Formal work on the development of "low-observable" or "stealth' aircraft in the US began in late 1974, when the Defense Advanced Research Projects Agency (DARPA), a Pentagon organization that works on "blue sky" advanced technologies, began Project HARVEY, an effort to build a stealthy aircraft. The project was named after a famous comedy about a giant invisible rabbit named, of course, Harvey.
Project Harvey was not actually the first time the US had incorporated stealth features into aircraft. In the early 1960s, Firebee target drones had been modified for the reconnaissance role as "Lightning Bugs" or "Fireflies". They had been enhanced with stealth features, including pads of radar-absorbing material (RAM) on the sides of the fuselage; and a wire mesh over the air intake to mask the blades of the engine compressor, which tends to sparkle or "glint" on radar as it spins, like a spinning disco ball in a lights show. The high-flying Lockheed SR-71 Blackbird reconnaissance aircraft was designed to be stealthy as well, though it also used high altitude and speed for protection.
The goals of Project HARVEY were much more ambitious: to create an aircraft that could survive on stealth alone. DARPA awarded study contracts to McDonnell Douglas and Northrop in January 1975. Lockheed officials found out about Harvey through the grapevine and insisted on participating, paying for their design effort out of company funds. That was a gamble, but it paid off: Northrop and Lockheed were selected by DARPA to design a stealth demonstrator, the "Experimental Survivable Testbed (XST)", while McDonnell Douglas was eliminated from the competition. The XST program's goals did not include building a flight demonstrator; Northrop and Lockheed were to build large-scale mockups, which would then be mounted on a pole at Holloman AFB in New Mexico and subjected to tests to determine their "radar cross section (RCS)".
Work on the Northrop demonstrator was conducted by a team under John Cashen, a pushy sort who had come to Northrop after working at Hughes on how targets appeared to radar and infrared sensors, and Irv Waaland, a designer who had come over to Northrop from Grumman. Although the Lockheed team used a computer program to come up with their design for the XST, Cashen said later that Northrop didn't have such a luxury, and worked up their design using a combination of theoretical analysis and cut-and-try experiments.
The Lockheed team won the XST competition in March 1976, and went on to build two HAVE BLUE stealth demonstrator aircraft, which paved the way to the larger Lockheed F-117 stealth fighter. Northrop lost because one the team's initial design assumptions was that a stealthy aircraft should be hardest to pick up from the front and below, but the DARPA requirement, rightly or wrongly, insisted on measuring stealthiness from four quadrants. The Lockheed design proved better able to meet the all-round stealth requirement. Lockheed also had an advantage in possessing a good knowledge of RAM technology, which that company had developed for the SR-71.
However, in December 1976 DARPA officials called up Northrop to discuss a stealth aircraft as part of the Pentagon's ASSAULT BREAKER effort. ASSAULT BREAKER was a wide-ranging program that envisioned use of new "smart" munitions, deep-penetrating strike platforms, and advanced sensors to smash numerically-superior Soviet armor forces in the case of a European war. DARPA wanted Northrop to study a stealthy "Battlefield Surveillance Aircraft -- Experimental (BSAX)" that would spot targets for ASSAULT BREAKER weapons. Since BSAX was supposed to loiter around a battlefield instead of performing an attack and leaving, it would present all angles to an enemy and so required all-round stealth. An initial model of BSAX was tested in the summer of 1977, with results that Waaland later described as "disastrous". One of the design team members, Fred Oshira, did some rethinking of the design and came up with a solution, a new airframe design that gave very little for a radar beam to grab on to. In April 1978, DARPA awarded Northrop a contract for a single flying prototype of the design, which was given the codename TACIT BLUE".
TACIT BLUE performed its initial flight in February 1982, followed by 134 more flights over a three-year evaluation. It was unarguably one of the ugliest aircraft ever built, and was unflatteringly known as the "Whale". It featured a fuselage resembling a stretched upside-down bathtub with a wedge-shaped flat panel under the nose; an engine intake buried in the back; wedge-shaped wings; and a vee tail shielding the exhaust. TACIT BLUE was powered by twin high-bypass turbofan engines, had a wingspan of 14.7 meters (48 feet 2 inches), a length of 17 meters (55 feet 10 inches), and a weight of 13,605 kilograms (30,000 pounds).
In 1984, the Army and Air Force decided to collaborate on a non-stealthy battlefield surveillance platform, which would emerge as the E-8 Joint Stars, based on the Boeing 707 airliner. TACIT BLUE was put in storage in 1985. It was finally announced to the public in 1996, and is now on display in the USAF Museum at Wright Patterson Air Force Base in Ohio.
* While Northrop was beginning work on TACTIC BLUE, back at the Pentagon the top brass were becoming very interested in stealth. In 1977, William "Bill" Perry, Secretary of Defense for the Carter Administration, formed a group to perform studies on the military potential of stealth. The group's conclusion was that improvements in adversary air defenses were threatening to make the current "non-stealthy" US bomber force obsolete. In addition, stealth would allow a single aircraft to make a precision attack on a target, instead of requiring a full "strike package" of multiple bombers, with fighter escorts, jamming platforms, and defense-suppression ("Wild Weasel") aircraft.
The group recommended that two stealthy strike aircraft should be built, an "A Airplane", a fast-track development of the Lockheed HAVE BLUE demonstrator, which would emerge as the F-117; and a "B Airplane" that would be bigger and more capable but would take more time to roll out.
The B Airplane concept grew over time into a full-blown, long-range heavy bomber. Lockheed had proposals, one apparently being a machine something like a scaled-up F-117 and codenamed SENIOR PEG, but the Pentagon also asked Northrop to investigate. Northrop officials were uneasy about working on a heavy bomber, since the company's last effort along such lines, the XB-35 / YB-49 flying wings of three decades earlier, had come close to financially wrecking the company. They did agree, however, and responded with two proposals, one of which, cooked up by designer Hal Markarian, took its inspiration from the YB-49. Incidentally, there is a story, possibly true, that the YB-49 had shown a surprising ability to disappear from radar at certain viewing angles.
The proposals were duly submitted in August 1979, and Bill Perry came back with a study contract, asking Northrop to refine the flying wing concept. Waaland joined up with Markarian, and the team also acquired aerodynamicist Hans Grellman, as well as Dick Scherrer, a designer who had recently come over from Lockheed. At the outset, the Northrop "Advanced Strategic Penetration Aircraft (ASPA)", as it was known, was seen strictly as an insurance policy, since Lockheed was regarded by the brass as the front-runner.
However, by the time the Air Force issued a request for an "Advanced Technology Bomber" in September 1980, formalizing the ASPA studies into a program to develop an operational aircraft, Northrop's design was looking much more attractive, and company officials felt they had a shot at winning the contract. Lockheed was partnering with Raytheon on their ATB proposal, and so Northrop approached Boeing to sign up as a partner. Northrop's chairman, Tom Jones, had a meeting with his counterpart at Boeing, Thornton Wilson. Wilson, to his embarrassment, was almost completely ignorant of the ATB program, but Jones filled him in, and Wilson agreed to join immediately. Witnesses claim that Wilson then turned to one of his people and said: "Don't ever let me be caught in this position again!"
The Northrop concept, codenamed SENIOR ICE, was judged superior to the Lockheed "Senior Peg" proposal, and Northrop won the ATB contract in October 1981. The contract covered delivery of two static-test airframes, one flying prototype, and five evaluation machines. While the Carter Administration had pushed stealth, there had been some ambivalence about production, but the new, hawkish Reagan Administration wanted to go full speed ahead on the ATB. The initial plan envisioned production of 127 ATBs, in addition to the five evaluation machines, which would be brought up to operational specification.
The Pentagon wanted to keep the contract a secret, but Tom Jones pointed out that Northrop had to publicly declare large company contracts in order to be in compliance with securities laws. The government, caught by their own regulations, issued the shortest and least informative statement possible about the contract. It would be the last public mention of the program until 1988.
* There was much more work to be done to get such a complicated machine into the air, all the more so because the ATB requirements had expanded over time. Aircraft size and munitions load had grown, and although the ATB was originally seen as a high-altitude penetration machine, the Air Force decided that a low altitude capability would be nice as well -- there was no saying that the Soviets might eventually develop more powerful and smarter radars that could pick up a high-flying stealthy aircraft.
In any case, the work went forward, and the first "B-2" prototype, "Air Vehicle One (AV-1)", was rolled out at the Northrop plant in Palmdale, California, on 22 November 1988. The rollout was public, but observers were restricted to stands that kept them well away from the aircraft and limited their view of it to the front. Although the F-117 had been kept secret for years after its first flight, its test flights had been restricted to night, and that wasn't regarded as acceptable for the B-2. Since it would have been quickly spotted during daylight flights there was no sense it keeping it a complete secret, and nobody tried.
However, the security restrictions at the rollout weren't completely "airtight", in a highly literal sense of the word. The late Michael A. Dornheim, a reporter from AVIATION WEEK magazine, flew a light aircraft over the B-2 and had a photographer take pictures, obtaining one of the magazine's biggest scoops of all time and justifying its nickname of AVIATION LEAK. It was all perfectly legal.
The damage, if any, had been done, and the program went forward. AV-1 performed its first flight on 17 July 1989, flying from Palmdale to Edwards AFB in California. Northrop Test pilot Bruce Hinds and USAF Colonel Richard Couch were at the controls. AV-2, the first of the five evaluation machines, performed its initial flight on 19 October 1990. The first production B-2A was accepted by the US Air Force Air Combat Command (USAF ACC) at Whiteman AFB in Missouri on 17 December 1993. Due to the merger of Northrop and Grumman in the 1990s, the aircraft is now the "Northrop Grumman B-2".
The B-2 is organic in appearance, a simple flying wing, with absolutely no vertical control surfaces. It has very smooth contours and few features that could "catch" radar waves and reflect them. It has a sweepback of 55 degrees and a "W"-shaped trailing edge. The aircraft is aerodynamically unstable, kept in the air with a quadruple-redundant fly-by-wire (FBW) system, under the control of a General Electric Flight Control Computer (FCC).
The B-2 was designed to be survivable, not merely in penetrating enemy airspace and performing attacks, but in riding out enemy nuclear attacks or counterstrikes. The B-2 is thoroughly radiation hardened; Waaland commented that about all that isn't radiation hardened is the antiskid braking system. It can also operate from dispersed bases, one of the design criteria being the capability to use any airstrip capable of supporting a Boeing 727 airliner.
The B-2 makes heavy use of titanium for structural elements, with much of the rest of the aircraft built of carbon-reinforced plastic (CRP) material. Large CRP skin assemblies are used to make the aircraft as "seamless" as possible, reducing radar reflections. The principle of seamlessness also means that the number of access panels has been minimized, reversing the trend of the past decades to provide maximum maintenance access. Maintenance access is mostly provided through absolutely essential apertures, such as the bombbays and crew boarding hatch. There are also no drain holes, with drainage flowing into collectors that are emptied on the ground.
Designing the CRP assemblies, tooling up for their production, and fitting them in place in aircraft manufacture was a major engineering challenge. Special heat-resistant CRP formulations are used around engine exhausts and other hot spots, where carbon-reinforced epoxy simply won't do. The aircraft was initially coated with a conductive elastomer material to ensure that it had uniform electrical conductivity. This material was not actually RAM, but RAM was used selectively where needed. The B-2 is painted in a bluish-gray anti-reflective paint to reduce its visual signature. It is not painted black, as is the F-117, since the B-2 is expected to perform both daylight and night attacks, and black is a high-visibility color for daylight flight operations.
The leading edge of the wing has an internal structure that helps it absorb radar energy. The outermost wing segment features a "rudderon" or "deceleron", a vertically-split airbrake / rudder that simultaneously opens up and down. To act as an airbrake, both the decelerons are opened, while to act as a rudder only one is. This clever gimmick goes back to the original Northrop flying wings. There is an elevon inboard of the deceleron on the outermost segment of each wing, and then two elevons further inboard, on the next segment. Finally, there is a single control surface for pitch control on the "beavertail" at the center end of the aircraft, giving a total of nine control surfaces.
The decelerons have to be opened about five degrees before they are effective, and in normal cruising flight they are left slightly open. However, this undermines stealth, so when the bomber is in combat, it uses differential engine thrust for yaw control.
* The B-2's four General Electric F118-GE-110 non-afterburning bypass turbojets, providing 84.56 kN (8,620 kgp / 19,000 lbf) of thrust each, are derived from the popular GE F110 engine. The F118s are buried in the wings, with two engines clustered together inboard on each wing. An AlliedSignal auxiliary power unit is fitted on the forward end of the left engine assembly for engine starting and ground power. The B-2 also features a built-in Halon engine fire extinguishing system.
The engine intakes and exhausts are on the top of the wings for concealment. The intakes have a zigzag lip to scatter radar reflections, and there is a zigzag slot just before each intake to act as a "boundary layer splitter", breaking up the stagnant turbulent airflow that tends to collect on the surface of an aircraft. The inlet ducts are built as an s-curve and lined with RAM to keep radar from picking up the compressor blades.
The exhaust is mixed with airflow obtained through the boundary layer splitter slot to reduce the infrared signature. The aircraft was also designed to eliminate its contrail, with a tank outboard of the main landing gear to store a chemical that would be mixed with the exhaust flow to suppressed the formation of a contrail. This scheme wasn't actually used in practice, with a "lidar" (laser radar) system instead eventually developed to detect the formation of a contrail and alert the pilot to descend to lower altitude.
maximum speed 764 KPH 475 MPH / 416 KT service ceiling +15,240 meters +50,000 feet range 11,675 kilometers 7,255 MI / 6,310 NMI _____________________ _________________ ______________________
The B-2 has tricycle landing gear, with twin-wheel nose gear and four-wheel bogey systems for the main gear. The main gear is built by Boeing and is derived from that used on the Boeing 767 airliner. The landing gear doors have stealthy zigzag leading and trailing edges. Since it is difficult to find a place on the smoothly-contoured airframe to paint such "display" items as the aircraft name or serial number, they are painted on the main gear outer doors, making them visible to onlookers when the aircraft is on the ground, or during takeoff and landing. There is a boom-refueling port in the center of the back, which is normally covered by doors and pops up when needed.
* The bomber is fitted with two side-by-side weapons bays that can accommodate a total of 22,680 kilograms (50,000 pounds) of stores. The leading and trailing edges of the weapons bay doors have the classic stealthy zigag pattern. When the doors are open, twin grilles pop out into the airstream at the front of each weapons bay to ensure proper stores separation. Each of the two weapons bays can be fitted with a Boeing Advanced Rotary Launcher (ARL), capable of carrying eight 1,000 kilogram (2,200 pound) class munitions, or a Bomb Rack Assembly (BRA) for carriage of smaller munitions.
Since the B-2 was originally designed for the strategic bombing role, it was qualified initially for nuclear stores such as the B83 strategic nuclear bomb, with selectable yield in the megatonne range, and the smaller B61 "Silver Bullet" nuclear bomb, with selectable yield in the range of hundreds of kilotonnes. The bomber was later qualified for the penetrating B61-11 penetrating nuclear weapon. A B-2 can carry 16 nuclear stores.
The B-2 has also been qualified for use with "dumb" bombs, such as sixteen 900 kilogram (2,000 pound) bombs, or eighty 225 kilogram (500 pound) bombs or cluster munitions based on the Tactical Munitions Dispenser (TMD). However, such stores are likely better carried by other platforms such as the B-52 or B-1B, and so the emphasis with the B-2 has been on precision-guided weapons. Some sources claim it can also carry the AGM-84 Harpoon antiship missile for maritime strike, but it seems more likely that this was simply listed as a potential store as a political expedient to emphasize additional roles for the B-2.
A Global Positioning System (GPS) guided bomb, the "GPS Aided Munition (GAM)", was developed on a fast-track basis for the B-2, but GAM was strictly an interim fix until the real solution, the "Joint Direct Attack Munition (JDAM)", was introduced in the late 1990s. JDAM was initially a 900 kilogram bomb fitted with gliding strakes and GPS guidance; kits were later introduced for 225 kilogram bombs as well. The B-2 can also carry the AGM-154 Joint Stand-Off Weapon (JSOW) glide bomb, and the AGM-158 Joint Air to Surface Standoff Missile (JASSM).
* The B-2 is highly automated and only requires two crew. A centerbody provides crew accommodation, with crew access through a hatch in the belly. The cockpit has large windows, so large in fact that they tend to make the B-2 look smaller than it really is, though the downward view is poor. Fighter pilots taking the controls of the B-2 say it makes them feel like they are "flying in a dumpster". A fine wire mesh is built into the windows to block radar signals.
The two crew sit side-by-side on ACES II zero-zero (zero speed, zero altitude) ejection seats, which blast through frangible roof panels. The "mission commander", who handles navigation and weapons delivery, sits on the left, while the pilot sits on the right. The mission commander is also a rated pilot and can fly the aircraft if need be. They control the aircraft using a "glass cockpit", with each crew using a dashboard featuring four 15 centimeter (6 inch) color CRT multifunction displays (MFDs) and a fighter-style control stick. There was provision for a third seat in case the crew workload proved too high, but a third crewperson proved unnecessary. A chemical toilet and rollup mattress can be carried for long missions. It is unclear if there are other conveniences, such as a small refrigerator or microwave oven.
The B-2's original "Navigation Sub-System (NSS)" included a Kearfott Inertial Management Unit and a Northrop NAS-26 "Astro-Inertial Unit (AIU)", which obtains position fixes using a telescope to lock on to star positions, using a noticeable port on top of the wing off to the left side of the cockpit. It even works in daylight when the bomber is at high altitude, and is a descendant of an AIU developed for the SR-71.
The B-2 is fitted with an AN/APQ-181 radar, with some similarities to the AN/APG-70 used on the F-15E Strike Eagle fighter. The AN/APQ-181 is a Ku band (high microwave, from 12 GHz / 3 centimeters to 18 GHz / 2 centimeters) radar, with an electronically steered antenna in the lower leading edge of each wing. The Ku band suffers from greater atmospheric attenuation than lower frequency bands, but it also provides very high resolution for navigation and targeting.
The AN/APQ-181 provides "low probability of intercept (LPI)" operation, with the radar dancing over frequencies and changing pulse patterns so that its signals can't be picked out of background noise until it's too late. Apparently the TACIT BLUE program did much to advance LPI radar technology; it would have made absolutely no sense to design a stealthy battlefield surveillance aircraft and then have it announce its presence by blasting out strong and easily detected radar signals. The AN/APQ-181 provides 20 operational modes, including a "Synthetic Aperture Radar (SAR)" mode for ground mapping, with a "Ground Moving Target Indicator (GMTI)" capability; a "Terrain Following / Terrain Avoidance (TF/TA)" mode for low-level flight; a mode for spotting and linking up with a tanker; and weather mapping and navigation modes.
Finally, the B-2 includes a countermeasures suite, the "Defensive Management System (DMS)", for which most details still remain secret. All the avionics is controlled by a total of 13 radiation-hardened "Avionics Control Units (ACUs)", run by sophisticated software to help reduce flight load and provide sophisticated cockpit data display to enhance the crew's "situational awareness".
* B-2 aircrew find the big bomber a very pleasant ride and easy to fly. Its FBW system offloads a good deal of the work, and a flying wing is about as aerodynamically clean an aircraft design as could be conceived. It is an aircraft that wants to get into the air but doesn't want to come back down, and so pilots have to use steep carrier-style landings. Apparently this causes some problems when they go back to more conventional aircraft and are inclined to try the same trick.
The aerodynamic cleanliness of the B-2 makes it very responsive to throttle changes. Midair refueling also takes a little practice, since once the B-2 gets into the slipstream of the tanker the bomber tends to slide forward a bit. The B-2 is very stable, and by the other side of the same coin not particularly maneuverable. B-52 aircrew moving up to the B-2 find it more agile than the "Buff", but B-1B aircrew feel the "Bone" is superior in this respect, and with its higher wing loading the B-1B also gives a smoother low-level ride than the B-2. The B-2s systems are complicated and require extensive training to master, but aircrew who grew up on computer games find the systems aspect fun and no monster to deal with.
Although the official name of the B-2 is "Spirit", as is usually the case with official names, the aircrews don't call it that. Apparently there is no particular nickname. However, all the operational B-2s have been given SPIRIT OF names, such as SPIRIT OF TEXAS, SPIRIT OF KANSAS, SPIRIT OF CALIFORNIA, and so on. Only one doesn't use a US state in the name: number 82-1066 is, appropriately, SPIRIT OF HASTINGS. All fly out of Whiteman AFB with the USAF 509th Bomb Wing.
RobinHoodSEO © 2009
+ robin hood + taboo + 911revolution + spiney + mp3
+ home + Huddersfield +