North American XB-70 Valkyrie

Developed to USAF General Operational Requirement 38 for an intercontinental bomber to replace the Boeing B-52, the Mach 3 North American XB-70A was the subject of an order for three prototypes, awarded on 4 October 1961, although the third was later cancelled.

The North American XB-70 Valkyrie first flew in prototype form on 21 September 1964. When the first prototype flew it was simultaneously the longest (56.4 m/185 ft), fastest (Mach 3+), most powerful and costliest aircraft ever built, US$2000 million, and weighing 305-tonne (300-ton).

A delta-winged canard design, the airframe made extensive use of contemporary ‘exotic’ alloys to overcome the problems associated with kinetic heating. The wings were swept back at 65 degrees 34 minutes on the leading edge, and were covered with brazed stainless steel honeycomb panels welded together to produce an extremely strong yet heat-resistant whole. Similar construction was used for the huge rectangular engine duct under the centreline, the twin vertical tail surfaces and part of the fuselage. The advanced aerodynamics of this elegant yet menacing warplane were based on a large delta wing from whose centre grew a slim forward fuselage complete with canard foreplanes.

The powerplant comprised six 31,000-lb (14.062-kg) thrust General Electric YJ93-GE-3 afterburning turbojets in a ducted arrangement under virtually the full chord of the delta wing. Its outer portions were arranged to hinge downward in flight under hydraulic power to improve stability and maneuverability. An anhedral angle of 25 degrees was used for low-altitude supersonic flight, increasing to 65 degrees for high-altitude flight at Mach 3. Control was provided by a combination of flaps on the canard foreplanes, no fewer than 12 wide-chord elevons across much of the trailing edge of the wings outboard of the variable-geometry engine exhausts, and large rudders on each of the vertical surfaces. Control of so complex an aerodynamic platform moving at high supersonic speeds was effected with the aid of a three-axis stability-augmentation system.

The first prototype was flown by Alvin S. White and Colonel Joseph F. Cotton on 21 September 1964. The first flight had been so long postponed and the entire project downgraded to only two prototypes. By the flight, the first US had spent $1.34 billion on its development. $92 million was then allocated to see the two prototypes through the flight program. Both XB-70’s were programmed for a 180 hr flight test schedule, including experiments for NASA. It first achieved its design speed of Mach 3 on 14 October 1965.

The improved second prototype flew on 17 July 1965, but was lost in a mid-air collision on 8 June 1966. The surviving aircraft carried out a number of test programmes, including work in connection with the US supersonic transport programme, but on 4 February 1969 it was flown to retirement at the US Air Force Museum, Wright Patterson AFB, Dayton, Ohio.

Even before the fist prototype flew, however, technological developments in air defence had made the XB-70 obsolete. In 1963 the U.S. government ended the XB-70 development programme and turned the prototypes over for research purposes although one of the XB-70s was lost on 8 June 1966. The surviving XB-70 is now a museum piece.

Engines: 6 x General Electric YJ93-GE-3 afterburning turbojets, 31,000-lb (14.062-kg)
Wing span: 105 ft 0 in (32 m)
Length: 196 ft 0 in (59.74 m)
Max TO wt: 530,000 lb (240,400 kg)
Max level speed: M3 / 3218 km/h / 2000 mph
Height: 9.1 m / 29 ft 10 in
Wing area: 565.0 sq.m / 6081.60 sq ft
Ceiling: 21336 m / 70000 ft
Range w/max.fuel: 12000 km / 7457 miles
Crew: 2

North American XB-70 Valkyrie