North American X-15
The Bell X-1 had taken mankind over the Mach 1 supersonic mark; subsequent X-1s and X-2s would reach Mach 2 and Mach 3, respectively. Yet as technology progressed, still faster speeds were made possible, and space travel was within reach. The problem was how to enable human beings to survive at speeds above Mach 3, and in the airless environment of space. German rocket designer Walter Dornberger had proposed a design for a hypersonic test aircraft, and this was adapted by North American Aircraft into a project commissioned by NACA (the forerunner of NASA) as the X-15.
By its very nature, the X-15 would have to be revolutionary. It would need to operate at speeds between Mach 4 and Mach 10, at the very edge of space. Paramount amongst the designers’ concerns was heat: at the speeds the X-15 was expected to regularly reach, temperatures along the nose and wings could exceed 1200 degrees Fahrenheit, which would melt any then-known steel. Yet the aircraft still had to be light enough to fly at all. To solve both problems, North American used an airframe made of light, durable, heat-resistant titanium with a covering of a unique nickel alloy. To achieve speed and minimize drag, a long, flattened fuselage was designed, but this also presented a problem: at hypersonic speeds, the X-15 would be uncontrollable. A compromise was reached in which a wedge-shaped tail was added, which added enormous amounts of drag; small tailplanes could be extended in flight to either further stabilize the X-15 or act as speedbrakes.
To reach altitude and speed, and overcome the tail’s drag, the engine would need to be large: the Reaction Motors XLR-99 was chosen, a mammoth engine capable of 70,000 pounds of thrust—yet the XLR-99 could be controlled with a conventional throttle, a first in aviation design. Because the XLR-99 ate fuel quickly, the X-15 would be carried to launch altitude by a B-52 Stratofortress mothership. Once detached, the X-15 pilot would ignite the rocket and accelerate to the needed speed and altitude. Once there, at the very edge of space, the air would be so thin the X-15’s control surfaces would be useless, and the pilot would have to switch over to hydrogen peroxide nozzles in the nose and tail to maintain control, in exactly the same fashion as spacecraft. The X-15 would then be glided to a landing on a combination of a conventional nose gear and tail skids; the lower half of the tail, which would scrape the ground otherwise, was jettisoned before landing and recovered later.
Three X-15s would be built in various configurations, with the later aircraft carrying auxiliary fuel tanks beneath the wings to extend its miniscule range. The first aircraft (lacking at the time the XLR-99 engine) flew in June 1959. An absolute speed record of 4,520 mph (Mach 6.72) was achieved in October 1967, while its absolute altitude record of 67 miles above sea level was achieved in August 1963; the latter allowed the pilot, Joe Walker, to qualify for astronaut wings. The speed record stands to this day, whereas the altitude record was matched only in 2004 with the flight of the civilian SpaceShip One. The pilots that flew the X-15 read like a list of aviation pioneers and American heroes: Scott Crossfield, Robert White, Joseph Engle, Joseph Walker, and Neil Armstrong were among the best known X-15 pilots. Despite the highly dangerous working environment of the X-15, only one aircraft was lost, when test pilot Michael Adams went into an uncontrollable hypersonic spin and died when the X-15 broke up at 60,000 feet. Otherwise, the program was not marred by significant problems.
The X-15 did more than just achieve high speeds and altitudes: the research gained in the program led directly to innovations used in the Apollo moon program, including the peroxide thrusters and heat shielding, while flight profiles and other research led to the Space Shuttle. 199 flights were made before the program ended in October 1968, with the two survivors going on to the National Air and Space Museum and the National Museum of the USAF.
Known to the USAF as 56-6671, this was the second X-15 to be built and the fastest: its speed record of Mach 6.7, achieved in 1967, still stands today as the fastest ever achieved by an aircraft. After the X-15 program ended in 1969, 56-6671 was retired to the National Museum of the USAF.
Like all X-15s, 56-6671 wears hybrid NASA and USAF markings; though it appears to be black paint, the X-15s were actually bare metal--the nickel alloy covering appeared black. The white and orange objects to either side of the fuselage are fuel tanks, carried aloft to extend the X-15's range and jettisoned before it would go to full speed.
After my visit to the NMUSAF in May 2017 and my visit to the Smithsonian in May 2014, I've now seen both surviving X-15s. The other X-15 can be seen here at the National Air and Space Museum: www.flickr.com/photos/31469080@N07/15456762053/in/photoli....
My stepfather also built a model of this aircraft for the Malmstrom AFB Museum: www.flickr.com/photos/31469080@N07/16328626108/in/photoli...
North American X-15
The Bell X-1 had taken mankind over the Mach 1 supersonic mark; subsequent X-1s and X-2s would reach Mach 2 and Mach 3, respectively. Yet as technology progressed, still faster speeds were made possible, and space travel was within reach. The problem was how to enable human beings to survive at speeds above Mach 3, and in the airless environment of space. German rocket designer Walter Dornberger had proposed a design for a hypersonic test aircraft, and this was adapted by North American Aircraft into a project commissioned by NACA (the forerunner of NASA) as the X-15.
By its very nature, the X-15 would have to be revolutionary. It would need to operate at speeds between Mach 4 and Mach 10, at the very edge of space. Paramount amongst the designers’ concerns was heat: at the speeds the X-15 was expected to regularly reach, temperatures along the nose and wings could exceed 1200 degrees Fahrenheit, which would melt any then-known steel. Yet the aircraft still had to be light enough to fly at all. To solve both problems, North American used an airframe made of light, durable, heat-resistant titanium with a covering of a unique nickel alloy. To achieve speed and minimize drag, a long, flattened fuselage was designed, but this also presented a problem: at hypersonic speeds, the X-15 would be uncontrollable. A compromise was reached in which a wedge-shaped tail was added, which added enormous amounts of drag; small tailplanes could be extended in flight to either further stabilize the X-15 or act as speedbrakes.
To reach altitude and speed, and overcome the tail’s drag, the engine would need to be large: the Reaction Motors XLR-99 was chosen, a mammoth engine capable of 70,000 pounds of thrust—yet the XLR-99 could be controlled with a conventional throttle, a first in aviation design. Because the XLR-99 ate fuel quickly, the X-15 would be carried to launch altitude by a B-52 Stratofortress mothership. Once detached, the X-15 pilot would ignite the rocket and accelerate to the needed speed and altitude. Once there, at the very edge of space, the air would be so thin the X-15’s control surfaces would be useless, and the pilot would have to switch over to hydrogen peroxide nozzles in the nose and tail to maintain control, in exactly the same fashion as spacecraft. The X-15 would then be glided to a landing on a combination of a conventional nose gear and tail skids; the lower half of the tail, which would scrape the ground otherwise, was jettisoned before landing and recovered later.
Three X-15s would be built in various configurations, with the later aircraft carrying auxiliary fuel tanks beneath the wings to extend its miniscule range. The first aircraft (lacking at the time the XLR-99 engine) flew in June 1959. An absolute speed record of 4,520 mph (Mach 6.72) was achieved in October 1967, while its absolute altitude record of 67 miles above sea level was achieved in August 1963; the latter allowed the pilot, Joe Walker, to qualify for astronaut wings. The speed record stands to this day, whereas the altitude record was matched only in 2004 with the flight of the civilian SpaceShip One. The pilots that flew the X-15 read like a list of aviation pioneers and American heroes: Scott Crossfield, Robert White, Joseph Engle, Joseph Walker, and Neil Armstrong were among the best known X-15 pilots. Despite the highly dangerous working environment of the X-15, only one aircraft was lost, when test pilot Michael Adams went into an uncontrollable hypersonic spin and died when the X-15 broke up at 60,000 feet. Otherwise, the program was not marred by significant problems.
The X-15 did more than just achieve high speeds and altitudes: the research gained in the program led directly to innovations used in the Apollo moon program, including the peroxide thrusters and heat shielding, while flight profiles and other research led to the Space Shuttle. 199 flights were made before the program ended in October 1968, with the two survivors going on to the National Air and Space Museum and the National Museum of the USAF.
Known to the USAF as 56-6671, this was the second X-15 to be built and the fastest: its speed record of Mach 6.7, achieved in 1967, still stands today as the fastest ever achieved by an aircraft. After the X-15 program ended in 1969, 56-6671 was retired to the National Museum of the USAF.
Like all X-15s, 56-6671 wears hybrid NASA and USAF markings; though it appears to be black paint, the X-15s were actually bare metal--the nickel alloy covering appeared black. The white and orange objects to either side of the fuselage are fuel tanks, carried aloft to extend the X-15's range and jettisoned before it would go to full speed.
After my visit to the NMUSAF in May 2017 and my visit to the Smithsonian in May 2014, I've now seen both surviving X-15s. The other X-15 can be seen here at the National Air and Space Museum: www.flickr.com/photos/31469080@N07/15456762053/in/photoli....
My stepfather also built a model of this aircraft for the Malmstrom AFB Museum: www.flickr.com/photos/31469080@N07/16328626108/in/photoli...