Most transmitters have a feature referred to as wing type that allows you to set to " ailevator " this enables a mix so that when elevator is applied they both go up, when aileron is applied they go opposite. This would be a typical 2 servo arrangement. Prior to radio mixing we would have to use a 3 servo arrangement, one servo to drive an elevator located inboard and two servos or a belcrank system to drive ailerons out towards the wing tips. The Windfreak flying wing sailplane is a good example of the inboard elevators but uses rudder for roll control.