Complex sentence: The wing was "cut" at about two-thirds of the span, the portion outside of this line able to rotate independently of the rest of the wing in order to act as large ailerons, or as Republic called them, "tiperons".
Split into simpler sentences: The wing was "cut" at about two-thirds of the span, the portion outside of this line able to rotate independently of the rest of the wing. These movable portions acted as large ailerons, or as Republic called them, "tiperons".