Bombers from B-70 to Stealth
The XB-70 Valkyrie was designed to cruise at Mach 3 over 75,000 feet. Such a tremendous advance in performance required both an entirely new aircraft configuration and a radical change in construction. Since the temperatures of up to 600 degrees F encountered on these flights were too much for the usual aluminum alloys, about 69.5 percent of the airframe weight was of welded steel honeycomb sandwich and 9.5 percent was titanium for the forward structure.
Prominent features were the canard foreplane near the long nose, delta wing with tips folding down for stability in supersonic flight, and twin rudders. Six General Electric YJ93-GE-3s with continuous afterburning and two intakes with controlled air induction were mounted under the center section. Boron fuel had been considered, but was replaced by JP-6 in August 1959, and inflight refueling was provided.
Continuous review of future manned-aircraft requirements for the USAF caused many disturbances in the program. While SAC wanted a manned bomber, President Eisenhower and his Defense Department officials said that bomber-penetration chances had been reduced by surface-to-air missile progress, but no defense against our intercontinental and submarine-launched ballistic missiles was in sight.
Expensive bomber programs were becoming unnecessary to deter a nuclear attack. Eisenhower said that “speaking of bombers in the missile age was like talking about bows and arrows in the gunpowder era.”*
The conflict among the DoD, Air Force, and Congress swung back and forth. The first cancellation on December 1, 1959, cut back the program to one prototype, so that the next fiscal year’s budget could be balanced, but Congress restored funding for a 265 million dollar program in October 1960.
However, on March 28, 1961, the new President, John F. Kennedy, also recommended that the program be limited to research prototypes and considered development as a weapons system unnecessary and economically unjustifiable. Three XB-70 prototypes authorized October 4, 1961, were to have no weapons provisions and only two – not four – crewmen in the pressurized nose with an ASQ-28 Bomb Navigation Subsystem.
Although bays for 25,000 pounds of munitions were provided, guns were no longer part of American bomber designs, as hostile air-to-air missiles were the main threat. But the Valkyrie would not become a bomber, but only an “air vehicle to demonstrate airworthiness in a sustained Mach 3 high altitude environment.”
An RS-70 (reconnaissance-strike) version was offered to introduce a capability not available in missiles, but the faster SR-71 Lockheed secret development reduced the RS-70’s appeal. Defense Secretary Robert McNamara disagreed with General LeMay’s advocacy of manned bombers and the third prototype was canceled on February 15, 1964, along with rejection of an Air Force request for 60 RS-70s to be operational in 1969. Nearly four years behind the 1958 schedule, the first XB-70A rolled out of the Palmdale, California, factory with much ceremony on May 11, 1964, and was flown on September 21.
The refined second prototype flown July 17, 1965, was destroyed by a midair collision with an F-104N on June 8, 1966. The first XB-70A made its 83rd and last flight February 4, 1969, to the Air Force Museum at Wright-Patterson AFB, Ohio. Over $1.5 billion had been expended on the B-70 program.