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Early
(Pre-flight) History
By 1961, following
the shooting down of the U-2 flown by Gary Powers over
Russia, it became obvious that the performance of
surface-to-air missiles were improving much faster than that
of manned aircraft. Following long, loud, and bitter debate,
it was decided that the XB-70 would not be a viable bomber
platform, and the XB-70 program, as such, was cancelled.
Development of the F-108 Rapier, intended as a fighter
escort to the XB-70, was also cancelled.
Replacing the
production bomber program was a limited program calling for
three XB-70 prototypes to perform high-speed flight
research. Although this vastly downsized program would have
to carry the entire financial burden for the development of
the XB-70s radically new construction techniques, as well as
the J93 engine, the research data the the program would
gather would be vitally important for the future SST and
other military projects. NASA and the Air Force would
jointly manage and share the data garnered from the
XB-70.
To help limit costs,
a number of non-aerodynamic changes were made to the XB-70.
Positions for the navigator and bombardier were removed,
leaving the XB-70 with just a pilot and co-pilot. The
computerised navigation and bomb-guidance systems were
replaced by the bare minimum instrumentation needed to fly
safely. In fact, only one TACAN (Tactical Air Navigation)
system was installed, which later proved a great annoyance
to the XB-70 pilots.
All three XB-70s were
intended to be slightly different from each other. The first
XB-70 (referred to as AV/1 (Air Vehicle/1) or Ship 1) was
built entirely from wind tunnel results and initial
computer-generated models (at this time, the computer
modelling took almost 18 months to complete!). AV/2 would be
slightly modified based on further computer modelling and
early experiences with AV/1. The third airframe, AV/3, would
have greater changes based on additional modelling, and
extensive flight data gathered from the first two aircraft.
The astute observer will notice that the 6' wind tunnel
model at the Smithsonian (National Air and Space Museum) is
actually of AV/3 (that is, it's a modified version of AV/2
-- note the canard angles).
Constructing the
XB-70 required new fabrication techniques, reflecting the
production-oriented original design. Extensive use of costly
titanium and composite materials would have resulted in a
bomber too expensive for mass production, so North American
decided to use a stainless steel honeycomb construction --
something that had never been tried before. To keep the
weight down, the honeycomb itself was formed of stainless
steel just .02" thick! (for perspective, this was the
TOLERANCES (variation allowed) in the holes drilled in the
frames of WWII fighters to lighten them!) One production
manager, after seeing the specifications and being assured
they were correct, exclaimed, "that's not metal, that's
FOIL!" Welding such thin materials was impossible, so a
brazing technique had to be developed to assemble the
honeycomb structures. Titanium was used in certain
heat-critical areas, but overall, the expensive (and
difficult to work with) metal makes up only 9 percent of the
Valkyrie's structure.
XB-70 number one,
with the tail number 20001 (generally referred to as AV/1
(Air Vehicle/1) or Ship 1) was rolled out of its hanger at
North American's Palmdale, California facility and into the
public's view on a bright and sunny May 11th, 1964. Just
sitting on the ground, the Valkyrie awed the audience. Her
long, graceful neck over their heads, air intakes a man
could stand in (and 80' long -- longer than an SR-71!), and
sleek lines left no doubt she was designed for speed. But
just two months later, the budget axe took its swing,
chopping AV/3 (which was in the early stages of
construction) out of the program, and, unknowingly, crippled
the entire XB-70 program.
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