how would i meausre the bays for the ribs and cut the foam to get the ribs outline and where to put the main spar etc, thanks

Take 1 wing (or stab) and make a mark on top of the foam at the high point of the airfoil at both the root and tip and then connect the lines. That is where your main spar would go. For the main wing, you probably also want a rear spar as well. I would put that just in front of the aileron and carry the line down to the root of the wing. Then use a square to draw lines perpendicular to the main spar at an appropriate spacing (maybe 6 ribs for each stab half and 12 ribs for each wing half). You can then cut through the foam with a hot wire or a zona saw at the rib locations. The cut ends should give you the appropriate rib shape and spar notch locations. You probably want to adjust the spacing to place a rib(s) at the landing support location and use lite ply or ply in that location.