North American X-15

The rocket plane that flew to the edge of space

Updated: by Tim de Vries

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North American X-15
The X-15 landed on its rear skids on a dry lakebed, with the nose gear touching down last. – © NASA

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Overview

North American Aviation (NAA) United States Military: X-15 1900–Onward

The North American X-15 was a rocket-powered research aircraft that flew from 1959 to 1968. It still holds the speed record for a crewed winged aircraft and flew above 50 miles, which the U.S. counts as space.

Specifications

Units
Engine
1 × Reaction Motors XLR99-RM-2
Engine type
-
Thrust
70,400 lbf · 313 kN
Avionics
—
Wing tips
No winglets
Seats
1
Crew
1
Cabin width
—
Cabin height
—
Cabin length
—
Exterior length
49 ft 2 in  ·  14.99 m
Tail height
13 ft 1 in  ·  3.99 m
Fuselage diameter
—
Wing span
22 ft 4 in  ·  6.81 m
Baggage volume
—
Gross weight
—
Empty weight
14,600 lb  ·  6,622 kg
Max takeoff weight
33,500 lb  ·  15,200 kg
Max landing weight
—
Max payload
—
Fuel capacity
Maximum speed
3,930 kt  ·  4,523 mph  ·  7,278 km/h
Cruise speed
—
Approach speed
—
Range
240 nm  ·  280 mi  ·  440 km
Fuel burn
—
Ceiling
354,330 ft  ·  108,000 m
Rate of climb
60,000 ft/min  ·  305 m/s
Takeoff distance
—
Landing distance
—
(/) tap to zoom
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The X-15 rode under the wing of a B-52 to launch altitude, because it could not take off on its own.

Operational Context

Table of Contents

What was the X-15?

The North American X-15 was a rocket-powered research aircraft flown by the U.S. Air Force and NASA. It explored hypersonic flight and the edge of space between 1959 and 1968.

Only three were built. Together they flew 199 missions, and the program ended with the last flight on October 24, 1968.

How fast was the X-15?

The X-15 flew at Mach 6.7 on October 3, 1967, when William “Pete” Knight reached 4,520 mph. That remains the fastest flight by a crewed, winged aircraft.

So the answer to “what plane goes 7,000 mph” is close but not quite. The X-15 topped out near 4,520 mph, or about 7,270 km/h.

How high did it fly?

On August 22, 1963, Joseph Walker flew Flight 91 to 354,200 feet, about 67 miles (108 km). NASA lists it as an unofficial world altitude record.

That is above the 50-mile line the U.S. uses to award astronaut wings. The X-15 reached the edge of space without ever going into orbit.

How did the X-15 launch?

The X-15 could not take off under its own power. A modified B-52 carried it under the wing and dropped it at about 45,000 feet.

The North American X-15 falling away from the B-52 mothership at the moment of launch
Every flight began as a drop from a B-52, because the rocket burned through its fuel in minutes. – © NASA

The pilot lit the Reaction Motors XLR99 engine after release. The rocket burned for only a short time, and the rest of the flight was a coast up and a glide down.

Each flight ended with an unpowered landing on a dry lakebed at Edwards Air Force Base.

Black North American X-15 landing on a dry lakebed with skids touching down
The X-15 touched down on rear skids first, with the nose gear coming down last. – © NASA

The three airframes

X-15-1 flew 81 free flights. X-15-3 flew 65, and X-15-2 flew 53 across two configurations.

The second aircraft was damaged in a landing accident on November 9, 1962, injuring pilot John McKay. It was rebuilt as the X-15A-2 with a longer fuselage and external fuel tanks, and first flew again on June 25, 1964.

The X-15A-2 also received a heat-resistant ablative coating, which gave it a chalky white finish.

White North American X-15A-2 with ablative coating parked in front of a hangar
The ablative layer was meant to burn away and protect the airframe at the heat of Mach 6. – © NASA

Explaining the numbers

The full specification table for the aircraft is on this page. A few figures need context.

The weight shown is the launch weight when the X-15 left the B-52, with its tanks full. The thrust figure is the one Wikipedia prints for the XLR99, and some sources quote a lower sea-level number.

The range is the published figure for a flight profile, and the rocket burned for only a short part of it. The service ceiling is Wikipedia’s figure, and NASA’s record flight is a little lower.

Flight 191 and the death of Michael Adams

The X-15 had one fatal accident. On November 15, 1967, X-15-3 broke apart at about 60,000 feet during descent on Flight 191, killing pilot Michael J. Adams.

The flight had reached about 50 miles (81 km). Adams was posthumously awarded Air Force astronaut wings.

Why the X-15 mattered

The program ran for nearly a decade and gave engineers real data on hypersonic heating, control above the atmosphere and reentry. NASA’s chronology shows steady milestones, from the first Mach 4 flight in 1961 to flights above 300,000 feet in 1962.

Its test pilots included Neil Armstrong, who flew the X-15 before joining the astronaut corps.

Frequently Asked Questions

Was the X-15 manned?

Yes. A single pilot flew every mission in a pressure suit.

What plane goes 7000 mph?

No crewed winged aircraft has. The X-15 holds the record at 4,520 mph (about 7,270 km/h), set on October 3, 1967.

How fast is Mach 6.7 in mph?

The X-15’s record flight at Mach 6.7 came to 4,520 mph. The exact conversion depends on altitude and air temperature.

Did the X-15 crash?

Yes, once fatally. X-15-3 broke apart on Flight 191 on November 15, 1967, killing Michael Adams. The second aircraft was also damaged in a landing accident in 1962, and its pilot survived.

How many X-15s were built?

Three were built, and they flew 199 missions between 1959 and 1968.