is the way they expect you to mount your aileron servos, by the time you have hacked away at the wing to get a Futaba S9150 servo in there is nothing left of the plywood former and if a 5 kg force was applied to the servo it would just be ripped out of whats left of the wing. You even have to cut away the rib. That is very bad planning. At least make the gap wide enough to take a proper servo.