The X-1 was the first in a series of rocket-powered research aircraft built for the US Air Force and the National Advisory Committee for Aeronautics (NACA). Originally designated the XS-1 (Experimental Sonic-1) it was built by the Bell Aircraft Company, Niagara Falls, New York, in the hopes of breaking the alleged "sound barrier" and investigating the transonic speed range.

This was a truly pioneering effort. Transonic speeds were technological no-man's land when the program began in 1945. There were no research techniques or flight experience to duplicate them exactly.

The speed of sound was popularized as a danger zone that caused aircraft control reversal and shock waves that could tear a plane apart. To play it safe, the fuselage of the XS-1 was based on the shape of a 50 caliber bullet (a known supersonic projectile), the aircraft was stressed to an amazing plus or minus 18 g's, and the control yoke was designed to give the pilot maximum leverage in case the supersonic speed bump was violent.

Three first-generation X-1 aircraft were built under the original 1940's contract, and three modified versions (X-1A, X-1B, and X-1D) were built in the 1950's.

Setting a pattern that was to follow with many of the NACA and later NASA, research aircraft, it was taken aloft attached to a "mothership" in order to conserve fuel for the research flight. The X-1 aircraft were air-launched from modified B-29 and B-50 bombers.

X-1 Number 1 was glide-tested at Pinecastle Air Force Base, Florida, in early 1946. Subsequent powered flights began on December 9, 1946, at what soon became the NACA Muroc Flight Test Unit, now known as NASA Dryden Flight Research Center, Edwards, California. Flying this plane on October 14, 1947, USAF Captain Charles "Chuck" Yeager became the first person to exceed Mach 1, passing through the dreaded barrier with barely a ripple. On March 10, 1948, NACA pilot Herb Hoover became the first civilian to fly supersonic, while at the controls of XS-1 Number 2.

Yeager's "Glamorous Glennis" XS-1 was painted orange, for visibility. So was the first NACA-Navy D-558-1 research plane, as well as X-1 Number 2, but it soon became apparent that the dark color was in fact, difficult to see from the ground. When Number 2 was turned over to NACA after its Air Force flights, the agency painted it white, which became the standard color for its research aircraft.

The maximum speed attained in an X-1 was 957 miles per hour, set by Yeager in Number 1, during 1948. Number 2 had a thicker wing than the other X-1s, with a thickness/chord ratio of 10 percent as compared with the other thickness/chord ratios of 8 percent. Mainly for this reason it was a slower airplane, with a maximum speed of 792 miles per hour.

The X-1 was powered by a four-chamber, XLR-11 rocket engine, fueled by a mixture of liquid oxygen and diluted ethyl alcohol. Although not throttleable, the chambers could be fired individually or in groups to produce a maximum rated thrust of 6000 pounds at sea level. Fuel capacity limited full-power of the engine to a time frame of approximately five minutes.

The cockpit was pressurized, but the windscreen on Numbers 1 and 2 required external strapping to prevent blow-out. Number 3 had a stronger windscreen that did not need the straps.

X-1 Number 3 was the most advanced of the X-1 aircraft. It had an increased fuel capacity, and an advanced, steam-drive turbopump to transfer propellants. But it was also the most ill-plagued. Delays in its development postponed delivery by about three years, and it made only one flight: a glide test on July 20, 1951. It was accidentally destroyed a few months later, when it exploded on the ground while attached to a B-50 mothership.

Despite some features that now seem almost quaint, the X-1 aircraft were technologically advanced. They repeatedly broke world speed and altitude records during the 1940's, and made significant breakthroughs in the understanding of transonic flight.

All but one of the X-1 flights began with an air-launch. In early 1949 Chuck Yeager made the one and only ground-launch of a rocket-powered X-plane. He took off from an Edwards runway, and rocketed to 23,000 feet in only 90 seconds. Yeager then cut the power and made a normal, gliding return to the field jettisoning the remaining fuel before landing.

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