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B52 Stratofortress

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 The Boeing B-52 Stratofortress is a long-range, subsonic, jet-powered strategic bomber designed and built by Boeing and operated by the United States Air Force (USAF).

Beginning with the successful contract bid on 5 June 1946, the B-52 design evolved from a straight-wing aircraft powered by six turboprop engines to the final prototype YB-52 with eight turbojet engines and swept wings. The aircraft first flew on 15 April 1952 with "Tex" Johnston as pilot. Built to carry nuclear weapons for Cold War-era deterrence missions, the B-52 Stratofortress replaced the Convair B-36. Although a veteran of a number of wars, the Stratofortress has dropped only conventional munitions in combat. The B-52 carries up to 70,000 pounds (32,000 kg) of weapons. Its Stratofortress name is rarely used outside of official contexts; it has been referred to by Air Force personnel as the BUFF (Big Ugly Fat Fucker/Fellow).

The B-52 has been in active service with the USAF since 1955. The bombers flew under the Strategic Air Command (SAC) until it was disestablished in 1992 and its aircraft absorbed into the Air Combat Command (ACC). This remained the case until February 2010 when all B-52 Stratofortress and B-2 Spirit aircraft were transferred from ACC to the recently established Air Force Global Strike Command (AFGSC). Superior performance at high subsonic speeds and relatively low operating costs have kept the B-52 in service despite the advent of later aircraft, including the Mach-3 North American XB-70 Valkyrie, the supersonic Rockwell B-1B Lancer, and the stealthy Northrop Grumman B-2 Spirit. The B-52 marked its 50th anniversary of continuous service with its original primary operator in 2005. (Other aircraft with similarly long service include the English Electric Canberra, the Tupolev Tu-95, the Lockheed C-130 Hercules, the Boeing KC-135 Stratotanker, and the Lockheed U-2.).

Design
Upgrades and modificationsIn 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:

1.Ability to perform all-weather, low-altitude (below 500 feet or 150 m) interdiction as a response to advancements in Soviet Union's missile defenses. The low-altitude flights were estimated to accelerate structural fatigue by at least a factor of eight, requiring costly repairs to extend service life.
2.Ability to launch AGM-28 Hound Dog standoff nuclear missiles
3.Ability to launch ADM-20 Quail decoys
4.An advanced electronic countermeasures (ECM) suite

The ability to carry up to 20 AGM-69 SRAM nuclear missiles was added to G and H models starting in 1971. 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.

Ongoing problems with advanced avionics were addressed in the Jolly Well program, completed in 1964, which improved components of the 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). The navigational capabilities of the B-52 were later augmented with the addition of GPS.

To improve safe day and night operations at low altitude, the AN/ASQ-151 Electro-Optical Viewing System (EVS), consisting of a Low Light Level Television (LLLTV) and a Forward Looking Infra-Red (FLIR) system mounted in blisters under the noses of B-52Gs and Hs between 1972 and 1976. 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 originally intended to replace the AGM-86, its high cost and the end of the Cold War stopped production after only 450 were made. Unlike the AGM-86, no conventional (that is, non-nuclear) armed version was built. The B-52 was to have been modified to utilize Northrop Grumman's AGM-137 weapon; however, the missile was canceled due to development costs.

The aircraft landed safely.Structural fatigue, exacerbated by the change to low-altitude missions, was first dealt with in the early 1960s by the three-phase High Stress program which enrolled aircraft at 2,000 flying hours. This was followed by 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.

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). The RR engines will increase the range and payload of the fleet and reduce fuel consumption. However, the procurement would cost approximately US$2.56 billion for the whole fleet (US$36 million × 71 aircraft). 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. The higher cost was blamed on significant up-front procurement expenditure, necessary re-tooling, and the RB211's higher maintenance cost. The GAO report was subsequently disputed in a Defense Sciences Board report in 2003 and revised in 2004 that identified numerous errors in the prior evaluation of the Boeing proposal, and urged the Air Force to re-engine the aircraft without delay. Further, the DSB report stated the program would save substantial funds, reduce greenhouse gas emissions, and increase aircraft range and endurance. This finding was in line with the results of a Congressionally funded US$3M program office study conducted in 2003. The re-engining has not been approved as of 2010.

Lower deck of the B-52 dubbed the battle stationIn 2007 the LITENING targeting pod was fitted, increasing 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.

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, tail number 61-0034 Checkmate, 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, a Pentagon-led aim to reduce the usage of crude oil from foreign producers 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 test and certify every airframe in its inventory to use the fuel by 2011.

Future of the B-52Even while the Air Force works on its Next-Generation Bomber and 2037 Bomber projects, it intends to keep the B-52H in service until at least 2040, 78 years after production ended, 85 years after it entered service. This will be an unprecedented length of service for a military aircraft. B-52s are periodically refurbished at USAF maintenance depots such as Tinker Air Force Base, Oklahoma.

The USAF continues to rely on the B-52 because it remains an effective and economical heavy bomber, particularly in the type of missions that have been conducted since the end of the Cold War against nations that have limited air defense capabilities. The B-52's capacity to "loiter" for extended periods over (or even well outside) the battlefield, while delivering precision standoff and direct fire munitions, has been a valuable asset in conflicts such as Operation Iraqi Freedom.

The speed of the B-1 Lancer and the stealth of the B-2 Spirit have only been useful until enemy air defenses were destroyed, a task that has been swiftly achieved in recent conflicts. The B-52 boasts the highest mission capable rate of the three types of heavy bombers operated by the USAF. Whereas the B-1 averages a 53% ready rate, and the B-2 achieved 26%, the B-52 averages 80% as of 2001.

Additionally, a proposed variant of the B-52H was the EB-52. This version would have modified and augmented 16 B-52H airframes with additional electronic jamming capabilities. This new aircraft would have given the USAF an airborne jamming capability that it has lacked since retiring the EF-111 Raven. The program was canceled in 2005 following removal of funding for the stand-off jammer. The program was revived in 2007 but funding was again cut in early 2009.

Variants

Variant  -  Produced  -  Entered Service

XB-52   2 (1 redesignated YB-52) prototypes
B-52A   3
NB-52A 1   Modified B-52A  
B-52B   50  29 June 1955
RB-52B 27 Modified B-52Bs  
NB-52B  1 Modified B-52B  
B-52C  35 June 1956
B-52D 170 December 1956
B-52E 100 December 1957
B-52F  89 June 1958
B-52G 193 13 February 1959
B-52H 102 9 May 1961

Grand total 744 production  

The B-52 went through several design changes and variants over its 10 years of production.

XB-52
Two prototype aircraft with limited operational equipment, used for aerodynamic and handling tests

YB-52
One XB-52 modified with some operational equipment and re-designated

B-52A
Only three of the first production version, the B-52A, were built, all loaned to Boeing for flight testing. The first production B-52A differed from prototypes in having a redesigned forward fuselage. The bubble canopy and tandem seating was replaced by a side-by-side arrangement and a 21 inch (53 cm) nose extension accommodated more avionics and a new sixth crew member. In the rear fuselage, a tail turret with four 0.50 inch (12.7 mm) machine guns with a fire-control system, and a water injection system to augment engine power with a 360 US gallon (1,363 L) water tank were added. The aircraft also carried a 1,000 US gallon (3,785 L) external fuel tank under each wing. The tanks acted as dampeners to reduce wing flex and also kept wingtips close to the ground for ease of maintenance.
The last B-52A (serial 52-0003) was modified and redesignated NB-52A in 1959 to carry the North American X-15. A pylon was fitted under the right wing between the fuselage and the inboard engines with a 6 feet x 8 feet (1.8 m x 2.4 m) section removed from the right wing flap to fit the X-15 tail. Liquid oxygen and hydrogen peroxide tanks were installed in the bomb bays to fuel the X-15 before launch. Its first flight with the X-15 was on 19 March 1959, with the first launch on 8 June 1959. The NB-52A, named "The High and Mighty One" carried the X-15 on 93 of the program's 199 flights.

B-52B/RB-52B
The B-52B was the first version to enter service with the USAF on 29 June 1955 with the 93rd Bombardment Wing at Castle AFB in California. This version included minor changes to engines and avionics, enabling an extra 12,000 pounds of thrust to be produced using water injection. Temporary grounding of the aircraft after a crash in February 1956 and again the following July caused training delays, and at mid-year there were still no combat-ready B-52 crews.
Of the 50 B-52Bs built, 27 were capable of carrying a reconnaissance pod as RB-52Bs (the crew was increased to eight in these aircraft). The 300 pound (136 kg) pod contained radio receivers, a combination of K-36, K-38, and T-11 cameras, and two operators on downward-firing ejection seats. The pod required only four hours to install.
Seven B-52Bs were brought to B-52C standard under Project Sunflower.

NB-52B
The NB-52B was B-52B number 52-0008 converted to an X-15 launch platform. It subsequently flew as the "Balls 8" in support of NASA research until 17 December 2004, making it the oldest flying B-52B. It was replaced by a modified B-52H.

B-52C
The B-52C's fuel capacity (and range) was increased to 41,700 US gallons by adding larger 3000 US gallon underwing fuel tanks. The gross weight was increased by 30,000 pounds (13,605 kg) to 450,000 pounds. A new fire control system, the MD-9, was introduced on this model.
The belly of the aircraft was painted with antiflash white paint, which was intended to reflect thermal radiation away after a nuclear detonation.

RB-52C
The RB-52C was the designation initially given to B-52Cs fitted for reconnaissance duties in a similar manner to RB-52Bs. As all 35 B-52Cs could be fitted with the reconnaissance pod, the RB-52C designation was little used and was quickly abandoned.

B-52D
The B-52D was a dedicated long-range bomber without a reconnaissance option. The Big Belly modifications allowed the B-52D to carry heavy loads of conventional bombs for carpet bombing over Vietnam, while the Rivet Rambler modification added the Phase V ECM systems, which was better than the systems used on most later B-52s. Because of these upgrades and its long range capabilities, the D model was used more extensively in Vietnam than any other model. Aircraft assigned to Vietnam were painted in a camouflage colour scheme with black bellies to defeat searchlights.

B-52E
The B-52E received an updated avionics and bombing navigational system, which was eventually debugged and included on following models.
One E aircraft (AF Serial No. 56-0631) was modified as a testbed for various B-52 systems. Redesignated NB-52E, the aircraft was fitted with canards and a Load Alleviation and Mode Stabilization system (LAMS) which reduced airframe fatigue from wind gusts during low level flight. In one test, the aircraft flew 10 knots (11.5 mph, 18.5 km/h) faster than the never exceed speed without damage because the canards eliminated 30% of vertical and 50% of horizontal vibrations caused by wind gusts.

B-52F
This aircraft was given J57-P-43W engines with a larger capacity water injection system to provide greater thrust than previous models. This model had problems with fuel leaks which were eventually solved by several service modifications: Blue Band, Hard Shell, and QuickClip.

B-52G

The B-52G was proposed to extend the B-52's service life during delays in the B-58 Hustler program. At first, a radical redesign was envisioned with a completely new wing and Pratt & Whitney J75 engines. This was rejected to avoid slowdowns in production, although a large number of changes were implemented. The most significant of these was the brand new "wet" wing with integral fuel tanks which considerably increased the fuel capacity; gross aircraft weight went up by 38,000 pounds (17,235 kg) compared with prior variants. In addition, a pair of 700 US gallon (2,650 L) external fuel tanks was fitted under the wings. In this model, the traditional ailerons were eliminated. Instead, spoilers were utilized for roll control. The tail fin was shortened by 8 feet (2.4 m), water injection system capacity was increased to 1,200 US gallons (4,540 L), and the nose radome was enlarged. The tail gunner was provided with an ejection seat and moved to the main cockpit. Dubbed the "Battle Station" concept, the offensive crew (pilot and copilot on the upper deck and the two bombing navigation system operators on the lower deck) faced forward, while the defensive crew (tail gunner and ECM operator) on the upper deck faced aft. The B-52G entered service on 13 February 1959 (a day earlier, the last B-36 was retired, making SAC an all-jet bomber force). Nearly all B-52Gs were destroyed in compliance with the Strategic Arms Reduction Treaty of 1992; a few examples remain in museums and as static displays.

B-52H

The B-52H had the same crew and structural changes as the B-52G. The most significant upgrade was the switch to TF33-P-3 turbofan engines which, despite the initial reliability problems (corrected by 1964 under the Hot Fan program), offered considerably better performance and fuel economy than the J57 turbojets.The ECM and avionics were updated, a new fire control system was fitted, and the rear defensive armament was changed from machine guns to a 20 mm M61 Vulcan cannon (later removed in 1991–94). A provision was made for four AGM-48 Skybolt ballistic missiles. The aircraft's first flight occurred on 10 July 1960, and it entered service on 9 May 1961. This is the only variant still operational. A total of 744 B-52s were built. The last production aircraft, B-52H AF Serial No. 61-0040, left the factory on 26 October 1962.

General characteristics

Crew: 5 (pilot, copilot, radar navigator (bombardier), navigator, and Electronic Warfare Officer)
Length: 159 ft 4 in (48.5 m)
Wingspan: 185 ft 0 in (56.4 m)
Height: 40 ft 8 in (12.4 m)
Wing area: 4,000 sq?ft (370 m²)
Airfoil: NACA 63A219.3 mod root, NACA 65A209.5 tip
Empty weight: 185,000 lb (83,250 kg)
Loaded weight: 265,000 lb (120,000 kg)
Max takeoff weight: 488,000 lb (220,000 kg)
Powerplant: 8× Pratt & Whitney TF33-P-3/103 turbofans, 17,000 lbf (76 kN) each
Fuel capacity: 47,975 U.S. gal (39,948 imp gal; 181,610 L)
Zero-lift drag coefficient: 0.0119 (estimated)
Drag area: 47.60 sq?ft (4.42 m²)
Aspect ratio: 8.56

Performance

Maximum speed: 560 kt (650 mph, 1,000 km/h)
Combat radius: 4,480 mi (3,890 NM, 7,210 km)
Ferry range: 10,145 mi (8,764 nm, 16,232 km)
Service ceiling: 50,000 ft (15,000 m)
Rate of climb: 6,270 ft/min (31.85 m/s)
Wing loading: 120 lb/ft² (586 kg/m²)
Thrust/weight: 0.31
Lift-to-drag ratio: 21.5 (estimated)

Armament

Guns: None currently mounted. 1× 20 mm (0.787 in) M61 Vulcan cannon in a remote controlled tail turret on H-model, removed from all current operational aircraft; 4x .50 caliber machine guns, quad mounted in a remote controlled tail turret on G-model, later removed from all operational aircraft
Bombs: Approximately 70,000 pounds (31,500 kg) mixed ordnance; bombs, mines, missiles, in various configurations

Avionics

Electro-optical viewing system that uses platinum silicide forward-looking infrared and high resolution low-light-level television sensors
Sniper Advanced Targeting Pod.

 
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