PHOTO: The XB-70A-1 retained its U.S. Air Force markings after NASA took over the flight-test program. BOEING ARCHIVES Frontiers September 2014 11 could withstand the high temperatures of hypersonic flight. It was manufactured using a brazing process, a technique that became widely used throughout the aerospace industry, rather than being welded. Interest in a commercial supersonic transport, or SST, was growing and the XB-70 was similar in size and had the speed of some SST engineering concepts. But the first prototype achieved only Mach 3 on one flight. Improvements were made to the second Valkyrie, which resulted in much better handling. It made a number of Mach 3 flights. NASA and the Air Force signed an agreement to use the second XB-70 for high-speed research flights for the SST program, beginning in mid-June 1966. But on June 8 tragedy struck during a photo flight with the second XB-70. Several chase planes had just finished filming the Valkyrie when one of them, an F-104 flown by NASA pilot Joe Walker, who had been named project pilot for the SST research, drifted into the Valkyrie’s wingtip and was captured by its wake vortex. The small fighter then clipped off the XB-70’s vertical fins, resulting in the loss of both aircraft, along with Walker and XB-70 co-pilot Carl Cross; Al White, who was piloting the XB-70, ejected and survived the accident. The surviving Valkyrie, XB-70A-1, continued to fly for NASA, testing the flight regime of a supersonic transport. The aircraft made its final flight in February 1969—from Edwards Air Force Base in California to Wright-Patterson AFB in Ohio, where it was put on display at the National Museum of the U.S. Air Force. With a maximum takeoff weight of 542,000 pounds (246,000 kilograms), the XB-70 remains the largest and heaviest airplane ever to fly at Mach 3. Its size, speed and design, even 50 years after that first flight, still serve as an inspiration—and perhaps an influence—for engineers who continue to tackle the many challenges to efficient and affordable supersonic commercial air travel. n michael.j.lombardi@boeing.com
Frontiers September 2014 Issue
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