B-29 Superfortress

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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, a few being employed as flying television transmitters for Stratovision. By the time it was retired in the 1960s, some 3,900 planes had been built.

A B-29 being flown during training at Maxwell Air Force Base
for transition to bombing from the B-29

Contents

1 Development

2 Manufacturing

3 Operational History

3.1 Currently Airworthy Aircraft

4 Variants and Design Stages

5 Units Using the B-29

5.1 United States Army Air Force
5.2 Royal Air Force

6 Specifications (B-29)

6.1 General Characteristics
6.2 Performance
6.3 Armament

7 References and Links

8 Related content

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, 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 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.

The Tupolev Tu-4 was almost copied bolt-for-bolt from the B-29

Shortly after World War II, the Tupolev design bureau in the Soviet Union manufactured a near-copy of the B-29, the Tupolev Tu-4, based on the reverse engineering of three captured B-29s. Some of these remained in service into the 1960s in the Soviet Union, and a few examples may still be in use in the People's Republic of China.

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

Main article: B-29 Superfortress Variants

Unlike many other aircraft designed to play a similar role, the variants of the B-29 were all essentially the same. The developments made between the first prototype XB-29 and any of the three versions flown in combat were all minuscule. There was some specialisation for more narrow mission types, but this was also for the most part negligible.

The biggest differences were between variants modified for non-bomber missions. In addition to acting as cargo carriers, rescue aircraft, weather ships, and trainers, some were used for odd purposes such as flying relay television transmitters under the name of Stratovision. Other aircaft acted as the mothership for experimental aircraft, including the Bell X-1 and XF-85 Goblin. One modified B-29 was used to develop the Airborne Early Warning programme; it was the ancestor of various modern radar picket aircraft.

Some B-29s were modified to act as test beds for various new systems or special conditions, including a fire-control systems, cold weather operations, and various armament configurations. Several converted B-29s were used to experiment with aerial refueling. Perhaps the most important tests were conducted by the XB-29G; it carried prototype jet engines in its bomb bay, and lowered them into the air stream to conduct measurements.

Units Using the B-29

United States Army Air Force

Twentieth Air Force
- XX Bomber Command
- XXI Bomber Command

Royal Air Force

Specifications (B-29)

General Characteristics

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: 27 ft 9 in (8.46 m)
Wing area: 1736 ft² (161.3 m²)
Empty: 74,500 lb (33,793 kg)
Loaded: 120,000 lb (54,432 kg)
Maximum takeoff: 133,500 lb (60,560 kg)
Powerplant: 4× Wright R-3350-23 turbo-supercharged radial engines, 2,200 hp (1641 kW) each

Performance

Maximum speed: 357 mph (446 km/h)
Range: 5,600 miles (9,010 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× .50 in M2 machine guns in remote controlled turrets; 2× .50 in machine guns in manual turrets; 1× 20 mm M2 cannon in tail
20,000 lb (9,072 kg) of bombs

References and Links

Wheeler, Keith. Bombers over Japan (World War II). Time-Life Books, 1982
Higham, Robin, et al. Flying American Combat Aircraft of WW II: 1939-1945. Stackpole Books, 2004.
B-29.org
B-29 Restoration Gallery
Encyclopedia of American Aircraft
National Air and Space Museum
Preserved Aircraft
Tu-4, Soviet B-29 copy
University of San Diego
USAF Museum
Warbirds Resource Group