Technology Explained

World War II saw the first major strategic campaigns, these being carried out by the RAF and USAAF. While the Americans preferred the brute force and initially very costly approach of precision daylight bombing, the RAF opted for night raids and in the process pioneered the use of Electronic countermeasures (ECM) as a penetration aid. German air defences were countered with window (chaff), active radar and communication link jammers and radar warning receivers. Though many of the systems were highly effective, tactics were not always matched as a result of which loss rates were far from the optimum attainable (eg, the practice of penetrating with radar and IFF turned on provided the Luftwaffe with much valuable information). The difficulties were exacerbated by the limited accuracy of the bombing, which led to larger numbers of sorties required in turn increasing losses.

The USAAF daylight campaign was also costly, until the arrival of the P-38 and P-51 escort fighters the bombers were at the mercy of the Luftwaffe and experienced enormous loss rates on longer sorties (eg, Schweinfurt-Regensburg cca 16%). The Luftwaffe however could not sustain its own attrition and eventually succumbed to a loss of manpower and dwindling fuel supplies.

The nuclear strikes on Hiroshima and Nagasaki heralded a new era in strategic bombing. The long-range bomber became the basic delivery system for nuclear weapons and a whole generation of postwar bombers were developed to match the rote. The USAF fielded the B-50, the B-36 and followed up with the turbojet-powered B-47 and B-52. The RAF developed its V force of Valiants, Vulcans and Victors. The Russians copied the B-29 (captured aircraft) and followed with the turboprop Tu020 Bear and turbojet Tu-16 Badger and Mya-4 Bison. All of these aircraft would penetrate defences at high altitudes and speeds to defeat fighters while employing ECM to frustrate interception. In the nuclear age loss rates became less critical; only one to two sorties would be flown against a target. While conventional bombing could be discouraged by leaky defences through gradual attrition, the nature of a nuclear strike imposed the need for an airtight air defence if it was to be of any real use.

The Surface to Air Missile (SAM) was thus developed to counter the strategic bomber. Saturation attacks with salvoes of missiles against single penetrating aircraft would sooner or later defeat the onboard EMC and score a hit. The difficulty of designing ECM to counter unknown weapon systems was an equally serious problem, particularly in a Cold War situation. The early sixties also saw the initial deployment of all aspects of semi-active radar-guided air-to-air missiles (AAMs) carried by high speed interceptors. Clearly the days of high altitude high-speed strategic penetration were nearing an end and a new approach was sought.

Given the limitations of radar at the time, the obvious strategy was low-level, high-speed penetration and both the UK and the US developed aircraft to match the role. Britain’s iSR-2 and the US F-111 were both dedicated high-speed terrain-following bombers, the former was killed off through political ineptitude, the latter survived and despite its age, now represents the cutting edge of NATO’s deep strike forces. By the mid sixties, emphasis had shifted away from tactical nuclear strikes while the Vietnam War put the new strategy of Flexible Response to the test.

Although the war itself represented the classical case of political misapplication of air power it did see the historically (to date) final application of medium altitude saturation bombing and the debut of precision-guided munitions and low-level penetrators.

The air war against North Vietnam saw the Americans in an unfortunate situation. Ill-considered political decisions established numerous sanctuaries for both NVAF fighters and SAM sites. The NVA deployed incredible quantities of AAA (some sources suggest hundreds to thousands of barrels per Square mile) and built up a very dense network of air defence radars taking advantage of politically imposed periods of no bombing.

Until the 1972 Linebacker campaigns, most raids were flown with tactical fighters such as the F-105 and F-4. These aircraft were supported by EB-66 tactical jammers and F-105/F-4 Wild Weasels (refer p21 July 86 AA) as neither the Thuds of the Phantoms had the jamming capability or low-level terrain-following ability to penetrate without assistance. The F-111A entered the battle during the Linebacker I campaign and quickly assumed the responsibility of attacking the most heavily defended targets taking advantage of both darkness and foul weather. The aircraft demonstrated a loss rate of the order of 0. 2% which clearly vindicated the use of expensive jammers, radar warning systems and terrain-following radar.

This was in stark contrast with the performance of the B-52 which was used to attack Hanoi and Haiphong during the December Linebacker II campaign. Given the amount of AAA present the B-52s attacked in formations flying at 30,000ft, relying on powerful jammers to defeat the SA-2 SAMs launched by the North Vietnamese. The B-52D was the principal type used. These aircraft were configured for conventional bombing and were fitted with additional ECM systems. Typical loads were 42 750lb M-117 bombs internally and 24 500lb Mk82 bombs on pylons. The B-52D force was augmented by B-52G aircraft, which carried more internal fuel but were fitted with less capable ECM and carried a mere 27 750lb bombs internally.

Strikes were flown with three aircraft cells to increase the concentration of jamming power, most targets were attacked by streams of aircraft often approaching from different directions to confuse the SAM operators. The NVA put up a desperate effort and fired almost everything they had, in some instances the ECM was so effective that SAMs were launched at the B-52s blind. By the end of the eleven-day air battle, fifteen B-52s were lost to the SAMs yielding a loss rate of 2%, it appears that up to 60 SAMS were fired for each B-52 kill. Two NVAF MIGs were destroyed by B-52 tail gunners.

Linebacker II however was expensive, the logistical effort of supporting the B-52 force with ordnance, inflight refuelling, defence suppression and MIGCAP has yet to be matched.

It was clear that medium altitude bombing would be just as costly as in WWII if a technologically sophisticated opponent was to be tackled, by the same token the effectiveness of the F-111A demonstrated the path for the future. SAC had certainly learned through the Vietnam experience and quite promptly shifted the B-52 to low-level penetration while also pressing ahead with its B-1A programme. The B-52G/H force today thus operates at low level and will continue in this role until the turn of the century.

B-52G Offensive and Defensive Systems

An aircraft as large and unmanoeuvrable as the B-52 is almost totally dependent upon its onboard electronics when penetrating hostile airspace. Its eight turbojet engines have a large infra-red signature while its radar cross-section (RCS) is greater than that of any other Allied combat aircraft (the Russian Tu-20 Bear wins the prize for greatest RCS). Under these circumstances, the B-52 will attack targets from stand-off positions either with AGM-69 SRAM missiles or AGM-86 ALCM cruise missiles to avoid overflying heavily defended areas. Although this approach avoids SAMs, long-range lookdown/shootdown interceptors are a serious threat to the aircraft.

Both the B-52G and the newer B-52H have experienced major avionics upgrades to improve survivability, involving both offensive and defensive systems. The B-52G’s offensive systems aid in navigation and attacking of targets. The primary sensor is the multimode Norden APQ-156 Attack Radar which some sources suggest employs near real-time synthetic aperture techniques (refer p61 March 85 AA) to provide high-resolution ground maps. The radar is complemented by the ASQ-151 Electro-optical Viewing System (EVS) comprised of a Hughes AAQ-6 Forward Looking Infra-red (FLIR) and a Westinghouse AVQ-22 Low Light Television (LLTV) system. EVS imagery and superimposed symbology appear on cockpit CRT displays. The aircraft was fitted with a Honeywell SPN/GEANS inertial navigator from 1978 onward, the unit offers drift better than 0. 1nm/hr. Together with the nav-attack equipment these systems support both the pilots and the operators of the offensive system, ie. the navigator and radar navigator/bombardier.

The defensive systems are more complex and may be grouped into passive and active systems. Of the publicly known systems the passive digital ALR-46 Radar Homing and Warning (RHAW) system is of great importance. The RHAW analyses and identifies radar emissions that impinge upon the aircraft, the ALR-46 handles 16 emitters simultaneously and can feed its output into other onboard systems (the ALR-46 supplants the older APR-25 crystal video radar warning receiver). These are essentially active jammers which may be grouped into deception jammers and noise jammers. Noise jammers beam electrical noise into the receiving arrays of hostile radar which results in a loss of receiver sensitivity and thus shortened detection range – it is an essentially brute force technique most effective at long ranges. The B-52G carries the powerful Northrop ALQ-155/ALT- 28 Power Management System/CW Noise Jammer. The ALQ-155 is comprised of a set of automated set-on receivers (these may be locked onto a particular radar and then ensure that an allocated jammer is tuned in and timed correctly) which are cued by a RHAW system on to a given threat radar. This approach allows optimum use of the available jamming power which is generated by a set of ALT-28 noise jammers. The ALT-28 employs high power backward wave oscillator tubes which operate down to UHF frequencies, their output is fed into a set of electronically steerable antennas and then beamed at the hostile radar.

The prominent radome on top of the aircraft’s nose covers an ALT-28 antenna. The ALQ-155 is complemented with an ITT ALQ-117/172 noise deception jammer of which two are carried. Installed under the Rivet Ace programme this I/J band system is power-managed and can defeat monopulse systems.

Subtler deception jamming is provided by the Motorola ALQ- 122 false target generator and its associated ALT-16A solid-state power amplifiers. The ALQ-122 will analyse hostile radar signals and then generate false radar returns with incorrect range and azimuth information, the unit is highly automated.

The jammers are complemented with a set of ALE-24 chaff dispensers and the aft-facing gun system. All aircraft were built with the four . 50 cal guns in a tail barbette, these are aimed with the ASG-15 fire control radar. The upper search and lower tracking antenna radomes are easily distinguishable. A recent addition to the suite is the Westinghouse ALQ-153 tail warning radar which alerts the crew to aircraft approaching in the aft hemisphere. The defensive systems are operated by an electronic warfare officer and tail gunner.

Clearly the amount of jamming power required to cover an aircraft the size of the 8-52 is considerable and given recent advances in Warpac radar capability (eg, Fulcrum/APG-65ski) keeping the aircraft’s jammers up to date will be expensive. That is the primary reason why the B-52 Destiny tasks it as a stand-off cruise missile carrier, the deep penetration role being undertaken by the newer 8-1.

Rockwell B-1A

The supersonic swing wing terrain following B-1 must rank next to the F-111 as one of the most politically contentious weapon system development programmes in recent history. The 8-1 was conceived as a result of several USAF strategic studies conducted during the sixties; the long-running ‘Forecast’ programme from 1962 to 1969, the 1961 SLAB (subsonic low altitude bomber), the 1963 ERSA (extended range strike aircraft) and LAMP (low altitude manned penetrator), the 1964 AMPSS (advanced manned precision strike system) programmes and finally the 1965 AMSA (advanced manned strategic aircraft) programme which led to the issue of the November 1969 RFP for the B-1A. The 8-1A was specified as a nuclear hardened, terrain-following high-speed penetrator, essentially an airframe and system with F-111-like penetration capability and B-52 like payload/range.

North American Rockwell, General Dynamics and Boeing responded with Rockwell winning the RDT&E contract for 5 aircraft and 2 static airframes (later 3 + 1) on the 5 June 1970. General Electric was awarded a contract for 40 (later 27) F101- GE-100 turbofans to power the aircraft with Boeing and AILCutler-Hammer nominated as offensive and defensive avionics integrators respectively.

The development programme was fairly smooth, involving 20,000hr of wind tunnel tests including full-scale engine/inlet test, lift/drag ratio vs wing sweep angle and various stability tests. As with the F-111, structural loads were found to be very high and particular attention was paid to fatigue life. The first B-1A was rolled out on the 26 October 1974. Flight tests proceeded successfully and on schedule resulting in the Ford administration authorising full-scale production in 1976. SAC sought 241 aircraft each at US$34m.

Disaster however struck Rockwell and the 3,000 subcontractors involved when the Carter Administration assumed power. The B-1A programme was swiftly terminated, with air launched cruise missiles being fitted to B-52s as a substitute. Needless to say the decision was strategically myopic· as Russian long-range lookdown/shootdown fighters were only years away. Congressional support for the programme was however sufficient to allow continued development and airframe tests on existing prototypes. Rockwell’s 14,000 B-1 staff dropped to 3,200 and then to 1,200.

SAC however still wanted its bomber and proceeded with the highly classified Bomber Penetration Evaluation programme at Nellis using the No3 B-1A prototype. The results of this programme ultimately led the Reagan Administration to resurrect the programme (this will be covered in Part II). Historically the B-1A represents the pinnacle of conventional Western bomber design, something that is most apparent from a close look at the airframe and systems.

The B-1A Airframe

The B-1 airframe was much like the F-111, optimised for high-speed terrain following flight, with attention being paid to minimising radar cross-section. Cost constraints however quickly brought the Titanium content in the airframe down from 45% to 21%, with most of the airframe built of conventional Aluminium alloys. Again much like the F-111 the B-1 is very densely packed. Structurally the B-1 is split into a number of modules. The Forward Fuselage contains the radar sets, forward undercarriage bay, inflight refuelling receptacle and supports the crew ejection module. The module, inspired by the F-111, seats the 2 pilots,

Offensive Systems Operator and Defensive Systems Operator.

Weighing of the order of 8,000lb it is propelled by two rockets, it was deleted to save weight and complexity in later aircraft. Crew access is via a well aft of the forward undercarriage and beneath the central avionics bay. Most of the structure is of Al alloys.

The forward fuselage mounts the actuators and forward surfaces for the LARC (low altitude ride control system) which, also using the lower rudder segment, alleviates vertical and lateral loads that arise through flexing of the long fuselage in terrain-following flight. Employing gyros and accelerometers to sense rates, the LARC will drive its forward vanes at rates up to 200°/sec to reduce both airframe and aircrew fatigue.

The Forward IntermediateFuselage is built around the forward and intermediate weapon bays. Each of these can carry a single Mk1 rotary launcher (as used in the B-52G/H) with 8 SRAMs. The forward fuel cells are wrapped around the top of the bays while the ‘glove’ section mounts a group of ECM antennas. The structure is primarily of A 1 alloys. The forward intermediate fuselage attaches to the massive diffusion bonded 6A1-4V Titanium al!OY wing carry through structure. This assembly supports the wins pivots and the steel main undercarriage structure, it is designed to allow safe flight in the event of one of its main plates suffering catastrophic failure.

The Aft Intermediate Fuselage contains the main undercarriage wells, the environmental control systems and the aft weapon bay. It supports the engine nacelle bearers and is primarily an Al alloy structure. The fuselage is area-ruled. The nacelles each carry two GE F101 30,000lb class afterburning fans and an APU for the pair. The inlets were one of the areas requiring careful tradeoff to optimising for both low-level subsonic and high-altitude supersonic flight. Initially, a mixed compression inlet was later changed to an eternal precision intake saving 1,400Ib of structure while improving subsonic performance with a moderate penalty at supersonic speeds (the

sensItIvIty of fans to flow distortion caused major problems in the F-111 programme). The configuration conceals the from lookdown radars, the nacelle structure is mainly Al alloy with some Titanium about the tailpipes.

The wings are built about an Al alloy main box which also serves as an integral fuel tank. The pivot attachment plates are Ti alloy, full span slats, large flaps and outboard upper surface spoilers are employed. The wings can pivot from 15° to 67. 5°, the latter used at low-level or supersonic dash speeds.

The Aft Fuselage contains the aft fuel cell, an avionics bay and supports the tail structure. As another design tradeoff the horizontal tail was raised from the aft fuselage onto the vertical stabiliser increasing weight and reducing stability but gaining fuselage volume for avionics and moving the surfaces away from the hostile exhaust stream. The rudder is split into three sections, the lowest being coupled into the LARC system. The tail radome conceals ECM antennas.

The GE F101-GE-100 Turbofan

The B-1A is powered by four F101 reheated turbofans. The F101 is a two-spool engine. The low-pressure spool with variable inlet guide vanes and two stages is driven by a two-stage turbine, while the high-pressure spool has nine stages, the first three of which have variable stators and is driven by a cooled single stage turbine. Annular combustors are used and the afterburner stage is fitted with convergent divergent nozzles. The bypass ratio is 2:1, mass flow 350Ib/sec, pressure ratio 26. 5:1 and weight around 4,000Ib. The F101-GE-100 delivers 17,000lb in military power and about 30,000lb in reheat.

Systems

The complexity of the B-1A rules out an exhaustive review of the systems, although some items are noteworthy. The APUs are each attached to a pair of engines and are tied into a rapid start system which brings the engines automatically up to idle upon depressing a switch on the forward undercarriage leg. This facilitates escape from a strip about to be hit by SLBMs. The swing-wing configuration of the B-1 causes shifts in the aircraft’s centres of gravity and pressure with sweep angle and fuel state. A CG management system is installed which pumps fuel between the fore and aft cells to maintain the CG within specified limits. The 8-1A is fitted with a 4,000psi quadruply redundant hydraulic system, an advance on the 3,000psi systems of the day.

The primary sensor is a GE APQ-144 Attack Radar which is complemented by a Texas Instruments APO-146 Terrain Following Radar, both of which are installed in the F-111F. A low drift dual redundant Litton LN-15S inertial system is used, complemented with a Singer-Kearfott Doppler set and Honeywell low altitude radar altimeter. The core of the OAS are a pair of Singer-Kearfott SKC-2070 digital computers one of which handles navigation and the other the weapon system.

Details of the AIL-Cutler-Hammer defensive avionic suite were not publicised although the system eventually evolved into the 8-1 B’s highly integrated ALQ-161 RFS/ECM (radio frequency surveillance/electronic countermeasures) system, an advance on earlier equipment by virtue of complete integration of RHAW and jamming equipment in a centrally coordinated system.

The combination of the B-1A’s low-level performance, sophisticated RHAW/ECM and radar cross section an order of magnitude significantly lower than that of the B-52 represented a quantum leap in capability without the application of any special stealth techniques in the design. These, together with a completely upgraded avionic system and significant structural changes, resulted in the production 8-1B aircraft, the subject of Part II which will be featured in our January edition.