by Rynoth » Thu Apr 30, 2015 10:56 am
Those 3 middle holes are just for alignment... the plans say to drill them to 1/4" during the initial spar mating, so you typically use some spare AN4 bolts (or other 1/4" material) during the rigging process to "pin" the wings together. Once the rigging is complete, those holes are no longer used (no bolts go in those holes in the completed aircraft.)
That said, I don't suppose you'd be hurting anything by installing some bolts in those holes (though you'd need to enlarge the sight holes in the spar tunnel to fit bolts/nuts through), but the main spar is designed to be secured with just the 2 main AN6 wing bolts.