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.