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The Boeing B-29 Superfortress was a four-engine heavy bomber propeller aircraft flown by the United States Army Air Forces in World War II and other military organizations afterwards. The name "Superfortress" was derived from its well-known predecessor, the B-17 Flying Fortress.
The B-29 Boeing Model 345 (earlier models were not accepted) was one of the largest aircraft to see service during World War II. 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 as a high-altitude daytime bomber, but flew more low-altitude nighttime incendiary bombing missions. It was the primary aircraft in the U.S. firebombing campaign against Japan in the final months of World War II, and B-29s carried the atomic bombs that destroyed Hiroshima and Nagasaki. Unlike many other bombers, the B-29 remained in service long after the war 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 airframe was further developed into the B-50 for the USAF, and the Soviet Union developed a virtual carbon copy Tupolev Tu-4 which was reverse engineered from confiscated B-29 airplanes.
Design and developmentEdit
Manufacturing the B-29 was a complex task. It involved four main assembly factories: two Boeing plants at Renton, Washington and Wichita, Kansas, a Bell plant at Marietta, Georgia ("Bell-Atlanta"), and a Martin plant at Omaha, Nebraska ("Martin-Omaha"). Thousands of subcontractors were involved in the project. Because of its highly advanced design, challenging requirements, and immense pressure for production, development was deeply troubled. On February 18, 1943 the second prototype crashed during testing due to an engine fire that spread to the wing, killing the entire ten man crew and twenty others in the Frye meat packing plant just north of Boeing Field. 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' (a trouble-shooting modification program to get four groups ready for combat by January 1, 1944) 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 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, many caused by demands that the B-29 be put in operation as soon as possible. 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. The 18 radial cylinders, compactly arranged in front and rear rows, overheated because of insufficient flow of cooling air, which in turn caused exhaust valves to unseat.
These weaknesses combined to make an engine that would overheat regularly at combat weights, particularly during climbs after takeoff. Unseated valves released fuel-air mixtures during engine combustion that acted as a blowtorch against the valve stems. When these burned through the engines disintegrated and caught fire. A fire that was not immediately contained in the forward part of the engine by fire extinguishers became impossible to put out. An accessory housing manufactured of magnesium alloy in the back of the engine would often catch fire and produce heat so intense it burned through the firewall to the main wing spar in no more than 90 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. Interim measures included cuffs placed on propeller blades to divert a greater flow of cooling air into the intakes, which had baffles installed to direct a stream of air onto the exhaust valves. Oil flow to the valves was also increased, asbestos baffles installed around rubber push rod fittings to prevent oil loss, thorough pre-flight inspections made to detect unseated valves, and frequent replacement of the uppermost 5 cylinders (every 25 hours of engine time) and engines (75 hours).
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. One helpful technique was doing a rolling start, rather than a braked start, and checking the magnetos while already in motion.
In wartime, the B-29 was capable of flight up to 30,000ft high at speeds of up to 350 mph (true airspeed). This was its best defense, for fighters of that day could barely get that high, and few could catch it, even if they were already up there and waiting. Only the heaviest of anti-aircraft weapons could reach it and as Axis forces did not have proximity fuzes actually hitting the plane was next to impossible.
The crew enjoyed, for the first time in a bomber, full pressurized comfort. This first-ever cabin pressure system for a production bomber was developed for the B-29 by Garrett AiResearch Manufacturing Co. The nose and the cockpit were pressurized, but the designers were faced with deciding whether to have bomb bays that were not pressurized, between fore and aft pressurized sections, or a fully pressurized fuselage with the need to de-pressurize to drop their loads. The decision was taken to have a long tunnel over the two bomb bays so that crews could crawl back and forth between the fore and aft sections, with both areas and the tunnel pressurized.
World War IIEdit
The initial plan, implemented at the direction of President Roosevelt as a promise to China and called Operation Matterhorn, was to use B-29s to attack Japan from four forward bases in Guangxi, Southern China, with five main bases in Bangladesh,India, and to attack other targets in the region from China and India as needed. The Chengdu region was eventually chosen over the Guilin region to avoid having to raise, equip, and train fifty Chinese divisions to protect the advanced bases from Japanese ground attack. The XX Bomber Command, initially intended to be two combat wings of four groups each, was reduced to a single wing of four groups because of the lack of availability of aircraft, automatically limiting the effectiveness of any attacks from China.
This was an extremely costly scheme, as there was no overland connection available between India and China, and all the supplies had to be flown over the Himalayas. 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 (Five B-29s were lost to non-combat causes).
On 15 June 1944, 47 B-29s launched from Chengdu 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 one 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: July 7, 1944 (14 B-29s), 29 July (70+), 10 August (24), 20 August (61), 8 September (90), 26 September (83), 25 October (59), November 12 (29), November 21 (61), December 19, (36) and for the last time on January 6, 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 Southeast 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 five major airfields, each constructed as a base for a four-group wing of B-29s, became the launch sites 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 October 12 1944, and the first combat mission was launched from there on October 28, 1944, with 14 B-29s attacking the Truk atoll. The first mission against Japan from bases in the Marianas was flown on November 24, 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 (with the exception of Kyoto) and gravely damaged Japan's war industries. Although less appreciated, the aerial mining program carried out by B-29s against Japanese shipping routes and harbor approaches had profoundly degraded Japan's ability to support its population and fight the war.Perhaps the most famous B-29 is the Enola Gay, which dropped the atomic bomb 'Little Boy' on Hiroshima on August 6, 1945. Bockscar, another B-29, dropped another atomic bomb 'Fat Man' on Nagasaki three days later. Both aircraft were handpicked for modification from the assembly line at the Omaha plant that was to become Offutt Air Force Base.
The B-29 was used in World War II only in the Pacific Theatre.
Alerted to the existence of the secret B-29 project by comments made by Captain Eddie Rickenbacker during a government mission to Russia in 1943, the Soviets mounted an extensive espionage campaign to learn details of the new design. Then three battle-damaged Superfortresses made emergency landings in Soviet territory after missions to Japan, providing templates for a daunting task of reverse-engineering that represented a quantum leap in Russian aeronautical design. In 1947, the Soviets debuted both the Tupolev Tu-4 copy of the B-29, and the Tupolev Tu-70 transport variant. The three B-29s were named Ramp Tramp (42-6256), Ding Hao (42-6358), and The General H.H. Arnold Special (42-6365).  
Korean Conflict and Postwar ServiceEdit
The B-29 was later used in the Korean War. At first, the bomber was used in normal strategic daylight bombing missions, though North Korea's few strategic targets and industries were quickly reduced to rubble. More importantly, in 1950 numbers of Soviet MiG-15 'Fagot' jet fighters appeared over Korea (a plane specifically designed to shoot down the B-29), and after the loss of several aircraft, future B-29 raids were restricted to night-only missions, largely in an interdictive role. Over the course of the war, B-29s flew 20,000 sorties and dropped 200,000 tons (180,000 tonnes) of bombs. B-29 gunners were credited with shooting down 27 enemy aircraft.
The B-29 was soon made obsolete by the development of the jet engine. With the arrival of the mammoth Convair B-36, the B-29 was reclassified as a medium bomber with the new Air Force. However, the later B-50 variant (which was initially designated B-29D) was good enough to handle auxiliary roles such as air-sea rescue, electronic intelligence gathering, and even air-to-air refueling. The B-50D 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. 3,970 B-29s were built before they were retired in 1960.
In flight, the pilot called for engine and flap settings, much like a ship captain would call for "left rudder" or "full speed ahead," instead of moving the throttles and the flap levers himself. Another innovation was the number of calculations the crew had to perform before and during the mission. Prior to the B-29, flight manuals provided only approximate performance figures and pilots relied largely on instincts and experience. The B-29 manual had charts to compute takeoff and landing speeds based on weight, elevation, and temperature. Finding the optimum power settings for cruise required consideration of cruise altitude, outside temperature, aircraft weight, and desired true airspeed. The power settings were recalculated every two hours or with every change in altitude. These types of computations are routine in modern civil and military aviation but were a groundbreaking innovation in 1944. The benefits of improved range and performance were irrefutable.
Most pilots found the B-29 relatively mild-mannered, though its unboosted controls were extremely heavy and required considerable physical strength to operate (Higham 1975). Though it could be flown with only two engines once airborne, the plane suffered from engine overheating issues throughout its service; several B-29s crashed in Saipan after a single engine failure on takeoff at full gross weight.
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, excluding the Silverplate models built for the Manhattan Project. 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.
A later variant of the B-29, the B-50 which was powered by four 3500 hp Pratt & Whitney R-4360-35 Wasp Major engines acted as the mothership for experimental aircraft, including the Bell X-1, the XF-85 Goblin and F-84s as in flight lock on and offs. It was also 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 KB-29. 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.
- USSR - Tupolev Tu-4 based on the three B-29s which forced landed in the USSR during World War II
- United Kingdom - 88 standard B-29 Leased to the UK as the Washington Mk I
- United States
Three other B-29 projects are being restored for flight.
Another 25 confirmed B-29s are preserved at various museums worldwide, along with known wreck sites of three more.
- Johnson, Robert E. "Why the Boeing B-29 Bomber, and Why the Wright R-3350 Engine?" American Aviation Historical Society Journal 1988 33(3): 174-189. ISSN 0002-7553
- Mann, Robert A. (2004). The B-29 Superfortress: A Comprehensive Registry of the Planes and Their Missions. Jefferson, North Carolina: McFarland & Company. ISBN 0-7864-1787-0.
- Pace, Steve (2003). Boeing B-29 Superfortress. Ramsbury, Marlborough, Wiltshire, United Kingdom: Crowood Press. ISBN 1-86126-581-6.
- Vander Meulen, Jacob (1995). Building the B-29. Washington, D.C.: Smithsonian Books. ISBN 1-56098-609-3). (The economic aspect of the B-29 program)
- Wheeler, Keith (1982). Bombers over Japan. Virginia Beach, Virginia: Time-Life Books. ISBN 0-8094-3429-6.
- Boeing B-29 Superfortress.Baugher's Encyclopedia of American Aircraft. Accessed on August 11, 2007.
- National Museum B-29 Superfortress Official Fact Sheet. Accessed on August 11, 2007.
- National Museum of the USAF New official website. Access on August 11, 2007.
- National Museum's Fact Sheets of B-29 versions Official USAF Website
- 330th.org, 20th AF, 314th BW, 330th BG history and first-hand accounts
- B-29 "DOC" Restoration Project, the restoration of Doc
- National Air and Space Museum, Smithsonian page on Enola Gay
- Preserved Aircraft, status of preserved B-29's
- Russian B-29 Clone, the reverse-engineered Tu-4
- Bombers Over Japan, development, photos, and history
- Warbirds Resource Group, specifications and photos
- 'Birth of the B29', film with anti-Japanese propaganda; footage of B-29 construction and testing begins at 4:00
- Pelican's Perch #56:Superfortress!, Article wrote by John Deakin, one of the pilots who regularly fly the world's only remaining flyable B-29
- WarbirdsRegistry.org B-29/B-50, Listing of surviving B-29's
- B-29.org, history and first-hand accounts
- New England Air Museum's B-29 "Jack's Hack"
- Annotated bibliography on the B-29 from the Alsos Digital Library
- T-Square-54: The Last B-29 website, by Tom Mathewson
- Museum of Flight
- China Lake Alumi Website by China Lake Museum Foundation, desert photos of aircraft under web sections: B-29s #1 and B-29s #2.
- US Naval Air Warfare Center Weapons Division
- A childhood memory of B29s
- On World of War Wiki
- KB-29 Superfortress
- XB-39 Superfortress
- XB-44 Superfortress
- B-50 Superfortress
- C-97 Stratofreighter
- Boeing 377
- Tupolev Tu-4
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