Boeing B-52 Stratofortress - Variants

Variants

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 inches (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 damped wing flutter 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 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 provided 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 manning the 4 .50 caliber machine guns (quad mounted in a remote controlled tail turret on the G-model, the guns were later removed from all operational aircraft) was relocated to the main cockpit and was provided with an ejection seat. 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). 193 B-52Gs were produced, making this the most produced B-52 variant. 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 GAM-87 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.

XR-16A

Allocated to the reconnaissance variant of the B-52B but not used and the aircraft were designated RB-52B instead.