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X-15



         


The North American X-15 rocket plane was perhaps the most important of the USAF/USN X-series of experimental aircraft. Although not as famous as the Bell X-1, the X-15 set numerous speed and altitude records in the early 1960s, reaching the edge of space and bringing back valuable data that was used in the design of later aircraft and spacecraft.

During the X-15 programme, 13 flights met the US criterion for a spaceflight by passing an altitude of 50 miles (80 km) and the pilots were accordingly awarded astronaut status by the USAF. Out of these, 2 also qualified for the international FAI definition of a spaceflight by passing the 62.5 miles (100 km) mark.

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History

The original Request for Proposals was issued for the airframe December 30, 1954, and for the rocket engine on February 4, 1955. North American received the airframe contract in November 1955, and Reaction Motors contracted in 1956 to build the engines.

As with many of the X-aircraft, the X-15 was designed to be carried aloft under the wing of a B-52. The fuselage was long and cylindrical, with fairings towards the rear giving it a flattened look, and it had thick wedge-shaped dorsal and ventral fins. The retractable landing gear consisted of a nose wheel and two skids - to provide sufficient clearance part of the ventral fin had to be jettisoned before landing. The two XLR-11 engines of the initial model X-15A delivered 36 kN (8,000 lbf) of thrust; the "real" engine that came later was a single XLR-99 that delivered 254 kN (57,000 lbf) at sea level, and 311 kN (70,000 lbf) at peak altitude.

The first flight was an unpowered test made by Scott Crossfield on June 8, 1959, who followed up with the first powered flight on September 17. The first flight with the XLR-99 was on 15 November 1960.

Three X-15s were built in all, and they made a total of 199 test flights, the last one on October 24, 1968. Twelve test pilots flew the plane, including Neil Armstrong, later the first man on the Moon and Joe Engle who went on to command Space Shuttle missions.

Test pilot Michael J. Adams was killed on November 15, 1967 when his X-15-3 began to spin on descent and then disintegrated when the acceleration reached 15 g (147 m/s²). On June 8, 2004 a memorial monument was erected at the crash site near Randsburg, CA. The crash site coordinates are 35° 25' 09" N - 117° 36' 08" W. Michael Adams was posthumously awarded Astronaut Wings for his last flight in the X-15-3, which had attained an altitude of 266,000 feet (81.1 km). In 1991 Adams' name was added to the Astronaut Memorial at the Kennedy Space Center in Florida.

The second X-15A was rebuilt after a landing accident. It was lengthened by about 0.74 m (2.4 ft), received a pair of auxiliary fuel tanks slung under the fuselage, and was given a heat-resistant surface treatment, the result being called the X-15A-2. It first flew June 28, 1964, and eventually reached an altitude of 107,960 m (354,200 ft or 67 mi), and a speed of 7,322 km/h (4,520 mi/h or 2,034 m/s).

The speeds and altitudes attained by the X-15 remain unsurpassed by any piloted aircraft except the Space Shuttle. They have, however, frequently been exceeded by unpiloted air-launched rockets, such as the Pegasus rocket which has carried several satellites all the way into orbit. The widely reported record achieved by the diminutive X-43A scramjet testbed on March 27, 2004 of Mach 7 at 95,000 ft (approx. 7,590 km/h or 2.1 km/s) is only a record for an air-breathing jet engine.

Of the two surviving X-15s, one is hanging at the National Air and Space Museum in Washington, DC, while the other is at the USAF Museum in Dayton, Ohio.

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General characteristics

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X-15 Pilots

Pilot Organization Flights
Total Space (USAF) Space (FAI)
Michael J. Adams U.S. Air Force 7 1 0
Neil A. Armstrong NASA 7 0 0
A. Scott Crossfield North American Aviation 14 0 0
William H. Dana NASA 16 1 0
Joseph H. Engle U.S. Air Force 16 3 0
William J. Knight U.S. Air Force 16 1 0
John B. McKay NASA 29 1 0
Forrest S. Petersen U.S. Navy 5 0 0
Robert A. Rushworth U.S. Air Force 34 1 0
Milton O. Thompson NASA 14 0 0
Joseph A. Walker U.S. Air Force 25 3 2
Robert M. White U.S. Air Force 16 1 0


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See also

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References

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