National Geographic : 1953 Dec
© National Geographic Society 774 + Man-made Superhurricanes Roar Past a Swept-wing Model Air attains twice the speed of sound in this wind tunnel. Plastic tubes connected with small holes dis tributed over the model's surface give pressure readings on a manometer board (right). Profile of colored liquid at differing heights shows how pressure varies over the wings at Mach 1.78 (1,350 miles an hour). The National Advisory Committee for Aeronautics con ducts the tests in its Ames Aeronautical Laboratory. + A Stub-wing Airplane Model Breaks Through the Sound Barrier Air flows smoothly at subsonic speeds. Shock waves form as the aircraft moves faster. At exactly Mach 1 (760 mph, the speed of sound at sea level) a standing shock wave appears ahead of the wings. As the plane speeds up, this shock wave approaches the wings and bends backward. These are some of the first schlieren (shock-wave-visualization) photographs made in color. Figures on each picture show the Mach number.