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Northrop B-2 Spirit

northropb-2


Development of the B-2 was begun in 1978, and in designing the Advanced Technology Bomber (ATB), as the B-2 project was originally known, the Northrop Company decided on an all-wing configuration from the outset. Flying-wing devotees such as Hugo Junkers and Jack Northrop argue that a flying wing will carry the same payload as a conventional aircraft while weighing less and using less fuel. The weight and drag of the tail surfaces are absent, as is the weight of the structure that supports them. The wing structure itself is far more efficient because the weight of the aircraft is spread across the wing, rather than concentrated in the centre.

The B-2 design is a flying wing with straight 40 degree sweep leading-edges and a sawtooth trailing edge. Its centrebody is smoothly contoured into the upper wing surface. The centrebody houses the two-man crew compartment and the two weapons bays, one on each side of the centreline. The cockpit compartment is accessed through a ventral hatch and has large cockpit windows to improve the pilots angular field of view, yet the nose-down view remains very limited. The engines lay outboard the weapon bays in the upper wing surface. The exhausts are positioned forward of the wing trailing edge to reduce heat signature.

Because of the big wing area and wing span, the lift needed per square foot of wing is not as high compared to other designs of the same weight. Therefor the B-2 does not need complex flaps. It operates over a smaller angle of attack.

 

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The all-wing approach was selected because it promised to result in an exceptionally clean configuration for minimizing radar cross-section, including the elimination of vertical tail surfaces, with added benefits such as span-loading structural efficiency and high lift/drag ratio for efficient cruise. Outboard wing panels were added for longitudinal balance to increase lift/drag ratio and to provide sufficient span for pitch, roll and yaw control. Leading-edge sweep was selected for balance and trans-sonic aerodynamics, while the overall planform was designed for neutral longitudinal (pitch) static stability. Because of its short length, the aircraft had to produce stabilizing pitchdown moments beyond the stall for positive recovery. The original ATB design had elevons on the outboard wing panels only but, as the design progressed, additional elevons were added inboard, giving the B-2 its distinctive 'double-W trailing edge. The flight-control surfaces are operated by a fly-by-wire control system to ensure optimum control responses in this design of relaxed stability intended for positive aerodynamic control at all times, throughout the airframe, emphasis is placed on completely smooth. The wing leading edge is so designed that air is channelled into the engine intakes from all directions, allowing the engines to operate at high power and zero airspeed. In trans-sonic cruise, air is slowed from supersonic speed before it enters the hidden compressor faces of the GE F118 engines.

A stores management processor is in place to hande the B-2's 22,730kg weapons load. A separate processor controls the Hughes APQ-181 synthetic-aperture radar and its input to the display processor. The Ku-band radar has 21 operational modes, including high-resolution ground mapping. The B-2 lifts off at 260km/h, the speed independent of take-off weight. Normal operating speed is in the high subsonic range and maximum altitude around 15,240m. The aircraft is highly manoeuvrable, with fighter-like handling characteristics.

The US Air Force originally wanted 133 examples, but by 1991 successive budget cuts had reduced this to 21 aircraft.

First revealed in November 1988, the prototype flew on 17 July 1989, and the first production B-2 was delivered to the 393rd Bomb Squadron of the 509th Bomb Wing at Whiteman AFB, Missouri, on 17 December 1993. Northrop delivered 21 B-2A Spirit stealth bombers, achieving initial operational capability with the USAF in April 1997 and full capability with the 715th Bomb Squadron in 1999.

With a crew of two, it is powered by four 19,0001b thrust F-118-GE-100 engines (as used in the F-16) and has a published speed of 0.72 Mach. The multi-role bomber is publicised as fuel efficient, able to carry a "substantial bomb load" and with "excellent range”. Unit cost: Approximately US$750 million.

 

When B-2 89-0127, named the Spirit of Kansas, crashed on takeoff at Andersen Air Force Base in Guam, it immediately became the most expensive accident in USAF history. The crash was determined to have been caused by moisture in the port transducer units which resulted in the distortion of information sent to the aircraft’s air data system. The B-2’s flight control computers calculated an incorrect air speed and angle of attack, causing the nose to pitch-up 30 degrees and sending the aircraft into an unrecoverable stall. The pilots ejected safely, though the Spirit of Kansas was reduced to a $1.4 billion pile of burning wreckage.
 
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Gallery


Northrop B-2A Spirit
Engines: 4 x General Electric F-118-GE-100 turbofan, 17,300 lb / 7,847 kg
Length: 69 ft (20.9 m
Height: 17 ft / 5.1 m
Wingspan: 172 ft / 52.12 m
Wing area: 3982.68 sq.ft / 370.0 sq.m
Takeoff Weight (Typical): 336,500 lb / 152,635 kg
MTOW: 371,000 lb / 168,286 kg
Max speed: 475 mph / M0.76
Cruising speed: 516 kt / 955 km/h
Ceiling: 50,000 ft / 15,152 m
Op radius: 3800 mile / 6115 km
Payload: 40,000 lb / 18,144 kg
Crew: Two pilots, with provisions for a third crew station

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