Hi Marc,

What I did for building this, was to leave a very small (about 1/32") gap between the sheeting of the wing and the sheeting of the aileron. Thos clearly sohws you where to cut the parts.

After the aileron is cut out a cap strip gets glued on the front. This means that you can sand the fornt of the rib + sheeting assy before gluing the cap strip on - so if you end up sanding more than you want on the front of the aileron, just increase the width of the cap strip slightly if needed.