Technology Explained – Rockwell 8-18

It was this aspect of the USAF’s Bomber Penetration Evaluation (BPE) that ultimately led to the revival of the B-1 programme, killed off by the Carter Administration at the end of June, 1977. Fortunately enough, sufficient support existed among US legislators at the time to provide funds for continuing research, development, test and evaluation (RDT&E) of the B-1 aircraft after the cancellation of the production order.

This saw a series of penetration tests flown at the Nellis range, under the BPE programme. B-1A prototype #3, with a baseboard cross-eye deception jammer fitted, flew a series of sorties against targets covered by ground-based radars, AWACS platforms and F-15 fighters. The results were encouraging and in July, 1980, the USAF brought B-1A prototype #4, equipped with the full prototype defensive and offensive avionic systems, into the test programme. By April, 1981, seventy sorties were flown and the results of these offered substantial support for the aircraft’s capability.

Although SAC’s long-term planning envisaged the Stealth/ Advanced Technology Bomber (ATB) as the front-line long-range penetrator at the turn of the century, the loss of 240 B-1As resulted in a major reduction in force capability in the near term. The B-52s could not be considered a credible strike force for hitting key Soviet targets and thus a gap filler was required. Various options were reviewed, including a rather pregnant-looking derivative of the FB-111, while lobbyists acting on behalf of many of the 5,300 contractors and suppliers involved in the B-1A programme continued working hard at raising support for reviving the stalled B-1 programme.

Amidst these events an Air Force Scientific Advisory Board study identified a future need for far broader capabilities in strategic aircraft and concluded that a derivative of the B-1A would be best suited to near term SAC requirements. Meanwhile, the Reagan Administration had pledged to upgrade US strategic forces and the decision was made to provide SAC with 100 new B-1B multi-role long-range aircraft. In January 1982 President Ronald Reagan stated that 100 B-1B aircraft could be produced for US$20. 5 billion in 1981 dollars, with an Initial Operational Capability (IOC) to be attained in 1986. A US$2. 2 billion full scale development and B-1B lot 1 production contract followed shortly.

One of the most significant arguments supporting the decision was the maturity of the basic B-1 airframe design, largely frozen by then and the availability of a capable baseline offensive avionic system developed for a B-52 upgrade. Both would contain costs, a view borne ciut by the subsequent development programme.

Rockwell B-1 B Long-Range Combat Aircraft

The new B-1B was optimised for the split role of a strategic nuclear and long-range conventional bomber. The latter role included maritime reconnaissance/strike, aerial mine laying, anti-submarine patrol and conventional strike in support of theatre operations. The heavy conventional payloads and shift to electronic means in defence penetration both led SAC to discard top-end supersonic performance in order to reduce radar cross section (RCS) and improve payload/range performance. The new aircraft, with 1/10th the RCS of the B-1A (presumably in the J-band so beloved of Soviet SAM designers. . . ), would penetrate at high subsonic speeds several hundred feet above the ground and use its electronic arsenal as its primary penetration aid. This led to the adoption of new engine nacelles with fixed inlets, greatly enhanced offensive and defensive avionics and structural changes to cope with an 82,000lb increase in maximum gross weight. Significantly, 8,000Ib of empty weight was saved by the use of ejection seats. The new B-1 would carry the AGM-86B cruise missile internally and on external hard points which could also carry other ordnance. The planned reduction in wing sweep angle to simplify the wing glove was later abandoned.

To accelerate the development programme, flight tests were carried out on B-1A 2 which received some modifications to bring it closer to B standard. B-1A 4 was performed as a test bed for the offensive and defensive avionics, and it was supported later by the first production of B-1B. Tragically 2 was lost in an accident in August, 1984 killing Rockwell test pilot Tommie Benefield. The crash was attributed to aircrew error in handling the aircraft at a low level with the automatic CG/fuel management system disengaged.

The first production B-1B was rolled out on the 4th September, 1984, five months ahead of schedule and first flew in mid October, 1984. SAC received its first aircraft on the 29th June, 1985. Over the next two years 98 aircraft are scheduled to be delivered, 29 to Dyess AFB in Texas, 17 to McConnell AFB in Kansas, 35 to Ellsworth AFB in South Dakota and 17 to Grand Forks AFB in North Dakota. These locations were chosen to maximise the flight time of Soviet SLBMs launched off the coast on shallow trajectories thus discouraging a pre-emptive strike at the B-1 force.

The B-1B is a highly capable strike platform that will provide the USAF with significant conventional and nuclear muscle for at least two decades. The sophistication of this aircraft becomes most apparent upon closer examination.

The B-1B Airframe

The airframe of the B-1B is very close to that of the A-model but incorporates aerodynamic, detail and structural changes to match the revised role and to ease production. The basic structural assemblies of the B-1A are retained with the exception of the crew module which was deleted to save weight and increase crew survivability. The Forward Fuselage is built by Rockwell’s North American Aircraft Operations (NAAO) and includes a revised radar/avionic bay and the new crew area. To cut assembly costs the avionic equipment racks and associated cabling in the central avionic bay are fitted into and debugged in the fuselage halves prior to joining. The Forward Intermediate Fuselage section previously containing the forward and intermediate weapon bays experienced numerous structural changes. These resulted from the need to carry the Common Strategic Rotary Launcher (CSRL) with eight ALCMs. The added length forced the removal of the fixed bulkhead between the bays and its replacement with a movable one. The resulting single 31ft Forward Weapon Bay required in turn structural changes for launcher attachment points and fuel lines for an optional extra fuel tank. A retractable spoiler was added to the front of the bay to avoid difficulties with the previously troublesome turbulent airflow under the open bays.

The new weapon bay is more flexible than its predecessors. Fitted with a pair of rotary launchers fore and one launcher aft the aircraft can carry 24 B-61 or B-83 nuclear devices, or 24 AGM-69 SAAM missiles or 12 8-28 or 8-43 nuclear devices. External hard points for six dual and two single pylons allow carriage of a further 14 ALCMs or further SRAMs. Flying conventional strikes the aircraft can carry 24 2,000Ib Mk. 84 demolition bombs or up to 84 500Ib Mk. 82 demolition bombs, placing it in the class of the 8-520.

The Aft Intermediate Fuselage and Aft Fuselage are both built by Vought and joined at the Rockwell assembly facility. The wings, built by Abco, retain their integral fuel storage. Skinned above with Alcoa 2124 and below with Alcoa 2219 Aluminium alloys, they are exceptionally stiff to cope with the structural loads induced by the terrain following. The inboard wing about the pivots is Titanium alloy with stainless steel bushes inserted (after cooling with liquid nitrogen they expand to achieve a permanent fit) The NAAO-built nacelles were an area of major changes. The Automatic Inlet Control System (AICS) of the Mach 2 B-1A was removed together with its sensors and associated doors, ramps and actuators although ram scoops for the air conditioning are still used. Inlet geometry was optimised for low altitude high subsonic cruise with some inlet curvature to conceal the engine fans from radar. This appears to have been successful in spite of the relatively short inlet ducts. The changes in inlet geometry and aircraft mission necessarily resulted in changes to the General Electric F101 powerplants, leading to the new F101-GE-102. Flight tests demonstrated that the low level role was far more punishing than anticipated, with five times the number of thermal cycles expected. The additional wear led to a degradation of engine performance over time which was unacceptable given that the 8-18 would spend a lot more time at low level and high gross weights.

The new F101-GE-102 differs from the -100 in several respects. The low and high pressure turbine stages employ more durable materials, several forgings have been replaced with cheaper castings and the afterburner stage was redesigned. Fuel flow was redistributed about the spray bars to improve combustion stability in some flight regimes, while the nozzle was changed substantially. The -102 nozzle employs 12 flaps (segments) with six actuators and no flap seals; this arrangement avoids the seal wear out problem of the eight flap-100 nozzle while also saving on two actuators. These changes were a major contribution to bringing mean time between overhauls up to the USAF requirement of 3,000hrs.

Meanwhile other modifications were needed to cope with the ‘serpentine’ low RCS inlet geometry. The first stage fan blades were altered to increase pumping capacity by 5%, three of the twenty strut frames in front of the fan were removed to increase airflow and the fan vanes were re-staggered to reduce flow distortion at the vane tips. In spite of the number of specific changes to the engine, it still retains 95% commonality with the core of the F-11O derivative fighter engine powering the F-14D, F-15 and F-16. With a 2:1 bypass ratio the -102 delivers 15,000lb thrust in military power and 30,000lb in reheat though SFC (Specific Fuel Consumption) figures on dry thrust have not been released. The engine can also be changed in less than 30 minutes.

e-18 Systems

The complexity of the 8-1B stems to a great degree from the large number of systems installed. The two major groups are the Offensive and Defensive Avionic Systems, which are complemented by the various services and systems associated with the airframe and support of the mission avionics. The Flight Control System of the B-18 defies brief explanation. Although essentially a conventional Stability Control Augmentation System (SCAS) built with eleven Systron-Donner accelerometer/gyro packages, with one group at the CG and one in the nose, it must cope with the problems of variable geometry and large weight/CG changes. Because the B-1 will pitch its nose up uncontrollably beyond a given AOA (angle of attack), (ie. stall). The SCAS is fitted with a Stall Inhibitor System (SIS) which restricts AOA to avoid entering this unstable mode. However, AOA close to this limit is often required to maintain desired lift at higher gross weights so the SCAS is being fitted with a Stability Enhancement Function (SEF) from aircraft #19. The SEF has been described as providing similar high authority control as the SCAS in the statically unstable F-16A thus enabling the flight envelope to be expanded up to the airframe’s high gross weight stability limit.

The B-1B’s Fuel Center of Gravity Management System has also received some modifications primarily to improve aircrew awareness of CG state so that a repeat of the #2 crash will be avoided. The LARC ride control system is now called the Structural Mode Control System (SMCS) which perhaps better describes its function. It drives the nose vanes and lower rudder segment (see Part 1 Nov AA) to reduce structural loads at low level.

Terrain Following (TF) flight is an important part of the B-1B’s role enabling it to avoid surface radars and to degrade the performance of lookdown/shootdown radars. The B-1B employs two of its eight IBM AP-101F computers as dedicated redundant TF computers. The AP-101F is a dual instruction set derivative of the earlier and slower AP-101C used for the B-52 offensive avionic upgrade. The F-model runs at about 1 MIPS (million of instructions/sec) and is micro-coded either to a proprietary instruction set or MIL-STD-1750. Most of the software running on the eight AP-101Fs is written in Jovial J3B, it is very likely that much of it was derived from that written for the B-52 avionic upgrade. The TF computers interface with the SCAS via a pair of Boeing Signal Data Converters which would provide analogue/ digital, digital/analogue and timing conversion functions.

The aircraft’s weight computers are split into four groups; four form the core of the offensive avionics, two perform as TF computers, one as the defensive avionics supervisory processor and the last unit serves as the Central Integrated Test System’s (CITS) central computer. These processors are tied into four dual redundant MIL-STD-1553B serial data busses which connect to almost all on board systems, they are also supported by an IBM nonvolatile Core Mass Storage Device and a pair of Sundstrand Data Transfer Units. Both of these would be used for targeting cruise missiles. The CITS system is of great importance, it monitors the operational status of all other subsystems and reports any battle damage or malfunctions detected.

The Boeing ASQ-184 Offensive Weapon Control System

The Boeing Offensive Avionic System (OAS) integrates all navigation and attack functions. It was developed from an upgrade package designed for the B-52G/H force and is built around four AP-101F computers, termed Avionic Computer Control (ACC) units. One ACC provides Nav functions, one Task Display and Control, one Weapon Management (see AA Sept 85 p73) with the last ACC serving as a monitor and backup unit. These four ACCs are supplemented by the pair of TF computers. The OAS receives inputs from a number of sensors. A pair of Honeywell APN-224 Low Altitude Radar Altimeters (LARA) provide high-rate altitude measurements for terrain following. while a Teledyne APN-218 Doppler set provides precise velocity measurement in all axis to supplement the inertial systems. The primary navigation reference is a pair of Singer Dearfott SKN. 2440 Inertial Navigation Units (INU).

The OAS is supervised by the Offensive Systems Operator (OSO) who sits at the starboard aft station. He will use two Multi Function Displays (MFD) and a radar display all of which are tied into the data busses. From this station the OSO will navigate and acquire/attack targets. Display and system control is implemented with multi function keyboards and a Tracking Control Handle, a facility to upload mission particulars with a magnetic tape cartridge is also apparently available.

The Westinghouse APQ-164 Offensive Radar System

The ORS is the primary attack sensor in the B-1B and fulfils several key functions, including terrain following. The 164 was developed out of the EAR (electronically agile radar) programme of the late seventies which aimed at exploiting phased array technology in tactical radar, it is unique in that it combines both attack radar and terrain following radar functions in a single antenna two channel unit.

The extremely difficult requirement for a TF/attack radar which could offer a 99% probability of survival over 15 hours of operation led to the adoption of a two channel architecture, which follows through from the receivers up to the independent TF ACCs (computers). At any instant one channel is active while the other is in hot standby, the only element in the radar common to both channels is the actual phased array antenna. To reduce costs and improve reliability Westinghouse designed the 164 about several LRUS (black boxes) used in the mature APG-68 F-16 radar, itself most reliable with a 120hr class MTBF.

The ORS offers 19 operating modes and time-shared use between the pilots and OSO (thus offering the illusion of an independent radar for each). This versatility is a result of two design features, the use of programmable signal processors and the use of an electronically controlled phased array antenna. The unique honeycomb appearance of the antenna is due to the 1526 miniature phase shifter modules, each of which is an independent receive/transmit element. By electronically manipulating the microwave signal phase lead/lag of these elements the radar can shape and point its beam, within certain limits, almost instantaneously. While this technique allows concurrent TF/ attack modes it also offers lower radar cross section than a conventional antenna and graceful degradation rather than catastrophic failure as individual elements fail.

In TF mode the ORS scans terrain up to 10nm ahead of the aircraft and stores a height vs distance profile. Scan rates depend on which of the 11 clearance altitudes are set and upon velocity and terrain. Only a narrow corridor is covered to minimise detectable emissions. Terrain Avoidance mode assists penetration by displaying only terrain features above a set altitude while Velocity Update mode emulates a Doppler nav set. A Weather mode is available offering circular beam polarization.

Several attack modes may be used. Real Beam Groundmap and Synthetic Aperture Radar mode offer coarse and high resolution mapping for attack and INS updating, while a side looking Strip Mapping mode is available for standoff attacks. Moving Target Indicator and Moving Target Track modes are offered including overlay presentation, these are essentially tactical strike modes. A unique mode offered by the 164 is High Altitude Calibrate in which the antenna is tilted down and the beam fired vertically down to obtain precise altitude supplementing the LARA and barometric altimeter when bombing.

The high reliability of the APQ-164 and its flexibility offer a lot of system level redundancy which reduces the aircraft’s sensitivity to failures in other OAS sensors; this should substantially reduce instances of mission aborts. Coupled with the use of standoff munitions the OAS provides the B-1B with the ability to accurately hit point targets deep inside hostile territory. To survive in this environment the aircraft must exploit both its low radar cross section and defensive avionics.

The Eaton-AIL ALQ-161 Radio Frequency Surveillance/ Electronic Counter Measures System

The vast ALQ-161 is the most complex defensive jamming system ever installed in a combat aircraft. Built up of 107 LRUS of 52 different types weighing in at 5,200lb the 161 represents a major exercise in system engineering. It is unique in that it is the first system to provide complete integration of RHAW (radar warning) and jamming functions in a single system – a feature that greatly improves the utilization of jamming resources available.

The 161 divides the world outside the B-1B into three 120° segments each covered by one of its three antenna bays; one in each glove fairing and one in the tail cone. The receivers, transmitters and antennas in these bays tie into the remainder of the 161 via six redundant MIL-STD-15538 data busses: Control is exercised, via Jam Logic units, by the 161’s Defensive Management Subsystem (OMS) AP-101F ACC which also provides an interface between the 161 and the Defensive Systems Operator (DSO). The DSO occupies the port aft station and monitors the threat situation through two Electronic Display Units and a Multi-Function Display. Although the system is highly automated the DSO may intervene thus vastly increasing flexibility (there is no substitute for a devious mind. . . ). The 161 relies on sets of directional receivers, each for particular bands, to detect hostile radar emissions impinging on the aircraft. These are analyzed and, after encoding and data filtering, passed onto the OMS computer for threat assessment and display.

The receivers and programmable jammers are under the direct control of two Jamming Allocation Logic Units, dubbed ‘Jam Logic A and B’ boxes which via the 1553 busses communicate with the electronically steerable antennas and programmable transmitters. The AIL designed solid state low band transmitters and Northrop Travelling Wave Tube high band transmitters feed via waveguides into a strip line network. which feeds the multiple phase shift elements in the steerable Sedco antenna arrays (which use a technique similar to that in the radar to achieve near instant beam pointing). The jam logic will coordinate beam pointing and jammer transmissions to hit each victim’s radar when it is most vulnerable (eg into its antenna side lobes), the system’s ability to time share and allocate priority enables it to cope with multiple threats most effectively. Much of the computing horsepower used in analyzing threat signals and computing jamming waveforms is provided by a set of dedicated microprogrammable high-speed Litton LC-4561D computers, which thus allow the OMS computer to efficiently perform in its dedicated management role.

Packaging the immense 161 appears to have been a problem, as much of the low-band hardware and power supplies have been buried deep in the aft fuselage and main wheel well. The jam logic and OMS ACC reside in the central avionic bay racks. Some sources indicate that difficulties with the 161’s taii warning radar subsystem have led to its replacement with the ALQ-153 although this was not confirmed at the time of writing.

Although SAC are understandably reluctant about describing what the 161-can do, it appears that it will cover bands up to and including the 1/J band thus enabling it to defeat newer Soviet SAMs such as the RIM-66A Standard look alike SA-11 Gadfly arid the new lookdown/shootdown air intercept radars carried by the Foxhound and Flanker. Techniques for mono pulse radar deception jamming are almost certainly implemented.

Penetrating hostile airspace the 8-1B will rely primarily upon low altitude, its low radar cross-section and radar warning receivers to avoid detection by threats. If the aircraft must close to a range where a threat can detect it, for instance through local geography or while hitting a target, it would then unleash its arsenal of jammers to confuse its opponents; Although lookdown/shootdown fighters represent the most effective counter to this aircraft one cannot lose sight. of the fact that any interceptor (having actually managed tb find it) attempting to kill it must contend with the difficulties of a lookdown attack and the considerable jamming power output of the ALQ-161. Infra-red Search & Track Sets may be of use under some circumstances but are hampered severely by atmospheric water vapour and background infra-red emissions (ie. clutter). Given the vast area to be covered by the Russian Voyska PVO and the quality of much of their equipment and aircrew it is reasonable to assume that in the foreseeable future the 8-1B will defeat their defensive system.

The 8-1B is an awesome combat aircraft with a broad range of both nuclear and conventional capabilities. Hopefully it will never by called upon to demonstrate what it can do. It is, after all, very much a Doomsday Machine.