Supersonic flight

On October 14, 1947, at 10:26 AM over the Mojave Desert, Captain Chuck Yeager's Mach meter jumped from 0.965 to 1.06. For fourteen minutes, the Bell X-1 'Glamorous Glennis'—named after Yeager's wife—had flown faster than sound. The 24-year-old pilot, ribs still taped from a horseback riding accident two nights earlier, had broken the sound barrier. The transition was remarkably uneventful; the turbulence and control problems that had killed pilots in previous high-speed attempts simply did not occur. What had seemed an impenetrable barrier turned out to be just another speed.

The adjacent possible for supersonic flight required solutions to aerodynamic, propulsion, and structural problems that only converged in the late 1940s. The transonic region—speeds near Mach 1—created control problems that had killed test pilots. As aircraft approached the speed of sound, shock waves formed on the wings and control surfaces, sometimes reversing control responses or causing structural failure. Propeller aircraft could not generate enough thrust to push through this regime. The turbojet engine, developed during WWII, solved the propulsion problem. Rocket engines provided even more thrust in a lighter package.

The X-1's design reflected hard-won knowledge. Bell Aircraft shaped its fuselage like a .50 caliber bullet—because bullets were known to be stable at supersonic speeds. The aircraft used a four-chamber XLR-11 rocket engine providing 6,000 pounds of thrust. It was air-launched from a B-29 bomber at 20,000 feet, climbing under rocket power to 42,000 feet for its test runs. This approach conserved fuel and avoided the risks of supersonic takeoff and landing.

Why did America achieve supersonic flight first? The war had ended before Germany could complete its supersonic projects, despite their advanced research. British attempts were hampered by the 1946 death of test pilot Geoffrey de Havilland Jr. in the DH.108 Swallow. America had the industrial capacity, captured German research data, and crucially, the institutional infrastructure of NACA (later NASA) coordinating research with the Air Force. When Bell's civilian test pilot demanded $150,000 to fly the X-1, the Air Force simply assigned the mission to Yeager—their best test pilot, a WWII ace with 13 victories who understood machines intuitively.

The flight was kept secret for eight months, announced publicly only in June 1948 after Aviation Week leaked the story. The X-1 program continued for 78 flights, reaching Mach 1.45 and 71,900 feet. The data gathered flowed directly into the design of America's first generation of supersonic fighters—the F-100 Super Sabre entered service in 1954. By the 1960s, supersonic flight had become routine for military aircraft, and the Concorde and Tu-144 would bring it to commercial aviation.

The sound barrier, feared for a decade as an absolute limit, proved to be a phantom. Like many technological barriers, it existed primarily because the engineering solutions had not yet matured. When they did, the barrier dissolved. Today, military aircraft routinely exceed Mach 2, and the original X-1 hangs in the Smithsonian's National Air and Space Museum—a reminder that technological limits are often just temporary states of incomplete knowledge.