The United States bomber described below is one of the most remarkable aircraft ever developed. It could fly very high and very fast. However, the introduction of high-altitude surface to air missiles (SAM’s)made the deployment of such a bomber impractical. The project was cancelled with only two prototype aircraft built. These bombers were the most sleek looking big aircraft ever built.
The North American Aviation XB-70 Valkyrie was the prototype version of the proposed B-70 nuclear-armed deep penetration bomber for the United States Air Force’s Strategic Air Command. Designed by North American Aviation in the late 1950s, the Valkyrie was a large six-engined aircraft able to fly Mach 3+ at an altitude of 70,000 ft (21,000 m), which would have allowed it to avoid interceptors, the only effective anti-bomber weapon at the time.
The introduction of effective high-altitude surface-to-air missiles, the program’s high development costs, and changes in the technological environment with the introduction of ICBMs led to the cancellation of the B-70 program in 1961. Although the proposed fleet of operational B-70 bombers was cancelled, two prototype aircraft were built as the XB-70A and used in supersonic test flights from 1964 to 1969. One prototype crashed following a midair collision in 1966; the other is on display at the National Museum of the United States Air Force in Ohio.
Designed for high-altitude flight, the B-70 lost this edge to improved Soviet high-altitude, anti-aircraft missiles. The aircraft would become increasingly vulnerable at high altitudes as newer missile systems were introduced, and at low altitudes it lost its supersonic performance and range. Using the original Mach 3 high altitude mission profile, the aircraft had a design range of 6,447 nmi (7,419 mi, 11,940 km) without refueling, but flying over the target area “on-the-deck” at Mach 0.95 reduced range to 5,312 nmi (6,113 mi, 9,838 km), even with in-flight refueling. Realizing that the bomber would not be practical combined with high cost overruns President Eisenhower cancelled the project in 1959. Both Presidents Kennedy and Johnson subsequently left the program cancelled.
The experimental XB-70As were used for the advanced study of aerodynamics, propulsion, and other subjects related to large supersonic transports. The production order was reduced to three prototypes in March 1961 with the third aircraft to incorporate improvements from the previous prototype. The crew was reduced to only the pilot and co-pilot for the XB-70; the navigator and bomb-aimer were not needed. The first XB-70 was completed on 7 May 1964 (the second on 15 October 1964), and XB-70A #1 was displayed on 11 May 1964 in Palmdale, California. One report claimed “nothing like it existed anywhere“. The planned third prototype was canceled in July 1964 while being built. The first XB-70 had its maiden flight in September 1964 and flight testing followed.
The XB-70 flight test data and materials development aided the later Rockwell B-1 Lancer supersonic bomber program, the US supersonic transport program and, through intelligence, the Soviet Tupolev Tu-144. The development of the US U-2 and SR-71 reconnaissance aircraft along with the B-70 bomber led the Soviet Union to design and develop the MiG-25 interceptor.
The Valkyrie was designed to be a high-altitude bomber-sized Mach 3 aircraft with six engines. Harrison Storms (engineer who designed the command module for the Apollo program) shaped the aircraft with a canard surface and a delta wing, which was built largely of stainless steel, sandwiched honeycomb panels, and titanium. The XB-70 was designed to use supersonic technologies developed for the Mach 3 Navaho, as well as a modified form of the SM-64 Navaho’s all-inertial guidance system.
The XB-70 used compression lift, which was generated from a prominent wedge at the center of the engine inlets that created a shock wave below the aircraft. The wing included inboard camber to more effectively use the higher pressure field behind the strong shock wave (the airflow at the XB-70 wing’s leading edge was subsonic). The compression lift increased the lift by five percent. Unique among aircraft of its size, the outer portions of the wings were hinged, and could be pivoted downward by up to 65 degrees. This increased the aircraft’s directional stability at supersonic speeds, shifted the center of lift to a more favorable position at high speeds, and strengthened the compression lift effect. With the wingtips drooped downwards, the compression lift shock wave would be further trapped under the wings.
On 8 June 1966, XB-70A #2 was in close formation with four other aircraft (an F-4, F-5, T-38, and F-104) for a photoshoot at the behest of General Electric, manufacturer of the engines of all five aircraft. With the photoshoot complete, the F-104 drifted into contact with the XB-70’s right wing, flipped over and rolled inverted over the top of the Valkyrie, striking the vertical stabilizers and left wing of the bomber. The F-104 exploded, destroying the Valkyrie’s rudders and damaging its left wing. With the loss of both rudders and damage to the wings, the Valkyrie entered an uncontrollable spin and crashed into the ground north of Barstow, California. NASA Chief Test Pilot Joe Walker (F-104 pilot) and Carl Cross (XB-70 co-pilot) were killed. Al White (XB-70 pilot) ejected, sustaining serious injuries, including one arm being crushed as it was caught in the clamshell-like escape capsule as it closed around him just before ejection from the aircraft.
The formation of aircraft shortly after the collision on 8 June 1966.
- Length: 185 ft 10 in(56.6 m)
- Wingspan:105 ft 0 in (32 m)
- Height:30 ft 9 in (9.4 m)
- Wing area:6,296 ft² (585 m²)
- Airfoil:Hexagonal; 0.30 Hex modified root, 0.70 Hex modified tip
- Empty weight: 210,000 lb(93,000 kg)
- Loaded weight:534,700 lb (242,500 kg)
- Max takeoff weight:550,000 lb (250,000 kg)
- Powerplant:6 × General Electric YJ93-GE-3 afterburning turbojet
- Dry thrust: 19,900 lbf (84 kN) each
- Thrust with afterburner: 28,800 lbf (128 kN) each
- Maximum speed: Mach 3.1 (2,056 mph, 3,309 km/h)
- Cruise speed:Mach 3.0 (2,000 mph, 3,200 km/h)
- Range: 3,725 nmi (4,288 mi, 6,900 km) combat
- Service ceiling:77,350 ft (23,600 m)
- Wing loading:84.93 lb/ft² (414.7 kg/m²)
- lift-to-drag: about 6 at Mach 2
- Thrust/weight: 0.314