04.08.1960 odbył się 18. lot X-15 (prototyp nr 3) z Josephem Walkerem, który osiągnął wysokość 23809 metrów i prędkość 3533 km/h (3,31 Mach).
Joseph Albert Walker ustanowił nieoficjalny światowy rekord prędkości w North American Aviation X-15, 56-6670, osiągając 2195 mil/h.
Był to ósmy lot 56-6670 i czwarty lot Walkera na X-15.
1960 August 4 - . 16:59 GMT - . Launch Site: Edwards. Launch Complex: Silver Lake DZ. Launch Pad: Edwards RW04/22. Launch Platform: NB-52 003.
X-15A test - . Nation: USA. Agency: NASA, USAF. Spacecraft: X-15A. Apogee: 23 km (14 mi). Maximum Speed - 3533 kph. Maximum Altitude - 23809 m. Unofficial world speed record. This topped Captain Apt's speed of 2,094 mph attained in the X-2 on September 27, 1956. Air dropped in Silver Lake DZ..
http://www.astronautix.com/a/august04.html4 August 1960. NASA research pilot Joseph Albert Walker set an unofficial world speed record in North American Aviation X-15, 56-6670, to 2,195 miles per hour during the 18th flight of the X-15 Program. It was the eighth flight of 56-6670 and Walker’s fourth X-15 flight.
https://x.com/ron_eisele/status/1819807413186289918