The B-2 Spirit Stealth Bomber

The B-2 Spirit Stealth Bomber
During the late 1940s and early 1950s, Jack Northrop of the Northrop company worked on a series of flying-wing bombers, none of which actually reached production. However, they did attract a great deal of public attention, being seen as futuristic, and were even featured in science-fiction movies such as THE WAR OF THE WORLDS.

A few decades later the notion that the future belonged to the flying wing seemed laughable, but Northrop had the last laugh. Radar had trouble picking up the uncluttered lines of a flying wing, and as the US Air Force turned towards "stealthy" aircraft in the 1970s and 1980s, the flying wing bomber was revived in the form of the Northrop Grumman "B-2 Spirit", the first flying wing to enter full operational service, the biggest stealth aircraft built to date, and one of the most expensive aircraft ever made.
A bomber is a military aircraft designed to attack ground targets, primarily by dropping bombs.
Types

• Strategic bomber aircraft designed for long-range attack missions, targeting strategic targets such as supply bases, bridges, factories, and ports to reduce the enemy's fighting ability.
• Tactical Bomber is a smaller plane with a distance shorter range, typically as far as the position of ground troops, because the goal was to support ground troops. In the modern environment, any war plane that was not designed as a strategic bombers can fall into this category. This role is filled by many designs, including those written below.
• Ground attack aircraft (or aircraft close support) is designed for round the battlefield and attack tactical targets, such as tanks, troop concentration, and others.
• Fighter-bombers (also called tactical fighter and attack aircraft) is a fighter with many roles, which can be armed to attack air-to-air and air-to-surface missiles. Many of these types of aircraft designed for combat air immediately after the bomb dropped. Multi-role aircraft like this is also designed to save expenditure of funds.

The B-2 Spirit Stealth Bomber Described

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 were used to make the aircraft as "seamless" as possible, reducing radar reflections. The principle of seamlessness also meant that the number of access panels was minimized as much as possible, reversing the trend of the past decades to provide maximum maintenance access. Maintenance access was 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 wouldn'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 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 operation for yaw control.
B-2 Spirit powerplants

The B-2's four General Electric F118-GE-110 non-afterburning turbofans, 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.

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 the weapons bay to ensure proper stores separation. Each of the two weapons bays can be fitted with a Boeing Advanced Rotary Launcher (ARL), each 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 solution until the real solution, the "Joint Direct Attack Munition (JDAM)", was introduced in the late 1990s. JDAM is a 900 kilogram bomb fitted with gliding strakes and GPS guidance; kits are now in development for 225 kilogram bombs as well. The B-2 can also carry the new 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 left side of the cockpit. It works even 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, since 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".