When you jam-pack 6 monstrous jet engines
into one aircraft, and give it a sleek and futuristic design, you get something that
looks fast, even when it’s standing still. What set the XB-70 Valkyrie apart, wasn’t
that it could fly at supersonic speeds. Supersonic aircraft had already been around
for over a decade. But this one not only could generate shockwaves, it could also ride
those shockwaves, allowing it to fly more efficiently at over 3 times the speed of sound.
But it wasn’t all fun and games for the XB-70. It leaked fuel to the extent that they would
use funnels to collect the fuel in buckets. It flew so fast that even the paint would chip
off its body. It had various issues with its hydraulics and landing gear, causing multiple
accidents. Worst of all, out of the only two prototypes made, one was lost for the most
unnecessary flight that you can imagine. The other prototype ended up in a museum, never having
become operational. Of course due to its size, they had to take down traffic lights when they
moved the aircraft to its final resting place. But why the XB-70 did not have a flat nose, even
though a flat and smooth profile is absolutely necessary for a supersonic airplane, why it was
designed to have a tiny little wheel on its main landing gear, how the Soviet Union contributed to
the manufacturing of this airplane at the height of the Cold War, and the reason why a fighter
aircraft like the F-15 benefited from this strategic bomber, even though the XB-70 program
was canceled at inception, is Not What You Think! By 1955, the US Air Force had a
bomber fleet consisting primarily of the behemoth B-52 Stratofortress, the sleek
B-47 Stratojet, and the speedy B-58 Hustler. The B-52, while having the largest capacity of any
bomber ever built at the time, was too slow for a first-strike mission, and though the B-47 and B-58
were faster, they did not have the operational range needed to strike the Soviets, and could not
outrun the rapidly advancing Soviet air defenses. So the Air Force issued a contract known as the
General Operation Requirement No. 38, for a new bomber that could fly as far and carry as much
as the B-52 with a minimum top speed of Mach 2. Only two aircraft companies at the time were brave
enough to approach the challenge: The first was Boeing, which had become the standard for bomber
designs in the aviation industry thanks to their B-29, B-47, and B-52 designs, and the second
was the venerable North American Aviation, which historically had a primary focus on
high-speed fighter designs like the P-51 and F-86. Knowing they were the underdog, North American
Aviation came to the proposal stage swinging. Their design concept incorporated
highly experimental and theoretical features for their time, such as
canards, variable wing geometry, and a combined high-pressure inlet system for
the six massive engines powering the aircraft. But one design detail above the rest secured
the contract for North American Aviation. The XB-70 Valkyrie could tilt down its
wingtips to take advantage of a newly discovered phenomenon called compression
lift. But what is compression lift exactly? As a boat with a planing hull speeds up, it can
surf on the bow wave that it generates itself. This reduces drag and allows the boat to
move faster. Similarly, an aircraft that is moving at supersonic speeds can generate
shockwaves. If the shockwaves’ high pressure could be captured underneath the wing of the
aircraft, it could generate additional lift.
These shockwaves are generated off
of sharp points on the aircraft. In the XB-70 design, that sharp point was the
leading edge of the engine intake splitter. In order to trap those shockwaves, Valkyrie
had wing tips that could fold down. If you are wondering why they didn't just design
the wings to be folded downward permanently, as opposed to them being adjustable,
there were multiple reasons for this. One was that the airplane couldn’t have been able
to get off the ground with its wing tips folded down, because of its aerodynamics at low speeds.
You have to remember, these wingtips were not small. Each one was over 500 ft2 in area, which is
bigger than the first apartment that I lived in. The folding wing tips of the XB-70 were in fact the largest flight surfaces to have
ever been moved during any flight. Another reason was that the angle of the
shockwaves varied greatly with speed. So to effectively capture them, the downward angle
of the wingtips had to be adjusted depending on how fast the airplane was moving. At its top
speed, the wingtips would be tilted all the way down to 65 degrees. Compression lift could
increase the lift in the XB-70 by as much as 30%. Another interesting thing was the windshield
design. Supersonic aircraft require a smooth nose and body to streamline airflow. But as you
can see, there was clearly an angle between the nose of the aircraft and the windshield. This
was done in order to improve the pilot's view during nose-high low-speed flight and when
the aircraft was taxiing on the ground. But during high speed flights, the forebody
could be streamlined by raising a ramp which raised the outer windshield. A similar design
was implemented on other supersonic airplanes, like the Concorde, giving it the ability to
adjust its aerodynamic properties as needed. With such stunning design characteristics, Valkyrie handily beat out Boeing’s submission
and secured funding for its prototyping phase, but it would soon become obvious to the
engineers that all of the promises they made might be just as mythical as the namesake
of their airplane. The sheer design complexity and size of the XB-70 meant that nearly
anything that could go wrong did go wrong. One overly complicated system in the Valkyrie
was its hydraulics. Aside from moving the control surfaces, the hydraulics system
is what kept the aircraft from melting! Flying at such high speeds meant that the air
friction would cause the plane’s external aluminum shell to soften from the heat, so engineers found
two cost-effective solutions to this problem. First, the aircraft would use a steel
honeycomb between the aluminum panels to re-distribute the heat. Second, fuel
would be hydraulically pumped through heat converters in the fuselage and wings, acting
as a cooling fluid throughout the aircraft. But this was risky, because the
JP-6 fuel could auto-ignite. To reduce the likelihood of auto-ignition,
nitrogen was injected into the JP-6 during refueling. The fuel pressurization and
inerting system vaporized 700 lbs of liquid nitrogen to fill the fuel tank
vent space and maintain tank pressure. The hydraulics system was
also utilized in rotating, folding and unfolding the landing gear in
order to maneuver it in and out of stowage. By the way, see that little fifth wheel? What
problem do you think this tiny wheel solved? Just skidding! Seriously, just skidding
during landing. To accomplish this, the fifth wheel measured the true ground speed
of the aircraft with no slippage. One of the main wheels also had a speed sensor. These two data
points were sent to a braking computer, which would predict the slip point and relieve the brake
pressure to prevent the aircraft from skidding. The landing gear tires were also special. Not
only were they painted with a special compound to reflect heat, the tires were infused all
throughout the body with that heat-resistant compound. This is how they could withstand
temperatures up to 360F during landing. To detect possible leaks, the tires were
pressurized to 500 psi for 24 hours. If no leaks appeared, the
tire pressure was released, and was then pumped to 100 psi with nitrogen
gas to prevent deterioration during storage. With that said, these tires had a devastating
fate on the very first landing ever of the XB-70. September 21st, 1964 was the big day for
this big boy. Two chase planes accompanied the aircraft as it took off, and soon
they saw a problem they had to report. The main landing gear had rotated in
preparation for stowage, but then had got stuck. Landing this massive airplane in that condition
would have jeopardized the life of its crew. Or if they ejected, it meant the XB-70
would have been lost on its maiden flight. The decision was made to short-circuit the landing
gear retraction system, But there were no tools onboard. The co-pilot was lucky to be carrying
a paper clip in his briefcase that day, which he used to short-circuit the breaker and that
moved the landing gear back in proper position. But that wasn’t the end of it.
Upon landing, two of the rear tires on the port side blew up and burst
into flames due to a locked brake. As they taxied down the runway, the pilot and
co-pilot had no idea about the tire issue, until the control tower told them
what was going on: It was not ideal, but hey, at least the airplane was
back on the ground in one piece! Three weeks later, on its third test flight,
the XB-70 became supersonic, reaching Mach 1.1. Did you ever think an airplane could fly so fast
that paint would chip off of its fuselage? Well, that’s what happened. Although this was more
due to how hot the outer skin of the aircraft would get at high speeds. Apparently the paint
was too thick, so it got brittle and fell off. In the year that followed, dozens
of test flights were performed, in which different aspects of the design
were progressively tested, and of course that came hand in hand with more tires on fire,
and even damage to the engines and the fuselage. But during all this, a second
prototype was being built, XB-70 No. 2, which had dealt with almost all the
deficiencies discovered on the first prototype. A crowd of 6,500 people showed up for
the unveiling of the second prototype. Those were the good old days when you could
touch a brand new X-plane with your fingers! On October 14th, 1965, the first vehicle
reached the speed of Mach 3, which was one of the goals of the program. Coincidentally,
exactly 18 years earlier on that same day, Chuck Yeager had become the first person to
break the sound barrier in level flight.. Even though this was all happening during
the Cold War, the Soviets had helped the Americans with the XB-70 program quite a
bit. Well, the Soviets didn’t know that, but high drag areas of the airplane, such as the
nose cone and inlet had to be made of titanium. The United States had no titanium. So they had
used third-parties and shell companies to procure titanium from the Soviet Union, which was used
in high tech aircraft like XB-70 and SR-71. But despite all the success with the two prototypes,
just around the corner, tragedy was lurking. On June 8th, 1966, XB-70 No. 2 was flying in close
formation with an F-4, F-5, T-38, and an F-104. All 5 aircraft had one thing in common. Their
engines had been manufactured by General Electric. In fact, this was a photo op that the
advertising and marketing agency of General Electric had put consistent
pressure on to get approval for. After the photoshoot, for reasons that are
not exactly known, the F-104 drifted into the XB-70's right wingtip, flipped and rolled
inverted over the top of Valkyrie. The F-104 then exploded killing its pilot, destroying Valkyrie's
vertical stabilizers and damaging its left wing. Within seconds, the XB-70 lost control and shortly
after plummeted onto the California desert.. Al White, who was piloting the XB-70 ejected
and survived, although he was severely injured, including his arm being crushed by the
closing clamshell-like escape crew capsule. The cushion underneath his capsule also
failed to inflate, making for a harsh landing. Carl Cross, who was co-piloting the aircraft, never ejected. He had likely lost consciousness
during the accident. Mike Bell has made an excellent video on the details of this
accident. Make sure to check it out. It’s a pity, how a multi-billion dollar
cutting edge airplane and the lives of two pilots were lost, for a marketing photoshoot. But let me tell you what actually crashed
the XB-70 program in the first place. On May 1st, 1960, the Soviets shot
down Gary Powers and his U-2 spy plane. At the time, the XB-70 program was at its infancy,
and its construction hadn’t even yet begun. The downing of the U-2 plane was one of the
first things to put a dent in the XB-70 program. Up until that point, the Pentagon believed
that no Soviet anti-air systems could reach an airplane flying at 70,000 feet, the
altitudes that the U-2 spy plane operated at. Guess what? The XB-70 was also
designed to operate at that altitude. Around the same time, nuclear first-strike
capability was shifting from bomber airplanes to ICBMs, making the concept of a nuclear bomber
obsolete. The XB-70 program was dead at inception. So it made sense for President
Eisenhower to cancel the program, right? Well, John F. Kennedy, who was at the time
campaigning for the presidency, used Eisenhower and the Republicans’ decision to cancel the XB-70
as an example of their weak policy on defense. Kennedy ended up winning the presidency, and only
3 months after taking office, he canceled the XB-70 program because it ”stood little chance
of penetrating enemy defenses successfully". $800 million dollars had already been spent on
the project. So the work on XB-70 continued, but only as a program to investigate Mach 3 flight,
not as a supersonic bomber for nuclear strikes. Ironically, it was the XB-70 program
that gave the US military the F-15. The initial reports that the United States was
working on the XB-70 had scared the Soviets. In response, they started designing the MiG-25 Foxbat
specifically to counter the XB-70. Ironically, the news that Soviets were working on an airplane
to intercept Valkyrie scared the Americans. So they designed the F-15 Eagle to counter
the Soviets’ counter! You’re welcome, America. On February 4th, 1969, the only remaining XB-70
took its final flight to Wright-Patterson Air Force Base. The airplane was then moved to
the National Museum of the United States Air Force in Dayton, Ohio, where it tells
the tale of a true engineering masterpiece, leaving a trail of awe in its supersonic wake.
