Body construction of the Valkyrie involved a "honeycombed" core encased in stainless steel panels (sandwich arrangement) while titanium was used at high temperature surfaces (much heat was generated as the speeds/altitudes required of the aircraft). The overall design of the aircraft was made to take advantage of "compression lift", a naturally occurring byproduct of flight appearing at high speed/high altitude that could use some of the generated shock waves as high pressure air to generate additional lift. This approach gave the XB-70 a wholly unique appearance in relation to other aircraft of the period (its sharp angles, the intake positioning, etc...). The lowering of the wingtips was another high-speed design feature meant to aid directional stability during flying.
The XB-70 was to have individual encapsulated seats for ejection in the case of emergency. A whole-cabin ejection system was also tested.
The Evolution of Missile Technology
Missile defenses were in use since the 1950s and in the 1960s, the available technology was such that it began rendering such high-flying supersonic bomber products like the XB-70 obsolete. This led to a late-November 1959 request by authorities to revise the XB-70 as strike-reconnaissance platform to target Soviet missile launchers. However, this initiative was not followed and the XB-70 program suffered a reduced development role instead as its initial value quickly diminished. The rise of America's own ICBM missile program also helped to derail the XB-70's development further. In late 1959, the XB-70 program's funding covered just one prototype.
Popular support for the XB-70 then began to rise due to public mentions during the 1960 presidential campaign. The XB-70 gained new life to the point that the USAF commissioned for completion of an XB-70 prototype and this to be followed by eleven improved developmental vehicles under the "YB-70" designation. Funding followed in November of 1960.
With John F. Kennedy's victory over Richard Nixon, Kennedy's new administration moved to nix the XB-70 bomber program in full in March of 1961 and shift American priorities to missiles. It was decided to retain the services of the XB-70 as a research and development product exploring Mach 3 flight. A short-lived initiative to revive the XB-70 as a missile-carrying reconnaissance-strike aircraft (as the "RS-70") was not enough to resurrect the XB-70 bomber program. This revised version was to keep its crew of four and sport an in-flight refueling capability. Regardless, the reduced research role of the XB-70 would continue and modifications to the original design were enacted to better serve the new purpose.
The XB-70 as a Research Platform
Despite three XB-70s planned for the new program, the procurement was later reduced to two airframes under the "XB-70A" designation. The aircraft were individually recognized as "AV-1" and "AV-2" (AV = "Air Vehicle)". AV-1 was arrived in May of 1964 and AV-2 followed in October. First flight of AV-1 took place on September 21st, 1964 though this event was marred by one engine shutdown and an undercarriage warning that forced the crew to fly the large aircraft with its legs down. Furthermore, upon landing, the rear wheels along the portside of the aircraft locked in place and this friction then led to their rubber rupturing and a flame starting - an ominous start for the long-gestating program.
Promising Results
Mach 1 flight for the XB-70 was not experienced until October of 1964 and it was not until October of 1965 that Mach 3 flight (at 70,000 feet) was finally attained. Improvements discovered through testing of the AV-1 were instituted into the AV-2 which recorded its own first flight on July 17th, 1965. Further work evolved AV-2 to serve in sonic boom testing with the aircraft appropriately outfitted with special components and systems.
Tragedy Strikes the Program
On June 8th, 1966, AV-2 was used in a General Electric photograph promotional (for a corporate brochure) which attempted to showcase all of the then-current USAF aircraft outfitted with GE engines in one shot (formation flying involving four total aircraft). However, the formation was rocked when the accompanying Lockheed F-104 "Starfighter" was pulled into a vortex air stream of the XB-70, sucking the F-104 into the XB-70's wing and driving into the large aircraft's vertical stabilizers (fins). The F-104 erupted into flames while the XB-70 - initially continuing in level flight for some 16 seconds, its crew unaware of the contact - became unstable, began an uncontrollable (flat) spin, and entered into a downward flight path. The incident further stained the career of the expensive bomber program that began which so much promise in the late 1950s. Of the three pilots involved - Al White and Joe Cross in the XB-70 and Joe Walker in the F-104 - only White survived after having used his escape capsule against the growing G-forces of the massive aircraft.
General Electric certainly received publicity from the accident - though not the kind it sought.
The End of the Road
AV-1 continued on as a test vehicle into 1969. After 83 total flights (the last to Wright-Patterson AFB), the airframe was officially retired to become a protected showpiece of the National Museum of the United States Air Force in Dayton, Ohio.
While a failed bomber project on its own, the data collected from the Valkyrie as a research platform became priceless for new generation bomber projects and supersonic flight in general. Indeed, results were used in the development of the low-altitude Rockwell B-1 "Lancer" penetration bomber of USAF/SAC. The Mach 3-capable XB-70 also forced the Soviet Union to develop their Mach 2.5-capable Mikoyan-Gurevich MiG-25 "Foxbat" as an XB-70 counter. While the B-70 failed to see the light of day in service, the Foxbat has gone on to have a lengthy flying career for the Russians and others. The Tupolev Tu-144 supersonic passenger airliner is also said to have benefitted from stolen XB-70 data - it certainly holds some design features of the XB-70 prototype as well as that of the European Aerospatiale / BAC Concorde airliner. Another North American project - the abandoned XF-108 "Rapier" supersonic interceptor - was also to have used the GE engine (two side-by-side) developed for the XB-70.
The XB-70 also failed as the successor to the storied B-52 and the Boeing product also survived the B-1 Lancer as its other designated replacement. Due to the procurement and operating costs of the B-1 bomber and the Northrop B-2 "Spirit" stealth bomber, the B-52 has remained in service with the USAF - all three operated concurrently.
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