Eko Triyanggono: Bomber Aircraft

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B-1 Lancer

The Rockwell (now part of Boeing) B-1 Lancer is a four-engine variable-sweep wing strategic bomber used by the United States Air Force (USAF). It was first envisioned in the 1960s as a supersonic bomber with Mach 2 speed, and sufficient range and payload to replace the Boeing B-52 Stratofortress. It was developed into the B-1B, primarily a low-level penetrator with long range and Mach 1.25 speed capability at high altitude.

Designed by Rockwell International, the bomber's development was delayed multiple times over its history, as the theory of strategic balance changed from flexible response to massive retaliation and back again. This change in stance repeatedly demanded then ignored the need for manned bombers. The initial B-1A version was developed in the early 1970s, but its production was canceled, and only four prototypes were built. The need for a new platform once again surfaced in the early 1980s, and the aircraft resurfaced as the B-1B version with the focus on low-level penetration bombing. However by this point development of stealth technology was promising an aircraft of dramatically improved capability. Production went ahead as this version would be operational before the "Advanced Technology Bomber", during a period when the B-52 would be increasingly vulnerable. The B-1B entered service in 1986 with the USAF Strategic Air Command as a nuclear bomber.

In the 1990s, the B-1B was converted to conventional bombing use. It first served in combat during Operation Desert Fox in 1998 and again during the NATO action in Kosovo the following year. The B-1B has supported U.S. and NATO military forces in Afghanistan and Iraq. The Lancer is the supersonic component of the USAF's long-range bomber force, along with the subsonic B-52 and Northrop Grumman B-2 Spirit. The bomber is commonly called the "Bone" (originally from "B-One"). With the retirement of the General Dynamics/Grumman EF-111A Raven in 1998 and the Grumman F-14 Tomcat in 2006, the B-1B is the U.S. military's only active variable-sweep wing aircraft. The B-1B is expected to continue to serve into the 2030s, when it is to be supplemented by the Next-Generation Bomber.

Design

The B-1's variable-sweep wings and thrust-to-weight ratio provide it with better takeoff performance, allowing it to use more runways than previous bombers. The length of the aircraft presented a flexing problem due to air turbulence at low altitude. To alleviate this, Rockwell included small triangular fin control surfaces or vanes near the nose on the B-1. The B-1's Structural Mode Control System rotates the vanes automatically to counteract turbulence and smooth out the ride.

Engines

The B-1A's engine was modified slightly to produce the GE F101-102 for the B-1B, with an emphasis on durability, and increased efficiency. The core of this engine has since been re-used in several other engine designs, including the GE F110 which has seen use in the F-14 Tomcat, F-15K/SG variants and most recent versions of the General Dynamics F-16 Fighting Falcon. It is also the basis for the non-afterburning GE F118 used in the B-2 Spirit and the U-2S. However its greatest success was forming the core of the extremely popular CFM56 civil engine, which can be found on some versions of practically every small-to-medium sized airliner. The nose gear cover door has controls for the auxiliary power units (APUs), which allow for quick starts of the APUs upon order to scramble.

Avionics

The B-1's defensive electronics include the Eaton AN/ALQ-161A radar warning and defensive jamming equipment, which has three sets of antennas; one at the front base of each wing and the third rear-facing in the tail radome. The ALQ-161 is linked to a total of eight AN/ALE-49 flare dispensers located on top behind the canopy, which are handled by the AN/ASQ-184 avionics management system. Each AN/ALE-49 dispenser has a capacity of 12 MJU-23A/B flares. The MJU-23A/B flare is one of the world's largest infrared countermeasure flares at a weight of over 3.3 pounds (1.5 kg). The B-1 has also been equipped to carry the ALE-50 Towed Decoy System.

Also aiding the B-1's survivability is its relatively low radar cross-section (RCS). Although not technically a stealth aircraft in a comprehensive sense, thanks to the aircraft's structure, serpentine intake paths and use of radar-absorbent material its RCS is about 1/50th that of the B-52 (probably about 26 ft² or 2.4 m²), although the Lancer is not substantially smaller in mass than the Stratofortress.

Variants

B-1A

The B-1A was the original B-1 design with variable engine intakes and Mach 2.2 top speed. Four prototypes were built; no production units were manufactured.

B-1B

The B-1B is a revised B-1 design with reduced radar signature and a top speed of Mach 1.25. It was otherwise optimized for low-level penetration. A total of 100 B-1Bs were produced.

B-1R

The B-1R is a proposed upgrade of existing B-1B aircraft. The B-1R (R for "regional") would be fitted with advanced radars, air-to-air missiles, and new Pratt & Whitney F119 engines. This variant would have a top speed of Mach 2.2, but with 20% less range.

Existing external hardpoints would be modified to allow multiple conventional weapons to be carried, increasing overall loadout. For air-to-air defense, an Active Electronically Scanned Array (AESA) radar would be added and some existing hardpoints modified to carry air-to-air missiles. If needed the B-1R could escape from unfavorable air-to-air encounters with its Mach 2+ speed. Few aircraft are currently capable of sustained speeds over Mach 2.

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B-2 Spirit (Stealth Bomber) Design

The B-2 Spirit (Stealth Bomber) was developed to take over the USAF's vital penetration missions, able to travel deep into enemy territory to deploy their ordnance, which could include nuclear weapons. The B-2 is a flying wing aircraft, meaning it has no fuselage or tail. The blending of low-observable technologies with high aerodynamic efficiency and large payload gives the B-2 significant advantages over previous bombers. Low observability provides a greater freedom of action at high altitudes, thus increasing both range and field of view for onboard sensors. The U.S. Air Force reports its range as approximately 6,000 nautical miles (6,900 mi; 11,000 km).

Due to the aircraft's complex flight characteristics and design requirements to maintain very-low visibility to multiple means of detection, both the development and construction of the B-2 required pioneering use of computer-aided design and manufacturing technologies. Northrop Grumman is the B-2's prime contractor; other contributing subcontractors include Boeing, Raytheon (formerly Hughes Aircraft), G.E. and Vought Aircraft. The B-2 bears a resemblance to earlier Northrop aircraft, the YB-35 and YB-49 were both flying wing bombers that had been cancelled in development in the early 1950s; allegedly for political reasons.

The B-2 has a crew of two: a pilot in the left seat, and mission commander in the right; the B-2 has provisions for a third crew member if needed. For comparison, the B-1B has a crew of four and the B-52 has a crew of five. The B-2 is highly automated and, unlike most two-seat aircraft, one crew member can sleep, use a toilet or prepare a hot meal while the other monitors the aircraft; extensive sleep cycle and fatigue research was conducted to improve crew performance on long sorties.

Armaments and equipment

The B-2, in the envisaged Cold War scenario, was to perform deep-penetrating nuclear strike missions, making use of its stealthy capabilities to avoid detection and interception throughout missions. There are two internal bomb bays in which munitions are stored either on a rotary launcher or two bomb-racks; the carriage of the weapons loadouts internally results in less radar visibility than externally mounting of munitions. Nuclear ordnance includes the B61 and B83 nuclear bombs; the AGM-129 ACM cruise missile was also intended for use on the B-2 platform.

It was decided, in light of the dissolution of the Soviet Union, to equip the B-2 for convention precision attacks as well as for the strategic role of nuclear-strike. The B-2 features a sophisticated GPS-Aided Targeting System (GATS) that uses the aircraft's APQ-181 synthetic aperture radar to map out targets prior to deployment of GPS-aided bombs (GAMs), later superseded by the Joint Direct Attack Munition (JDAM). In the B-2's original configuration, up to 16 GAMs or JDAMs could be deployed; an upgrade program in 2004 raised the maximum carriable capacity to 80 JDAMs.

The B-2 has various conventional weapons in its arsenal, able to equip Mark 82 and Mark 84 bombs, CBU-87 Combined Effects Munitions, GATOR mines, and the CBU-97 Sensor Fuzed Weapon. In July 2009, Northrop Grumman reported the B-2 was compatible with the equipment necessary to deploy the 30,000 lb (14,000 kg) Massive Ordnance Penetrator (MOP), which is intended to attack reinforced bunkers; up to two MOPs could be equipped in the B-2's bomb bays, the B-2 is the only platform compatible with the MOP as of 2012. As of 2011, the AGM-158 JASSM cruise missile is an upcoming standoff munition to be deployed on the B-2 and other platforms.

Avionics and systems

In order to make the B-2 more effective than any previous bomber, it has integrated many advanced and modern avionics systems into its design, these have been modified and improved in light of the switch to conventional warfare missions. The B-2 features the low probability of intercept AN/APQ-181 multi-mode radar, a fully digital navigation system that is integrated with terrain-following radar and Global Positioning System (GPS) guidance, and a Defensive Management System (DMS) to inform the flight crew against possible threats. The onboard DMS is capable of automatically assessing the detection capabilities of identified threats and indicated targets.

For safety and fault-detection purposes, an on-board test system is interlinked with the majority of avionics on the B-2 to continuously monitor the performance and status of thousands of components and consumables; it also provides post-mission servicing instructions for ground crews. In 2008, many of the standalone distributed computers on board the B-2, including the primary flight management computer, were being replaced by a single integrated system.

In addition to periodic software upgrades and the introduction of new radar-absorbent materials across the fleet, the B-2 has had several major upgrades to its avionics and combat systems. For battlefield communications, both Link-16 and a high frequency satellite link have been installed, compatibility with various new munitions has been undertaken, and the AN/APQ-181 radar's operational frequency was shifted in order to avoid interference with other operator's equipment. The upgraded radar features entirely replaced arrays by those of a newer design, the AN/APQ-181 is now an Active Electronically Scanned Array (AESA) radar.

Flight controls

In order to address the inherent flight instability of a flying wing aircraft, the B-2 uses a complex quadruplex computer-controlled fly-by-wire flight control system, that can automatically manipulate flight surfaces and settings without direct pilot inputs in order to maintain aircraft stability. The flight computer receives information on external conditions such as the aircraft's current air speed and angle of attack via pitot-static sensing plates, as opposed to traditional pitot tubes which would negatively affect the aircraft's stealth capabilities. The flight actuation system incorporates both hydraulic and electrical servoactuated components, it was designed with a high level of redundancy and fault-diagnostic capabilities.

Northrop had investigated several means of applying directional control that would least infringe on the aircraft's radar profile, eventually settling on a combination of split brake-rudders and differential thrust. Engine thrust became a key element of the B-2's aerodynamic design process early on; thrust not only affects drag and lift but pitching and rolling motions as well. Four pairs of control surfaces are located along the wing's trailing edge; while most surfaces are used throughout the aircraft's flight envelope, the inner elevons are normally only in use at slow speeds, such as landing. To avoid potential contact damage during takeoff and to provide a nose-down pitching attitude, all of the elevons remain drooped during takeoff until a high enough airspeed has been attained.

Stealth

The B-2's low-observable, or "stealth", characteristics enable the safe penetration of sophisticated anti-aircraft defenses and to attack even heavily defended targets. This stealth comes from a combination of reduced acoustic, infrared, visual and radar signatures to evade the various detection systems that could be used to detect and be used to direct attacks against an aircraft. The majority of the B-2 is made out of a carbon-graphite composite material that is stronger than steel and lighter than aluminium, perhaps most crucially it also absorbs a significant amount of radar energy. Reportedly, the B-2 Spirit has a radar signature of about 0.1 m2.

In contrast to the flat surfaces of the earlier F-117 Nighthawk, the B-2 is composed of many curved and rounded surfaces across its exposed airframe to deflect radar beams, additional reduction in its radar signature was achieved by the use of various radar-absorbent materials (RAM) to absorb and neutralise radar beams. The B-2's clean, low-drag flying wing configuration not only gave it exceptional range, but was also beneficial to reducing its radar profile as well.

Another design feature is the placement of the engines, which are buried within the wing to conceal the engines' fans and minimize thermal visibility of the exhaust. The original design had tanks for a contrail-inhibiting chemical, but this was replaced in production aircraft by a contrail sensor that alerts the crew as to when they should change altitude. To reduce optical visibility during daylight operations, the B-2 is painted in an anti-reflective paint.

Innovations such as alternate high-frequency material (AHFM) and automated material application methods were also incorporated into the aircraft to enhance its radar-absorbent properties and lower maintenance requirements. In early 2004, Northrop Grumman began applying a newly-developed AHFM to operational B-2s. In order to protect the operational integrity of its sophisticated radar absorbent material and coatings, each B-2 is kept inside a climate-controlled hangar large enough to accommodate its 172-foot (52 m) wingspan.

B-1 Lancer Bomber

Design

Engines

Avionics

Variants

B-1A

The B-1A was the original B-1 design with variable engine intakes and Mach 2.2 top speed. Four prototypes were built; no production units were manufactured.

B-1B

The B-1B is a revised B-1 design with reduced radar signature and a top speed of Mach 1.25. It was otherwise optimized for low-level penetration. A total of 100 B-1Bs were produced.

B-1R

Rockwell B-1 Lancer

Design

The B-1 has a blended wing body configuration, with variable-sweep wing, four turbofan engines, and triangular fin control surfaces. The wings can sweep from 15 degrees to 67.5 degrees (full forward to full sweep). Forward-swept wing settings are used for takeoff, landings and high-altitude maximum cruise. Aft-swept wing settings are used in high subsonic and supersonic flight. The wings of the B-1B originally were cleared for use at settings of 15, 25, 55 and 67.5 degrees. The 45-degree setting was later cleared in 1998–99 timeframe. The B-1's variable-sweep wings and thrust-to-weight ratio provide it with better takeoff performance, allowing it to use more runways than previous bombers. The length of the aircraft presented a flexing problem due to air turbulence at low altitude. To alleviate this, Rockwell included small triangular fin control surfaces or vanes near the nose on the B-1. The B-1's Structural Mode Control System rotates the vanes automatically to counteract turbulence and smooth out the ride.

Unlike the B-1A, the B-1B made no attempt at Mach 2+ speeds. Its maximum speed is Mach 1.25 (about 950 mph or 1,530 km/h at altitude), but its low-level speed increased to Mach 0.92 (700 mph, 1,130 km/h). Technically, the current version of the aircraft can exceed its speed restriction, but not without risking potential damage to its structure and air intakes. To help lower its radar cross section (RCS), the B-1B uses serpentine air intake ducts and fixed intake ramps, which limit its speed compared to the B-1A. Vanes in the intake ducts serve to deflect and shield radar emissions from the highly reflective engine compressor blades. The B-1A's engine was modified slightly to produce the GE F101-102 for the B-1B, with an emphasis on durability, and increased efficiency. The core of this engine has since been re-used in several other engine designs, including the GE F110 which has seen use in the F-14 Tomcat, F-15K/SG variants and most recent versions of the General Dynamics F-16 Fighting Falcon. It is also the basis for the non-afterburning GE F118 used in the B-2 Spirit and the U-2S. However its greatest success was forming the core of the extremely popular CFM56 civil engine, which can be found on some versions of practically every small-to-medium sized airliner. The nose gear cover door has controls for the auxiliary power units (APUs), which allow for quick starts of the APUs upon order to scramble.

The B-1's main computer is the IBM AP-101, which is also used on the Space Shuttle orbiter and the B-52 bomber. The computer is programmed with the JOVIAL programming language. The Lancer's offensive avionics include the Westinghouse (now Northrop Grumman) AN/APQ-164 forward-looking offensive passive electronically scanned array radar set with electronic beam steering (and a fixed antenna pointed downward for reduced radar observability), synthetic aperture radar, ground moving target indicator (MTI), and terrain-following radar modes, Doppler navigation, radar altimeter, and an inertial navigation suite. The B-1B Block D upgrade added a Global Positioning System (GPS) receiver beginning in 1995. The B-1's defensive electronics include the Eaton AN/ALQ-161A radar warning and defensive jamming equipment, which has three sets of antennas; one at the front base of each wing and the third rear-facing in the tail radome. The ALQ-161 is linked to a total of eight AN/ALE-49 flare dispensers located on top behind the canopy, which are handled by the AN/ASQ-184 avionics management system. Each AN/ALE-49 dispenser has a capacity of 12 MJU-23A/B flares. The MJU-23A/B flare is one of the world's largest infrared countermeasure flares at a weight of over 3.3 pounds (1.5 kg). The B-1 has also been equipped to carry the ALE-50 Towed Decoy System. Also aiding the B-1's survivability is its relatively low radar cross-section (RCS). Although not technically a stealth aircraft in a comprehensive sense, thanks to the aircraft's structure, serpentine intake paths and use of radar-absorbent material its RCS is about 1/50th that of the B-52 (probably about 26 ft² or 2.4 m²), although the Lancer is not substantially smaller in mass than the Stratofortress.

Operational History

Strategic Air Command

The second B-1B, "The Star of Abilene", was the first B-1B delivered to the USAF Strategic Air Command (SAC) in June 1985. Initial operational capability was reached on 1 October 1986 and the B-1B was placed on nuclear alert status. The B-1 received the official name "Lancer" on 15 March 1990. However, the bomber has been commonly called the "Bone"; a nickname that appears to stem from an early newspaper article on the aircraft wherein its name was phonetically spelled out as "B-ONE" with the hyphen inadvertently omitted.

In late 1990 engine fires in two Lancers caused the grounding of the fleet. The cause was traced back to problems in the first-stage fan, the aircraft were placed on "limited alert"; in other words, they were grounded unless a nuclear war broke out. Following inspections and repairs they were returned to duty beginning on 6 February 1991. Due to the engine problems, the B-1B was effectively sidelined in the First Gulf War. Originally designed strictly for nuclear war, the B-1's development as an effective conventional bomber was delayed until the 1990s. The collapse of the Soviet Union had brought the B-1's nuclear role into question, leading to President George H. W. Bush ordering a $3 billion conventional refit. By 1991, the B-1 had a fledgling conventional capability, forty of them able to drop the 500 lb (230 kg) Mk-82 General Purpose (GP) bomb, although mostly from low altitude. Despite being cleared for this role, the problems with the engines precluded their use in Operation Desert Storm. B-1s were primarily reserved for strategic nuclear strike missions at this time, providing the role of airborne nuclear deterrent against the Soviet Union. The B-52 was more suited to the role of conventional warfare and it was used by coalition forces instead. After the de-activation of Strategic Air Command (SAC) and the establishment of the Air Combat Command (ACC) in 1992, the B-1 developed a greater conventional weapons capability. Part of this development was the start-up of the US Air Force Weapons School B-1 Division. In 1994, two additional B-1 bomb wings were also created in the Air National Guard, with former fighter wings in the Kansas Air National Guard and the Georgia Air National Guard converting to the aircraft. By the mid-1990s, the B-1 could employ GP weapons as well as various CBUs. By the end of the 1990s, with the advent of the "Block D" upgrade, the B-1 boasted a full array of guided and unguided munitions. The B-1B no longer carries nuclear weapons; its nuclear capability was disabled by 1995 with the removal of nuclear arming and fuzing hardware.

Conventional Role

Operationally, the B-1 was first used in combat in support of operations against Iraq, during Operation Desert Fox in December 1998, employing unguided GP weapons. B-1s have been subsequently used in Operation Allied Force (Kosovo) and, most notably, in Operation Enduring Freedom in Afghanistan and the 2003 invasion of Iraq. The B-1's role in Operation Allied Force has been criticized as the aircraft was not used until after enemy defenses had been suppressed by aircraft like the older B-52 it was intended to replace. The B-1 has deployed an array of conventional weapons in war zones, most notably the GBU-31, 2,000 lb (900 kg) Joint Direct Attack Munition (JDAM). JDAM munitions were heavily used by the B-1 over Iraq, notably on 7 April 2003 in an unsuccessful attempt to kill Saddam Hussein and his two sons. At the height of the Iraq War, a B-1 was permanently airborne to provide rapid precision bombardment upon important targets as intelligence identified them. During Operation Enduring Freedom, the B-1 was able to raise its mission capable rate to 79%.

The B-1 has higher survivability and speed when compared to the older B-52, which it was intended to replace. It also holds 61 FAI world records for speed, payload, distance, and time-to-climb in different aircraft weight classes. In November 1983, three B-1Bs set a long distance record for the aircraft, which demonstrated its ability to conduct extended mission lengths to strike anywhere in the world and return back to base without any stops. The National Aeronautic Association recognized the B-1B for completing one of the 10 most memorable record flights for 1994. Of the 100 B-1Bs built, 93 remained in 2000 after losses in accidents. In June 2001, the Pentagon sought to place a third of its then fleet of 93 into reserve; this proposal resulted in several Air National Guard officers and members of Congress lobbying against the proposal, including the drafting of an amendment to prevent such cuts. The 2001 proposal was intended to allow money to be diverted to further upgrades to the remaining B-1Bs, such as computer modernization. In 2003, accompanied by the removal of B-1Bs from the two bomb wings in the Air National Guard, the USAF decided to retire 33 aircraft to concentrate its budget on maintaining availability of remaining B-1Bs. In 2004 a new appropriation bill called for some of the retired aircraft to return to service, and the USAF returned seven mothballed bombers to service to increase the fleet to 67 aircraft.

On 14 July 2007, the Associated Press reported on the growing USAF presence in Iraq as a result of "surge" in forces. Also mentioned is the reintroduction of B-1Bs to be a close-at-hand "platform" to support Coalition ground forces. B-1s have been used in Iraq and Afghanistan. Since 2008 B-1s have been used there in an "armed overwatch" role. They loiter over the region maintaining surveillance, ready to deliver guided bombs in support of ground troops if contacted. The B-1B underwent a series of flight tests using a 50/50 mix of synthetic and petroleum fuel; on 19 March 2008, a B-1B from Dyess Air Force Base, Texas, became the first US Air Force aircraft to fly at supersonic speed using a synthetic fuel during a flight over Texas and New Mexico. This was conducted as part of an ongoing Air Force testing and certification program to reduce reliance on traditional oil sources. On 4 August 2008, a B-1B flew the first Sniper Advanced Targeting Pod equipped combat sortie where the crew successfully targeted enemy ground forces and dropped a GBU-38 guided bomb in Afghanistan. The USAF had 65 B-1Bs in service in September 2010, split between four squadrons organized into two Bomb Wings: the 7th Bomb Wing at Dyess AFB, Texas, and the 28th Bomb Wing at Ellsworth AFB, South Dakota. In March 2011, B-1Bs from Ellsworth Air Force Base attacked undisclosed targets in Libya as part of Operation Odyssey Dawn. With upgrades to keep the B-1 viable, the Air Force may keep the bomber in service until approximately 2038. Despite upgrades, the B-1 has repair and cost issues resulting from its age. For every flight hour it needs 48.4 hours of repair. The fuel, repairs and other needs for a 12-hour mission costs $720,000 as of 2010. The $63,000 cost per flight hour is, however, less than the $72,000 for the B-52 and the $135,000 of the B-2. In June 2010, senior US Air Force officials met to consider retiring the entire fleet to meet budget cuts. It is expected to be supplemented by the Next Generation Bombers in the 2020s. And in the meantime its "capabilities are particularly well-suited to the vast distances and unique challenges of the Pacific region, and we'll continue to invest in, and rely on, the B-1 in support of the focus on the Pacific" as part of President Obama's "Pivot to East Asia".

Boeing B-52 Stratofortress Design

In November 1959 SAC initiated the Big Four modification program (also known as Modification 1000) for all operational B-52s except early B models, intended to improve the aircraft's combat capabilities in the changing strategic environment. The program was completed by 1963. The four modifications were the ability to launch AGM-28 Hound Dog standoff nuclear missiles and ADM-20 Quail decoys, an advanced electronic countermeasures (ECM) suite, and upgrades to perform the all-weather, low-altitude (below 500 feet or 150 m) interdiction in the face of advancing missile air defenses. The switch to low-altitude flight was estimated to accelerate structural fatigue by at least a factor of eight, which required costly repairs to extend service life. The first program to counter structural fatigue was the three-phase High Stress program in the early 1960s, which enrolled aircraft at 2,000 flying hours. Follow-up programs addressing fatigue were conducted, such as a 2,000-hour service life extension to select airframes in 1966–1968, and the extensive Pacer Plank reskinning, completed in 1977. The wet wing introduced on G and H models was even more susceptible to fatigue due to experiencing 60% more stress during flight than the old wing. The wings were modified by 1964 under ECP 1050. This was followed by a fuselage skin and longeron replacement (ECP 1185) in 1966, and the B-52 Stability Augmentation and Flight Control program (ECP 1195) in 1967. Fuel leaks due to deteriorating Marman clamps continued to plague all variants of the B-52. To this end, the aircraft were subjected to Blue Band (1957), Hard Shell (1958), and finally QuickClip (1958) programs. The latter fitted safety straps which prevented catastrophic loss of fuel in case of clamp failure. For a study for the U.S. Air Force in the mid-1970s, Boeing investigated replacing the engines, changing to a new wing, and other improvements to upgrade B-52G/H aircraft as an alternative to the B-1A, then in development. Boeing later suggested re-engining the B-52H fleet with the Rolls-Royce RB211 535E-4. This would involve replacing the eight Pratt & Whitney TF33s (total thrust 8 × 17,000 lb) with four RB211s (total thrust 4 × 37,400 lb); which would increase range and reduce fuel consumption, at a cost of approximately US$2.56 billion for the whole fleet (71 aircraft at $36 million each). A Government Accountability Office study concluded that Boeing's estimated savings of US$4.7 billion would not be realized and that it would cost US$1.3 billion over keeping the existing engines; citing significant up-front procurement and re-tooling expenditure, and the RB211's higher maintenance cost. The GAO report was subsequently disputed in a Defense Sciences Board report in 2003; the Air Force was urged to re-engine the aircraft without delay. Further, the DSB report stated the program would have significant savings, reduce greenhouse gas emissions, and increase aircraft range and endurance; in line with the conclusions of a separate Congress-funded study conducted in 2003. The re-engining has not been approved as of 2010. In September 2006, the B-52 became one of the first US military aircraft to fly using alternative fuel. It took off from Edwards Air Force Base with a 50/50 blend of Fischer-Tropsch process (FT) synthetic fuel and conventional JP-8 jet fuel which was burned in two of the eight engines. On 15 December 2006, a B-52 took off from Edwards with the synthetic fuel powering all eight engines, the first time an Air Force aircraft was entirely powered by the blend. The seven hour flight was considered a success. This program is part of the Department of Defense Assured Fuel Initiative, which aims to reduce crude oil usage and obtain half of its aviation fuel from alternative sources by 2016. On 8 August 2007, Air Force Secretary Michael Wynne certified the B-52H as fully approved to use the FT blend. With the success upon the B-52, the Air Force intends to certify every airframe in its inventory to use the fuel by 2011.

Avionics

AN/ASQ-38 bombing navigational computer and the terrain computer. The MADREC (Malfunction Detection and Recording) upgrade fitted to most aircraft by 1965 could detect failures in avionics and weapons computer systems, and was essential in monitoring the Hound Dog missiles. The electronic countermeasures capability of the B-52 was expanded with Rivet Rambler (1971) and Rivet Ace (1973). To improve safe day and night operations at low altitude, the AN/ASQ-151 Electro-Optical Viewing System (EVS), which consisted of a Low Light Level Television (LLLTV) and a Forward looking infrared (FLIR) system mounted in blisters under the noses of B-52Gs and Hs between 1972 and 1976. The navigational capabilities of the B-52 were later augmented with the addition of GPS in the 1980s. The IBM AP-101, also used on the B-1B Lancer bomber and the Space Shuttle, was the B-52's main computer. In 2007 the LITENING targeting pod was fitted, which increases the combat effectiveness of the aircraft during day, night and poor weather conditions in the attack of ground targets with a variety of standoff weapons, using laser guidance under the guidance, a high resolution forward-looking infrared sensor (FLIR) and a CCD camera used to obtain target imagery. LITENING pods have been fitted to a wide variety of other US aircraft, such as the McDonnell Douglas F/A-18 Hornet, the General Dynamics F-16 Fighting Falcon and the McDonnell Douglas AV-8B Harrier II.

Weapons

The ability to carry up to 20 AGM-69 SRAM nuclear missiles was added to G and H models, starting in 1971. To further improve the B-52's offensive ability, Air Launched Cruise Missiles (ALCMs) were fitted. After testing of both the Air Force-backed Boeing AGM-86 and the Navy-backed General Dynamics AGM-109 Tomahawk, the AGM-86B was selected for operation by the B-52 (and ultimately by the B-1 Lancer). A total of 194 B-52Gs and Hs were modified to carry AGM-86s, carrying 12 missiles on underwing pylons, with 82 B-52Hs further modified to carry another eight missiles on a rotary launcher fitted in the aircraft's bomb-bay. To conform with the requirements of the SALT II Treaty for cruise missile capable aircraft to be readily identified by reconnaissance satellites, the cruise missile armed B-52Gs were modified with a distinctive wing root fairing. As all B-52Hs were assumed to be modified, no visual modification of these aircraft was required. In 1990, the stealthy AGM-129 ACM cruise missile entered service; although intended to replace the AGM-86, a high cost and the Cold War's end led to only 450 being produced; unlike the AGM-86, no conventional (non-nuclear) version was built. The B-52 was to have been modified to utilize Northrop Grumman's AGM-137 TSSAM weapon; however, the missile was canceled due to development costs. Those B-52Gs not converted as cruise missile carriers were subject to a series of modifications to improve their conventional bombing capability, being fitted with a new Integrated Conventional Stores Management System (ICSMS) and new underwing pylons which were able to be fitted with larger bombs or other stores than could be carried on the external pylons. 30 B-52s were further modified to carry up to 12 AGM-84 Harpoon anti-ship missiles each, while 12 B-52Gs were fitted to carry the AGM-142 Have Nap stand-off air-to-ground missile. When the B-52G was retired in 1994, an urgent scheme was launched to restore an interim Harpoon and Have nap capability (the Have Nap missile was only carried by the B-52, and allowed stand-off attacks on targets while maintaining a "man-in-the-loop" of the guidance system), the four aircraft being modified to carry Harpoon and four to carry Have Nap under the Rapid Eight program. The Conventional Enhancement Modification (CEM) program gave the B-52H a more comprehensive conventional weapons capability, adding the modified underwing weapon pylons used by conventional-armed B-52Gs, Harpoon and Have Nap, and the capability to carry new-generation weapons including the Joint Direct Attack Munition and Wind Corrected Munitions Dispenser guided bombs, the AGM-154 glide bomb and the AGM-158 JASSM missile. The CEM program also introduced new radios, integrated Global Positioning System into the aircraft's navigation system and replaced the under-nose FLIR with a more modern unit. Forty-seven B-52Hs were modified under the CEM program by 1996, with 19 more by the end of 1999.