North American X-15

The X-15 was based on a concept study from Walter Dornberger for the National Advisory Committee for Aeronautics (NACA) of a hypersonic research aircraft. The requests for proposal (RFPs) were published on 30December 1954 for the airframe and on 4February 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 many X-series aircraft, the X-15 was designed to be carried aloft and drop launched from under the wing of a B-52 mother ship. Air Force NB-52A, "The High and Mighty One" (serial 52-0003), and NB-52B, "The Challenger" (serial 52-0008, also known as Balls 8) served as carrier planes for all X-15 flights. Release of the X-15 from NB-52A took place at an altitude of about and a speed of about . 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 (the outer skin) were heat-resistant nickel alloy (Inconel-X750). The retractable landing gear comprised a nose-wheel carriage and two rear skids. The skids did not extend beyond the ventral fin, which required the pilot to jettison the lower fin just before landing. The lower fin was recovered by parachute. Cockpit and pilot systems The X-15 was the product of developmental research, and changes were made to various systems over the course of the program and between the different models. The X-15 was operated under several different scenarios, including attachment to a launch aircraft, drop, main engine start and acceleration, ballistic flight into thin air/space, re-entry into thicker air, unpowered glide to landing, and direct landing without a main-engine start. The main rocket engine operated only for a relatively short part of the flight but boosted the X-15 to its high speeds and altitudes. Without the main rocket engine thrust, the X-15's instruments and control surfaces remained functional, but the aircraft could not maintain altitude. As the X-15 also had to be controlled in an environment where there was too little air for aerodynamic flight control surfaces, it had a reaction control system (RCS) that used rocket thrusters. The RAS was typically used for approximately three minutes of an X-15 flight before automatic power off. The MH-96 could automatically blend aerodynamic and rocket controls, depending on how effective each system was at controlling the aircraft. In the event of ejection, the seat was designed to deploy fins, which were used until it reached a safer speed and altitude at which to deploy its main parachute. The X-15 reaction control system (RCS), for maneuvering in the low-pressure/density environment, used high-test peroxide (HTP), which decomposes into water and oxygen in the presence of a catalyst and could provide a specific impulse of . Additional tanks for helium and liquid nitrogen performed other functions; the fuselage interior was purged with helium gas, and liquid nitrogen was used as coolant for various systems. This produced a significant amount of base drag at lower speeds; the blunt end at the rear of the X-15 could produce as much drag as an entire F-104 Starfighter. Stability at hypersonic speeds was aided by side panels that could be extended from the tail to increase the overall surface area, and these panels doubled as air brakes. ==Operational history==

promotional film reel. Before 1958, United States Air Force (USAF) and NACA officials discussed an orbital X-15 spaceplane, the X-15B that would launch into outer space from atop an SM-64 Navaho missile. This was canceled when the NACA became NASA and adopted Project Mercury instead. By 1959, the Boeing X-20 Dyna-Soar space-glider program was to become the USAF's preferred means for launching military crewed spacecraft into orbit. This program was canceled in the early 1960s before an operational vehicle could be built. Various configurations of the Navaho were considered, and another proposal involved a Titan I stage. In July and August 1963, pilot Joe Walker exceeded in altitude, joining NASA astronauts and Soviet cosmonauts as the first human beings to cross that line on their way to outer space. The USAF awarded astronaut wings to anyone achieving an altitude of , while the FAI set the limit of space at . On 15November 1967, U.S. Air Force test pilot Major Michael J. Adams was killed during X-15 Flight 191 when X-15-3, , entered a hypersonic spin while descending, then oscillated violently as aerodynamic forces increased after re-entry. As his aircraft's flight control system operated the control surfaces to their limits, acceleration built to vertical and lateral. The airframe broke apart at altitude, scattering the X-15's wreckage across . On 8May 2004, a monument was erected at the cockpit's locale, near Johannesburg, California. Major Adams was posthumously awarded Air Force astronaut wings for his final flight in X-15-3, which had reached an altitude of . In 1991, his name was added to the Astronaut Memorial. after a landing accident on 9November 1962 which damaged the craft and injured its pilot, John McKay. The new plane renamed X-15A-2, had a new fuselage extension to carry liquid hydrogen. The 200th flight over Nevada was first scheduled for 21November 1968, to be flown by William "Pete" Knight. Numerous technical problems and outbreaks of bad weather delayed this proposed flight six times, and it was permanently canceled on 20December 1968. This X-15 (56-6670) was detached from the B-52 and then put into indefinite storage. The aircraft was later donated to the Smithsonian Air & Space Museum for display. ==Aircraft on display==

Both surviving X-15s are currently on display at museums in the United States. In addition, three mockups and both B-52 Stratofortresses used as motherships are on display as well. • X-15-1 (AF Ser. No. 56-6670) is on display in the National Air and Space Museum "Milestones of Flight" gallery, Washington, D.C. • X-15A-2 (AF Ser. No. 56-6671) is at the National Museum of the United States Air Force, at Wright-Patterson Air Force Base, near Dayton, Ohio. It was retired to the museum in October 1969. The aircraft is displayed in the museum's Research and Development Gallery alongside other "X-planes", including the Bell X-1B and Douglas X-3 Stiletto. Mockups • Dryden Flight Research Center, Edwards AFB, California, United States (painted with ) • Pima Air & Space Museum, adjacent to Davis-Monthan AFB, Tucson, Arizona (painted with ) • Evergreen Aviation & Space Museum, McMinnville, Oregon (painted with ). A full-scale wooden mockup of the X-15, it is displayed along with one of the rocket engines. Stratofortress mother ships '' takes off with an X-15 • NB-52A (AF Ser. No. 52-003) is displayed at the Pima Air & Space Museum adjacent to Davis–Monthan AFB in Tucson, Arizona. It launched the X-15-1 30times, the X-15-2, 11times, and the X-15-3 31times (as well as the M2-F2 four times, the HL-10 11times and the X-24A twice). • NB-52B (AF Ser. No. 52-008) is on permanent display outside the north gate of Edwards AFB, California. It launched the majority of X-15 flights. ==Record flights==

Highest flights During 13 of the 199 total X-15 flights, eight pilots flew above , thereby qualifying as astronauts according to the US Armed Forces definition of the space border. All five Air Force pilots flew above 50miles and were awarded military astronaut wings contemporaneously with their achievements, including Adams, who received the distinction posthumously following the flight191 disaster. However the other three were NASA employees and did not receive a comparable decoration at the time. In 2004, the Federal Aviation Administration conferred its first-ever commercial astronaut wings on Mike Melvill and Brian Binnie, pilots of the commercial SpaceShipOne, another spaceplane with a flight profile comparable to the X-15's. Following this in 2005, NASA retroactively awarded its civilian astronaut wings to Dana (then living), and to McKay and Walker (posthumously). Forrest S. Petersen, the only Navy pilot in the X-15 program, never took the aircraft above the requisite altitude and thus never earned astronaut wings. Of the thirteen flights, only flights 90 and 91, piloted by exceeded the altitude used by the FAI to denote the Kármán line. † fatal Fastest recorded flights ==Pilots==

File:X-15 Pilots - GPN-2000-000143.jpg|The X-15 flight crew, left to right: Air Force Captain Joseph H. Engle, Air Force Major Robert A. Rushworth, NASA pilot John B. "Jack" McKay, Air Force Major William J. "Pete" Knight, NASA pilot Milton O. Thompson, and NASA pilot William H. Dana. File:X-15 Pilots.jpg|The X-15 pilots clown around in front of the #2 aircraft. From left to right: Joseph Engle, Robert Rushworth, John McKay, William Knight, Milton Thompson, and William Dana. † Killed in the crash of X-15-3 †† Died in a group formation accident on 8 June 1966. ==Gallery==

File:Boeing NB-52A carrying X-15.jpg|NB-52A (s/n 52-003), permanent test variant, carrying an X-15, with mission markings; horizontal X-15 silhouettes denote glide flights, diagonal silhouettes denote powered flights. File:X-15 launched bw.jpg|X-15 just after release File:NorthAmericanX-15600.jpeg|X-15 touching down on its skids, with the lower ventral fin jettisoned. File:X15A2 with tanks.jpg|X-15A-2 (56-6671) with external fuel tanks File:North American X-15 at the National Air and Space Museum, Dec 2017 2.jpg|X-15-1 on display at the National Air and Space Museum X-15 profiles (English).jpg|X-15 profiles File:X-15A2 2.jpg|X-15A-2 with pink ablative coating before being covered with white sealant ==Specifications==

Other configurations include the Reaction Motors XLR11 equipped X-15, and the long version. • 22’ 4” Standard aircraft • 23’ 8” With wing tip pods }} • 13’ 1” Standard aircraft • 11’ 6” Without lower ventral fin and with landing gear extended }} • Burn-out weight: 14,500 lb Standard aircraft • Landing weight: 13,800 lb Standard aircraft }} }} ==In popular culture==