North American XB-70 Valkyrie

https://en.wikipedia.org/wiki/North_...XB-70_Valkyrie

The North American Aviation XB-70 Valkyrie was the prototype version of the
planned B-70 nuclear-armed, deep-penetration strategic bomber for the United
States Air Force Strategic Air Command. Designed in the late 1950s by North
American Aviation (NAA), the six-engined Valkyrie was capable of cruising for
thousands of miles at Mach 3+ while flying at 70,000 feet (21,000 m).

At these speeds, it was expected that the B-70 would be practically immune to
interceptor aircraft, the only effective weapon against bomber aircraft at the
time. The bomber would spend only a brief time over a particular radar station,
flying out of its range before the controllers could position their fighters in
a suitable location for an interception. High speed also made the aircraft
difficult to see on radar displays and its high-altitude and high-speed capacity
could not be matched by any contemporary Soviet interceptor or fighter aircraft.

The introduction of the first Soviet surface-to-air missiles in the late 1950s
put the near-invulnerability of the B-70 in doubt. In response, the United
States Air Force (USAF) began flying its missions at low level, where the
missile radar's line of sight was limited by terrain. In this low-level
penetration role, the B-70 offered little additional performance over the B-52
it was meant to replace, while being far more expensive with shorter range.
Other alternate missions were proposed, but these were of limited scope. With
the advent of intercontinental ballistic missiles (ICBMs) during the late 1950s,
manned bombers were increasingly seen as obsolete.

The USAF eventually gave up fighting for its production and the B-70 program was
canceled in 1961. Development was then turned over to a research program to
study the effects of long-duration high-speed flight. As such, two prototype
aircraft, designated XB-70A, were built; these aircraft were used for supersonic
test-flights during 1964–69. In 1966, one prototype crashed after colliding with
a smaller aircraft while flying in close formation; the remaining Valkyrie
bomber is in the National Museum of the United States Air Force near Dayton,
Ohio.


Role
Strategic bomber
Supersonic research aircraft

National origin
United States

Manufacturer
North American Aviation (NAA)

First flight
21 September 1964

Retired
4 February 1969

Status
Retired

Primary users
United States Air Force
NASA

Number built
2

Program cost
US$1.5 billion (equivalent to $10.5 billion today)

Unit cost

US$750 million (average cost)(equivalent to $5.2 billion today)

The XB-70's maiden flight was on 21 September 1964. In the first flight test,
between Palmdale and Edwards AFB, one engine had to be shut down shortly after
take-off, and an undercarriage malfunction warning meant that the flight was
flown with the undercarriage down as a precaution, limiting speed to 390 mph –
about half that planned. During landing, the rear wheels of the port side main
gear locked, the tires ruptured, and a fire started.

The Valkyrie first became supersonic (Mach 1.1) on the third test flight on 12
October 1964, and flew above Mach 1 for 40 minutes during the following flight
on 24 October. The wing tips were also lowered partially in this flight. XB-70
No. 1 surpassed Mach 3 on 14 October 1965 by reaching Mach 3.02 at 70,000 ft
(21,000 m). The first aircraft was found to suffer from weaknesses in the
honeycomb panels, primarily due to inexperience with fabrication and quality
control of this new material. On two occasions, honeycomb panels failed and were
torn off during supersonic flight, necessitating a Mach 2.5 limit being placed
on the aircraft.

The deficiencies discovered on AV-1 were almost completely solved on the second
XB-70, which first flew on 17 July 1965. On 3 January 1966, XB-70 No. 2 attained
a speed of Mach 3.05 while flying at 72,000 ft (22,000 m). AV-2 reached a top
speed of Mach 3.08 and maintained it for 20 minutes on 12 April 1966. On 19 May
1966, AV-2 reached Mach 3.06 and flew at Mach 3 for 32 minutes, covering 2,400
mi (3,900 km) in 91 minutes of total flight.

A joint NASA/USAF research program was conducted from 3 November 1966 to 31
January 1967 for measuring the intensity and signature of sonic booms for the
National Sonic Boom Program. Testing was planned to cover a range of sonic boom
overpressures on the ground similar to but higher than the proposed American
SST. In 1966, AV-2 was selected for the program and was outfitted with test
sensors. It flew the first sonic boom test on 6 June 1966, attaining a speed of
Mach 3.05 at 72,000 ft (22,000 m). Two days later, AV-2 crashed following a
mid-air collision with an F-104 while flying in a multi-aircraft formation.
Sonic boom and later testing continued with XB-70A #1.

The second flight research program (NASA NAS4-1174) investigated "control of
structural dynamics" from 25 April 1967 through the XB-70's last flight in 1969.
At high altitude and high speed, the XB-70A experienced unwanted changes in
altitude. NASA testing from June 1968 included two small vanes on the nose of
AV-1 for measuring the response of the aircraft's stability augmentation system.
AV-1 flew a total of 83 flights.

The XB-70's last supersonic flight took place on 17 December 1968. On 4 February
1969, AV-1 took its final flight to Wright-Patterson Air Force Base for museum
display (now the National Museum of the United States Air Force). Flight data
were collected on this subsonic trip. North American Rockwell completed a
four-volume report on the B-70 that was published by NASA in April 1972.

Mid-air collision

On 8 June 1966, XB-70A No. 2 was in close formation with four other aircraft (an
F-4 Phantom, an F-5, a T-38 Talon, and an F-104 Starfighter) for a photoshoot at
the behest of General Electric, manufacturer of the engines of all five
aircraft. After the photoshoot, the F-104 drifted into the XB-70's right wing,
flipped and rolled inverted over the top of the Valkyrie, before striking the
bomber's vertical stabilizers and left wing. The F-104 then 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
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 the crushing of his arm by the closing
clamshell-like escape crew capsule moments prior to ejection.

The USAF summary report of the accident investigation stated that, given the
position of the F-104 relative to the XB-70, Walker, the F-104 pilot, would not
have been able to see the XB-70's wing, except by uncomfortably looking back
over his left shoulder. The report said that it was likely that Walker
maintained his position by looking at the fuselage of the XB-70, forward of his
position. The F-104 was estimated to be 70 ft (21 m) to the side of the fuselage
of the XB-70 and 10 ft (3.0 m) below. The report concluded that from that
position, without appropriate sight cues, Walker was unable to properly perceive
his motion relative to the Valkyrie, leading to his aircraft drifting into the
XB-70's wing. The accident investigation also pointed to the wake vortex from
the XB-70's right wingtip as the reason for the F-104's sudden roll over and
into the bomber.

Specifications (XB-70A)

General characteristics
Crew: 2
Length: 185 ft 0 in (56.39 m)
Wingspan: 105 ft 0 in (32.00 m)
Height: 30 ft 0 in (9.14 m)
Wing area: 6,297 sq ft (585.0 m2)
Airfoil: Hexagonal; 0.30 Hex modified root, 0.70 Hex modified tip
Empty weight: 253,600 lb (115,031 kg)
Gross weight: 534,700 lb (242,536 kg)
Max takeoff weight: 542,000 lb (245,847 kg)
Fuel capacity: 300,000 pounds (140,000 kg) / 46,745 US gal (38,923 imp gal;
176,950 l)
Powerplant: 6 × General Electric YJ93-GE-3 afterburning turbojet, 19,900 lbf (89
kN) thrust each dry, 28,000 lbf (120 kN) with afterburner

Performance
Maximum speed: 1,787 kn (2,056 mph, 3,310 km/h)
Maximum speed: Mach 3.1
Cruise speed: 1,738 kn (2,000 mph, 3,219 km/h)
Combat range: 3,725 nmi (4,287 mi, 6,899 km)
Service ceiling: 77,350 ft (23,580 m)
Lift-to-drag: about 6 at Mach 2
Wing loading: 84.93 lb/sq ft (414.7 kg/m2)
Thrust/weight: 0.314




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