RE: The Swee' Pea is next
Reference lines are drawn for the ribs and the spar end location.
Then a profile gauge is used to get the shape of the root and tip locations so that the spar size can be determined.
The spar size is critical. If it is oversize, the wing will not close properly. Either the seams will be too thick, or they won't be sealed. If the spar is undersized too much, a lot of extra glue will be required and that adds weight in a hurry.
I drew the root and tip sections. The root measured just over 0.8". With 1/16" skins plus the cloth, this sounds about right since the wing should be close to 1". I have a fiberglass mockup wing and I will check it from the outside to see just what the maximum thickness is at the root..