RE: How to install servos in a foam core wing?
Cut a 2 1/4 in. square hole, about 1/4 in. deeper than the thickness of the servo. I use a soldering gun with copper house wire shaped to the size of the hole you need. Line the inside with 1/16 balsa, only up to the top of the foam. Glue in the corners, 1,4 sq. spruce or aircraft plywood the full depth of the hole, up to the foam. Make an aircraft plywood cover the same thickness of the foam, 1/16 or 3/32. to go in and sit on the corner posts. Mount the servo on the inside of the cover on 1/4 in. or thicker plywood rails. Cut a slot in the cover for the servo arm and full movement. Screw the cover down with wood screws into the corner posts. Hope this helps.