Structure and Systems

Requirements for rapid startup and getway, the use of short runways and austere airfields, Mach 2 at altitude and high subsonic penetration at low level, heavy payloads and intercontinental range made the use of a variable-geometry wing for the B-1 almost essential. At the same time, the decision to carry weapons and fuel internally placed a premium on available volume, leading to wing/body blending and in turn reducing radar signature.

The heart of the aircraft is the massive Wing Carry-Through Box, which is made of titanium. As well as supporting the wings it also has to carry and support the main landing gear, and it also carries about 9000 kg of fuel. The wing pivot pin is 430mm in diamter and weighs about 272 kg. Made of titanium, it is hollow and is carried on a two-race spherical bearing.

The wing is a conventional two-spar aluminium box structure, which also serves as a fuel tank. The wing fairing seal is similar to that used on the Tornado, with sliding "feathers" supported by an inflatable bag.

The fuselage is of conventional monocoque construction, with internal frames roughly every 250mm for its entire length. The wing-body blending provides space for fuel and avionics, produces lift and also reduces the aircraft's radar signature. Near the nose are two small Structural Mode Control System foreplanes. These are used to smooth out aeroelastic fuselage whipping, which can be severe in large aircraft at low level.

The B-1 has three fuselage bays, each 4.57m long. There is a removable bulkhead between the first and second bays to allow cruise missiles to be carried internally. The bay doors are made of composite materials.

When the B-1A was turned into the B-1B, several measures were taken to reduce the aircraft's radar signature. These included changing the main radar antenna and completely redesigning the engine intakes so that radar cannot illuminate the engine fan faces. The front and rear bulkheads were canted downwards so that radar pulses reach them at an oblique angle. RAM has been used extensively, in such places as the engine air intakes, the bulkheads, glove vanes, the wing fairings, and anywhere there is an angle which could trap and reflect back radar energy. B-1B RCS is classified, but is widely reported to be about 1/100th that of the B-52.

Crew

The B-1 normally carries a crew of four, the aircraft commander (AC), co-pilot (CO) (front left and front right seats, respectively), defensive systems operator (DSO) and offensive systems operator (OSO) (rear left and right seats, respectively) . There is a middle rear seat but it isn't used any longer after it was ruled to have contributed to the loss of two crew in a crash in Colorado in 1987. In the event of an ejection, the order is OSO, DSO, CO and finally the AC.

Aircraft commander and co-pilot Defensive and offensive systems operators

Dimensions

Length:44.5m
Wingspan, forward:41.8m
Wingspan, swept aft:24.1m
Height:10.4m
Empty Weight:About 86183 kg
Maximum T/O Weight:214650 kg

Performance

Speed: 1400 km/hr+ (Mach 1.2 at sea level)
Range: Intercontinental, unrefueled
Ceiling: 9000m+

Powerplant

The B-1B is powered by four General Electric F101-GE-102 afterburning turbofan engines. Each engine has a dry thrust of 75.6 Kn, or 135 kN in full afterburner.

The F101 is a twin-spool turbofan with a bypass ratio of 2:1. It has nine high-pressure (HP) compressor stages driven by two low-pressure (LP) and one HP turbine stages. Its total pressure ratio is 27:1. The engine is 4.6m long and 1.4m in diameter, and weighs just under 2 tonnes.

The engines are housed in pairs in nacelles under the wing root. The aircraft can be safely controlled even if both engines in one nacelle fail, and single-engine operation is possible at light weights.

The engine air intake ducts were completely changed when the B-1B was created. Instead of a complex moving ramp, the B-1B has a plain intake with no variable ramp. The S-shaped duct contains baffles to disperse radar energy, and extensive use is made of radar-absorbing material in the duct.

B-1B fuel capacity is around 93 tonnes, held in eight tanks. The forward two weapons bays are also plumbed for fuel tanks. In order to prevent the aircraft's centre of gravity getting out of balance, the Fuel and Center of Gravity Management Subsystem (FCGMS) automatically pumps fuel around the tanks in response to a variety of data inputs. The FCGMS can also be run in manual mode, and in the event of CG limits being exceeded (which led to the loss of B-1A number two) the crew receives visual and aural warnings.

The B-1B can be air-refuelled by the boom method. The refuelling receptacle is forward of the cockpit.

Avionics

The B-1B's electronic jamming equipment, infrared countermeasures, radar location, and warning systems complement its low-radar cross-section and form an integrated defense system for the aircraft. The Offensive Avionics System (OAS) was produced by the Boeing Military Airplane Company, while the Defensive Avionics System (DAS) was built by AIL Systems Inc.

The heart of the B-1B's avionic system comprises four redundant MIL-STD-1553 data buses, which control the routing of data around the various on-board systems. Vital to the efficient operation of the B-1B is the Central Integrated Test System (CITS). This constantly monitors and verifies the performance of the various parts of the system.

As part of the Comventional Mission Upgrade Program (CMUP), Boeing upgraded the B-1B's avionics flight system, replacing its six existing computers with four new ones that added significantly more computing power and memory. The avionics flight system provides both offensive and defensive capability, including weapons delivery, radar, terrain following and navigation. The computing platform for the new system utilizes a tandem of four computers, each containing a pair of PowerPC processor cards. The Green Hills Software Integrity RTOS provides real-time multitasking, I/O and memory management services for the avionics flight system and hosts the application software that runs on the PowerPC processors.

The CMUP adds a family of smart weapons to the B-1B arsenal, and provide the flexibility needed to up-load multiple types of weapons for each mission and launch the appropriate weapon against the selected target. Integrity enhances the B-1B's onboard avionics flight system so that it can take advantage of CMUP's smart weapons and multiple-target capabilities.

Offensive Avionics System

The APQ-164 radar is at the heart of the OAS. This is a multimode coherent pulse-Doppler set with a low-observable (downward-canted) antenna. The antenna is fixed and scanning is carried out electronically by the phased array. The radar has a number of modes, including high-resolution SAR ground mapping, real-beam ground mapping, weather depiction, beacon, terrain avoidance and terrain folllowing. The system is dual-redundant in all areas except the phased-array antenna.

The OAS contains a total of 66 LRUs, including 4 IBM AP-101F central computers. and the complete system weighs 1300 kg. 20 kVA of power is needed to run it.

On April 20th 2006 the US Air Force awarded Boeing a $180m contract to upgrade the B-1B's fire control radar. Under a nine-year Reliability and Maintainability Improvement Program (RMIP), Boeing will start to deliver modification kits to replace the bombers' receiver and processor in 2011. The RMIP kit, built principally by Northrop Grumman Electronic Systems, comprises a new radar transmitter/receiver, a new radar processor computer and a new software package. Initial flight tests of the new hardware and software are due to take place later in 2006.

Navigation and Communications

Navigation is handled by a single Singer-Kearflott SKN-2440 inertial system. Its associated sensors are the Teledyne APN-218 Doppler velocity sensor, and two Honeywell APN-224 radar altimeters. Also installed are an AN/ARN-118 TACAN and an AN/ARN-108 ILS system.

As part of the Block D upgrade, GPS receivers were installed both for aircraft and JDAM navigation.

The B-1B is equipped with an AN/ARC-164(V) VHF radio, AN/ARC-210 VHF/UHF radio, AN/ARC-190 HF radio, AN/ASC-19 AFSATCOM, AN/APX-101A IFF transponder and an AN/APX-105 rendezvous beacon.

Defensive Avionics System

ALQ-161

The AN/ALQ-161A is a totally integrated radio-frequency countermeasures system ("jammer") unlike any other ever produced. Its physical size as well as its performance capacity are unmatched (although the ALQ-161A has never fully met Air Force specifications). The system provides 360-degree receive and jamming coverage against a large number of simultaneous threats, and also provides a Tail Warning Function (TWF). The ALQ-161 comprises 120 separate items, which weigh about 2500 kg. When its full jamming capacity is utilised, it consumes roughly 120 kW of power. The system was originally controlled by a single IBM AP-101F computer.


Normally the AN/ALQ-161A system operates in a fully automatic mode, where the system receives, identifies, and jams threat radars instantaneously. However, the Weapons System Officer (WSO) can manually intervene when desired. Complete situational awareness is provided on two threat display formats to the WSO to include constant information of threat type, mode, location jamming status, frequency and relative amplitude. Other additional system and/or threat information is available on call to the operator through a joystick that allows him to designate specific threats and request data from either display format. Additional manual functions such as jamming modifications, receiver attenuation changes, and threat characteristic changes are available to the WSO.

The system can be rapidly reprogrammed, on the ground and in the air, which allows it to adapt quickly to any scenario. The receiver continually observes the entire environment to detect most conventional threats at a moderate sensitivity. For those emitters that require higher sensitivity for detection, the receiver uses its directed high sensitivity search routine that is programmed by the user for maximum effectiveness.

The AN/ALQ-153 tail warning radar is a pulse-Doppler set which detects any missile threatening the bomber from the aft sector. If a missile is detected, the system provides immediate warning to the crew for evasive action, and can automatically dispense RF and IR decoys to counter the threat.

Because of the known limitations of the ALQ-161, the Air Force had been seeking to replace it under the Defensive Systems Upgrade Program (DSUP). However, on December 19th 2002 the Air Force announced that it had cancelled DSUP after its developers (Boeing & BAE Systems) said the improvements would run 17 months late and $175 million over budget. The system was found to be "high risk" by an independent Air Force review board because of its performance of "mixed results and limited success" during 11 test missions.

The Air Force said the $600 million saved by terminating the program would fund "much needed, near-term B-1 combat capability improvements," including upgrading the ALQ-161's ECM system, developing and integrating the Joint Air To Surface Standoff Missile - Extended Range (JASSM-ER) for increased stand-off capability, increasing B-1 sustained engineering efforts, and improving Wind Corrected Munitions Dispenser/Chaff Dispenser capabilities.

On May 22nd 2003 EDO Corporation announced that it had received two US Air Force contracts in support of the ALQ-161. The first was to develop an upgrade to its digital radio-frequency memory. The upgrade will provide advanced technique waveforms to counter known advanced-enemy threats. Upon completion of this developmental contract, the program will then enter a formal test phase before commencing under a full production contract.

The second award was to continue development on the next generation of AN/ALQ-161 preprocessor flight software. This contract covers all the required software testing and data analysis prior to Air Force flight tests, as well as flight-test support. The contract also provides for engineering analysis of potential future software enhancements.

In July 2004 EDO Corporation announced that it had been awarded contracts worth $21.3 million to maintain and upgrade the ALQ-161 system. These contracts support the migration of existing software to a new state-of-the-art processor, and the testing of upgraded jamming processes. The new jamming technology will considerably enhance the capabilities of the ALQ-161, and allow the system to be rapidly reprogrammed to address future threats.

ALE-50

The B-1B is equipped with the ALE-50 Towed Decoy System. This is towed hundreds of meters behind the aircraft and provides a more inviting target for missiles. The TDS was first utilized operationally during Operation "Allied Force" in 1999.

Block E

Boeing announced on September 27th 2006 that it had completed the Block E upgrade on the USAF's fleet of 67 B-1Bs. The Block E modification replaces six computers with four, providing a 25-fold increase in throughput, memory and input/output margins required for conventional weapons capability, defensive systems upgrades and future growth. The package also integrates the Wind-Corrected Munitions Dispenser, the Joint Standoff Weapon and the Joint Air-to-Surface Standoff Missile, substantially augmenting the bomber's standoff capability.

Sniper targeting pod

The Lockheed Martin Sniper XR targeting pod features a third-generation mid-wave FLIR system, diode-pumped laser operating up to 40,000 feet altitude, enhanced stabilization, a laser spot-tracker, laser marker, CCD television camera and a combat-identification capability. The pod weighs 199kg (440lb), is 0.3m (11.9in) in diameter and 2.9m (94in) long. The pod's wedge-shaped nose is made of highly durable sapphire which is transparent to visible and infrared wavelengths, and presents extreme durability to impact and damage. The unique design gives Sniper a semi-low-observable characteristic, but also makes it compatible with fighters carrying the system on an engine inlet. At supersonic speeds, an oblique shock surface forming on the pod reduces disturbances in air entering the inlet.

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© David Hastings