Boeing B-29 Superfortress

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B-29 Superfortress
Description
Role Heavy bomber
Crew 10
First Flight September 1942
Entered Service 1943
Manufacturer Boeing Corp.
Dimensions
Length 99 ft 30 m
Wingspan 141 ft 3 in 43 m
Height 27 ft 9 in 8.5 m
Wing Area ft² m²
Weights
Empty lb kg
Loaded lb kg
Maximum Takeoff 133,500 lb 60,600 kg
Capacity
Powerplant
Engines 4 x Wright R-3350
Power 4 x 2,200 hp 4 x 1,640 kW
Performance
Maximum Speed 357 mph 575 km/h
Combat Range miles km
Ferry Range 3,700 miles 6,000 km
Service Ceiling 33,600 ft 10,200 m
Rate of Climb ft/min m/min
Wing Loading lb/ft² kg/m²
Thrust/Weight
Power/Mass hp/lb kW/kg
Armament
Guns 0.5 in (12.7 mm) machine guns in remote controlled turrets (8); 0.5 in (12.7 mm) machine guns (2); 20 mm cannon in tail (1)
Bombs 20,000 lb (9,000 kg)

The Boeing B-29 Superfortress (Boeing Model 341/345) was a four-engine heavy bomber flown by the United States Army Air Force. It was one of the largest aircraft of World War II to see active service. When it entered service, it was one of the most advanced bombers of its time, featuring innovations such as a pressurised cabin, a central fire-control system, and remote-controlled machine gun turrets. It was designed to be a high altitude daytime bomber, but was most used in low-altitude nighttime incendiary bombing. It was the primary strike weapon used by the United States against Japan, and is best known for carrying the atomic bombs that destroyed Hiroshima and Nagasaki. Unlike many other bombers, the B-29 remained in service long after World War II ended; by the time it was retired in the 1960s, some 3,900 planes had been built.

Development

Boeing began planning for a very large, long-range bomber in 1938, an aircraft far larger than any yet built. The project was very ambitious; many felt it was too ambitious. The Model 341 project was not Boeing’s first attempt at a giant bomber. In 1936, they began work on the XB-15 (Model 294). While only a single prototype was built, it dwarfed anything on active duty at the time; its empty weight was only 13% less than that of the B-29. A descendant of this project, the Y1B-20 (Model 316), was actually heavier by 17% than the B-29; this project never made it past the design stage. The famous B-17 Flying Fortress had been almost as ambitious when it was first planned in 1934. The B-17 did not fit the specifications requested by the Army Air Corps, but they were intrigued by its performance. In 1938, Boeing agreed to do a design study on a more advanced development of the B-17, which would feature a pressurised cabin. This design study (Model 322), submitted to the Army Air Corps in 1939 would become the B-29.

Around 1938, General Henry H. ‘Hap’ Arnold, the head of the Army Air Corps, was growing alarmed at the possibility of war in Europe and in the Pacific. Hoping to be prepared for the long-term requirements of the Air Corps, Arnold created a special committee chaired by Brigadier General W. G. Kilner; one of its members was Charles Lindbergh. After a tour of Luftwaffe bases, Lindbergh became convinced that Nazi Germany was far ahead of other European nations. In a report in 1939, the committee made a number of recommendations, including development of new long-range heavy bombers. When war broke out in Europe, Arnold requested design studies from several companies on a Very Long-Range bomber capable of traveling 5000 miles (8000 km). Approval was granted on December 2. This request, R-40B, fitted perfectly with the research Boeing was doing at the time.

By 1940 January, the B-17 was just entering service and the somewhat larger Consolidated B-24 was still more than a year away. At this time, the Air Corps issued a request for proposals for a much larger bomber, which was to have the range for operation over the Pacific; this bomber would serve in the inevitable war with Japan. Four firms submitted design studies, which would be the Boeing XB-29, Lockheed XB-30, Douglas XB-31, and Consolidated XB-32. Douglas and Lockheed soon withdrew, in part because Boeing was significantly ahead of them in the design process. In 1940 September, Boeing and Consolidated were awarded development contracts for the XB-29 and the XB-32, respectively.

In early 1940, the Army Air Corps analysed the performance of bombers used in Europe against the Luftwaffe, concluding that for the B-29 to be successful, it needed several upgrades in its defence equipment. The Army Air Corps requested the addition of self-sealing fuel tanks, more machine guns, and upgrade to higher calibre guns. Boeing incorporated these into a redesign of the Model 341, and resubmitted it to the Army Air Corps as Model 345, which would become the XB-29.

The combination of Boeing’s extensive design work and its experience with huge bombers worked well for Boeing. Even before the prototype had flown for the first time in 1942 September, the Army Air Corps had placed a massive order for 1500 B-29s, impressed by the mock-up completed in the spring 1941. A long-range bomber was urgently needed, so the service testing proceeded largely in tandem with production. The first B-29 rolled off the assembly line two months after the first service test flight. In under a year, the B-29 was in full-scale production.

At the time it was built, the B-29 was a giant airplane: it was 99 ft (30 m) long, had a wingspan of 141 ft (43 m), weighed more than 74,000 lb (34,000 kg) when empty, and was nearly twice as heavy as the heaviest previously serving bomber. Its exceptional range was achieved using mid-set wings with a high aspect ratio. To reduce the dangerously high landing speed of the B-29, it was fitted with enormous Fowler flaps. It had three separate pressurised crew compartments: one in the nose, a second one aft of the wing for the gunners, and an isolated compartment for the tail gunner.

Rather than fit the traditional bulky manned gun turrets, Boeing used small, remote-control units ‘networked’ together with a digital computer that compensated for factors such as air temperature and bullet drop. This system was very difficult to develop, but it proved effective. There are several accounts of ‘healthy’ B-29s peeling out of formation to drive off—successfully—fighters preying on damaged brethren.

Manufacturing

Manufacturing the B-29 was an immense task. It involved four main factories: two Boeing plants at Renton, Washington and Wichita, Kansas, a Bell plant at Marietta, Georgia, and a Martin plant at Omaha, Nebraska. Thousands of sub-contractors were involved in the project. Because of its highly advanced design, challenging requirements, and immense pressure for production, development was deeply troubled. The first prototype crashed during testing, killing the entire crew and several ground personnel. Changes to the production craft came so often and so fast that in early 1944, B-29s would leave the production lines and fly directly to modification depots for extensive rebuilds to incorporate the latest changes. This ‘battle of Kansas’ nearly sank the program, which was only saved by General Hap Arnold’s direct intervention. It would still be nearly a year before the aircraft was operated with any sort of reliability.

The most common cause of maintenance headaches and catastrophic failures, even more so than the advanced gunnery system, was the engine. Though the Wright R-3350 would later become a trustworthy workhorse in large piston-engined aircraft, early models were beset with dangerous reliability problems. It had an impressive power-to-weight ratio, but this came at a heavy cost to durability. Worse, the cowling Boeing designed for the engine was too close (out of a desire for improved aerodynamics), and the early cowl flaps caused problematic flutter and vibration when open in most of the flight envelope.

These weaknesses combined to make an engine that would overheat regularly when carrying combat loads; it frequently swallowed its own valves. The resulting engine fires were exacerbated by a crankcase designed mostly of magnesium alloy. The heat was often so intense the main spar burned through in seconds, resulting in catastrophic failure of the wing. This problem would not be fully cured until the aircraft was re-engined with the more powerful Pratt & Whitney R-4360 ‘Wasp Major’ in the B-29D/B-50 program, which arrived too late for World War II. Pilots, including the present-day pilots of the Commemorative Air Force’s Fifi, describe flight after takeoff as being an urgent struggle for airspeed; generally, flight after takeoff should consist of striving for altitude. Radial engines need that airflow to keep cool, and failure to get up to speed as soon as possible could result in an engine failure and risk of fire.

Operational History

Perhaps the most recognized B-29 is the Enola Gay, which dropped the atomic bomb ‘Little Boy’ on Hiroshima on 1945 August 6. The Bock's Car, also a B-29, dropped ‘Fat Man’ on Nagasaki three days later.

The B-29 was used in World War II only in the Pacific Theatre. It was later used in the Korean War, over the course of which they flew 20,000 sorties and dropped 200,000 tons (180,000 tonnes) of bombs. 3970 of the aircraft were built before they were retired in 1960.

The Soviet Air Force’s Tupolev Tu-4 was a bolt-for-bolt copy of the B-29, first widely revealed to the world audience in 1947 August. It was based on four downed B-29s that were captured and interned by the Soviet Union when they crashed during bombing raids on Japan.

Obsolescense

The B-29 was soon made obsolete by the development of the jet engine. With the arrival of the mammoth B-36, it suffered its first ignominy by being classified a medium bomber with the new Air Force. However, the later B-29D/B-50 variant was good enough to be tasked with a number of auxiliary roles such as air-sea rescue, electronic intelligence gathering, and even air-to-air refueling. It was replaced in its primary role during the early 1950s by the Boeing B-47 Stratojet, which was later replaced by the Boeing B-52 Stratofortress. The final active duty variants were phased out in the mid 1960s.

Currently Airworthy Aircraft

As of 2003 August, the only B-29 in the world which is still airworthy is the Commemorative Air Force’s Fifi. However, work is actively proceeding at the Boeing plant in Wichita, Kansas on restoring a B-29 named Doc, and the airplane is expected to fly in 2004. Also, the United States Air Force Museum at the old Wright-Patterson Air Force base is considering restoring Bock’s Car to airworthy condition; it is presently restored as a static display. The Smithsonian has not decided whether to restore Enola Gay as a static display or to bring the airplane back to flight status.

Variants and Design Stages

  • XB-29—The XB-29 (Model 345), was the prototype model of the B-29 delivered to the Army Air Corps. It incorporated a number of improvements on the Model 341 design originally submitted, including more and bigger guns and self-sealing fuel tanks. Two aircraft were ordered in 1940 August, and a third was ordered in December. A mock-up was completed in the spring of 1941, and it first flew in 1942 September 21. Testing continued until 1943 February 18, when the second prototype crashed due to an in-flight engine fire that burned through the wing. Following the crash, the Army Air Corps took over the testing programme. (×3)
  • YB-29—Improved version of the XB-29 used in service testing. The engines were upgraded from Wright R-3350-13s to R-3350-21s, and it was changed from three blade propellers to four. The machine guns on the YB-29 were standardised at five .50-calibre turret-mounted pairs. It also featured a better fire control sytem. Testing began in the summer of 1943, and dozens of modifications were made to the planes. (×14)
    • XB-39—The first YB-29 delivered to the Army was modified by General Motors to use Allison V-3420-17 liquid-cooled inline engines; it was redesignated XB-39. Testing on it began in early 1944. The primary purpose of it was similar to that of the XB-38: a proof-of-concept plane to demonstrate that liquid-cooled engines could be used if the Wright R-3350 was scarce. Since this was never a problem, and most flaws of the B-29 were worked out by the time production began, the XB-39 was never ordered. (×1, converted)
    • YB-29 Defence Test—The fourth YB-29 delivered was modified to test arrangements of defensive armament. In the first arrangement, there was a nose-mounted ball turret and two forward-fixed blisters on the fuselage with a pair of .50-calibre machine guns in each. The second arrangement used a manned dorsal turret, a manned ball turret in the belly, and two manned waist gunner positions, with remote turrets in the cheeks. (×1, converted)
  • B-29—As the B-29 was urgently needed, production aircraft were developed in parallel with service testing: the first B-29 was produced just two months after the first YB-29 was delivered. (×2,513)
  • B-29A—Improved version of B-29; built exclusively at the Boeing plant in Renton, Washington. In the B-29A, the wing design was improved, and the number of guns in the forward dorsal turret was increased from two to four, due to a demonstrated weakness in head-on fighter attacks. Where previous models had wings manufactured in two sections, the B-29A was made in three, increasing its strength and ease of construction. The B-29A was produced until 1946 May, when the last aircraft was completed. It was much used during the Korean War, but was quickly phased out when the jet bomber became operational. (×1,119)
  • B-29B—A B-29 modifcation used for low-level raids against Japan during World War II. Since fighter opposition was minimal over Japan in late 1944, many of the Army Air Corps leadership (particularly General Curtis LeMay), felt that a lighter faster bomber would better evade the flak being thrown against American bombers. In the B-29B, all defensive armament (with the exception of the tail turret) was removed. The M-2 cannon was replaced with two .50 in machine guns. The tail turret was fired automatically by an AN/APG-15B radar fire control system. With the General Electric gun system removed, the top speed of the B-29B was increased from 357 mph (574 km/h) to 364 mph (586 km/h). All were built by Bell. (×311)
  • B-29C—The B-29C was a B-29A development re-engined with improved Wright R-3350 engines. The Army Air Corps ordered 5,000 but cancelled the orders when World War II ended. (×0)
  • B-29D—Improved B-29 featuring Pratt and Whitney R-4360-35 engines of 3500 hp (2611 kW) each, a taller vertical stabilizer and a strengthened wing. The B-29D was designed as an improved version of the basic B-29 featuring Pratt & Whitney R-4360-35 radial engines of 3500 horsepower each, a taller vertical stabilizer and a strengthened wing. When World War II ended, drastic cutbacks in spending changed the B-29 programme. Because Congress was reluctant to continue funding wartime programmes, it was redesignated B-50 to make it appear completely new, and the design changes were significant enough to keep the programme from being scrapped. (×0)
  • XB-29E—A B-29 modified to test various fire-control systems in flight. (×1, converted)
  • B-29F—A number of B-29s were modified to test cold weather operations in Alaska. (×6, converted)
  • XB-29G—A modified B-29B with jet engine test stations and instrumentation. It was stripped of all armament, and used its bomb bay to house prototype jet engines for flight testing; they were extended into the air stream for testing and retracted when on the ground. The XB-29G was used to test the Allison J35, General Electric J47, and General Electric J73. (×1, converted)
  • XB-29H—A B-29A modified to test various armament configurations. (×1, converted)
  • YB-29J—A number of B-29s of various designation received engine upgrade to Pratt and Whitney R-3350-79. Other engine-associated items were also upgraded, including the installation of Curtiss propellers, and engine cowlings with separate oil cooler air intakes—an arrangement called the ‘Andy Gump’ cowling. One of these (originally a B-29B) dubbed the ‘PACUSAN Dreamboat’, set a number of long-distance flight records. (×6, converted)
    • YKB-29J—Two YB-29Js were converted to aerial refueling tanker prototypes. Both were originally B-29s. (×2, converted)
    • RB-29J—Designated FB-29J prior to 1948, the RB-29J was a conversion of the B-29 used for reconnaissance. (×2 or more)
  • B-29K
    • CB-29K—Cargo conversion. (×1)
    • KB-29K—Original designation of KB-29M.
  • B-29L—Original designation of B-29MR.
  • B-29M
    • KB-29M—At first designated KB-29K, the KB-29M was a modification of B-29s and B-29As to perform In-Flight Refueling. In the first system used by the KB-29M, the KB-29M would unreel its hose towards the receiving aircraft, which would snag it and reel it in. The hose would then connect with internal fuel compartments and pumping would begin. While this system was clumsy, it was often used in the late 1940s before a better system was developed. (×92, converted)
      During the famous circumnavigation by the Lucky Lady II in 1949, this was the technique used to refuel.
      As better techniques were developed, some KB-29Ms were modified to use ‘probe-and-drogue’ systems, in which the refueling hose has a basketlike ‘para-drogue’ attached to the end, and the receiver has a probe mounted on the nose or wing, which the pilot would fly into the torus to link the hose.
    • B-29MR—At first designated B-29L, the B-29MR was a modification of B-29s and B-29As to be the receiver aircraft for KB-29Ms. (×74, converted)
  • B-29P
    • KB-29P—In an effort to improve on the probe-and-drogue system, Boeing developed a rigid flying boom system, which was first used on the KB-29P. The boom was mounted on the aftmost end of the KB-29P, and had two small wings. With these wings, the boom could be manoevered by the operator. The flying boom system became the most common method for In-Flight Refueling and was used on KB-50s and KC-97s; it is also used on modern tankers such as the KC-135 and KC-10. (×116, converted)
  • B-29T
    • YKB-29T—Modified KB-29M with refueling hoses on each wingtip, for a total of three. It served as the prototype for the KB-50D. (×1, converted)
  • EB-29—The EB-29 (E stands for exempt), was used as a carrier aircraft in which the bomb bay was modified to accept and launch experimental aircraft. They were converted in the years following World War II. One EB-29 was converted to carry the Bell X-1 until it was replaced by a B-50. Another was used to carry and test the XF-85 ‘parasite bomber’. (×1 for X-1 programme; ×1 for XF-85 programme)
  • SB-29 ‘Super Dumbo’—B-29s adapted for air rescue duty after World War II. Modified to carry a droppable A-3 lifeboat under the fuselage, the SB-29 was used mainly as rescue support for air units that flew long distances over water. With the exception of the forward lower gun turret, all defensive armament was retained. It was used throughout the Korean War into the mid-1950s. (×16, converted (15 B-29s, 16 B-29As))
  • TB-29—Trainer conversion of B-29 used to train crew for bombing missions; some were also used to tow targets. They also served as radar targets in the 1950s when the United States Air Force was developing intercept tactics for its fighters. The TB-29 designation was also used for B-29s modified for target towing.
  • WB-29—Production aircraft modified to do weather missions. They conducted standard data-gathering flights, but were also ordered to fly into the eye of a hurricane or typhoon to gather information. Following nuclear weapons tests, some WB-29s would use air sampling scoops to test radiation levels. (×)
  • Airborne Early Warning—In the middle of 1951, three B-29s were modified to participate in the Airborne Early Warning programme. The upper section of the forward fuselage was extensively modified to house an AN/APS-20C search radar, and the interior was modified to house radar and Electronic Counter Measures (ECM) equipment. This development led to production radar picket aircraft, including the EC-121 Warning Star. (×3, converted)

Units Using the B-29

United States Army Air Corps

  • 20th Air Force
  • 58th Bombardment Wing

Royal Air Force

Specifications (B-29)

General Characteristics

Dimension diagram

  • Crew: 10: Pilot, Co-Pilot, Flight Engineer, Bombardier, Navigator, Radio Operator, Side Gunners (2), Top Gunner, and Tail Gunner
  • Length: 99 ft 0 in (30.18 m)
  • Wingspan: 141 ft 3 in (43.05 m)
  • Height (taxi position): 27 ft 9 in (8.46 m)
    • …to centreline of propeller hub:
      • Inboard engines: 9 ft 6 in (2.9 m)
      • Outboard engines: 10 ft 8 in (3.3 m)
    • Clearance of inboard propellers: 14 in (360 mm)
  • Maximum fuselage diameter: 9 ft 6 in (2.9 m)
  • Wing area: 1736 ft² (161.3 m²)
    • …without ailerons: 1610 ft² (149.6 m²)
    • …with flaps extended, plus ailerons: 2071 ft² (631.2 m²)
    • Total aileron area: 129.2 ft² (12 m²)
    • Total flap area: 332 ft² (30.8 m²
  • Wings:
    • Root: 22%
    • Tip: 7%
    • Chord Root: 17 ft (5.2 m)
    • Chord tip: 7 ft 5 in (2.3 m)
    • Incidence Angle: 4º
    • Dihedral Angle: 4.5º
    • Sweepback Angle: 7º
  • Stabliser:
    • Span: 43 ft (13.1 m)
    • Maximum chord: 11 ft 2 in (3.4 m)
  • Empty: 74,500 lb (33,793 kg)
  • Loaded: 120,000 lb (54,432 kg)
  • Maximum takeoff: 133,500 lb (60,556 kg)
  • Fuel Tanks: 7912 gal (29,950 L)
    • Regular Wing (22 cells): 4669 gal (17,674 L0
    • Auxiliary Centre Wing (4 cells): 1110 gal (4201 L)
    • Auxiliary Bomb Bay (4 cells): 2133 gal (8074 L)
  • Powerplant: 4× Wright R-3350-21, R-3350-23, R-3350-41, R-3350-57, or R-3350-79 B-11 turbo-supercharged radial engines; 2,200 hp (1641 kW) each; gear ratio of 20:7 (.35)
    • Propeller diameter: 16 ft 7 in (5 m); four-blade, full feathering

Performance

  • Maximum speed: 357 mph (446 km/h)
  • Cruising speed: 220 mph (354 km/h)
  • Combat Range: 3,250 miles (5229 km)
  • Ferry Range: 5,600 miles (9010 km)
  • Service ceiling: 33,600 ft (10,241 m)
  • Rate of climb: 900 ft/min (274 m/min)
  • Wing loading: 69.12 lb/ft² (337.46 kg/m²)
  • Power/Mass: 0.073 hp/lb (0.121 kW/kg)

Armament

  • 8× 0.50 in (12.7 mm) machine guns in remote controlled turrets; 2× 0.5 in (12.7 mm) machine guns in manual turrets; 1× .79 in (20 mm) cannon in tail
  • 20,000 lb (9072 kg) of bombs

References and Links

Related content
Related Development

B-50 Superfortress - Tupolev Tu-4

Similar Aircraft
Designation Series

B-26 - XB-27 - XB-28 - B-29 - XB-30 - XB-31 - B-32

Related Lists

List of military aircraft of the United States - List of bomber aircraft

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