I put 3 on each elevator, 3 or 4 on the rudder cant remember and 4 or 5 on each wing. There should be a very small gap between the control surface and the surface you mount it to. You want to get the smallest gap while allowing max. deflection. I would also suggest pinining the hinges in as a safety measure. I usually drill a small hole through where the hinge is and glue a tooth pick through the hole. It looks kinda ugly but you wont have hinges coming off in air (which sucks).