While the SR-71 Blackbird remains the world’s fastest air-breathing aircraft, the rocket-powered X-15 has its own richly deserved place in the aviation history record books: on October 3, 1967, U.S. Air Force test pilot William “Pete” Knight became the fastest flying pilot ever when he achieved a speed of Mach 6.7, a record that has stood for nearly 55 years.
The Baby Steps Before that “One Small Step for Man…”
As if that one particular superlative weren’t impressive enough, the X-15 helped make history in other ways: before Neil Armstrong became the first man to walk on the Moon, he was taught to fly the X-15 to the edge of space by then-Colonel Chuck Yeager, who, of course, made history in his own right as the first man to break the sound barrier whilst flying the first of the “X” planes, the Bell X-1.
The X-15 was produced by North American Aviation, whose other big claims to fame were the iconic P-51 Mustang of WWII – coincidentally another significant airplane in Chuck Yeager’s career – and the B-25 Mitchell medium bomber immortalized by the Doolittle Raid on Tokyo in 1942 (and, as a personal aside, was the plane my own Dad worked on as an Armorer during his WWII service with Marine Air Group [MAG] 61). Only a total of three airframes were built, but they were darn sure productive, as they conducted a total of 199 flights over a nearly ten-year period from June 1959 to October 1968.
The X-15 was conceived as part of a hypersonic flight research program designed to test and investigate several aspects associated with piloted hypersonic flight, and information gained from the X-15 program would be used in the development of the Mercury, Gemini, and Apollo piloted spaceflight programs – hence cry fortuitous for Mr. Armstrong in particular – as well as in the Space Shuttle Program. Indeed, the X-15 made its actual foray into outer space, albeit just barely: on August 22, 1963, NASA test pilot Joseph A. (Joe) Walker reached 354,200 feet (107,960 meters), an unofficial record altitude of almost 67 miles (107.82 km), thus exceeding the Kármán line, the internationally recognized 100 km altitude used by the Fédération Aéronautique Internationale (FAI) to denote the edge of space.
As impressive as the X-15’s feats were, as is true of any manmade technology, it still had its weaknesses. As described by my 1945 colleague Eli Furhman, “Even with its impressive technical feats and significant contributions to piloted hypersonic and space flight, the X-15 was not perfect. One X-15 pilot lost his life while operating the aircraft, while William Knight, only a few months before his record-setting flight, managed to safely land his aircraft after its entire electrical system failed.”
Bearing these maladies in mind, the X-15’s designers came up with an innovative ejection system that included the use of a pressure suit that protected the pilot from both the windblast of ejecting at Mach 3 and allowed pilots to survive at altitudes of over 250,000 feet (76,200 meters). In addition, the ejection seat included measures designed to help transfer weight from the pilot’s rear to the seat given the thrust involved in the ejection mechanism that was required to ensure that the pilot would clear the aircraft’s hypersonic shockwave. Special restraints were also added that prevented the pilot’s arms and legs from flailing during ejection, which helped to protect against heat burns. Much of the credit for this survival system belongs to engineer/test pilot A. Scott Crossfield and North American Aviation designer Jerry Madden.
Where Are They Now? The Planes, That Is, Not the Pilots
Fellow aviation history buffs who would like to see one of these history-making, record-breaking airplanes in person currently only have one option to choose from if they’re insistent on seeing “the real deal,” namely X-15A-2 (AF Ser. No. 56-6671) which is at the National Museum of the United States Air Force at Wright-Patterson AFB, near Dayton, Ohio. For the less nitpicky museum-goers amongst you who are willing to settle for realistic mockups, you have three choices: the Dryden Flight Research Center, Edwards AFB, California; the Pima Air & Space Museum, adjacent to Davis-Monthan AFB, Tucson, Arizona; and the Evergreen Aviation & Space Museum, McMinnville, Oregon
Length: 50 ft (15.24 m)
Wingspan: 22 ft (6.71 m)
Height: 13 ft 8 in (4.21 m)
Wing area: 200 sq ft (60.96 m)
Empty weight: 13,000 lb (5,897 kg)
Gross weight: 15 tons (13607.8 kg)
Powerplant: Thiokol 57,000-pound thrust liquid propellant rocket engine
Maximum speed: mach 6.7
Range: 280 mi (451 km)
Service ceiling: 354,331 ft (108,000 m)
Rate of climb: 60,000 ft/min
Christian D. Orr is a former Air Force officer, Federal law enforcement officer, and private military contractor (with assignments worked in Iraq, the United Arab Emirates, Kosovo, Japan, Germany, and the Pentagon). Chris holds a B.A. in International Relations from the University of Southern California (USC) and an M.A. in Intelligence Studies (concentration in Terrorism Studies) from American Military University (AMU). He has also been published in The Daily Torch and The Journal of Intelligence and Cyber Security.
May 24, 2022 at 8:35 pm
You know I wish whoever approves these articles would edit them properly. X 15 56-6670 is at the National Air and Space Museum in Washington DC. However!! It’s temporarily off display because of renovation. This tidbit should have been included in the article.
May 25, 2022 at 8:48 am
Thank you for the response. I was going to point out that the National Air and Space Museum in Washington has an X-15. My favorite “airplane/rocketship” as a child I have visited it many times at the museum. Otherwise, a great article.
May 24, 2022 at 11:44 pm
My father was stationed at Edward AFB during this time. I got to see things first hand on my many trips with him. Such a beautiful sight to see. Dad was in the 2nd B52 on its drop as chief inspector.
David C Arnold
May 24, 2022 at 11:59 pm
My dad is Bill Arnold who was a field engineer for Thiokol. I witnessed the first drop of the X-15 when I was in the first grade.
May 26, 2022 at 9:42 pm
Imagine the technology the government doesn’t let us see.
May 28, 2022 at 1:52 am
57,000 lbs of thrust is over 1 million hp!
May 28, 2022 at 7:45 pm
As stated, X-15 #2 is at the USAF museum at Wright Patt AFB outside Dayton Ohio. X-15 #2 is the one that set the speed and altitude records. It has two side mounted fuel tanks for the extra fuel that was required to go faster and higher. I saw it at the USAF museum three years ago. I also saw it at Edwards AFB in 1967 slung under the wing of the B-52 launch ship when I was in the Air Force.