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North American X-15

Air-launched rocket plane. NASA and the Air Force both print 4,520 mph for William J. Knight's flight on 3 October 1967, and NASA calls the mark unofficial.

Also known as X-15, X-15A-2
Post on X (opens in a new tab)

Top speed

Published as 4,520 mphPublished as 4,520 mphPublished as 4,520 mphPublished as 4,520 mph

X-15A-2, Mach 6.7, air-launched, pilot William J. Knight. NASA calls the mark unofficial.

VerifiedNASA (opens source in a new tab)

In context

  • London to New York in 46 minConstant · London to New York, 5,570 km great-circle
  • 70× a cheetah's timed top speedSourced · Cheetah, 29 m/s. Sharp 1997, mean of three timed runs over 201.2 m
  • 22 football fields a secondConstant · American football field, 100 yd (91.44 m)

Worked out from the sourced figure above, which stays the ranked number.

This list

Why it's so fast

A rocket plane carries its own oxidizer, so it does not have to gulp the thin air it is flying through. That is why it can outrun every air-breathing plane.

  1. No inlet limit

    A jet has to slow the oncoming air before the compressor. A rocket does not. The limit becomes heat, structure and how long the propellant lasts.

  2. A research flight

    These are timed flights with a pilot and a drop, not an airliner cruise. The entry names the flight the record belongs to.

The airplane is the X-15.

This is how the category works. A note written for this entry appears here once it is in the database.

Provenance

Every measurement

Claimed, measured and official figures side by side, each with its source. The ranked figure is marked.

  1. 7,274km/h4,520mph2,021m/s3,928knMach5.94Ranked figure

    Top speed. X-15A-2, Mach 6.7, air-launched, pilot William J. Knight. NASA calls the mark unofficial.

    Verified
    NASA (opens source in a new tab)
  2. 7,274km/h4,520mph2,021m/s3,928knMach5.94Ranked figure

    Absolute speed. X-15A-2, Mach 6.7, air-launched, pilot William J. Knight. NASA calls the mark unofficial.

    Same figure as this entry's home ranking, so the human-built hub can sort it. Not a second trial.

    Verified
    NASA (opens source in a new tab)

Reference

Specs

Pilot
William J. Knight
Flight
3 October 1967
Speed
4,520 mph
Launch
Air-launched

Context

Background

NASA fact sheet FS-052 prints an unofficial world speed of 4,520 mph, Mach 6.7, on 3 October 1967, with Air Force pilot Pete Knight in the X-15. NASA's pilot biography for William J. Knight uses the same speed, the same day, and the modified X-15A-2, and says it remains the highest speed attained in an airplane.

The U.S. Air Force Test Center's history page for that day also prints Mach 6.7 (4,520 mph) and calls it the highest speed reached by a manned airplane. The qualifier is verified, not official, because NASA itself says the record is unofficial: the X-15 was air-launched, so it is outside the FAI class of air-breathing aircraft that take off under their own power. That absolute record is a separate list.

Spot a wrong number?

Every report is read by a person, and corrections are dated on the page.