4 August 1960

4 August 1960: NASA research test pilot Joseph Albert Walker set an unofficial world speed record when he flew the number one North American Aviation X-15, 56-6670, to 2,195 miles per hour (3,532.5 kilometers per hour). This was the 18th flight of the X-15 Program. It was 56-6670’s eighth flight and Walker’s fourth X-15 flight. The purpose of this test was to gradually increase the rocket plane’s speed toward its design limit.

Airdropped from the Boeing NB-52A Stratofortress mothership, 52-003, over Silver Lake, near the California-Nevada border, at 08:59:13.0 a.m., PDT, Walker fired the X-15’s two Reaction Motors XLR11-RM-13 rocket engines for 264.2 seconds. The X-15 accelerated to Mach 3.31 and climbed to a peak altitude of 78,112 feet (23,810 meters). [The two XLR11s were used as an interim powerplant until the Reaction Motors XLR99 was ready. The combined thrust of both LR11s was only slightly more than the idle thrust of the XLR99.]

Walker touched down on Rogers Dry Lake at Edwards Air Force Base, California, after a flight of 10 minutes, 22.6 seconds.

Joe Walker with X-15 56-6670 on Rogers Dry Lake. (NASA)

© 2016, Bryan R. Swopes

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9 thoughts on “4 August 1960

  1. I think that it is incredible that Joseph Walker was able to fly 2,195 miles in one hour. I don’t know much about aviation, but that sounds pretty incredible. If this was able to be done in 1960, then why don’t all planes fly at that speed now?

    1. Excellent question. (To be accurate, the straight-line distance traveled by Walker on this flight was just over 110 miles, but the X-15 reached maximum speed of 2,195 m.p.h. during the 10-minute, 22 second flight.) 16 years later, 28 July 1976, a Lockheed SR-71A “Blackbird” set a World Absolute Speed Record of 2,193.17 m.p.h. This is the fastest speed ever reached by an airplane (as far as is publicly known, anyway) and was still about two miles slower than than Joe Walker and the X-15 on this date. The X-15 eventually reached 4,520 m.p.h.

      Today, commercial airliners are designed to reach high sub-sonic speed, of around 0.9 Mach. There are a number of reasons for this. In the 1950s, when military aircraft frequently “broke the sound barrier” (the “sound barrier” is Mach 1.0, the speed of sound through air, which varies with altitude: 761.1 m.p.h. at Sea Level, and 660.7 miles per hour at 35,000 feet, cruising altitude for jet airliners) they frequently broke windows and sometimes caused structural damage to buildings. Government agencies received tens of thousands of complaints and paid out a lot of money for damage claims. So the military restricted supersonic flights to a few geographic areas of the United States, or over the oceans.

      People of my age remember the frequent double “B-BOOM!”, but not many people today have ever heard it.

      The Aérospatiale-British Aerospace Concorde supersonic airliner was capable of Mach 2.05, about 1,350 miles per hour, but it was restricted to overwater routes and this effected its economic viability. Also, the Concorde’s very high cruise altitude of 60,000 feet raised concerns that damage to the Earth’s atmosphere could result. It was finally withdrawn from service in 2003.

      Another consideration limiting speeds of commercial aircraft is the saturation of the airspace. All jet aircraft fly under Instrument Flight Rules. Air Traffic Control organizations require that these aircraft be separated by time, distance and altitude, and fly very specific straight-line routes. There is only so much space available, and to maintain separation requirements, these airplanes are restricted to speeds much lower than they are actually capable of flying. Airliners have to slow down even further as they approach their destinations, as airport runways are also operating at maximum capacity.

      Today, the technology certainly exists to build commercial aircraft that could cruise at supersonic speeds, but technology is expensive. Manufacturers have determined that there is not sufficient demand for such aircraft. They keep building airplanes that fly at about 600 m.p.h. (The Boeing 787, for example, has a cruising speed of 0.85 Mach, and maximum speed of 0.89 Mach—588 miles per hour at 35,000 feet.)

      Thank you for your question.

      1. Hi Bryan,
        Excellent response and detailed explanation about why airlines cruise at the speeds they do.
        In 2001 Boeing was developing a concept called the Sonic Cruiser for the airlines. Designed to operate at .98 Mach.
        The airlines responded this speed would saturate gates… meaning the jet would get their sooner, but no gates available and then waiting on the ground. If you’ve flown recently to Newark you’d know. This topic is for another discussion at a different time.

        So, Boeing answered with what the customer wanted, lower operating costs over speed. Hence the 787 was born. A program that is now 20 years old already.
        The 87 cruises at .85 Mach.


  2. I was standing in front of the Ansel Adams photo shop in Yosemite National Park in the summer of 1960. Two F-4 Phantom IIs came through the valley from east to west supersonic. The B-boom was especially impressive echoing off the stone walls of the valley. Something as a young kid from Kansas I will never forget.

  3. Lockheed Martin and NASA are working on the X-59 QUESST project to combat the sonic boom problem that banned overflights of the USA. The design of the aircraft is supposed to take the sonic boom down to thump that sounds about like a car door closing. They are very close to taking it out for a first flight. It will then be flown over test cities to get the public’s reaction to the “Sonic Thump.” The data gathered will be used to draft a set of regulations, if approved by congress, that will allow supersonic overflights of the USA again. I wish I was in one of the test cities but I’m sure they’ll all be out in SoCal.

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