| 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 pressurized 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 night time 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.
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 pressurized 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). Part of Arnold's motivation for these studies was the fear that England might fall to the Nazis.
In that event, it would be imperative that the Army Air Force have a bomber capable of flying round-trip from the U.S. East Coast
to Europe to strike targets on the European mainland in active service. 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 analyzed 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 defense equipment. The Army Air Corps requested
the addition of self-sealing fuel tanks, more machine guns, and upgrade to higher caliber 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 pressurized 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 an
analog 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
The initial plan was to use B-29s to attack Japan from airfields in southern China,
with the main base in India, and to attack other targets in the region from China and India as needed. This was an extremely
costly scheme, as there was no land connection available between India and China, and all the supplies necessary had to be flown
over the Himalayas. The first B-29s started to arrive in India in early April, 1944. The
first B-29 flight to airfields in China (over the Himalayas, or "The Hump") took place on 24 April 1944. The first B-29 combat mission was flown on 5 June 1944, with 77 out of 98 planes launched from India
bombing the railroad shops in Bangkok (5 B-29s were lost to non-battle causes).
On June 15, 1944, 47 B-29s launched from
Chengtu in China bombed the Imperial Iron and Steel Works at Yawata, Japan. This was the
first attack on Japanese islands since the Doolittle raid in April,
1942. The first B-29 combat loss occurred during this raid, with 1 B-29 destroyed on the ground by Japanese fighters after an
emergency landing. Because of the extreme cost of operations, the raids against Japan from Chinese airfields continued at
relatively low intensity. Japan was bombed on: 7 July 1944 (14 B-29s), 29 July (70+), 10 August (24), 20 August (61), 8 September
(90), 26 September (83), 25 October (59), 12 November (29), 21 November (61), 19 December (36) and for the last time on 6 January
1945 (49). B-29s were withdrawn from airfields in China by the end of January, 1945. Throughout this period B-29 raids were also launched from China and India against many other
targets throughout South-East Asia. However, the entire B-29 effort was gradually shifted to the new bases in the Marianas, with
the last B-29 combat mission from India flown on March 29, 1945.
The need to use inconvenient bases in China for attacks against Japan ceased after the capture of the Marianas islands in 1944. On the islands of Tinian, Saipan and Guam a
series of airfields were built, which became the main bases for the large B-29 raids against Japan in the final year of the war.
The islands could be easily supplied by ship. The first B-29 arrived on Saipan on 12 October 1944, and the first combat mission was launched from there on
28 October 1944, with 14 B-29s attacking
the Truk atoll. The first mission against Japan from bases in the Marianas was flown on
24 November 1944, with 111 B-29s sent
to attack Tokyo. From that point ever more intense raids were launched regularly until
the end of the war. These attacks succeeded in devastating all large Japanese cities and gravely damaging Japan's war
industries.
Perhaps the most recognized B-29 is the Enola Gay, which dropped the
atomic bomb 'Little
Boy' on Hiroshima on 1945 August 6. The Bockscar, 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 in turn was replaced by the Boeing
B-52 Stratofortress. The final active duty variants were
phased out in the mid 1960s.
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 reverse engineering of three interned early-model B-29s. Some of
these remained in service into the 1960s in the Soviet Union. All but one of the Tu-4s
were scrapped in the 1960s. The lone example of a Tu-4 known to exist today is located at the Yuri Gagarin Air Force Academy near
Moscow, as a static display. This particular airplane was tasked with bombing the Budapest headquarters of the Hungarian rebel
movement during the 1956 rebellion; but although the mission was rehearsed it was never put into play.
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. As of December, 2004 the airplane has been moved to a
hangar on the flight line, with the fuselage (less tail empennage) mated to the center wing section which also contains the main
landing gear. The head of the project hopes Doc will fly in 2005.
Also, the United States Air Force
Museum at the old Wright-Patterson Air Force
base is considering restoring Bockscar to airworthy condition; it is
presently exhibited as a static display. The Smithsonian has the complete Enola Gay at
the Steven F. Udvar-Hazy Center as a static
display, but does not plan to bring the airplane back to flight status as that would likely compromise the preservation of the
plane as an historic item.
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. The
most specialisation was made in modifying planes for non-bombing mission profiles.
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 aircraft 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 program; 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 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
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 (30.2 m)
- Wingspan: 141 ft 3 in (43.1 m)
- Height: 27 ft 9 in (8.5 m)
- Wing area: 1736 ft² (161.3 m²)
- Empty: 74,500 lb (33,800 kg)
- Loaded: 120,000 lb (54,000 kg)
- Maximum takeoff: 133,500 lb (60,560 kg)
- Powerplant: 4× Wright R-3350-23 supercharged radial engines,
2,200 hp (1600 kW) each
Performance
- Maximum speed: 357 mph (574 km/h)
- Cruising speed: 220 mph (350 km/h)
- Combat range: 3,250 miles (5,230 km)
- Ferry range: 5,600 miles (9,000 km)
- Service ceiling: 33,600 ft (10,200 m)
- Rate of climb: 900 ft/min (270 m/min)
- Wing loading: 69.12 lb/ft² (337 kg/m²)
- Power/mass: 0.073 hp/lb (121 W/kg)
Armament
- 8× .50 in (12.7 mm) M2
machine guns in remote controlled turrets; 2× .50 in (12.7 mm) machine guns in manual turrets; 1× 20 mm M2 cannon in tail
- 20,000 lb (9,072 kg) of bombs
References and links
Related content
Related development: Boeing XB-15 - Boeing Y1B-20 - Tupolev Tu-4 - C-97 Stratofreighter - Boeing 377
Comparable aircraft: Lockheed XB-30 - Douglas XB-31 - B-32
Dominator - Messerschmitt Me 264
XB-39 Superfortress - XB-44 Superfortress -
B-50 Superfortress
Designation sequence: 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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