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Boeing B-52 Stratofortress
Variants

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

Model: ProducedEntered Service
XB-522 (1 redesignated YB-52)prototypes
B-52A3  
NB-52A 1 Modified B-52A  
B-52B5029 June 1955
RB-52B27 Modified B-52Bs 
NB-52B1 Modified B-52B  
B-52C35 June 1956
B-52D170 December 1956
B-52E100 December 1957
B-52F89June 1958
B-52G19313 February 1959
B-52H1029 May 1961
Grand total 744 production 

XB-52/YB-52 - First two prototypes, fitted with B-47 type bubble canopies, not used in production versions.


XB-52 prototype. (U.S. Air Force Photo)

B-52A - Only three of 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 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 6th 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 was 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.

NB-52A - 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 tanks were installed in the bomb bays to refuel the X-15 before launch. First flight with X-15 was on 10 March 1959, and NB-52A carried the X-15 on 59 of the program's 199 flights.


NB-52A Stratofortress/52-0003. (NASA Photo)

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, in the attempt to fix minor problems. Temporary grounding of the aircraft in February 1956, after a crash, and the following July, caused training delays, and at mid-year there were still no combat-ready B-52 crews.


Three B-52Bs of the 93rd Bomb Wing prepare to depart Castle Air Force Base, California, for their record-setting round-the-world flight in 1957 (U.S. Air Force Photo)

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.

NB-52B Stratofortress/52-0008. (NASA Photo)

B-52C - In the B-52C the 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. 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 given, but seldom used, to B-52Cs converted for reconnaissance duties in a similar manner to RB-52Bs.

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. Aircraft assigned to Vietnam were painted camouflage with black bellies to defeat searchlights.

B-52E - In the B-52E the aircraft had an updated avionics and bombing navigational system, which was eventually debugged and included on following models.

One E aircraft (number 56-0631) 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 - In the B-52F, the aircraft was given J57-P-43W engines with a larger capacity water injection system and new alternators. The aircraft had a problem with fuel leaks, which were eventually solved by service modifications Blue Band, Hard Shell, and QuickClip.


B-52F Stratofortress. (U.S. Air Force Photo)

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 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 gallons (2,650 L) external fuel tanks was fitted under the wings. The wing also had the traditional ailerons eliminated, instead utilizing spoilers 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, copilot, and the two bombing navigation system operators on the lower deck) faced forward, while the defensive crew (gunner and ECM operator) on the upper deck faced aft. The B-52G entered service 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 Ams Reduction Treaty START I of 1992. A few examples remain in museums and as static displays at various air force bases.

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. A provision was made for four AGM-48 Skybolt ballistic missiles. First flight 10 July 1960, entered service 9 May 1961. This is the only variant still operational.


B-52H, 2nd Bomb Wing, Barksdale AFB, LA. (U.S. Air Force Photo)

A total of 744 B-52s were built. The last production aircraft, B-52H number 61-0040, left the factory on 26 October 1962.

Sources:
Wikipedia: B-52 Stratofortress
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