The Boeing B-52 Stratofortress
The Cold War led the United States to develop a strategic nuclear deterrent force featuring a wide range of weapons. One of the more impressive was the big Boeing "B-52 Stratofortress" eight-engine jet bomber. Although it was designed for the nuclear strike mission, it never saw combat in that role, but it has seen plenty of action dropping conventional weapons in Vietnam and in post-Cold War conflicts. The B-52 still remains in service, if in dwindling numbers, in the 21st century, long after its builders would have expected its retirement. This document provides a history and description of the Boeing B-52.
Boeing B-52 Stratofortress Evolution
The United States Air Force (USAF) was hesitant to adopt the B-52, with the preliminary design program taking a roller-coaster ride and the project nearly abandoned several times. However, Boeing persisted with the design, and the Air Force finally decided it was the weapon they wanted. After that uncertain start, the USAF ended up buying over twice as many B-52s as originally planned, in one of the most expensive military procurement programs in US history. The big bombers went on to the flight lines of USAF Strategic Air Command (SAC) bases to become the backbone of America's nuclear deterrent against the Red Menace in the early 1960s.
Boeing B-52 Stratofortress Origins
Even before the end of World War II, the US Army Air Forces (USAAF) were looking forward to a next-generation strategic bomber to follow the huge Convair B-36, then in development. In late 1945, the USAAF began evaluating requirements for such a new bomber, and on 13 February 1946 the service issued a formal specification for it, specifying greater speed than the B-36 and an operational radius of 8,050 kilometers (5,000 miles).
This was a mighty big order. The Boeing company responded with a design with the company designation of "Model 462", which looked something like a scaled-up B-29 Superfortress with six Wright T35 Typhoon turboprop engines, providing 4,100 kW (5,500 SHP) each. The USAAF liked the idea, and on 5 June 1946 awarded Boeing a study contract for the machine, which was given the military designation "XB-52" not long after. The contract specified a full-scale mockup but not a functioning prototype.
The first flight prototype of the XT35 engine was fitted to the nose of a Boeing B-17 Fortress bomber to begin flight tests in September 1947, but as far as the Model 462 was concerned, it had become irrelevant. The USAAF had decided the bomber design couldn't meet the range specifications and cancelled the contract in October 1946.
With the cancellation of the Model 462, the design team for the project, led by Boeing Chief Engineer Ed Wells, went back to the drawing board and produced a set of "Model 464" concepts, which were at first basically scaled-down Model 462s with four turboprops, instead of six. The "464-16" was designed to carry a large bombload over relatively short range, while the "464-17" was designed to carry a small bombload over long range. The Air Force (as the USAAF became in 1947) was interested in the 464-17 concept but concluded that it still wasn't what was needed, since it didn't amount to much of an advance over the B-36.
Some Air Force brass wanted to kill the effort completely at this point, but the designers were allowed to explore improved concepts. By August 1947, they had gone through several more iterations, finally stabilizing for a while on the "Model 464-29", with a 20-degree swept wing, mounting four Pratt & Whitney (P&W) XT57 turboprops; landing gear consisting of four two-wheel assemblies in a row along the centerline; and defensive armament consisting solely of a tail turret.
The Model 464-29 didn't really answer the requirement, either. The Air Force was beginning to want better performance, and was also very interested in Northrop's flying wing bombers, which appeared to be the way of the future at the time. The XB-52 project edged back towards cancellation. Boeing's engineers kept up the momentum as best they could in this uncertain time, coming up with yet another concept, the "Model 464-35". The Air Force's adoption of inflight refueling meant that the 464-35 didn't have to be as big as earlier design concepts. It also had more aggressively swept wings, but it retained the four big turboprop engines, though fitted with contrarotating propellers.
In the meantime, events put the XB-52 project on firmer ground. In June 1948, Stalin imposed a blockade on Berlin, bringing the Cold War on in earnest. The Air Force immediately brought the B-52 project back to the front burner, awarding a contract for a mock-up and two flying prototypes, with the first prototype to be ready by early 1951. Government funding began to ramp up.
A Boeing design team, including George Schairer, Vaughn Blumenthal, and Art Carlsen, went to Wright-Patterson Air Force Base in Ohio and presented the 464-35 design to the Air Force representative, Colonel Pete Warden, on Thursday, 21 October 1948. Warden replied that the USAF was no longer interested in turboprop propulsion since it couldn't provide adequate performance or reliability; the Air Force wanted a jet-powered aircraft.
This must have come as a surprise to the Boeing team, since the company had proposed turbojet-powered versions of the bomber over the previous few months and been told bluntly to forget it by other senior Air Force officials. However, Warden had become a believer in and an advocate for turbojet propulsion, and had been encouraging Pratt & Whitney to develop an advanced turbojet engine, the JT3, which would become famous as the J57. Warden felt that the JT3 engine would be the powerplant of choice for the new bomber.
The Boeing group quickly threw off any confusion caused by this about-face. After some brainstorming at the hotel, they called Warden on Friday morning and told him they would have a new proposal fitting his requirements by Monday morning.
The design team had brought with them a proposal for a medium bomber that would use four Westinghouse J-40 turbojets, and that seemed like a good starting point for updating the 464-35 design. The team was joined by Ed Wells, H.W. Withington, and Maynard Pennell. The group of engineers worked from their hotel room in Dayton to scale up the medium bomber proposal to twice size, with eight JT3 engines mounted in pairs on pylons, fitted under a 35 degree swept wing. The 35-page proposal for the "464-49" was ready for Colonel Warden by Monday morning, along with a balsa-wood model Wells had built from materials obtained from a Dayton hobby shop.
The Air Force was very interested in this proposal, and the design team continued to tweak it to come up with a definitive design concept, the "464-67", in November 1949. The company began construction of the two prototypes on that basis but the USAF continued to waffle, considering alternatives for their strategic bomber requirement, such as enhancing the Boeing B-47 Stratojet bomber, then in advanced development, into an improved version designated the "B-47Z"; and a jet-powered, swept-wing version of the B-36, the "Convair YB-60".
Fortunately for Boeing, General Curtis LeMay, as of October 1948 commander of the Air Force's "Strategic Air Command (SAC)", remained enthusiastic about the XB-52. It still took over a year to get a commitment to the Boeing machine, with Boeing finally awarded a contract for 13 "B-52As" on 14 February 1951. The program now shifted into high gear.
Even after this milestone, ambiguities lingered. USAF Headquarters decided that the service didn't have a need for a long-range bomber like the B-52 and wanted them all built as reconnaissance aircraft. SAC, in contrast, wanted to build the machine to operate both as a bomber and as a reconnaissance aircraft, with a reconnaissance pod plugged into the bombbay for such missions. In October 1951, USAF HQ handed down an order that the new machines would be built as "RB-52" reconnaissance machines. On paper, SAC had lost. In practice, LeMay had got his way.
Development of the two prototypes had gone forward in the meantime. The first prototype was given the designation "XB-52" and the second the designation "YB-52". The second prototype was given a "Y" code, which would normally indicate an evaluation machine, not an "X" code as was appropriate to its experimental status, because the Air Force had scrounged funding for it from their Logistics Command, which was not formally allowed to fund experimental aircraft.
The XB-52 was rolled out on 29 November 1951. The rollout was done late at night and with the aircraft bundled under tarps to help maintain secrecy. Unfortunately, the XB-52 suffered a catastrophic failure of its pneumatic system during ground testing that caused extensive damage to the trailing edge of the wing. It had to be sent it back inside the factory for lengthy repairs before it could perform a flight.
The YB-52 was rolled out on 15 March 1952 and actually performed the first flight, on 15 April 1952, with Boeing test pilot A.M. "Tex" Johnson and Air Force Lieutenant Colonel Guy M. Townsend at the controls. The flight lasted a little under three hours, with takeoff from Boeing Field in Seattle and landing at Moses Lake, east over the mountains in central Washington state.
The flight went well, with a few minor technical problems as would be expected for such a big and complicated machine. Johnson complained that control forces were too high, making the machine tiring to fly, but they had been set high deliberately for whatever reasons and so that was easy to fix. Other than that, Johnson reported that the YB-52 was "a hell of a good airplane."
The flight trials went better than expected at first, the machine demonstrating no fundamental design flaws that would have dictated time-consuming major rework. Most of the test flights were initially from Boeing Field. Some factions in the Air Force wanted the tests to be conducted from Edwards Air Force Base (AFB) in California, since that was where the main USAF flight test center was based, and there was concern that notoriously damp Seattle weather would slow down testing.
Boeing protested that it would be easier to make fixes if the flight tests were conducted from the factory airfield, and that Seattle weather wasn't as bad as people made it out to be. In any case, the expense of moving the trials to Edwards kept it from happening, but in fact the weather did start to bog down the flight test schedule. As a result, the test flights were shifted to Moses Lake, in the sagebrush where rainy weather was generally not a problem, and then to Fairchild AFB, in Spokane, farther east in the state.
The XB-52 joined the test program with its initial flight on 2 October 1952. By this time, the schedule had slipped a few months and the "new" machine was welcome. Some difficulties had cropped up and the Air Force wanted them resolved so the bomber could be put into service. Problems included unfriendly flight characteristics when the machine was nearing a stall; inadequate brakes; and, in particular, poor reliability of the new J57 engines.
The XB-52 and YB-52 remained in use as test aircraft through the 1950s. The XB-52 was later modified with J75 engines replacing the outboard pods of two J57s, making it a six-engined aircraft. Although the YB-52 was donated on paper to the USAF Museum in Dayton, both aircraft ended up being scrapped during Lyndon Johnson's presidential administration, sometime in the mid-1960s.
Boeing B-52 Stratofortress Variants: XB-52 Though B-52B
The XB-52 set the basic pattern for all that followed, though there would be many detail variations in later machines. It incorporated many concepts from the earlier Boeing B-47 bomber, but it was in no way a simple scale-up of the B-47 design.
The XB-52 was a big, boxy machine with a high-mounted wing swept back 35 degrees and a conventional tail arrangement. It was powered by eight P&W YJ57-3 engines with 38.7 kN (3,950 kgp / 8,700 lbf) thrust each. The J57s were fitted in four pods, two engines to a pod, suspended on pylons below and forward of the wing. The inboard pods were 10.4 meters (34 feet 2 inches) from the centerline and the outboard pods were 18.29 meters (60 feet) from the centerline. Interestingly, in practice a pod suffering an uncontrollable fire would generally fall off the wing, sparing the rest of the aircraft, a "feature" Boeing engineers would later describe as an "unexpected benefit".
The wings were thick, with a chord (ratio of cross-sectional height to width) of 15% at the root, tapering to 8% in the outer wing. They could flex from 3 meters (10 feet) down to 6.7 meters (22 feet) up. The heavy engines helped dampen wing flutter. There were two oversized "Fowler-type" flaps -- extending well behind the trailing edge of each wing -- with an aileron between the two flaps, plus a row of spoilers on top of the wing.
Sources are peculiarly inconsistent on the number of spoilers. Some sources claim that all variants had seven above each wing, but others claim that the XB-52 had three above each wing, while the YB-52 had six, this number being retained in all following B-52 versions except the last two, which had the magic seven. Whatever their number, the spoilers could be used asymmetrically to help the ailerons with roll control, or symmetrically to act as airbrakes, eliminating the need for a secondary "deceleration parachute" as used on the B-47. However, the aircraft still required a main drag parachute, 13.4 meters (44 feet) in diameter, stowed under the tail.
Most of the flight surfaces used manual control. The oversized tailfin was hinged so it could be folded down to allow the aircraft to fit into a hangar. The tailplane was of "all moving" configuration, with no elevators on the rear and the entire tailplane adjusted for pitch control.
The wings and the fuselage were loaded up with flexible fuel bladders, providing a total capacity of 147,120 liters (38,820 US gallons). Bladders were used, instead of integral fuel tanks, to prevent leaks that would have been caused by the flexing of the airframe in flight. When fully fueled, the wingtips drooped 2.74 meters (nine feet) while sitting on the runway. They normally curved upward in flight. Fuel trim would be maintained manually by the copilot, following a set of regulations. No service B-52 would ever have an automatic fuel-trim system.
The landing gear scheme was unusual and elaborate, and in fact was kept secret during development. The main landing gear was organized in four big twin-wheel trucks mounted in the fuselage. The trucks were arranged in pairs, fore and aft of the bombbay. Each truck in each pair opened under opposite sides of the fuselage, with the truck on the left retracting forward and that on the right retracting backward. The trucks rotated 90 degrees to lie flat in the fuselage when retracted. Each truck could be extended or retracted independently.
The trucks could be steered up to 20 degrees in either direction from the centerline, allowing the bomber to takeoff or land at an angle in a crosswind. The steerable landing gear also helped during landings if an outboard engine failed. Some sources claim, plausibly, that the forward trucks could be turned 55 degrees off the centerline for taxiing. A small, stalky outrigger landing gear was fitted in the outboard section of each wing to prevent the wingtips from dragging the ground. Each outrigger retracted sideways into the wing, towards the fuselage. The outriggers would in principle permit a safe landing if only one truck in each pair could be extended. If the wing tanks had been drained, the outrigger wheels would usually not touch the ground on a landing.
As with the B-47, the landing gear arrangement prevented the bomber from performing a nose-up rotation during takeoff. To deal with this issue, the B-47 had been designed to sit on the runway with a nose-up attitude. In contrast, the B-52's fuselage was kept level, while the wing was canted up six degrees instead. This meant that the machine could be climbing rapidly when the nose was still pointed down, an experience that probably felt something like riding in an elevator.
System power was provided by a set of air turbines, protected by flak curtains and driven by engine bleed. The turbines provided power to electric generators, hydraulic pumps, the cabin pressurization and climate conditioning system, and other systems. Engine bleed was also used for de-icing the engine inlets, but the windscreen and other elements were de-iced with by electrical heating system.
The XB-52 and YB-52 used a twelve-pane "all round vision" fighter-style canopy with pilot and copilot sitting in tandem. The canopy could be blown off to allow them to eject upward. Details of what other crew the two initial prototypes carried, in the space below the pilot and copilot, is unclear and was probably variable, depending on the flight-test phase.
The bombbay was 8.5 meters long by 1.8 meters wide (28 by 6 feet), and had three sets of doors along its length. The doors could be folded up to improve access by armorers. A tail turret was planned as defensive armament, but the two prototypes were not armed, and in fact did not have full operational avionics. In service, B-52s would also be fitted with a belly camera for post-strike reconnaissance, but it is unclear when this feature was implemented and if it was implemented in all variants.
The two initial prototypes were followed by three B-52A evaluation aircraft, the initial order for 13 having been changed, with the other 10 to be operational "B-52Bs". The first B-52A was rolled out from the Boeing Seattle plant on 18 March 1954 and made its initial flight on 5 August 1954. The other two were also rolled out from Boeing-Seattle in 1954.
The B-52As featured a new side-by-side cockpit scheme, eliminating the fighter-style canopy, and a tail turret fitted with four 12.7 millimeter (0.50 caliber) Browning M3 machine guns, with 600 rounds per gun. However, the B-52As were still not fitted with full operational avionics kit. The new cockpit had been planned since before the flight of the two prototypes. It had been adopted after Curtis LeMay inspected a mockup of the XB-52 and expressed his strong dislike of the tandem seating arrangement. A side-by-side seating arrangement, he argued, would provide greater space for instrument indicators, and permit better interaction between the pilot and copilot.
The pilot, copilot, and electronic warfare officer (EWO or "e-dub") sat in the upper flight deck, with upward-firing ejection seats, while the navigator and "radar navigator" (bombardier, more or less) sat in the lower flight deck, sometimes called the "black hole" or "hell hole", on downward-firing ejection seats. Access to the cockpit was through a door on the bottom. Despite the size of the aircraft, the crew accommodations were hardly roomy. The cockpit was pressurized, with the consequence that the forward section of every B-52 built quickly acquired a "wrinkled" appearance due to pressurization and depressurization. It gave the aircraft a somewhat weary appearance even when it was fairly new.
The tail gunner sat in the turret and could direct the guns with an A-3A fire control system (FCS). He could go forward through a non-pressurized crawlway over the bombbay to join the rest of the crew if necessary. The turret could be blown off the tail of the aircraft in an emergency to allow the gunner to escape.
The B-52A was powered by P&W J57-9W engines, with 44.5 kN (4,535 kgp / 10,000 lbf) "dry" thrust each, or 49.0 kN (4,990 kgp / 11,000 lbf) "wet" thrust with water injection. Water injection added mass flow to boost thrust on takeoff, and had not been available in the evaluation J57s used in the two prototypes. It provided a substantial kick, though the engines were thunderously noisy when it was engaged and poured out thick ugly black smoke. The water, which was mixed with methanol as anti-freeze, was stored in a tank near the aircraft's tail.
An auxiliary fuel tank with a capacity of 3,787 liters (1,000 US gallons) was attached near each wingtip. Unlike the two prototypes, the B-52As were fitted with a boom receptacle behind the cockpit for inflight refueling. The refueling receptacle was retained in all following models of the B-52.
The three B-52As remained in service for a long time as test and special purpose aircraft, with some of their roles mentioned later. One of them was scrapped in 1961, while at least one of the remaining two still survives as a static display.
The "B-52B" was very similar to the B-52A but had (more or less) operational systems. 50 were built, all by the Boeing Seattle plant. 27 of these were "RB-52s", mentioned earlier, with provision for the installation of a pressurized reconnaissance capsule in the bombbay. Ironically, by this time, the Air Force had finally made up their minds that the B-52 was first and foremost a strategic bomber and had lost interest in using the aircraft in the reconnaissance role.
The reason for the "more or less" qualifier above was because Boeing and the Air Force had serious troubles obtaining workable operational systems. The B-52 was supposed to use the MA-2 bombing-navigation system (BNS), but the MA-2 ran into troubles, and so early production B-52Bs were fitted with the K-3A BNS, used on the Convair B-36. However, the B-52 flew at a substantially higher altitude than the B-36 and the K-3A simply didn't have the range to work properly. The system's manufacturer, Philco, implemented some temporary fixes to boost radar power output, but later B-52B production featured a better solution in the form of the MA-6A BNS, an improved version of the K-3A.
The other major systems problem with the B-52B was the tail turret and its FCS. Nine of the first ten RB-52Bs were fitted with the "quad-fifty" tail turret and A-3A FCS of the B-52A, but this was not a satisfactory solution, As a result, 18 RB-52Bs and 16 B-52Bs were fitted with an entirely different tail turret, fitted with twin M24A-1 20-millimeter cannon and an MD-5 FCS. This didn't work out much better, so the last 7 B-52Bs reverted to the quad-fifty turret, with a supposedly "improved" version of the A-3A.
Most of the B-52Bs were fitted with J57-P-29W or similar J57-P-29WA engines, but the last five were fitted with J57-P-19W engines. All these J57s had the same thrust rating, with 46.7 kN (4,760 kgp / 10,500 lbf) "dry" thrust and 53.9 kN (5,490 kgp / 12,100 lbf) "wet" thrust, but the J57-P-19W had compressor blades made of titanium, not steel, making it somewhat lighter.
|BOEING B-52B STRATOFORTRESS|
|Wingspan||56.39 meters||185 feet|
|Wing area||372 sq meters||4,000 sq feet|
|Length||47.74 meters||156.63 feet|
|Height||14.73 meters||48.33 feet|
|Empty weight||74,400 kilograms||164,100 pounds|
|MTO weight||190,500 kilograms||419,900 pounds|
|Max speed||1,010 kmh||628 mph|
|Service ceiling||14,400 meters||47,300 feet|
|Operational Radius||5,760 kilometers||3,580 miles|
|Engine type||Pratt & Whitney J57-P-29W|
|No. of Engines||8|
The pressurized reconnaissance capsule for the RB-52s could be fitted into the bombbay in about four hours. It had accommodations for two systems operators, who sat on downward-firing ejection seats, and could be configured with different suites of reconnaissance gear. Possible kit could consist of long-focal-length and panoramic cameras plus photoflash flares for imaging reconnaissance; mapping radar and electronic intelligence (ELINT) receivers for electronic reconnaissance; and atmospheric instruments for weather reconnaissance. However, although a batch of capsules were obtained, there is no evidence that they were ever put into service; they were stockpiled for a few years and then scrapped.
An RB-52B was the first B-52 to go into formal operational service at Castle AFB, California, on 29 June 1955. Despite its complexity and size, the B-52 proved generally reliable in service, though the hydraulic systems and the air turbines did cause troubles that took time and effort to resolve. Most of the early B-52 variants also suffered from nagging fuel line leaks that would take several years and a number of update programs to get under control.
The aircraft was demanding and only the most experienced crews were allowed to fly it. It also required that many airbases be upgraded with new runways, hangars, maintenance facilities, and so on to support the big bomber. In the late 1950s, the need to disperse B-52 operations to as many airfields as possible, including overseas installations, to protect them from a nuclear first strike led to a multiplication of this demand on resources.
On 21 May 1956, a B-52B flying from Eniwietok Island in the Pacific performed the first airdrop of a US hydrogen bomb in the CHEROKEE test, part of the REDWING series of nuclear shots. It was the first time the B-52 dropped a live nuclear bomb. The weapon, a Mark 15 "Zombie" with a yield of almost four megatonnes, was dropped over Bikini Atoll. Due to a procedural screwup, the bomb detonated 30 seconds too soon, with the B-52 and other aircraft flying in the exercise caught up in the blast. They were badly beaten up but survived, which was fortunate as bailing out was not an option under the circumstances. B-52s would perform other test drops of nuclear weapons until 1963, when the US signed the Nuclear Test-Ban treaty, which prohibited above-ground testing to reduce releases of radioactive fallout into the environment.
Starting on 16 January 1957, three B-52Bs flew around the world nonstop under Project POWER FLITE, using mid-air refueling to stay aloft 45 hours and 19 minutes. The exercise was a clear demonstration of SAC's ability to reach any place in the world, just as the nuclear test drops demonstrated what the B-52 could do when it got there.