Breaking the Sound Barrier: Chuck Yeager and the Bell X-1

Seventy-five years ago, on October 14, 1947, the Bell X-1 Glamorous Glennis, piloted by U.S. Air Force Captain Charles E. “Chuck” Yeager, became the first airplane to fly faster than the speed of sound (Mach 1). The experimental purpose-built aircraft reached 1,127 kilometers (700 miles) per hour (Mach 1.06). Air launched from the bomb bay of a Boeing B-29 bomber after a 30-minute climb to 20,000 feet above Rogers Dry Lake in the southern California desert, the X-1 used its rocket engine to climb to its test altitude of 42,000 feet and began its test run. Early attempts had confronted severe aerodynamic buffeting as the X-1 approached the speed of sound, which threatened the success of the program. This time the flight went smoothly. Engineers had recently upgraded the aircraft’s adjustable stabilizer allowing Yeager to make instantaneous incremental changes in the angle of attack which smoothed out the airflow as the aircraft approached the speed of sound maintaining elevator effectiveness.

On this, the ninth powered flight of the X-1, the Mach meter jumped from Mach .965 to Mach 1.06—faster than the speed of sound. The transition to supersonic flight was remarkably uneventful. After flying under power from the XLR-11 rocket engine for 20 seconds, Yeager cut the power and glided down to the lakebed for a safe landing. The world’s first piloted supersonic flight had lasted 14 minutes from release from the B-29 to landing.

The Bell X-1 flew 78 times—as fast as Mach 1.45 and as high as 21,900 meters (71,900 feet). The X-1 program gathered crucial flight data about transonic and supersonic flight for the Air Force and the National Advisory Committee for Aeronautics (NACA), NASA’s predecessor. It was the first of a series of “X” experimental piloted and unpiloted projects that continue to this day.

To overcome dangerous aerodynamic forces, the X-1 had extremely thin yet strong wings and a minutely adjustable horizontal stabilizer to improve control. Designers shaped the fuselage like a .50 caliber bullet, because high-powered bullets were stable at supersonic speeds. A four-chambered Reaction Motors, Inc., XLR-11-RM-3 rocket engine provided 26,500 newtons (6,000 pounds) of static thrust. The data gathered during the X-1 program were immediately applied to a new generation of high-performance combat aircraft, such as the North American F-100, America’s first supersonic fighter, during the early years of the Cold War.

Capt. Charles Yeager was chosen to fly the Bell X-1 as he was the Air Force’s most experienced test pilot. A World War II ace with 11 victories, the West Virginia native was a superb pilot with an innate understanding of machines and the rare ability to convey his feel for subjective flight characteristics into performance data for the engineers monitoring his flights. He named the aircraft Glamorous Glennis in honor of his wife. At the time, many feared that supersonic flight was impossible because of an invisible “barrier” that could destroy aircraft. This flight put that belief forever to rest. As Yeager later stated, “I realized that the mission had to end in a let-down because the real barrier wasn’t in the sky but in our knowledge and experience of supersonic flight.”

The X-1 experiments solved the challenge of supersonic flight but did not create the transformation people expected. Of great significance to the security and prosperity of the country, these lessons were directly applied to the next generation of military aircraft, keeping America in the forefront of aeronautical research. However, flying faster than sound proved too expensive for all but military applications, so the age of the civil supersonic transport was brief. Nevertheless, the data gathered on transonic and supersonic flight has made new generations of subsonic civil airliners safer and more efficient.

Today the Bell X-1 Glamorous Glennis is displayed temporarily at the Museum’s Steven F. Udvar-Hazy Center, appropriately between the Boeing Aviation Hangar and the entrance to the James S. McDonnell Space Hangar, as it helped bridge the gap between flight in the atmosphere and flight into space. It will return to display at the Museum in DC in the Boeing Milestones of Flight Hall later in our renovation project.

The Bell X-1 Glamorous Glennis photographed while on display at the Smithsonian’s National Air and Space Museum. (Smithsonian Institution)