"That's not a plane it's a three plane
formation" that's what General Curtis
LeMay said over plans of the WS-110
supersonic replacement for the B-52 back
in 1954. Back in the early 1950s the B-52
was the US Air Force's main nuclear
delivery platform but with the
increasing sophistication of the Soviet
defenses, a new supersonic bomber was
called for that would stretch the limits
of technology to beyond what was thought
possible just a few years earlier. The
plane that would emerge from the WS-110
design process was the XB-70 Valkyrie. It
will be one of the biggest in the world
and capable of cruising at Mach 3
something which no aircraft of this type
is capable of doing even now. It would
also fly at 77,000 feet
23,500
meters have a range of 4280 miles or 6900 kilometers and carry up to
14 nuclear weapons. The problem
with large planes and payloads is the
need for powerful engines which in turn
require a lot of fuel which has to be
carried making the plane heavier and
reducing the available payload. So in the
1940s and 50s alternative methods of
propulsion were researched. Nuclear was
seriously considered as a power source
for jet engines. A nuclear reactor would
heat the air in place for jet fuel and
it could run for weeks or months without
the need for refueling but problems with
the extra weight of a radiation
shielding required for the crew and the
low thrust output from early engine
designs meant that it became unpractical.
Also if a nuclear powered plane crashed
it would be a much bigger problem than a
conventional jet due to a radioactive
contamination. If you want to find out
more about nuclear power planes trains
and automobiles we have a video on the
link showing now. Also during the 1950's
a new type of jet fuel was being
developed called high energy fuel or
"Zip Fuel" this could deliver up to 40%
more energy for the same weight.
This was achieved by adding boron a
high-energy low mass element. The problem
with this is that it made both the fuel
and the exhaust toxic. When zip fuel was
burned in engines it produced solids that
were sticky,
corrosive and highly abrasive this also
created a lot of black smoke which could
reveal the plane's position even at high
altitude. These solids built up on the
turbine blades making them less
efficient and in some cases causing the
engines to fail completely. One method to
get around these issues was to use it in
the afterburners as this didn't affect
the engine itself. This would be used for
a quick dash up to supersonic speeds over
enemy territory whilst using normal jet
fuel for the rest of the journey. Due to
the high cost of making zip fuel and the
inability to overcome the engine damage
it caused meant that it went the same
way as of nuclear power engines and by
1959 zip fuels were also dropped. Both
nuclear engines and zip fuels
were proposed for the WS-110 before new
higher density type of conventional jet
fuel called JP-6 was developed. To
overcome the extra fuel needed, the North
American Aviation's WS-110 design had
floating wing panels at the end of the
wings which were essentially huge fuel
tanks these would have been jettisoned
when it went supersonic leaving much
shorter of trapezoid shape wings. LeMay head
of the US Air Force Strategic Air
Command thought that this was too
complicated and dismissed the idea and
in 1956 the US Air Force told the
designers to go back to the drawing
board and come back with a better design.
Research on supersonic flight was
progressing rapidly and narrow
delta-shaped wings took the place of a
swept back or trapezoid ones of the
original WS-110 design along with newer
engines that could cruise at supersonic
speeds. During the engine research a
discovery was made but if the engines
were optimized for supersonic speeds it
burnt twice as much fuel as it did a
subsonic speed but flew four times as
fast, meaning the most economical speed was
now the maximum speed. It was now easier
and more economical to cruise for most
of the entire flight at Mach 3 than it was
to fly slower to the target and then fly
over the enemy positions supersonically
as the old ws 1:10 design was intended.
North American also discovered some
obscure Windtunnel research into a
phenomenon now known as "compression lift"
which used the high pressure shock wave
created at the front of a plane at
supersonic speeds. By designing a
combination of the wing position
relative to the nose large wing tips
that could be tilted down to contain the
high pressure air and a specially shaped
engine intake of the six centrally
placed engines the plane could ride on
the shock wave created by flying
supersonically and thus reduce the
amount of fuel required. The new design
was approved and given the designation
B-70 with the prototypes getting the "X" for
experimental aircraft so they became the
XB-70. The name Valkyrie was chosen as
the winning entry in the US Air Force
"name the b70" contest. It was also around
this time in the late 1950s that Soviet
surface-to-air missile technology became
much more effective. This removed the
high-speed high-altitude advantage that
the new B-70 design would have and
flying it at low altitude under the
radar it was not much faster than the
B-52 it was made to replace but with a
smaller payload and shorter range. This
combined with the cost cutting as
intercontinental ballistic missiles or
ICBMs, became a cheaper unstoppable way
to deliver nuclear weapons meant that by
1961 when Kennedy was in office the
program was scaled back and the bomber
concept was dropped. Instead it would
become the XB-70 research plane to study
supersonic aerodynamics and propulsion
in large aircraft with first three, then
two prototypes being built. However
because of its cutting-edge design
things were not so straightforward once
the build got underway. Although the XB-70
was considered for reconnaissance as the
RS-70 the other Mach 3 aircraft in
development at a time the lockheed A-12
which would become the SR-71 blackbird
was superior in terms of altitude it
could fly at, the maximum speed and had a
much lower radar cross-section so it
would be much harder to detect.
Unlike the SR-71 the B-70s were designed
to be a large
fleet of aircraft but there wasn't
enough to titanium that could withstand
the heat generated at Mach 3 available
for that many aircraft. This led the US
Air Force earlier on in the design
process to request the body of the
aircraft we built out of cheaper more
readily available materials. So a special
combination of a stainless steel
honeycomb skin was used over areas where
the heat was going to be less of an
issue up to 450 degrees Fahrenheit 232
degrees Celsius. The forward 60 feet or
20 meters of the plane would use
titanium where the temperatures would
reach up to 650 degrees Fahrenheit 343
degrees Celsius and the engine
compartment used a nickel based alloy
called Rene 41 which would withstand
1,200 degrees Fahrenheit or 650 degrees
Celsius. But this mixture of different
metals caused an unforeseen issue of
electrolytic corrosion and led to a
two-year delay as the plane was stripped
and rebuilt. The design also called for
pressurized fuel tanks but when they
tested them with normal jet fuel they'll
leaked.. a lot. This was down to tiny flaws in
the welding as the tanks were fabricated.
It took a further 18 months to find a
fix by lining the inside with a special
coating. Finally on the 21st of September
1964, the maiden flight of the first
xb-70 took place but even that didn't go
to plan.
One of the six engines had to be shut
down and there was a malfunction on the
undercarriage, this led to the brakes
locking up on one side when it landed
which burst the tires and set fire to
the undercarriage. On the following tests
after the XB-70 was taken supersonic the
flexing of the airframe which it was
supposed to do, caused much of a thick
white paint to flake off and on two
occasions large pieces of the wings
leading edge was ripped off as a
stainless steel honeycomb skin failed
due to poor quality control. But the most
serious incident wasn't caused by
anything failing on the XB-70. On the 8th
of June 1966, after a successful
supersonic test flights
XB-70 number two was returning with four
chase planes in a tight formation and
being filmed for GE who made the engines
for all the planes. The filming had just
finished as a Starfighter F-104 was
flying about 70 feet or 20 meters from
the right wing tip. It's believed that
the pilot couldn't see the wingtip to
his immediate left and above and that he
was using the forward part of the XB-70
as his visual reference point. For some
reason he drifted a little too close and
touched the right wing. The vortex from
the large wing tip of the XB-70 sucked
the small fighter up and over the tail
of the XB-70 hitting both vertical fins
before it exploded and crashing into the
left wing tip which then broke away.
Without its rudders and the wing damage
the XB-70 entered an uncontrollable flat
spin and crashed to the ground. The
pilot Al White ejected and survived
but was seriously injured. The XB-70
co-pilot Carl Cross was unable to eject
and went down with the plane. The F-104
pilot and NASA chief test pilot and one
time X-15 pilot, Joe Walker also died as
a result of a collision.
The remaining XB-70 continued its
research until 1969 when it was retired
to the National Museum of United States
Air Force at wright-patterson Air Force
Base where it has been ever since and
the XB-70 valkyrie became part of
supersite history. And as always thanks
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