The present invention is directed to a unique foldable winglet assembly adaptable for use with an aircraft for maximizing the wing span of the aircraft during cruise operation while reducing wing bending moment during extreme flight maneuvers. A foldable winglet is pivotally joined to the aircraft wing and is rotatable during flight between a retracted position and a fully extended position. An actuator is mounted on the aircraft wing and attached to the foldable winglet. When the aircraft reaches cruise operation, the actuator can be manually or automatically energized to pivot the winglet from a substantially vertical, retracted position to a fully extended position wherein the winglet becomes an extension of the wing. During cruise, the wing and winglet form an enlarged wing that serves to maximize lift of the aircraft. When loads more severe than would occur at or near cruise, such as dive, are encountered, the loads overcome the action of the actuator and pivot the winglet to its initial, vertical position. This action, serves to reduce the bending moment acting on the wing as well as increase aerodynamic efficiency of the aircraft.