Ironically, though Bell engineers agreed that the swept wing was the future for supersonic flight, they chose not to incorporate it into the design of their X-1. Thus the world’s first supersonic airplane had a conventional straight-wing design. But the X-1’s straight-wing configuration was the only conventional aspect of the wings, which were both shorter and thinner than normal designs. In addition, the fuselage was modeled after the shape of a .50-caliber bullet, based on the bullet’s ballistic performance, and the horizontal stabilizer was also thinner and placed higher on the tail than in conventional aircraft. And, because jet engines then under development were incapable of producing the thrust needed to reach or exceed Mach 1, designers selected a four-chamber rocket engine built by Reaction Motors that produced 1,500 pounds of thrust from each chamber.
An X-5 multiple exposure photo showing its variable sweep wings, which could be moved during flight. Though “not a comfortable airplane to fly,” according to test pilot Scott Crossfield, it verified the qualities of
variable sweep wings. NASA image
On Oct. 14, 1947, Air Force Capt. Charles “Chuck” Yeager strapped into the cockpit of the X-1 (XS-1) “Glamorous Glennis,” named after his wife, and was released from a B-29 “mother ship.” A few minutes later, test personnel monitoring the flight at Rogers Dry Lake at Muroc Air Force Base 42,000 feet below heard a loud sonic boom as the X-1 went supersonic, reaching Mach 1.06. While this became the most famous X-1 flight, the X-1A, X-1B, X-1D, and X-1E pushed the envelope of exploration even further, investigating aerodynamic phenomena and aircraft design elements at greater altitudes and twice the speed of the X-1.
Though the NACA’s workload had been dominated by military needs during World War II, postwar it was not exclusively so. Commercial airline travel significantly increased after the war. Aircraft manufacturers were making civilian airliners that could fly farther, faster, and higher than ever before. The NACA launched a multi-faceted R&D program to study the various aspects of such flight. It included testing pressurized fuselages, the stresses imposed on landing gear subjected to repeated landings, and gathering global information about air currents and exploring their effects on aircraft, particularly air turbulence and gusts.
Though the swept-wing design proved to be the key to practical supersonic flight, it had not provided a complete solution to drag problems encountered by aircraft flying at transonic and low Mach speeds.
The importance of this research was underscored by a number of fatal crashes beginning in 1952 involving the de Havilland Comet, the world’s first production jet airliner. Eventually it was discovered the accidents were caused by catastrophic fuselage failure due to metal fatigue from repeated pressurization cycles, a danger unknown at the time, as well as failure due to severe turbulence in at least one case. One of those NACA researchers working on resolving the problems created by wind gusts – “gust alleviation” – was aeronautical research scientist Chris Kraft. Kraft had joined the NACA in January 1945 working in its Flight Research Division. He also assisted in the design of the X-1. At the time, even with hydraulic controls, flying an aircraft required muscle power. He recalled, “In crazy air conditions, the plane could be pitching, rolling, and bouncing all at the same time. If it was hard on the pilot, it was hell on the passengers. … Under the worst conditions, the jolting motions could damage the airplane itself.” In 1951, Kraft issued NACA Technical Note 2416 that proposed a theoretical solution to the problem. Tests first on a modified DC-3 and later on a C-45 validated the theory, and by 1955 the system was perfected. Though advances in airline technology wound up superseding the original reason for Kraft’s research, the knowledge gained proved to be invaluable data for other fields involving the atmosphere.