XB-70 Valkyrie

The North American XB-70 "Valkyrie" was conceived for the Strategic Air Command in the 1950s as a high-altitude bomber that could fly three times the speed of sound (Mach 3). Two aircraft were built and flew test flights in the 1960s.

Design

The Valkyrie was configured as a canard delta wing, built largely of stainless steel honeycomb sandwich panels and titanium. It was designed to make use of a phenomenon called "compression lift," achieved when the shock wave generated by the airplane flying at supersonic speeds supports part of the airplane's weight. Compression lift remains, to this day, a controversial theory as applied to the XB-70 and it is the only airplane of its size to ever feature drooping wingtips. For improved stability at supersonic speeds, the Valkyrie could droop its wingtips as much as 65 degrees.

Drooping the wingtips also strengthened the compression lift effect — with the wingtips drooped downwards, the shock wave caused by the compression wedge at the center of the wing would be further trapped under the wings, rather than simply flowing out past the end of the wings. There is a popular belief that this helps the XB-70 have the highest lift-to-drag ratio on a manned aircraft. While it does improve the performance, the ratio still is not as high as on most sailplanes. It is correct to say the XB-70 had the highest lift-to-drag ratio of any powered manned aircraft.

The intended role of the aircraft was to be a high-altitude supersonic bomber, to be escorted by the XF-108 Rapier, a proposed supersonic fighter which was developed by North American Aviation in parallel with the XB-70. The Rapier was also intended as a defensive aircraft to counter an anticipated Russian bomber with capabilities similar to the XB-70. As a cost saving measure, the engines and many subsystems were engineered to be common between the two aircraft. Following the downing of the U-2 flown by Gary Powers, the viability of the XB-70 as a bomber was questioned, and the program was changed to a research program for the advanced study of aerodynamics, propulsion, and other subjects related to large supersonic aircraft, in particular the American SST program. Initial plans were made to build 3 aircraft, each one incorporating modifications based on lessons learned from the previous aircraft's flight tests, but the program was cut down to two aircraft in July 1964.

Flight history

The first XB-70 made its maiden flight on September 21, 1964. The first aircraft would be found to suffer from weaknesses in the honeycomb construction, primarily due to inexperience with fabrication of this new material. Construction of the honeycombed panels was much more difficult than anticipated by the designers. The first aircraft was also continually troubled by hydraulic leaks, fuel leaks, and problems with the aircraft's unusually complicated landing gear. In flight on May 7, 1965, the divider separating the left and right halves of the engine inlet broke off and was ingested into the engines, damaging all six beyond repair. On October 14, 1965, on the first flight exceeding a speed of Mach 3, the stress again damaged the honeycomb construction, leaving two feet (0.6 m) of the leading edge of the left wing missing. These construction problems resulted in the imposition of a speed limit of Mach 2.5 on the first aircraft.

These honeycomb construction deficiencies were almost completely solved on the second aircraft, which first flew on July 17, 1965. On May 19, 1966 aircraft number two flew 2,400 miles (3,840 km) in 91 minutes, attaining Mach 3 for 33 minutes of that flight. On June 8, 1966, however, it crashed following a mid-air collision with an F-104 that occurred while the aircraft were flying in close formation for an ill-conceived photo shoot at the behest of General Electric. NASA Chief Test Pilot Joe Walker, piloting the F-104, and Carl Cross, copilot aboard the XB-70, were both killed in the crash, while Al White, the XB-70's pilot, successfully ejected. The exact cause of the collision is still debated. There are many different factors that can lead to such a crash, some of these being pilot failure and mechanical failure. Most likely, the F-104 got caught in the massive vortex generated by the XB-70's huge wing.

The first aircraft with its limited abilities continued research, making 33 more research flights. On February 4, 1969, Valkyrie number one was retired and flown to the National Museum of the United States Air Force at Wright-Patterson Air Force Base near Dayton, Ohio.

It is a popular misconception that the XB-70 caused so much concern in the Soviet Union that a special fighter aircraft design program was created to counter it, the MiG-25. In reality, this was a cover for the MiG's true purpose as a countermeasure to the SR-71, which was still highly classified at the time.

The Soviet Sukhoi T-4 was a medium-range bomber/missile carrier prototype built in response to the XB-70.

Aircraft

A full scale mock-up was completed in February 1959.
XB-70A #1 - (NA-278) 62-0001, 83 flights; total time: 160 hours - 16 minutes - At the U.S. Air Force Museum near Dayton, OH
XB-70A #2 - (NA-278) 62-0207, 46 flights; total time: 92 hours - 22 minutes - Crashed on 8 June 1966 north of Barstow, CA killing Air Force pilot Major Carl S Cross.
XB-70B #3 - (NA-274) 62-0208 originally to be first YB-70A in March 1961, this advanced prototype was cancelled in March 1964 while under construction.
YB-70A - additional 10 advanced prototypes cancelled in December 1960. These YB-70's would have been modified to B-70A specifications at completion of testing.
B-70A - planned fleet of 50 operational bombers (with wing-tip fuel tanks) cancelled in December 1959.
RS-70 - alternate planned fleet of 50 reconnaissance aircraft (with a crew of four and in-flight refuelling capability) was evaluated in February 1959.

Specifications (XB-70A)

References

External links

Unreal Aircraft - North American XB-70 Valkyrie
NASA XB-70 videos
NASA B-70 aircraft study (PDF format) Vol.1 Vol.2 Vol.3 Vol.4
B-70 Valkyrie, GlobalSecurity.org
The Flight of the Valkyrie

Original contents of this page copied from USAF Museum web site.

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