10 Facts About The Aircraft So Fast It Reached Space: The North American X-15

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The X-15 was a North American-made hypersonic rocket-powered aircraft developed in the 1950s by the United States Air Force and NASA. Here are ten facts about the X-15:

1. First manned aircraft to reach hypersonic speeds

It was the first manned aircraft to reach hypersonic speeds, with a top speed of up to Mach 6.7. The X-15 achieved stability at hypersonic speeds by using side panels that extended from the tail to increase the overall surface area.

2. Designed to be drop-launched

Like several of the X-series aircraft, the X-15 was launched from a B-52 bomber, which carried the aircraft before releasing it at an altitude of about 45,000 ft and a speed of 500 mph. The X-15 would then ignite its rocket engine and climb to its maximum altitude and speed.

3. Helped pilots qualify as astronauts

Thirteen flights flown by eight pilots met the Air Force’s spaceflight criterion by exceeding 260,000 ft of altitude, enabling the pilots to qualify for astronaut status. Only two of these flights, piloted by Joseph Walker, exceed the Karman Line. The two civilian pilots were awarded NASA astronaut wings in 2005, while the Air Force pilots earned their wings immediately.  

4. Set a lot of records

X-15s set numerous speed and altitude records during its flight program. Pilot Joe Walker reached the highest altitude of 354,200 feet in 1963. Meanwhile, William “Pete” Knight recorded the fastest X-15 flight on October 3, 1967, on Flight 188, where he achieved a top speed of Mach 6.70.

5. Experimental hypersonic rocket-powered aircraft

The X-15 was designed to test the limits of crewed flight and gather data on hypersonic flight, high-altitude flight, and re-entry. One of its many contributions was providing essential data that helped the development of technologies used in the Space Shuttle program.

6. Powered by a rocket engine

Early flights done by the X-15 used two Reaction Motors XLR11 engines. Later on, the X-15 would be fitted with a single XLR-99 rocket engine, which burned a mixture of liquid oxygen and anhydrous ammonia as the propellant. The engine produced up to 57,000 pounds of thrust and burned 15,000 lbs of fuel in just 80 seconds.

7. Flown by Neil Armstrong

Only twelve pilots flew the X-15 during its entire flight program. One of its pilots was Neil Armstrong, the well-decorated astronaut and the first man to walk on the moon. He flew the X-15 a total of seven times between 1960 and 1962.

8. It did not have the usual landing gear

The X-15 didn’t have traditional landing gears and instead landed on skids, which caused it to skid along the ground until it came to a stop. Furthermore, the skids didn’t extend beyond their ventral fins, forcing the pilot to jettison the fin before landing. 

9. Completed almost 200 flights

The test program ran from 1959 to 1968 and completed 199 flights. North American produced three X-15 planes: the first one completed 81 free flights, the second 53 flights, and the last flew 65 times. Two modified B-52 bombers were also used to deploy them – “The High and Mighty One” and “The Challenger.”

10. It cost a lot of money

In total, the X-15 program cost $300 million or $2.2 billion in today’s currency. Though “pricey,” the program was considered a significant achievement in aviation history. Its legacy includes helping the development of advanced materials, propulsion systems, and flight control technologies that have been used in subsequent aircraft and spacecraft programs.