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The Boeing B-52 Stratofortress is a long-range, subsonicjet-powered strategic bomber. The B-52 was designed and built byBoeing, which has continued to provide support and upgrades. It has been operated by the United States Air Force (USAF) since the 1950s. The bomber is capable of carrying up to 70,000 pounds (32,000 kg) of weapons,[5] and has a typical combat range of more than 8,800 miles (14,080 km) without aerial refueling.[6]

Beginning with the successful contract bid in June 1946, the B-52 design evolved from a straight wing aircraft powered by six turbopropengines to the final prototype YB-52 with eight turbojet engines andswept wings. The B-52 took its maiden flight in April 1952. Built to carry nuclear weapons for Cold War-era deterrence missions, the B-52 Stratofortress replaced the Convair B-36. A veteran of several wars, the B-52 has dropped only conventional munitions in combat. The B-52's official name Stratofortress is rarely used; informally, the aircraft has become commonly referred to as the BUFF (Big Ugly Fat Fucker).[7][8][Note 1]

The B-52 has been in active service with the USAF since 1955. As of 2012, 85 were in active service with nine in reserve. 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); in 2010 all B-52 Stratofortresses were transferred from the ACC to the newly created 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, more advanced aircraft, including the canceled Mach 3 B-70 Valkyrie, thevariable-geometry B-1 Lancer, and the stealth B-2 Spirit. The B-52 completed sixty years of continuous service with its original operator in 2015. After being upgraded between 2013 and 2015, it is expected to serve into the 2040s

Development

Origins

Early proposals of the B-52 planform shapes. The first of the three are of straight wing with six turboprops. The other two involve wings with varying degrees of swept.
Models 462 (1946)[14] to 464-35 (1948)[14]
Three early proposals of the B-52's planform shapes. Largely similar, except for slight differences in fuselage and placement of fuel tanks.
Models 464-49 (1949)[14] to B-52A (1952)

On 23 November 1945, Air Materiel Command (AMC) issued desired performance characteristics for a new strategic bomber "capable of carrying out the strategic mission without dependence upon advanced and intermediate bases controlled by other countries".[15] The aircraft was to have a crew of five or more turret gunners, and a six-man relief crew. It was required to cruise at 300 mph (260 knots, 480 km/h) at 34,000 feet (10,400 m) with a combat radius of 5,000 miles (4,300 nautical miles, 8,000 km). The armament was to consist of an unspecified number of 20 mm cannon and 10,000 pounds (4,500 kg) of bombs.[16] On 13 February 1946, the Air Force issued bid invitations for these specifications, with Boeing, Consolidated Aircraft, and Glenn L. Martin Company submitting proposals.[16]

On 5 June 1946, Boeing's Model 462, a straight-wing aircraft powered by sixWright T35 turboprops with a gross weight of 360,000 pounds (160,000 kg) and a combat radius of 3,110 miles (2,700 nmi, 5,010 km), was declared the winner.[17]On 28 June 1946, Boeing was issued a letter of contract for US$1.7 million to build a full-scale mock-up of the new XB-52 and do preliminary engineering and testing.[18] However, by October 1946, the air force began to express concern about the sheer size of the new aircraft and its inability to meet the specified design requirements.[19] In response, Boeing produced Model 464, a smaller four-engine version with a 230,000 pound (105,000 kg) gross weight, which was briefly deemed acceptable.[19][20]

Subsequently, in November 1946, the Deputy Chief of Air Staff for Research and Development, General Curtis LeMay, expressed the desire for a cruise speed of 400 miles per hour (345 kn, 645 km/h), to which Boeing responded with a 300,000 lb (136,000 kg) aircraft.[21] In December 1946, Boeing was asked to change their design to a four-engine bomber with a top speed of 400 miles per hour, range of 12,000 miles (10,000 nmi, 19,300 km), and the ability to carry a nuclear weapon; in total, the aircraft could weigh up to 480,000 pounds (220,000 kg).[22] Boeing responded with two models powered by the T-35 turboprops. The Model 464-16 was a "nuclear only" bomber with a 10,000 pound (4,500 kg) payload, while the Model 464-17 was a general purpose bomber with a 9,000 pound (4,000 kg) payload.[22] Due to the cost associated with purchasing two specialized aircraft, the air force selected Model 464-17 with the understanding that it could be adapted for nuclear strikes.[23]

In June 1947, the military requirements were updated and the Model 464-17 met all of them except for the range.[24] It was becoming obvious to the Air Force that, even with the updated performance, the XB-52 would be obsolete by the time it entered production and would offer little improvement over the Convair B-36; as a result, the entire project was postponed for six months.[25] During this time, Boeing continued to perfect the design, which resulted in the Model 464-29 with a top speed of 455 miles per hour (395 kn, 730 km/h) and a 5,000-mile range.[26] In September 1947, the Heavy Bombardment Committee was convened to ascertain performance requirements for a nuclear bomber. Formalized on 8 December 1947, these requirements called for a top speed of 500 miles per hour (440 kn, 800 km/h) and an 8,000 mile (7,000 nmi, 13,000 km) range, far beyond the capabilities of 464-29.[25][27]

The outright cancellation of the Boeing contract on 11 December 1947 was staved off by a plea from its president William McPherson Allen to the Secretary of the Air Force Stuart Symington.[28] Allen reasoned that the design was capable of being adapted to new aviation technology and more stringent requirements.[29] In January 1948 Boeing was instructed to thoroughly explore recent technological innovations, including aerial refueling and the flying wing.[30] Noting stability and control problems Northrop was experiencing with their YB-35 and YB-49 flying wing bombers, Boeing insisted on a conventional aircraft, and in April 1948 presented a US$30 million (US$295 million today[31]) proposal for design, construction, and testing of two Model 464-35 prototypes.[32] Further revisions during 1948 resulted in an aircraft with a top speed of 513 miles per hour (445 kn, 825 km/h) at 35,000 feet (10,700 m), a range of 6,909 miles (6,005 nmi, 11,125 km), and a 280,000 pounds (125,000 kg) gross weight, which included 10,000 pounds (4,500 kg) of bombs and 19,875 US gallons (75,225 L) of fuel.[33][34]

Design effort[edit]

XB-52 Prototype on flight line (X-4in foreground)
Side, black and white view of an early B-52, which features the bubble canopy. The aircraft is heading to sea, leaving behind the coastline on its right wing.
Side view of YB-52 bomber, withbubble canopy similar to that of the B-47

In May 1948, AMC asked Boeing to incorporate the previously discarded, but now more fuel-efficient, jet engine into the design.[35] That resulted in the development of yet another revision—in July 1948, Model 464-40 substituted Westinghouse J40 turbojets for the turboprops.[36] The Air Force project officer who reviewed the Model 464-40 was favorably impressed, especially since he had already been thinking along similar lines. Nevertheless, the government was concerned about the high fuel consumption rate of the jet engines of the day, and directed that Boeing still use the turboprop-powered Model 464-35 as the basis for the XB-52. Although he agreed that turbojet propulsion was the future, General Howard A. Craig, Deputy Chief of Staff for Material, was not very keen on a jet-powered B-52, since he felt that the jet engine had not yet progressed sufficiently to permit skipping an intermediate turboprop stage. However, Boeing was encouraged to continue turbojet studies even without any expected commitment to jet propulsion.[37][38]

On Thursday, 21 October 1948, Boeing engineers George S. Schairer, Art Carlsen and Vaughn Blumenthal presented the design of a four-engine turboprop bomber to the chief of bomber development, Colonel Pete Warden. Warden was disappointed by the projected aircraft and asked if the Boeing team could come up with a proposal for a four-engine turbojet bomber. Joined by Ed Wells, Boeing vice president of engineering, the engineers worked that night in the Hotel Van Cleve in Dayton, Ohio, redesigning Boeing's proposal as a four-engine turbojet bomber. On Friday, Colonel Warden looked over the information and asked for a better design. Returning to the hotel, the Boeing team was joined by Bob Withington and Maynard Pennell, two top Boeing engineers who were in town on other business.[39]

By late Friday night, they had laid out what was essentially a new airplane. The new design (464-49) built upon the basic layout of the B-47 Stratojet with 35 degree swept wings, eight engines paired in four underwing pods, and bicycle landing gear with wingtip outrigger wheels.[40] A notable feature of the landing gear was the ability to pivot the main landing gear up to 20° from the aircraft centerline to increase safety during crosswind landings.[41] After a trip to a hobby shop for supplies, Schairer set to work building a model. The rest of the team focused on weight and performance data. Wells, who was also a skilled artist, completed the aircraft drawings. On Sunday, a stenographer was hired to type a clean copy of the proposal. On Monday, Schairer presented Colonel Warden with a neatly bound 33-page proposal and a 14-inch scale model.[39] The aircraft was projected to exceed all design specifications.[42]

Although the full-size mock-up inspection in April 1949 was generally favorable, range again became a concern since the J40s and early model J57s had excessive fuel consumption.[43] Despite talk of another revision of specifications or even a full design competition among aircraft manufacturers, General LeMay, now in charge of Strategic Air Command, insisted that performance should not be compromised due to delays in engine development.[44][45] In a final attempt to increase range, Boeing created the larger 464-67, stating that once in production, the range could be further increased in subsequent modifications.[46] Following several direct interventions by LeMay,[47] Boeing was awarded a production contract for thirteen B-52As and seventeen detachable reconnaissance pods on 14 February 1951.[48] The last major design change—also at General LeMay's insistence—was a switch from the B-47 style tandem seating to a more conventional side-by-side cockpit, which increased the effectiveness of the copilot and reduced crew fatigue.[49] Both XB-52 prototypes featured the original tandem seating arrangement with a framed bubble-type canopy.[50]

Pre-production and production[edit]

The YB-52, the second XB-52 modified with more operational equipment, first flew on 15 April 1952 with "Tex" Johnston as pilot.[51][52] During ground testing on 29 November 1951, the XB-52's pneumatic system failed during a full-pressure test; the resulting explosion severely damaged the trailing edge of the wing, necessitating considerable repairs. A two-hour, 21-minute proving flight from Boeing FieldKing County, in Seattle, Washington to Larson AFB was undertaken with Boeing test pilot Johnston and air force Lieutenant Colonel Guy M. Townsend.[53] The XB-52 followed on 2 October 1952.[54] The thorough development,[Note 3] including 670 days in the wind tunnel and 130 days of aerodynamic and aeroelastic testing, paid off with smooth flight testing. Encouraged, the air force increased its order to 282 B-52s.[56]

Aircraft deliveries
 Fiscal 
Year
B-52 model  Annual
Total  
  Total  
  A  
[57]
  B  
[2]
  C  
[58]
  D  
[59]
  E  
[60]
  F  
[61]
  G  
[62]
  H  
[63]
1954333
1955131316
195635514157
195723092124181
19587710010187368
19597950129497
1960106106603
1961372057660
19626868728
19631414742
Total3503517010089193102742742

Only three of the 13 B-52As ordered were built.[64] All were returned to Boeing, and used in their test program.[57] On 9 June 1952, the February 1951 contract was updated to order the aircraft under new specifications. The final 10, the first aircraft to enter active service, were completed as B-52Bs.[57] At the roll out ceremony on 18 March 1954, Air Force Chief of Staff General Nathan Twining said:

The long rifle was the great weapon of its day. ... today this B-52 is the long rifle of the air age.[65][66]

The B-52B was followed by progressively improved bomber and reconnaissance variants, culminating in the B-52G and turbofan B-52H. To allow rapid delivery, production lines were set up both at its main Seattle factory and at Boeing's Wichita facility. More than 5,000 companies were involved in the massive production effort, with 41% of the airframe being built by subcontractors.[67] The prototypes and all B-52A, B and C models (90 aircraft)[68] were built at Seattle. Testing of aircraft built at Seattle caused problems due to jet noise, which led to the establishment of curfews for engine tests. Aircraft were ferried 150 miles (240 km) east on their maiden flights to Larson Air Force Base near Moses Lake, where they were fully tested.[69]

As production of the B-47 came to an end, the Wichita factory was phased in for B-52D production, with Seattle responsible for 101 D-models and Wichita 69.[70] Both plants continued to build the B-52E, with 42 built at Seattle and 58 at Wichita,[71] and the B-52F (44 from Seattle and 45 from Wichita).[72] For the B-52G, it was decided in 1957 to transfer all production to Wichita, which freed up Seattle for other tasks (in particular the production of airliners).[73][74] Production ended in 1962 with the B-52H, with 742 aircraft built, plus the original two prototypes.[75]

Upgrades[edit]

A proposed variant of the B-52H was the EB-52H, which would have consisted of 16 modified and augmented B-52H airframes with additional electronic jamming capabilities.[76][77] This variant would have restored USAF airborne jamming capability that it lost on retiring the EF-111 Raven. The program was canceled in 2005 following the removal of funds for the stand-off jammer. The program was revived in 2007, and cut again in early 2009.[78]

In July 2013, the Air Force began a fleet-wide technological upgrade of its B-52 bombers called Combat Network Communications Technology (CONECT) to modernize electronics, communications technology, computing, and avionics on the flight deck. CONECT upgrades include software and hardware such as new computer servers, modems, radios, data-links, receivers, and digital workstations for the crew. One update is the ARC-210 Warrior beyond-line-of-sight software programmable radio able to transmit voice, data, and information in-flight between B-52s and ground command and control centers, allowing the transmission and reception of data with updated intelligence, mapping, and targeting information; previous in-flight target changes required copying down coordinates. The ARC-210 allows machine-to-machine transfer of data, useful on long-endurance missions where targets may have moved before the arrival of the B-52. The aircraft will be able to receive information through Link-16. CONECT upgrades will cost $1.1 billion overall and take several years. Funding has been secured for 30 B-52s; the Air Force hopes for 10 CONECT upgrades per year, but the rate has yet to be decided.[79]

Weapons upgrades include the 1760 Internal Weapons Bay Upgrade (IWBU), which gives a 66 percent increase in weapons payload using a digital interface and rotary launcher. IWBU is expected to cost roughly $313 million.[79] The 1760 IWBU will allow the B-52 to carry the AGM-158B JASSM-ER and the ADM-160C MALD-J. All 1760 IWBUs should be operational by October 2017. Two bombers will have the ability to carry 40 weapons in place of the 36 that three B-52s can carry.[80] The 1760 IWBU allows precision-guided missiles or bombs to be deployed from inside the weapons bay; previous aircraft carried these munitions externally on wing hardpoints. This increases the number of guided weapons a B-52 can carry and reduces the need for guided bombs to be carried. The first phase will allow a B-52 to carry twenty-four 500-pound guided JDAM bombs or twenty 2,000-pound JDAMs, with later phases accommodating the JASSM and MALD family of missiles.[81] In addition to carrying more smart bombs, moving them internally from the wings reduces drag and achieves a 15 percent reduction in fuel consumption.[82]

Design[edit]

Overview[edit]

The B-52 shared many technological similarities with the preceding Boeing B-47 Stratojet strategic bomber. The two aircraft used the same basic design, such as swept wings and podded jet engines,[83] and the cabin included the crew ejection systems.[84] On the B-52D, the pilots and electronic countermeasures (EDM) operator ejected upwards, while the lower deck crew ejected downwards; until the B-52G, the gunner had to jettison the tail gun to bail-out.[85]

Black-and-white photo of a B-52 inflight with its vertical stabilizer sheared off.
B-52H (AF Ser. No. 61-0023), configured at the time as a testbed to investigate structural failures, still flying after its vertical stabilizersheared off in severe turbulence on 10 January 1964. The aircraft landed safely[86]

Structural fatigue was accelerated by at least a factor of eight in a low-altitude flight profile over that of high-altitude flying, requiring costly repairs to extend service life. In the early 1960s, the three-phase High Stress program was launched to counter structural fatigue, enrolling aircraft at 2,000 flying hours.[87][88] Follow-up programs 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.[74][89]The wet wing introduced on G and H models was even more susceptible to fatigue, experiencing 60% more stress during flight than the old wing. The wings were modified by 1964 under ECP 1050.[90] 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.[90] 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 that prevented catastrophic loss of fuel in case of clamp failure.[91]

In September 2006, the B-52 became one of the first US military aircraft to fly using alternative fuel. It took off fromEdwards Air Force Base with a 50/50 blend of Fischer-Tropsch process (FT) synthetic fuel and conventional JP-8 jet fuel, which burned in two of the eight engines.[92] 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.[92] 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.[92] On 8 August 2007, Air Force Secretary Michael Wynne certified the B-52H as fully approved to use the FT blend.[93]

Flight controls[edit]

Because of the B-52's mission parameters, only modest maneuvers would be required with no need for spin recovery.[94]The aircraft has a relatively small, narrow chord rudder, giving it limited yaw control authority. Originally an all-movingvertical stabilizer was to be used, but was abandoned because of doubts about hydraulic actuator reliability.[94] Because the aircraft has eight engines, asymmetrical thrust due to the loss of an engine in flight would be minimal and correctable with the narrow rudder. To assist with crosswind takeoffs and landings the main landing gear can be pivoted 20 degrees to either side from neutral.[95] This yaw adjustable crosswind landing gear would be preset by the crew according to wind observations made on the ground.

The elevator is also very narrow in chord like the rudder, and the B-52 suffers from limited elevator control authority. For long term pitch trim and airspeed changes the aircraft uses an all-moving tail with the elevator used for small adjustments within a stabilizer setting. The stabilizer is adjustable through 13 degrees of movement (nine up, four down) and is crucial to operations during take off and landing due to large pitch changes induced by flap application.[96]

B-52s prior to the G models had very small ailerons with a short span that was approximately equal to their chord. These "feeler ailerons" were used to provide feedback forces to the pilot's control yoke and to fine tune the roll axes during delicate maneuvers such as aerial refueling.[94] Due to twisting of the thin main wing, conventional outboard flap type ailerons would lose authority and therefore could not be used. In other words, aileron activation would cause the wing to twist, undermining roll control. Six spoilerons on each wing are responsible for the majority of roll control. The late B-52G models eliminated the ailerons altogether and added an extra spoileron to each wing.[94] Partly because of the lack of ailerons, the B-52G and H models were more susceptible to dutch roll.[96]

Avionics[edit]

Lower deck of a B-52, with instruments and displays featuring dominantly on the aircraft's side wall. This station is manned by two crew members.
A view of the lower deck of the B-52, dubbed the battle station

Ongoing problems with avionics systems were addressed in the Jolly Wellprogram, 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 countermeasurescapability of the B-52 was expanded with Rivet Rambler (1971) and Rivet Ace(1973).[97]

To improve operations at low altitude, the AN/ASQ-151 Electro-Optical Viewing System (EVS), which consisted of a Low Light Level Television (LLLTV) and aForward looking infrared (FLIR) system mounted in blisters under the noses of B-52Gs and Hs between 1972 and 1976.[98] The navigational capabilities of the B-52 were later augmented with the addition of GPS in the 1980s.[99] The IBM AP-101, also used on the Rockwell B-1 Lancer bomber and the Space Shuttle, was the B-52's main computer.[100]

In 2007 the LITENING targeting pod was fitted, which increased the effectiveness of the aircraft in the attack of ground targets with a variety of standoff weapons, using laser guidance, a high-resolution forward-looking infrared sensor (FLIR), and a CCD camera used to obtain target imagery.[101] 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.[102]

Armament[edit]

The ability to carry up to 20 AGM-69 SRAM nuclear missiles was added to G and H models, starting in 1971.[103] To further improve its offensive ability, air-launched cruise missiles (ALCMs) were fitted.[104] 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).[105] 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 bomb-bay. To conform with SALT II Treaty requirements that cruise missile-capable aircraft be readily identifiable by reconnaissance satellites, the cruise missile armed B-52Gs were modified with a distinctive wing root fairing. As all B-52Hs were assumed modified, no visual modification of these aircraft was required.[106] 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.[107] 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.[108]

A B-52D with anti-flash white on the under side

Those B-52Gs not converted as cruise missile carriers underwent a series of modifications to improve conventional bombing. They were fitted with a new Integrated Conventional Stores Management System (ICSMS) and new underwing pylons that could hold larger bombs or other stores than could the external pylons. Thirty B-52Gs 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.[109] When the B-52G was retired in 1994, an urgent scheme was launched to restore an interim Harpoon and Have Nap capability,[Note 4] the four aircraft being modified to carry Harpoon and four to carry Have Nap under the Rapid Eight program.[112]

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.[113][114]

Starting in 2016, Boeing is to upgrade the internal rotary launchers to the MIL-STD-1760 interface to enable the internal carriage of smart bombs, which can currently only be carried on the wings.[115]&a

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