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The XB-70, one of the world's most exotic airplanes, was conceived for the Strategic Air Command in the 1950s as a high-altitude bomber that could fly three times the speed of sound (Mach 3). Because of fund limitations, only two were built, not as bombers, but as research aircraft for the advanced study of aerodynamics, propulsion and other subjects related to large supersonic aircraft.

The Valkyrie was built largely of stainless-steel honeycomb sandwich panels and titanium. It was designed to make use of a phenomenon called "compression lift," achieved when the shock wave generated by the airplane flying at supersonic speeds supports part of the airplane's weight. For improved stability at supersonic speeds, the Valkyrie could droop its wingtips as much as 65 degrees.

The No. 1 XB-70 made its initial flight on Sept. 21, 1964, and achieved Mach 3 flight on Oct. 14, 1965. The No. 2 airplane first flew on July 17, 1965, but on June 8, 1966, it crashed following a mid-air collision. The No. 1 airplane continued in its research program until flown to the museum on Feb. 4, 1969.

 

Description

 

The B-70 bomber program resulted from an Air Force requirement for a high-speed, high-altitude strategic bomber to replace the B-52. North American engineers utilized NACA studies dealing with optimum Mach 3-6 configurations to develop the winning B-70 design . The aircraft was shaped to remain within its Mach cone throughout the flight regime thereby reducing drag and increasing lift. The latter was accomplished by manipulating the high pressure of the shock wave beneath the wing to generate compression lift. In addition, the wing tips were designed to pivot downward up to 65° to increase this compression lift while also providing greater directional stability.

Unfortunately, budget cuts of the late 1950s and early 1960s gutted the XB-70 advanced bomber project, and only two unarmed aerodynamic prototypes were actually built. Despite their exceptional performance, the XB-70 program had been cancelled by the time the Air Force flight tests were completed. The two prototypes were then transferred to NASA as high-speed research aircraft to prepare the way for supersonic transports. Both Valkyries served in this function well, flying 129 missions to study the aerodynamic, control, and heating issues associated with flight at Mach 2 to 3.

Tragedy struck on the 95th flight, however, when an F-104 flew too close to the second XB-70 prototype during a photo shoot. The fighter became caught up in the giant bomber's trailing vortices and the two planes collided before falling to earth in a fatal crash. The sole remaining XB-70 Valkyrie continued to fly until 1969 when it was placed in the USAF Museum.

Construction had also started on a third XB-70 prototype that carried a crew of four and would have been much closer to the final production design. As managers struggled to keep the B-70 program alive, proposals were made to equip this third aircraft with even more extensive research capabilities than the earlier prototypes had received. Among the proposals were plans to use the aircraft as a high-altitude astronomical observatory, a recoverable first stage booster for launching payloads into orbit, a platform for launching anti-satellite weapons, a high-altitude commutations relay, a high-speed propulsion test craft, and a vehicle to test methods of reducing radar cross section. Although construction of this aircraft was well underway, it was cancelled prior to completion.

Despite its failure to go into production, the B-70 Valkyrie provided invaluable high-speed flight test data that helped to bridge the gap between supersonic and hypersonic travel. Information collected during its test flights is still used by engineers today.

 

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The XB-70A, built by North American Aviation's Los Angeles (Calif.) Division for the U.S. Air Force, was an experimental high-speed, delta-wing aircraft designed to fly at three times the speed of sound and at altitudes in excess of 70,000 feet.

It was powered by six General Electric J-93 turbojet engines, each producing approximately 30,000 pounds of thrust. Primary purpose of the aircraft was to investigate the feasibility of long-range, high-speed flight and to advance the aeronautical state of the art in those areas.

Among its design features were a movable canard, the "compression lift" aerodynamic design principle, in-flight accessibility to electronics equipment, a shirt-sleeve environment for the crew, and encapsulated seats for crew ejection at speeds up to Mach 3 and at altitudes to above 70,000 feet.

An air-intake control system, necessarily different from conventional systems because of the high speed, sensed small changes in pressure during the XB-70's flight and adjusted accordingly, reducing the force of the supersonic speed at the intake duct to subsonic speed at the face of the engines.

A rugged landing gear, weighing more than six tons and consisting of two tons of wheels, tires and brakes, supported the XB-70 on the ground. Each main gear had four wheels and the nose gear two. In a single stop, the XB-70 absorbed kinetic energy equivalent to that used in stopping 800 medium-size automobiles from a speed of about 100 miles an hour.

 

HISTORY:
First Flight	21 September 1964
Service Entry	did not enter service
CREW:	(XB-70A) 2 pilots (B-70A) 2 pilots, 1 navigator/bombardier, 1 defensive systems officer
ESTIMATED COST:	$700 million (prototype)
AIRFOIL SECTIONS:
Wing Root	0.30 Hex (Mod)
Wing Tip	0.70 Hex (Mod)
DIMENSIONS:
Length	185.83 ft (56.69 m) without pitot tube 192.17 ft (58.63 m) with pitot tube
Wingspan	105.00 ft (32.03 m)
Height	30.75 ft (9.38 m)
Wing Area	6,298 ft2 (586.2 m2)
Canard Area	415.6 ft2 (38.68 m2)
WEIGHTS:
Empty	300,000 lb (136,365 kg)
Typical Load	534,700 lb (243,045 kg)
Max Takeoff	542,000 lb (246,365 kg)
Fuel Capacity	internal: unknown external: unknown
Max Payload	20,000 lb (9,070 kg) planned for production B-70
PROPULSION:
Powerplant	Six General Electric J-93 afterburning turbojets
Fuel:	JP-6
Thrust	180,000 lb (800.71 kN)
PERFORMANCE:
Max Level Speed	at altitude: 2,056 mph (3,310 km/h) at 73,000 ft (22,270 m), Mach 3.1 at sea level: unknown cruise speed: 2,000 mph (3,200 km/h) at 72,000 ft (21,965 m), Mach 3.0
Initial Climb Rate	unknown
Service Ceiling	77,350 ft (23,600 m)
Range	typical: 3,725 nm (6,900 km) [XB-70] typical: 6,600 nm (12,230 km) [B-70] ferry: unknown
G-Limits	unknown
ARMAMENT:
Gun	none
Stations	production model designed with 2 internal bomb bays
Air-to-Air Missile	none
Air-to-Surface Missile	none
Bomb	up to 14 nuclear bombs planned
Other	none
KNOWN VARIANTS:
XB-70A-1	First prototype that was capable of only Mach 2.5 due to structural and aerodynamic limitations
XB-70A-2	Second prototype with a redesigned wing, structural improvements, and improved hydraulics allowing flight at Mach 3, vehicle was lost after an in-flight collision
XB-70A-3	Proposed third prototype, cancelled during construction
B-70A	Proposed production model; 200 were to be built, cancelled
RS-70A	Proposed reconnaissance model; 150 were to be built, cancelled
KNOWN OPERATORS:	US Air Force NASA
3-VIEW SCHEMATIC:
SOURCES: Boeing North American XB-70 site Campbell, John M. and Pape, Garry R. North American XB-70 Valkyrie: A Photo Chronicle. Atglen, PA: Schiffer Military History, 1996. Donald, David, ed. The Complete Encyclopedia of World Aircraft. NY: Barnes & Noble, 1997, p. 698, North American B-70 Valkyrie. Dryden Research Center Photo Gallery Eggers, A. J. and Syvertson, Clarence A. Aircraft Configurations Developing High Lift-Drag Ratios at High Supersonic Speeds, NACA RM-A55L05, 1956. FAS B-70 Valkyrie site Flight of the Valkyrie Global Security B-70 Valkyrie site Rees, Ed. The Manned Missile: The Story of the B-70. NY: Duell, Sloan, and Pearce, 1960. Remak, Jeannette and Ventolo, Joe. XB-70 Valkyrie: The Ride to Valhalla. Osceloa, WI: MBI Publishing, 1998. US Air Force Museum XB-70 site