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X-plane simulator

NACA High-Speed Flight Station test pilot Stan Butchart flying the Iron Cross, the mechanical reaction control simulator. High-pressure nitrogen gas expended selectively by the pilot through the small reaction control thrusters maneuvered the Iron Cross through the three axes. The tanks containing the gas can be seen on the cart at the base of the pivot point of the Iron Cross.

Bell X-1 in flight

The Bell Aircraft Corporation X-1-1 (#46-062) in flight. The X-1 series aircraft were air-launched from a modified Boeing B-29 or a B-50 Superfortress bomber. The X-1-1 was painted a bright orange by Bell Aircraft.

XS-1 Research Team

NACA Muroc Flight Test Unit XS-1 Team members and USAF Pilots. 1948. From left to right: Joseph Vensel, Head of Operations; Gerald Truszynski, Head of Instrumentation; Captain Charles Chuck Yeager, USAF pilot; Walter Williams, Head of the Unit; Major Jack Ridley, USAF pilot; and De E. Beeler, Head of Engineers.

X-1-2 on ramp with Boeing B-29

The Bell Aircraft Corporation X-1-2 sitting on the ramp at NACA High-Speed Flight Research Station with the Boeing B-29 launch ship behind it. The painting near the nose of the B-29 depicts a stork carrying a bundle that is symbolic of the Mothership launching her babe (X-1-2).

Bell X-1B

The mission of the X-1B was flight research pertaining to aerodynamic heating and pilot reaction control systems. It made its first powered flight on October 8, 1954.

X-1E on Rogers Dry Lake with collapsed nose gear

This photo was taken June 18, 1956 on Rogers Dry Lake bed after Flight 7 of the Bell Aircraft Corporation X-1E with NACA High-Speed Flight Station test pilot Joseph Joe Walker at the controls. The first generation X-1s were well known for nose gear failures and the X-1E was no exception. The hard pitch down on landing usually resulted in a collapsed nose gear.

X-1E loaded in B-29 mothership on ramp

The Bell Aircraft Corporation X-1E airplane being loaded under the mothership, Boeing B-29. The X-planes had originally been lowered into a loading pit and the launch aircraft towed over the pit, where the rocket plane was hoisted by belly straps into the bomb bay. By the early 1950s a hydraulic lift had been installed on the ramp at the NACA High-Speed Flight Station to elevate the launch aircraft and then lower it over the rocket plane for mating.

X-2 with collapsed nose wheel

This 1952 photograph shows the X-2 #2 with a collapsed nose landing gear after landing on the first glide flight at Edwards Air Force Base. The aircraft pitched at landing, slid along its main skid, and hit the ground with the right wingtip bumper skid, causing it to break off. The nose wheel had collapsed upon hitting the ground.

Early X-Planes

At the end of World War II, the United States operated some of the most advanced aircraft in the world, such as the B-29. But the pace of change during the war had been so fast that it became clear to many top scientists and military leaders that unless the United States actively sponsored advanced aeronautics research, it could quickly fall behind. As a result, in 1945 the U.S. Army Air Forces (which became the U.S. Air Force in 1947) and the National Advisory Committee on Aeronautics, or NACA, began the first of a series of experimental aircraft projects, many of which were designed to develop technology for high-speed flight. These soon became known as X-planes. While prototype and experimental aircraft were not new, the X-planes were significant because they were solely intended to develop technology in general, not lead to operational aircraft.

The first aircraft produced by the joint team was the XS-1. The "S" stood for supersonic and was dropped early in the program. The X-1 was the first crewed vehicle to break the sound barrier. It was built by Bell Aircraft Company. Its fuselage was modeled on a 50-caliber bullet because that was the one shape that aerodynamics experts knew did not tumble at supersonic speeds. It had straight, very thin wings. It was powered by a rocket engine and dropped from the belly of a B-29 bomber. Its first flight was in January 1946. On October 14, 1947, the X-1, piloted by Captain Charles (Chuck) Yeager reached a speed of 700 miles per hour (1,127 kilometers per hour) while at 45,000 feet (13,716 meters), breaking the sound barrier. The X-1 proved that an aircraft could be controlled at speeds faster than the speed of sound, Mach 1. It led to several aerodynamic advances that were quickly incorporated into U.S. fighter aircraft designs.

The X-1 actually had a conventional tail with elevators for pitching the nose up and down. However, at high speeds, a shockwave formed on the tail surfaces near the hinge for the elevators, rendering them useless. But the X-1 also had a system for raising and lowering the entire tail a few degrees to adjust the trim of the airplane in flight (to enable it to fly level). Yeager and the X-1 flight engineers proposed using this system instead of the elevators at high speeds to control the airplane. It worked and this lesson was secretly incorporated into American fighter planes at the time, giving the United States a technological edge over Soviet, French, and British aircraft for several years. Today, all supersonic aircraft use all-moving tail surfaces.

After the success of the X-1 program, the Air Force and NACA teamed up again to develop the second generation X-1, which was intended to fly at twice the speed of sound, or Mach 2. Four aircraft were planned. The X-1A had its first flight on July 24, 1951. It and its sister craft the X-1B established new speed records, eventually reaching a speed of Mach 2.44 (1,650 miles per hour) (2,655 kilometers per hour) and an altitude of 90,440 feet (27,566 meters).

The Bell X-1E soon followed these earlier aircraft with its first flight in December 1955. Although it did not achieve speeds or altitudes as high as the X-1A or X-1B, the X-1E proved that an extremely thin wing could be used on supersonic aircraft. This research led to the Lockheed F-104 Starfighter interceptor aircraft. (The X-1C was canceled before completion. The X-1D was destroyed before it could make its first powered flight.)

In June 1952, the Bell X-2 had its first flight. The X-2 was equipped with a pointier nose and more powerful rocket engine than its predecessors. It was designed to reach speeds in excess of Mach 3 (2,094 miles per hour). At such high speeds, the friction from air brushing against the aircraft heats its skin to high temperatures. The X-2, therefore, had to be made of advanced lightweight heat-resistant steel alloy. The X-2 reached a record altitude of 125,907 feet (38,376 meters). Research on the X-2, including new construction techniques, contributed to the development of advanced materials for high-speed aircraft such as the XB-70 bomber and the SR-71 spyplane.

The Douglas X-3, which first flew in 1952, was not as successful as its predecessors. Unlike the earlier aircraft, it was not rocket-powered or dropped from the belly of a bomber, but instead took off from the ground like a conventional aircraft with jet engines. It had a short, thin wing that did not generate much lift except at high speeds. This meant that it did not lift off from the runway until it was traveling very fast, which caused its tires to overheat. As a result, several tire companies developed high temperature materials for aircraft tires.

Even the failure of an X-plane to achieve its goals was useful. The Northrop X-4, which flew from 1948 to 1953, proved that tailless aircraft were unsuitable for high-speed subsonic flight (under Mach 1). Other X-planes were developed to conduct various flight research. Some, such as the X-15, developed soon after the earlier X planes, were very successful whereas others demonstrated that certain technologies were essentially dead-ends

The X-planes that did fly were usually equipped with multiple recording instruments, some of which radioed their data to the ground. They often flew numerous flights, each one methodically advancing the flight envelope and providing insight into advanced aerodynamics, engines and materials.

Most X-planes have been developed by either the NACA or the National Aeronautics and Space Administration (NASA) in partnership with the military, usually the U.S. Air Force. Later on, the "X" designation was used in different ways. In one case, the designation was used to mislead people into thinking that a secret spyplane project (the X-16) was actually an experimental aircraft. In other cases, the X designation has been applied to early prototype versions of operational aircraft. But initially, the title "X-plane" indicated that an airplane was built solely to demonstrate and improve aviation technology.

--Dwayne A. Day


Gorn, Michael. Expanding the Envelope: Flight Research at NACA and NASA. Lexington: University Press of Kentucky, 2001.

Miller, Jay and Jenkins, Dennis R. American X-Vehicles, An Inventory – X-1 to X-45, AIAA X-Vehicles Symposium, Printed by NASA, June 2000.

Miller, Jay The X-Planes: X-1 to X-45, Motorbooks International, 2001

Further Reading:

Hallion, Richard. Supersonic Flight: The Story of the Bell X-1 and Douglas D-558. New York and London: Macmillan Company and Collier-Macmillan Company, Ltd. in association with the Smithsonian Institution, 1972.

___________. On the Frontier: Flight Research at Dryden, 1946-1981. (NASA SP-4303). Washington: Government Printing Office, 1984. Available at http://www.dfrc.nasa.gov/History/Publications/SP-4303/

Pearcy, Arthur. Flying the Frontiers: NACA and NASA Experimental Aircraft. Annapolis: Naval Institute Press, 1993.

Rotundo, Louis. Into the Unknown: The X-1 Story. Washington and London: Smithsonian Institution Press, 1994.

Mann, Paul "Breaking the Sound Barrier." Aviation Week and Space Technology 135 (August 12, 1991).

Yeager, Chuck. "Breaking the Sound Barrier." Popular Mechanics 194 (November 1987)

____________ and Janos, Leo. Yeager: An Autobiography. New York: Bantam Books, 1985.

On-Line References:

"X-1: Fiftieth Anniversary." NASA History Office. http://www.hq.nasa.gov/office/pao/History/x1/.

"X-1 Biographies." http://www.hq.nasa.gov/office/pao/History/x1/x1bio.html.

Educational Organization

Standard Designation (where applicable)

Content of Standard

International Technology Education Association

Standard 8

Students will develop an understanding of the attributes of design.

International Technology Education Association

Standard 9

Students will develop an understanding of the engineering design.

International Technology Education Association

Standard 10

Students will develop an understanding of the role of troubleshooting, research and development, invention and innovation, and experimentation in problem solving.

X-2 after drop from B-50 mothership

The Bell Aircraft Company X-2 (46-674) drops away from its Boeing B-50 mothership in this photo. Lt. Col. Frank "Pete" Everest piloted 674 on its first unpowered flight on August 5 1954. Everest made the first supersonic X-2 flight in 674 on April 25, 1956, achieving a speed of Mach 1.40.

Chuck Yeager with Glamorous Glennis

Chuck Yeager and Glamorous Glennis, named after his wife-the name he gave the X-1 that he piloted to Mach 1.06 on October 14, 1947.

Bell X-2

The X-2 had a pointier nose than the X-1 and was designed to reach speeds in excess of Mach 3.

X-3 cockpit

The cockpit of the X-3 "Stiletto," which made its first flight on October 20, 1952. Unlike the other planes in the X series, which were released in mid-air from a "mothership," the X-3 took off from the ground.

Douglas X-3 “Stiletto”

The twin-turbojet X-3 "Stiletto," the only one built, was designed to test features of an aircraft suitable for sustained flights at supersonic speeds and high altitudes. Its secondary mission was to investigate the use of new materials such as titanium and to explore new construction techniques. It made its first supersonic flight in June 1953.

Northrop X-4

The Northrop X-4 was developed for the study of flight characteristics of swept wing semi-tailless aircraft at transonic speeds. Northrop built two X-4s. 1 aircraft made its initial flight on December 16, 1948.

D-558-1 in flight

This is a 1952 NACA High-Speed Flight Research Station inflight photograph of the Douglas D-558-1 #3 Skystreak. Conceived in 1945, the D558-1 Skystreak was designed by the Douglas Aircraft Company for the U.S. Navy Bureau of Aeronautics, in conjunction with the National Advisory Committee for Aeronautics (NACA). The Skystreaks were turpojet powered aircraft that took off from the ground under their own power and had straight wings and tails.

D-558-2 being mounted to P2B-1 mothership

This 1954 photograph shows the Douglas D-558-2 #2 under the left wing of the P2B-1 launch aircraft.

D-558-2 dropped from B-29 mothership

Although not designated an "X vehicle," the D-558-2 was essentially an X-vehicle aircraft in design and function, and contributed much to aeronautics research. The D-558 Phase Two aircraft was quite different from its Phase One predecessor, the Skystreak. German wartime aeronautical research records, reviewed in 1945 by Douglas Aircraft Company personnel, pointed to many advantages gained from incorporating sweptback wing design into future research aircraft.

D-558-2 in flight with F-86 chase plane

The Douglas D-558-2 with a F-86 following behind as a chase plane.

Stamp commemorating first supersonic flight

This U.S. Postal Service stamp, issued in1997,commemorates the 50th anniversary of supersonic flight.