Science Fair Project Encyclopedia
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.
The earliest development of the B-29 can be traced to Project A, a 1934 Army feasibility study for a bomber that could fly 5000 miles while carrying a ton of bombs. This was an ambitious goal for an air force whose largest bombers at that time were two-engine models. In June of that year, Boeing presented the Army with the Boeing Model 294. The Army liked the design, and eventually designated it the XB-15. 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.
In August of 1934, Boeing also began work on a slightly less ambitious design, the Model 299. This design became the B-17 Flying Fortress. In 1938, Boeing agreed to do a design study on a more advanced development of the B-17, the Model 322, which would feature a pressurized cabin. However, the project was deemed infeasible and abandoned.
In March of 1936, a team lead by Lysle Wood began work on an updated XB-15, the Model 316. This plane already featured the all-glass nose that would later make the B-29 distinctive. Designated the Y1B-20, it was actually heavier by 17% than the eventual B-29, but the Army was not interested. Boeing continued heavy bomber development in 1938 and 1939 with Models 330, 333, 333A, 333B, 334, and 334A. In August of 1939 they began work on the Model 341, featuring a much improved wing, the Boeing Model 115 airfoil.
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 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.
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.
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 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
- 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
- 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)
- 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
- Bowers, Peter M. Boeing B-29 Superfortress (Warbirdtech Series , Volume 14). Minnesota: Voyageur Press, 1999. (ISBN 0933424795)
- LeMay, Curtis and Bill Yenne. Super Fortress. Berkley Book, 1988. ISBN 0425118800
- Pace, Steve. Boeing B-29 Superfortress. United Kingdom: Crowood Press, 2003. (ISBN 1861265816)
- Wheeler, Keith. Bombers over Japan (World War II). Time-Life Books, 1982. (ISBN 0809434296)
- Mann, Robert A. The B-29 Superfortress: A Comprehensive Registry of the Planes and Their Missions. McFarland & Company, 2004. (ISBN 0786417870)
- Vander Meulen, Jacob. Building the B-29. Smithsonian Books, 1995. (ISBN 1560986093)
- The economic aspect of the B-29 program
- Higham, Robin, et al. Flying American Combat Aircraft of WW II: 1939-1945. Stackpole Books, 2004. (ISBN 0811731243)
- Wagner, Ray. American Combat Planes. Doubleday, 1982. (ISBN 0930083172)
- 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
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