Oh! And another thing.

I examine all my long spans such a leading and trailing edges, spars etc. If some of the wood is bowed I'll try to use peices that are bowed such that the oppose each other. i.e. if a spar bows "up" I'll match it to one that bows "down". In this way they tend to straighten each other out. If you can't do that, do not worry about it.

Often building a wing I'll have to pin, clamp or weigh down the structure to get it to lie flat on the building board.

Your mantra building the wing is: flat building board, square & straight, pins & clamps.