North American X-15

Le X-15 sur Wikipedia de langue anglaise

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The North American X-15 rocket-powered aircraft/spaceplane was part of the X-series of experimental aircraft, initiated with the Bell X-1, that were made for the USAF, NASA, and the USN.

The X-15 set speed and altitude records in the early 1960s, reaching the edge of outer space and returning with valuable data used in aircraft and spacecraft design.

It currently holds the official world record for the fastest speed ever reached by a manned rocket powered aircraft.

During the X-15 program, 13 of the flights (by eight pilots) met the USAF spaceflight criteria by exceeding the altitude of 50 miles (80.47 km, 264,000 ft), thus qualifying the pilots for astronaut status.

The USAF pilots qualified for USAF astronaut wings, while the civilian pilots were later awarded NASA astronaut wings.

Of all the X-15 missions, two flights (by the same pilot) qualified as space flights per the international (Fédération Aéronautique Internationale) definition of a spaceflight by exceeding a 100 kilometer (62.137 mi, 328,084 ft) altitude.

Design and development

The X-15 was based on a concept study from Walter Dornberger for the NACA for a hypersonic research aircraft.

The requests for proposal were published on 30 December 1954 for the airframe and on 4 February 1955 for the rocket engine.

The X-15 was built by two manufacturers: North American Aviation was contracted for the airframe in November 1955, and Reaction Motors was contracted for building the engines in 1956.

Like most X-series aircraft, the X-15 was designed to be carried aloft, under the wing of a B-52 bomber plane.

The X-15 fuselage was long and cylindrical, with rear fairings that flattened its appearance, and thick, dorsal and ventral wedge-fin stabilizers.

Parts of the fuselage were heat-resistant nickel alloy (Inconel-X 750).

The retractable landing gear comprised a nose-wheel carriage and two rear skis. The skis did not extend beyond the ventral fin, which required the pilot to jettison the lower fin (fitted with a parachute) just before landing.

The two XLR-11 rocket engines for the initial X-15A model delivered 16,000 lbf (71 kN) maximum thrust each, for a total of 32,000 pounds-force.

The main engine (installed later) was a single XLR-99 rocket engine delivering 57,000 lbf (250 kN) at sea level, and 70,000 lbf (310 kN) at peak altitude.

The idle thrust of the XLR-99 was 15,000 lbf (67 kN).

Engines and fuel

Early flights used two Reaction Motors XLR11 engines.

Later flights were undertaken with a single Reaction Motors Inc XLR99 rocket engine generating 57,000 pounds-force (250 kN) of thrust powered the aircraft.

This engine used ammonia and liquid oxygen for propellant and hydrogen peroxide to drive the high-speed turbopump that delivered fuel to the engine.

The XLR99 could be throttled, and were the first such controllable engines that were "man-rated",[disputed – discuss] that is, declared safe to operate with a human aboard.

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The XLR99 engine was the first large, throttleable, restartable liquid propellant rocket engine. It was developed beginning in the 1950s by the Reaction Motors Division of Thiokol Chemical Company to steer the X-15 research aircraft.

It could deliver up to 57,000 pounds force (254 kN) of thrust with an Isp of 279 seconds (239 seconds sl). The thrust could be varied from 50 to 100 percent, and the restart capability allowed it to be shut down and restarted during flight when necessary.

The engine was propelled by liquid oxygen and anhydrous ammonia, pumped into the engine by turbines at a flow rate of over 10,000 lb (4,500 kg) per minute.

After operating for one hour, the XLR99 would have to be overhauled before another usage. Operating times nearly twice that were recorded in tests, but declared largely unsafe. The basic X-15 plane carried about 83 seconds of fuel for full-powered flight, while the X-15A-2 carried fuel for just over 150 seconds.

Therefore each XLR99 was capable, in theory, of between 20 and 40 flights before an overhaul.

Like many other liquid-fuel rocket engines, the XLR99s used regenerative cooling, in that the thrust chamber and nozzle had tubing surrounding it, through which the propellant and oxidizer passed before being combusted.

This both kept the engine cool, and preheated the fuel. The basic engine itself weighs 910 lb, or 413 kg.

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Development of XLR11 rocket engine began in 1944 at Reaction Motors, Inc.

Each of the four combustion chambers burning ethyl alcohol and liquid oxygen to produce 1500 lbf (6.7 kN) of thrust. The engine was not throttleable but each chamber could be turned on and off individually.

The XLR11 was used in the Bell X-1, the Dryden lifting bodies and other vehicles.

For early tests the North American X-15 was powered by two XLR11s.

These engines were boosted to 2000 lbf (8.9 kN) of thrust per chamber for a total of 16,000 lbf. In comparison, the idle thrust of the X-15's XLR99 engine was 15,000 lbf.

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Operational history

Three X-15s were built, flying 199 test flights, the last on 24 October 1968.

The first X-15 flight was an unpowered test flight by Scott Crossfield, on 8 June 1959; he also piloted the first powered flight, on 17 September 1959, with his first XLR-99 flight on 15 November 1960.

Twelve test pilots flew the X-15; among them were Neil Armstrong (first man on the moon) and Joe Engle (a space shuttle commander).

In July and August 1963, pilot Joe Walker crossed the 100 km altitude mark, joining the NASA astronauts and Soviet Cosmonauts as the only men to have crossed the barrier into outer space (Soviet Yuri Gagarin was the first man in space, reaching 327 km in apogee of his orbital flight, while Alan Shepard was the first American in space, reaching 187 km during suborbital flight) and becoming the first to exceed this threshold twice.

U.S. Air Force test pilot Major Michael J. Adams was killed on 15 November 1967 in X-15 Flight 191 when his craft (X-15-3) entered a hypersonic spin while descending, then oscillated violently as aerodynamic forces increased after re-entry.

As his craft's flight control system operated the control surfaces to their limits, the craft's acceleration built to 15 g vertical and 8 g lateral.

The airframe broke apart at 60,000 ft altitude, scattering the craft's wreckage for 50 square miles. On 8 June 2004, a monument was erected at the cockpit's locale, near Randsburg, California.

Major Adams was posthumously awarded Air Force astronaut wings for his final flight in craft X-15-3, which had reached 266,000 ft (81.1 km, 50.4 mi.) of altitude.

In 1991, his name was added to the Astronaut Memorial.

The second X-15A was rebuilt after a landing accident. It was lengthened 2.4 feet (0.73 m), a pair of auxiliary fuel tanks attached under the fuselage, and a heat-resistant surface treatment applied.

Re-named the X-15A-2, it first flew on 28 June 1964, reaching 7,274 km/h (4,520 mph, 2,021 m/s).