American started with evident determination to overcome the drag of
supersonic flight. They worked on a canard design, with outer wing and
fuel pod units which could be detached, allowing the bomber to land at
a little over a quarter of its takeoff weight. In this first design the
bomber was basically built in three parts, a central pod that contained
the engines, crew, some fuel and the bombs, and two very large side
units on the left and right that were most of the wing and tail area,
as well as containing large fuel tanks. The result looked something
like a very large P-38 Lightning, with the central pod being
much longer and including canards.
Normally the plane would "stay together" in one very large piece. It
was over a million pounds on launch, larger than a 747-400. On a combat
mission the plane would fly in this combination to enemy airspace at
subsonic speeds. By the time it arrived the fuel tanks in the outer
portions of the wings would be empty, and at that point the plane would
"break". The outer wings and tail would fall off, leaving the inner pod
and the stubs of the wings. With very little of the plane left, it
would now have a huge power-to-weight ratio, so it would accelerate to
Mach 3 for a "dash" to it's target.
Curtis LeMay was not enthusiastic about the design, and is credited
with the response, "Hell, this isn't an airplane, it's a three-ship
formation." North American, as one contender for the WS-110 contract,
had meanwhile been doing their homework. They calculated that the
amount of fuel needed to cruise at Mach 3 all the way to target turned
out to be less than that needed to fly the same distance at high
subsonic speed. It would need more fuel flow, but the aircraft would
cover the ground faster.
Three times the speed would not require three times the fuel flow, but
a good deal less. This is a result of something called "wave drag",
which means, simply, that it's actually hardest to fly right under the
speed of sound. As a result, if they could produce a plane that could
handle the heat, and has enough thrust to get through that wave drag,
they could fly faster without impossible fuel demands. They proposed
steel a construction because it could take the heat of high speed
flight, and it was cheap, a real concern if they were going to build
hundreds of them.
Their design was eventually accepted, with the long, graceful fuselage
lines, high canard and delta wing, with tilting wing tips which served
to trap compression under the wing, providing additional lift. In wind
tunnel tests it looked as if, with newly developed high-performance
aircraft fuels, compression lift would assist the WS-110A aircraft to a
cruise of Mach 3, a sustained speed which not long before had been out
Use of ethyl borane fuel stood to further enhance the bomber's
performance, and RAF Flying Review of September 1958 dubbed WS-110 the
"Boron Bomber". They guesstimated from "unofficial reports" that it
would fly at 100,000 feet, cruise at Mach 2 with room for Mach 3 "dash"
performance, and achieve a 6,000 mile range without refuelling.
In 1958 the project came together, and the aircraft had a name, the
B-70. After passing through five separate company design numbers with
North American, the B-70 would go ahead as their design NA-278. It
would be plagued by a series of structural problems largely related to
its ground-breaking technology, and very soon changing government views
would threaten the future of the project.
About 70% of the Valkyrie was to be of a new stainless steel.
The interior structure was mostly corrugated sheets, and the skin was a
brazed honeycomb sandwich of very thin steel, yet very strong. The
parts most subjected to heat were of a material never before used in an
aircraft, René 41. Aerofoil surface edges were machined to extreme
The six GE engines were housed in an engine box under the wings,
profiled to generate compression lift. On "zip fuel" one engine alone
made more noise than any air-breathing engine in history. Development
of the two prototypes was to cost around $1,500M, making them the most
expensive two aircraft built to that date, and worth, according to one
estimate, about ten times their weight in gold.
In mid-1959, the B-70's future came into question, with enormous
expenditure going into missile systems. Manned aircraft were considered
in some quarters to be near-obsolete. To make matters more awkward, the
expensive boron fuel program was cancelled.
Then, in December 1959, the B-70 project itself was cancelled, except
for completion of a single prototype. The planned first flight was
rescheduled from January to December, 1962. It was still hoped that by
1966 an SAC wing might use B-70s if the pro-missile lobby could be
persuaded to change their views.
After a review in 1960, the program was partially restored, and
allowance was made for up to twelve fully-operational B-70s to be
built, in addition to the prototype. In March 1961, during the Kennedy
administration, it was still held that missile development made the
B-70 unjustifiable. It was reduced to the status of a Mach 3 research
project, with an airframe potentially useful as a bomber. Secretary of
Defense Robert McNamara promptly cut back the program to three
prototypes, which were ordered on 4th October, 1961; but the third was
cancelled a few weeks later, leaving only aircraft with the USAF
numbers 62-001 and 62-207.
The USAF tried to keep some promise in the project by changing the role
of the B-70 to strike-reconnaissance late in 1962, and temporarily
redesignated the aircraft RS-70. They proposed an initial delivery of
sixty RS-70s to enter service in 1969 and a further 150 the year after.
Apart from a slight flicker of interest from the House Armed Services
Commission, it was wishful thinking on the USAF's part, the more so
when the existence of the purpose-built Lockheed A-12, which had also
been under development since the late 1950s, was revealed to President
Johnson late in 1963 and announced to the world in February 1964.
The first XB-70 was nearly complete in late 1962 when electrolytic
corrosion between the various grades of steel used in its structure was
discovered. Extensive inspection and rebuilding took up a further two
years. In 1963 funding dried up, and the XB-70 project was left to
starve, existing only as a research project. The first flight was
pushed ahead to late 1963 for the first prototype, and mid-1964 for the
of the first XB-70A was completed in mid-1963, but solution of a fuel
leak problem took another eighteen months. Finally, on May 11, 1964,
the XB-70A emerged from its hangar at Palmdale, California. Earlier
releases of information had not fully prepared its audience for its
size, its sleek lines, and its poised menace.
The canard design enabled the foreplane to be used to assist with
trimming the aircraft across a wide speed range from a minimum 150 kts.
(278 km/h) landing speed, up to Mach 3; they could also serve as flaps.
The compression lift derived from the shock wave at the front of the
intakes was a retained benefit, and apart from boosting lift by as much
as 30%, also reduced drag by allowing shallower angles of attack. The
tilting wing tips were kept level on takeoff, and tilted down to 25° at
low speeds and altitudes. They served to minimise trim changes in
pitch. At high speeds and altitudes, they would be dropped further, to
65°, enhancing compression lift.
A variable-geometry system was fitted to the nose, allowing a ramp
forward of the cockpit to be raised for supersonic flight or lowered
for a direct forward view. This visor was merely aerodynamic. The
cockpit was sealed behind a vertical pressure-bearing flat screen.
Inside their compartment, the four crew members were provided with
airliner comfort and could work in their shirt-sleeves. They sat in
cocoon-like seats with clamshell doors which, in the case of
pressurisation loss, would provide them with individual sealed escape
capsules. The capsules contained their own oxygen bottles and emergency
supplies, and basic controls to close the throttles and trim for an
emergency descent, whilst monitoring the instruments through a window
in the capsule. The capsules could be re-opened at a safe altitude, or
rocket-ejected through jettisonable roof panels.
A single bay between the engine ducts and engines could carry groups of
any nuclear bombs used by SAC. The bay had doors which slid open
automatically at the last moment before weapon release. Although not
part of the requirement, studies were also made into various external
ballistic weapon loads.
On its first flight on 21st September, 1964, the XB-70 was flown by
Colonel Joe Cotton and North American's chief test pilot Alvin S.
('Al') White. The aircraft failed to achieve Mach 1 due to an inability
to retract the main undercarriage. Number 2 engine suffered foreign
object damage; and another fault locked the two left rear main tyres,
which blew on touchdown. In general, flight development was encouraging
and proceeded much as predicted.
Both prototypes reached Mach 3 for the first time on their 17th
flights, respectively on October 15th, 1965 and January 3, 1966. The
XB-70A was flown for the first time using the crew capsule controls on
December 20, 1965.
On 8th June, 1966, aircraft 62-207 was to complete various tasks then
pose, with a small group of other General Electric-engined aircraft,
for some publicity shots for GE. Al White was to be pilot. As the work
load was light, Maj. Carl S. Cross was allowed on board for his first
ride as co-pilot. Accompanying the XB-70 were a McDonnell F-4
Phantom of the US Navy; a Northrop F-5 and a Northrop T-38 (both
North American crewed); and an F-104 Starfighter flown by NASA
pilot Joe Walker, who had flown the X-15.
formation was controlled by a GE-engined Learjet, with no radio
frequencies in common with the XB-70. Radio messages had to be relayed
via Edwards AFB. GE got a number of good photos by 9.30 am. and ended
the photo session about 9.35. Apparently against the dictates of common
sense, the NASA F-104 was edging up close to the XB-70, finally moving
in below the right wingtip.
The 30° crank-down of the Valkyrie's wingtips generated a strong
vortex, and this whipped the F-104 upside-down and across the top of
the larger aircraft's wings. It took away almost all of the XB-70's
tail fins. The F-104 fell back in a ball of fire; the Learjet resumed
For some seconds the Valkyrie flew steadily, then began a slow
roll, turning into a violent yawing. Descending flat-on to the airflow,
a large part of the left wing broke away. Soon after, White ejected in
his crew capsule. The XB-70 stopped oscillating and fell, slowly
rotating, hitting the ground almost flat about four miles north of
Barstow. Why Maj. Cross, with 8,528 flying hours, failed to eject is
unknown, and he died in the crash.
unfairly, GE suffered a great deal of ill-will for the incident,
although they had done nothing wrong, and for some time it was
impossible to arrange PR exercises and aerial photography.
The surviving XB-70, 62-001, continued to amass research data, largely
for NASA. Its last flight was on 4th February, 1969, to the USAF
Museum, Wright-Patterson, where it remains, alongside the Convair B-36,
the largest aircraft on display.
Span: 105 ft.
Length: 185 ft. 10 in. without boom; 192 ft. 2 in. with boom
Height: 30 ft. 9 in.
Weight: 534,700 lbs. loaded
Engines: Six General Electric YJ-93s of 30,000 lbs. thrust each
Maximum speed: 2,056 mph. (Mach 3.1) at 73,000 ft.
Cruising speed: 2,000 mph. (Mach 3.0) at 72,000 ft.
Range: 4,288 miles
Service Ceiling: 77,350 ft.