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a movable surface that is located along the trailing edge of an aircraft wing and that performs the functions of an elevator and an aileron. Right and left elevons can be moved up and down simultaneously (like ordinary elevators) or differentially (like ailerons). Elevons are used chiefly in such aircraft as the Tu-144 and the Concorde, which have a delta wing and no horizontal tail assembly. To increase the high-speed efficiency of the ailerons and control surfaces of an aircraft that does have a horizontal tail assembly, the right and left halves of the stabilizer as well as those of the elevators are sometimes disconnected from each other; thus the ailerons and control surfaces can operate like elevons. (SeeEMPENNAGE and AERODYNAMIC CONTROL SURFACES.)