- Length: 185 ft. 10 in.
- Wingspan: 105 ft.
- Height: 30 ft. 9 in.
- Wing Area: 6,296 sq. ft.
- Empty Weight: 210,000 lbs.
- Loaded Weight: 534,700 lbs.
- Crew: 2
- Power Plant: 6 × General Electric YJ93-GE-3 turbojet, 28,000 lbf each
- Range: 4,288 miles
- Cruise Speed: 2,000 mph (Mach 3)
- Ceiling: 77,350 ft.
Design & Development:
In January 1954, initial discussions began at Boeing and the Rand Corporation regarding the future direction of US Air Force bomber designs. The study concluded that not only was a large aircraft needed to carry the high-yield nuclear weapons then under development, but also one with a long range and the capability of flying at high altitudes and dashing at supersonic speeds to avoid enemy interceptors. Researchers also noted that in order to fulfill the required mission profile, while also meeting performance requirements, the new aircraft would need a large fuel capacity.
At the time, it was suggested that nuclear power or boron-enriched "zip fuels" be examined as possible solutions to the fuel issue. In October 1954, the Air Force issued General Operational Requirement No. 38 which initiated the new bomber program. The Air Research & Development Command subsequently designated the new program "Weapon System 110A," with the nuclear powered variant dubbed WS-125A. This latter option was dropped in 1955, due to problems in developing the power plant. Also that year, the Air Force issued GOR.96 which called for an intercontinental reconnaissance system.
As the two new systems had similar requirements, the Air Force decided to combine the programs under the designation WS-110A/L. In June 1955, the design requirements were given to the aviation industry and proposals were received from North American Aviation and Boeing. After reviewing these, the Air Force cleared both companies to move forward with developing their designs and building mock ups. The following year, NAA and Boeing presented their enhanced designs. As zip fuel research failed to provide an adequate answer to the fuel issue, both designs included elaborate wingtip drop tanks.
Finding the designs too complicated, the Air Force declined, but asked both companies to continue working on the project. In October 1956, the WS-110A/L project was briefly put on hold. Work resumed in March 1957, with new requirements stating that the aircraft be capable of flying at speeds up to Mach 3 for the entire mission. Taking this into account, both NAA and Boeing began extensive studies of supersonic flight. This led to two similar designs which possessed long narrow fuselages and large delta wings.
They differed only in the layout of their engines, with NAA's six engines clustered at the rear of the fuselage and Boeing's mounted in pods under the wings. Seeking an advantage, NAA began studying compression lift. Their research showed that in supersonic flight, the nose and other leading edges of the aircraft produced a shock wave. By shifting the position of wings, this shock wave could be captured to increase lift. To utilize this effect, NAA added unique hinged panels to their design's wingtips which moved to help trap the shock wave. Twin tails were also added, and the intakes altered and enlarged.
Competition & Demise of the Program:
On August 30, 1957, the Air Force officially notified NAA and Boeing that a design competition was underway and that the aircraft must be capable of cruising at Mach 3.0-3.2 at an altitude of 70,000-75,000 feet with a range of 10,500 miles. After assessing both final designs, NAA was declared the winner and was contracted to move forward. Designated the XB-70 Valkyrie, the new bomber was expected to enter service in late 1965. As the development contracts were being signed, new developments in missile technology began to darken the program's future.
Designed to fly above and past enemy interceptors, the XB-70 found its mission profile jeopardized by the introduction of effective surface-to-air missiles. This threat was made real in 1960, with the downing of a US U-2 spy plane by the Soviets. The introduction of these new defensive weapons led to a rapid shift away from high-altitude bombing to low-altitude penetration. Unsuited for this new doctrine, the XB-70 program was called into question. With the first generation of intercontinental ballistic missiles entering service, the Air Force announced the downsizing of the program on December 29, 1959.
A political football during the 1960 elections, the program was revived in August when the Air Force began work on the RS-70 "reconnaissance strike" version of the aircraft. Intended to strike targets in the wake of an ICBM attack, the RS-70 was to be in service by 1969. Upon taking office, President John F. Kennedy had the program reviewed. Seeing ICBMs as the future, Kennedy ordered the XB-70/RS-70 program limited to research and development on March 28, 1961. With this in place, a contract was issued to NAA for three aircraft. This was reduced to two in July 1964.
After some early manufacturing issues, the first XB-70 took to the sky on September 21, 1964. Plagued by fuel leaks and hydraulic issues, the first XB-70 underwent flight testing through the spring of 1965. It was joined by the second aircraft on July 17. Used in the National Sonic Boom Program, both XB-70s demonstrated that the sound from a sonic boom reached the ground in unacceptable levels. This led to the cancellation of several supersonic transport programs then underway.
On June 8, 1966, tragedy struck the XB-70 program when the second aircraft crashed during an in-flight photo shoot for General Electric. Flying in formation with an F-4, F-5, F-104, and T-38 the XB-70 had its left tail and part of the left wing sheared off when the F-104 collided with it. While the XB-70's pilot, Al White was able to eject, his copilot, Carl Cross, and the pilot of the F-104, Joe Walker, were both killed. The resulting investigation determined that the loss of suitable sight cues led to Walker drifting into the XB-70.
The remaining XB-70 flew thirty-three additional research flights for NAA and the US Air Force before being transferred to NASA's supersonic transport program in March 1967. Two years later, it was retired and taken to Wright-Patterson Air Force Base in Dayton, OH for display at the National Museum of the United States Air Force.