"Orlando Quattro" wrote in message
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The construction of the Valkyrie necessitated the development of new
metalworking technologies in both stainless steel and titanium. Most
of the skin of the aircraft was made from a honeycomb structure of
stainless steel with thin sheets bonded to both sides. Manufacture
of such sections was developed pretty much from scratch, and the use
of titanium was also in its infancy.

The first XB-70 (AV/1) turned out to have a number of structural
defects, mainly in the lamination of the honeycomb stainless steel
sections. After tests into the high mach regimes these sections
started to fail in various ways, and AV/1 was limited to a maximum
speed of mach 2.5 for all subsequent testing. The construction of
AV/2 incorporated lessons learned, and did not suffer from these
structural defects.

In addition, a large number of problematic areas such as hydraulic
systems and fuel management systems, to name but two, were very
significantly revised for the better. Cooling of the aircraft structure
included a very complex circulation of fuel to transfer heat, and the
fuel tanks used a pressurized nitrogen mechanism to ensure that there
was little or no (hot) fuel vapour in the emptying tanks. All of this
was innovative back at the beginning of the sixties.

There were also structural and aerodynamic modifications in such items
as the placement of the wing folds - the outer wing sections cranked
down in high speed flight to provide increased longitudinal stability
and to reduce some wing trailing edge effects. All of these changes
made AV/2 a significantly more capable aircraft than AV/1, as it
conclusively demonstrated before its tragic and unnecessary loss.

AV/2 demonstrated the ability to cruise above mach 3 for extended
periods, meaning several hours at a time, which was lost with the
aircraft, because of the restriction of AV/1 to mach 2.5 flight.

Bear in mind both the timeframe of development and the unprecedented
size of this aircraft. Every flight of both aircraft was an adventure,
and some of them were hairy in the extreme. The survivor is still an
awesome sight, if you visit it at the US Air Force museum. It is so
large that it cannot be seen in its entirety from any point, and it
looms unbelievably above you as you walk under it.

The only thing I have ever heard louder on take-off is the space shuttle,
but, as someone else has said, the climb out and acceleration of the
Valkyrie was awesome in a way that is somehow much more memorable than
the almost stately vertical departure of the shuttle.

For the conspiracy buffs, there is a persistent rumour that incomplete
AV/3 (intended to be the first YB-70A article) was not broken up but
quietly completed as a reconnaissance platform and mother ship for a
drone of some kind. Alas, I can't imagine keeping such a huge beast
secret, any more than I can imagine the crackling thunder of one of
its departures not being noticed by someone. It also produced a heavy,
heavy sonic footprint when it was in a hurry, even when up high at
above 60,000 feet. The six side-by-side engines also produced a unique
contrail, although the SR-71, of similar vintage, had an excellent
record of avoiding making contrails when necessary, so dreamers can
dream that the XB-70 could avoid leaving a trail too.

Sorry, must be getting old to wax so nostalgic.

OIV

Don't apologize! This is great info. How did you come to know so much about
this aircraft? Were you struck by its beauty/performance and became
interested in it or did you actually have some connection to the project?

Take care,

Nick