An air discharge valve for an aircraft has an inner valve flap (1) and an outer valve flap (3) which partially overlap each other to form a nozzle of the Laval type with a nozzle inlet (6) converging toward a nozzle neck (S) and with a nozzle outlet (7) diverging away from the nozzle neck (S). The inner valve flap (1) has a trailing edge (8A) hinged to the aircraft body and a first leading edge (8) facing in the flight direction and having a curved sectional configuration. The outer valve flap (3) has a second leading edge (9) hinged to the aircraft body and a trailing edge (9A). Both flaps (1, 3) have a wedge shape. An outwardly facing surface portion (11B) of the inner flap (1) forms an air flow guide for air flowing out of the nozzle outlet (7). An inwardly facing surface portion (15B) of the outer flap (3) forms an air flow guide into the nozzle inlet (6) formed by the curved sectional configuration of the first leading edge (8) and by the inwardly facing surface portion (15B).