21 August 1967

Major William J. Knight, U.S. Air Force, with the modified X-15A-2, 56-6671, at Edwards Air Force Base, California. (U.S. Air Force)
Major William J. Knight, U.S. Air Force, with the modified X-15A-2, 56-6671, at Edwards Air Force Base, California. (U.S. Air Force)

21 August 1967: On the 186th flight of the X-15 program, the modified North American Aviation X-15A-2, 56-6671, made the first of two flights with a heat-protective ablative coating, designed to protect the steel structure of the rocketplane from the extreme heat of flight at high Mach numbers.

After a landing accident which caused significant damage to the Number 2 X-15, it was rebuilt by North American. A 28-inch (0.71 meter) “plug” was installed in the fuselage forward of the wings to create space for a liquid hydrogen fuel tank which would be used for an experimental “scramjet” engine that would be mounted the the ventral fin. The modified aircraft was also able to carry two external fuel tanks. It was hoped that additional propellant would allow the X-15A-2 to reach much higher speeds. The external tanks were not carried on the 21 August 1967 flight.

With Major William J. (“Pete”) Knight, U.S. Air Force, in the cockpit, the X-15A-2 was airdropped from the Boeing NB-52B Stratofortress, 52-008, known as Balls 8, over Hidden Hills Dry Lake, just on the California side of the border with Nevada. This was Knight’s 11th X-15 flight, and the 52nd flight for 56-6671. The launch time was 10:59:16.0 a.m., PDT. Knight fired the 57,000-pound-thrust Reaction Motors XLR99-RM-1 rocket engine and accelerated for 82.2 seconds. The purpose of this flight was to attain a high speed rather than altitude. The X-15A-2 reached Mach 4.94 (3,368 miles per hour, 5,420 kilometers per hour) at 85,000 feet (25,908 meters) and reached a peak altitude of 91,000 feet (27,737 meters). Pete Knight touched down on Rogers Dry Lake at Edwards Air Force Base, just 7 minutes, 40.0 seconds after launch.

© 2015, Bryan R. Swopes

Share this article:

4 thoughts on “21 August 1967

  1. Hi Bryan – You have posted a photo of Jimmy Stewart and a crew of bombardiers at Kirkland. My uncle, Jack Drenan, is the first on the left. Could you point me to the source? I’ve a copy from a genealogy site no longer available. The image was apparently scanned from a magazine but I don’t know which. On close inspection your photo seems to be from the same source. Have not been able to find it in the AF images available online. – Thanks, Patrick

    1. Thanks for the information, Patrick. I located this photograph on the Internet, but I lost all my photos and their source data in a computer crash earlier this year. Photos already published were stored in the WordPress media library, but in checking there, the source data did not carry over. Sorry I can’t be of more help.


  2. Hi Bryan,

    I am with the Flight Test Historical Foundation, which supports Air Force Flight Test Museum at Edwards AFB. I love your posts, especially “This Day in Aviation”. I was wondering if you would be OK with us posting your excerpts on our Facebook page once in a while http://Facebook.com/AFFTMuseum Of course we will credit your website as the source. If not – no worries, that’s OK too. Thanks! AngellaRaisian

    1. Angella, I would be honored! Please feel free to use anything that you like. And thank you for checking my blog. In my view, Edwards is the center of the aviation universe!

Comments are closed.