5 Facts About the X-15, the Fastest Plane in History

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Fifty years ago this week, a pilot most people have never heard of set a remarkable aviation record that still stands. On Oct. 3, 1967, William J. “Pete” Knight flew an aircraft at Mach 6.72, or 4,520 mph. That remains the record for a manned, powered aircraft. Yet Knight remains virtually unknown compared to other aviation pioneers such as Charles Lindbergh and Chuck Yeager. And that record-setting plane, the X-15, has never received the credit it deserves for its role in aviation and space history. The X-15 was not only fast, it is regarded as the first spaceplane, predating America’s earliest space shuttle flights by more than 20 years. On the anniversary of Col. Knight’s historic flight, here’s a look back at the X-15 program.


5. X-15 Became the First Spaceplane in 1950s

The X-15 made 199 flights between 1959 and 1968, and predated the space shuttle as a spaceplane by more than 20 years. Credit: NASA

Development of the X-15 began in the mid-1950s, and the first flight launched in June 1959. As the first spaceplane, the X-15 truly was many years ahead of its time. Consider that the next spaceplane, the U.S. Space Shuttle Columbia, didn’t launch until 1981. And to date, there have only been three other space planes: Russia’s ill-fated Buran, which flew only one mission, in 1988; the privately owned SpaceShipOne, which went into space in 2004; and the U.S. Air Force’s X-37 (2010).


4. X-15 Set Stage For U.S. Manned Space Travel

The cockpit of the X-15.

Built by North American Aviation, the X-15 program was operated by NASA and the U.S. Air Force to learn more about hypersonic flight at high altitudes. Engineers wanted to know which materials, designs and controls worked best under those extreme conditions. The rocket-powered X-15 went airborne beneath the wing of a B-52, then launched at between 40,000 and 50,000 feet. The powered portions of flights were brief (less than 90 seconds), and flights continued with a rapid descent to landing. The X-15 program has been hailed for providing critical information for manned spaceflights, from the earliest missions all the way to the space shuttle program. In fact, those glide techniques X-15 pilots used were later adopted by space shuttle pilots.


3. First American to Die on Space Mission Was in X-15

Michael Adams became the first American to die during a space mission when his X-15 broke apart in flight in 1967. Credit: NASA

NASA endured a horrific tragedy on Jan. 27, 1967, when astronauts Virgil “Gus” Grissom, Edward White and Roger Chaffee were killed in a fire during a ground test aboard Apollo 1. But the first American astronaut killed during a space mission was Maj. Michael J. Adams. The test pilot lost his life in the crash of an X-15 on Nov. 15, 1967. As Adams, a Korean War veteran, piloted the rocket-powered plane at around 250,000 feet at Mach 5, the aircraft went into a hypersonic spin. With Adams unable to regain control, the aircraft plummeted toward the Earth, with aerodynamic forces causing the plane to break apart at around 60,000 feet.

Adams was posthumously awarded his astronaut wings for achieving space flight. And in 2004, NASA honored the pioneer with a monument in the Mojave Desert in California near the impact site.


2. Civilian Pilots Hailed as Astronauts 40 Years Later

X-15 pilots in December 1965 (from left) Joe Engle, Bob Rushworth, John McKay, Pete Knight, Milt Thompson, and Bill Dana. Credit: NASA

Between the X-15’s first flight in 1959 and the last flight in October 1968, 12 different pilots flew a combined total of 199 missions (among those pilots: Neil Armstrong). Thirteen of those missions exceeded an altitude of 50 miles; at the time, the U.S. designated anyone who traveled above that altitude as an astronaut (the current internationally recognized space boundary, the Karman Line, is at 100 kilometers, or 62 miles). Nevertheless, the USAF awarded astronaut wings in the 1960s to five military pilots who exceeded that 50-mile boundary.

Unfortunately, three other pilots weren’t honored in that manner because they were civilians. Finally, in 2005, NASA belatedly honored pilot Bill Dana and posthumously recognized John McKay and Joseph Walker as astronauts. Walker’s flight, in August 1963, reached an altitude of 354,200 feet (67.08 miles), a record for the X-15.


1. William Knight Set Speed Record in 1967 That Still Stands

William J. “Pete” Knight piloted an X-15 to a speed of 4,520 mph in 1967, a record for a manned, powered flight. Credit: NASA

It’s a bit surprising that Knight’s world-record speed of Mach 6.72, or 4,520 mph, set Oct. 3, 1967 still stands today. And how is that possible that while aviation pioneers such as the Wright Brothers, Charles Lindbergh and Chuck Yeager are enshrined in history books, the man who flew faster than anyone in history is mostly unknown? Knight, who flew more than 250 combat missions in Vietnam, became a test pilot in 1958. He spent five years and flew 16 missions in the X-15 program. He’d already had a close call in the aircraft just three months before his historic flight, when he lost all onboard controls at 107,000 feet and had to glide in on visual approach for a landing. He earned a Distinguished Flying Cross for that successful landing.

The record-setting X-15 flown by Knight is on display at the National Museum of the U.S. Air Force, at Wright-Patterson Air Force Base, near Dayton, Ohio. Only three X-15s were ever built. The other surviving X-15 is on display at the National Air and Space Museum in Washington, D.C.


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The author is a longtime professional journalist who has interviewed everyone from presidential contenders to hall of fame athletes to rock 'n' roll legends while covering politics, sports, and other topics for both local and national publications and websites. His latest passions are history, geography and travel. He's traveled extensively around the United States seeking out the hidden wonders of the country.