Air Force Captain Chuck Yeager accelerated the Bell Aircraft Company’s X-1 jet plane to seven hundred miles per hour, becoming the first person to fly faster than the speed of sound.
The speed of sound through air is approximately 761 miles per hour at sea level. That speed decreases with altitude—as the air’s composition, temperature, and density all change—to 660 miles per hour at a height of fifty thousand feet. The ratio of the speed of a given object through a given medium to the speed of sound traveling through the same medium is called the object’s “Mach number.”
Captain Chuck Yeager (left) poses with Major Gus Lundquist and Captain James Fitzgerald in front of the X-1 experimental aircraft.
During the early 1940’s, several attempts were made to fly aircraft at and beyond Mach 1. It was discovered, however, that as an airplane approaches Mach 1, strong local-pressure shock waves form on its wings, and airflow becomes unsteady enough to interfere with the aircraft’s stability and the pilot’s ability to control it. Although there was considerable interest in creating an airplane powerful enough to reach Mach 1, many engineers believed that the intense vibration induced by pressure shock waves would cause it to disintegrate. The term “sound barrier” was coined to describe the physical shock waves preventing planes from exceeding Mach 1, as well as the conceptual hurdle that the speed of sound came to represent for engineers and pilots.
As part of a military program to develop supersonic research aircraft, the Bell Aircraft Corporation
Because bullets were known to travel at speeds exceeding Mach 1, the fuselage of the X-1 was shaped like a .50 caliber bullet, with smooth contours constructed from high-strength aluminum built to withstand eighteen times the force of gravity. The wing sections were short and thin (the plane had only a twenty-eight-foot wingspan), but they were extremely strong. The power train consisted of a powerful four-chamber rocket engine capable of providing six thousand pounds of thrust. Because of safety concerns and the performance penalties resulting from a ground takeoff, the X-1 was designed to be launched from the bomb bay of a Boeing B-29 Superfortress bomber at high altitude.
By July, 1947, the X-1 was ready for experimental testing; Muroc Army Air Field in Southern California was chosen as the ideal spot because of its year-round excellent weather and the proximity of thousands of acres of desert and dry lake beds. Three men were chosen to accompany the aircraft to Muroc for its testing: Jack Ridley, a pilot with a master’s degree in engineering whose job was to analyze flight data, and two test pilots, Bob Hoover and Chuck Yeager. Although Hoover was an excellent and experienced test pilot, Yeager was chosen as the first pilot, relegating Hoover to the role of backup pilot. Yeager’s piloting skills, his ability to stay focused under pressure, and his interest in learning as much detail as possible about every aircraft he tested made him the logical choice.
The X-1’s first powered flight occurred on August 29, 1947, with Hoover flying chase in a Lockheed P-80. Although authorized only to go to Mach 0.82, Yeager was moved by the exhilaration of the moment to push the X-1 to Mach 0.85, beyond the velocity at which high-speed aerodynamics were well understood. Because the project engineers and pilots alike were learning about a new field of aerodynamics as they went along, the project’s protocol was to proceed cautiously and incrementally, increasing the plane’s speed by only Mach .02 in each consecutive flight. The data from each flight (recorded by five hundred pounds of special flight-test instrumentation) could then be analyzed prior to the next flight.
On October 5, 1947, during the sixth flight, Yeager experienced severe turbulence and buffeting when he reached Mach 0.86. The right wing dropped, and the controls became sluggish when Yeager tried to correct the problem. When he increased his speed to Mach 0.88 to try to rectify the situation, the aileron began to vibrate from the shock waves, making it extremely difficult to keep the wings level. Yeager aborted the mission. On his very next flight, however, he took the plane to Mach 0.94, at which point his controls ceased to function because of the shock waves forming on all the control surfaces. Yeager was forced to turn off the engine and jettison his remaining fuel in order to glide to a safe landing.
The project team then spent some time analyzing the situation, knowing that without elevator controls to angle the nose up or down, it would be impossible to take the X-1 to Mach 1. Jack Ridley, however, came up with a possible solution: using the horizontal stabilizer (the winglike structure on the tail that stabilized pitch control) to control the X-1’s angle of attack. After extensive tests on the ground, during the eighth powered flight Yeager slowly took the aircraft back to Mach 0.94. Using the horizontal stabilizer as Ridley had advised returned the necessary pitch control, and Yeager was able to achieve Mach 0.96 without difficulty.
The plan for October 14 was to take the X-1 to Mach 0.98. All proceeded well; the horizontal stabilizer gave Yeager stable control beyond Mach 0.94, so he switched on additional rocket engines and easily achieved Mach 0.96. At Mach 0.965, the aircraft’s Machmeter began to fluctuate wildly and went off scale. Simultaneously, the ground control crew heard the world’s first sonic boom; Chuck Yeager had smashed through the sound barrier. Later analysis showed that he had in fact achieved Mach 1.07, flying at 700 miles per hour. He later reported that penetrating the sound barrier was like punching through Jell-O, and that once he was flying at supersonic speeds, the flight became extremely smooth. As it turned out, the true barrier was not in the heavens, but in understanding the physics of supersonic flight.
From Orville and Wilbur Wright’s historic flight initiating airplane travel through the end of World War II, airplanes changed appearance, but there were relatively few innovative design changes. With the advent of jet engines, however, more power was available than existing airframes could tolerate, mandating basic redesigning for high-speed flight. The X-1 was a radical new design, built exclusively to determine whether Mach 1 could be reached and exceeded. The success of this venture proved conclusively that the “sound barrier” was more intellectual and psychological than factual.
Many supersonic flights at ever-increasing speeds were made over the ensuing decade; the first supersonic bomber became operational in 1956, and by the late 1950’s Mach 2 was achieved. During the 1960’s, as speeds approached Mach 2.5, further innovative designs were required to prevent the outer shell from overheating as a result of friction from the rapidly moving air. By the early 1970’s, Mach 3 had been achieved and the first commercial supersonic aircraft were introduced. The world’s first supersonic transport plane (SST), the TU-144, was tested by Soviet pilots in 1968 and began regular cargo service in 1975. Britain and France jointly constructed the Concorde SST, designed to fly at Mach 2, beginning passenger service in 1976. Due to the extreme annoyance factor of sonic booms (created continuously whenever an aircraft flies at supersonic speeds), commercial supersonic flights are now forbidden over the United States; only transoceanic supersonic flights are allowed.
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Abzug, Malcolm J., and E. Larrabee. Airplane Stability and Control: A History of the Technologies That Made Aviation Possible. New York: Cambridge University Press, 2002. Comprehensive coverage of airplane stability and the evolution of design and construction of control systems. -
Courtwright, David. Sky as Frontier: Adventure, Aviation, and Empire. College Station: Texas A&M University Press, 2005. Complete history of aviation from the first pioneers through the space shuttle. Details the significance of air and space in American history. -
Dwiggins, Don. Flying the Frontiers of Space. New York: Dodd, Mead, 1982. Readily accessible history of American experimental aircraft from 1947 to the early 1980’s. -
Hallion, Richard. “The Air Force and the Supersonic Breakthrough.” In Technology and the Air Force: A Retrospective Assessment, edited by J. Neufeld, G. M. Watson, and D. Chenoweth. Washington, D.C.: Air Force History and Museums Program, 1997. Concise history of the events leading up to and immediately following the first supersonic flight. -
Hansen, James R. The Bird Is on the Wing: Aerodynamics and the Progress of the American Airplane. College Station: Texas A&M University Press, 2004. Details a century of aeronautics research, concentrating on design and construction as well as the engineers who helped perfect modern airplanes. -
Kerrebrock, Jack. Aircraft Engines and Gas Turbines. 2d ed. Cambridge, Mass.: MIT Press, 1992. Technical description of the power plants necessary for supersonic flight. Requires some familiarly with physics or engineering. -
Yeager, Chuck, and Leo Janos. Yeager: An Autobiography. New York: Bantam Books, 1985. Chuck Yeager’s autobiography, with extensive information about his time as a test pilot. Includes details about his experiences testing the X-1. -
Yeager, Chuck, and Charles Leerhsen. Press On! Further Adventures in the Good Life. New York: Bantam Books, 1988. Another autobiography, with more information about Yeager’s friends and his personal life during his career as a pilot.
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