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B-29_Superfortress

B-29 Superfortress

The Boeing B-29 Superfortress was a four-engine propeller powered heavy bomber that was flown by the United States Military in World War II and the Korean War, and by other nations afterwards. The name "Superfortress" was derived from that of its well-known predecessor, the B-17 Flying Fortress, and carried on a series of names for Boeing-built bombers followed by the B-52 Stratofortress.

The B-29 was one of the largest airplanes 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. Though it was designed as a high-altitude daytime bomber, in practice it actually flew more low-altitude nighttime incendiary bombing missions. It was the primary aircraft in the U.S. firebombing campaign against the Empire of 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, with a few even being employed as flying television transmitters for the Stratovision company. The type was finally retired in the early 1960s, with 3,960 aircraft.

Subsequent improvements led to the USAF B-50 Superfortress.

Design and development

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 18 February 1943 the second prototype crashed during testing due to an engine fire that spread to the wing, killing the entire 10 man crew and 20 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 troubleshooting modification program to get four groups ready for combat by 1 January 1944) nearly ended 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 five cylinders (every 25 hours of engine time) and the entire engines (every 75 hours).

Pilots, including the present-day pilots of the Commemorative Air Force’s Fifi, the last-remaining flying B-29, 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 them 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/is doing a rolling start-off, rather than a braked start, and checking the magnetos while already in motion.

In wartime, the B-29 was capable of flight up to , at speeds of up to 350 mph (true airspeed). This was its best defense, because Japanese fighters of that day could barely get that high, and few could catch the B-29, even if they were at altitude and waiting. Only the heaviest of anti-aircraft weapons could reach it, and since the Axis forces did not have proximity fuzes, hitting or damaging the airplane in combat was next to impossible.

With the revolutionary Central Fire Control System (CFCS), the B-29 had four remote controlled turrets, each armed with two .50 cal M2/AN machine guns. Four gunners were able to control these turrets with the use of four General Electric made analog computers, one above the Norden bombsight in the nose and three in a pressurized compartment in the rear fuselage which incorporated clear blown sighting blisters. The gunner manning the sight in the upper rear station was the "Central Fire Control gunner" whose job was to allocate turrets to each of the other three gunners, avoiding confusion in the heat of battle. The CFCS had (at that time) a highly advanced analog computer which corrected for the B-29's airspeed, the target's speed, target lead, gravity, temperature, barrel wear, and humidity. Because of this, the .50 caliber machine guns of the B-29 had a maximum effective range of , double the range of the manually-aimed machine guns of the B-17 Flying Fortress. The tail gunner could only control his own weapons (two M2/AN Brownings plus, in early production B-29s, a 20 mm M2 cannon) and the lower rear turret. The tail guns eventually got their own APG-15 gun control radar sets.

In early 1945, with a change of role from high altitude day bomber to low altitude night bomber, Le May ordered the removal of most of the defensive armament and remote controlled sighting equipment from his B-29s so that they could carry greater fuel and bomb loads. As a consequence of this requirement Bell, Marietta ((BM) produced a series of 311 B-29Bs which had the turrets and sighting equipment removed, except for the tail position which initially had the two .50 cal Browning machine guns and single M2 cannon with the APG-15 radar fitted as standard. This armament was quickly changed to three .50 caliber Brownings. This version also had an improved APQ-7 "Eagle" bombing-through-overcast radar fitted in an airfoil shaped radome under the fuselage. Most of these aircraft were assigned to the 315th Bomb Wing, Northwest Field, Guam.

The crew enjoyed, for the first time in a bomber, full-pressurization comfort. This first-ever cabin pressure system for an Allied 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. The bomb bays were not pressurized.

Flying characteristics

In flight, the pilot called for engine and flap settings 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 instinct 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 they were an innovation in 1944. The benefits of improved range and performance were irrefutable.

Unlike aircraft such as the B-24 Liberator, the B-29 lacked boosted controls. As a consequence they required considerable physical strength to operate.As it was, most aircrews found the B-29 to be relatively mild-mannered.

Though it could be flown with only two engines once airborne, the bomber suffered from engine overheating issues throughout its service, and several B-29s crashed in Saipan due to single engine failures on takeoff at full gross weight.

Operational history

World War II

The initial plan, implemented at the direction of President Franklin D. Roosevelt as a promise to China and called Operation Matterhorn, was to use B-29s to attack Japan from four forward bases in southern China, with five main bases in 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 50 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 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 B-29s launched from India bombing the railroad shops in Bangkok, Thailand. (Five B-29s were lost to non-combat causes).

On 15 June 1944, 47 B-29s launched from Chengdu, 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 losses occurred during this raid, with one B-29 destroyed on the ground by Japanese fighters after an emergency landing in China, one lost to anti-aircraft fire over Yawata, and another, the Stockett's Rocket B-29-1-BW 42-6261, disappeared after takeoff from Chakulia, India, over the Himalayas (12 KIA, 11 crew and one passenger)(Source: 20th Bomb Group Assn.) This raid nearly exhausted fuel stocks at the Chengtu B-29 bases, resulting in a slow-down of operations until the fuel stockpiles could be replenished. Starting in July, 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).

The tactic of using aircraft to ram American B-29s was first recorded on the 20 August raid on the steel factories at Yawata. Sergeant Shigeo Nobe of the 4th Sentai intentionally sliced his Kawasaki Ki-45 into a B-29; debris from the explosion following this attack severely damaged another B-29, which also went down. The B-29s were Colonel Robert Clinksale's B-29-10-BW 42-6334 Gertrude C and Captain Ornell Stauffer's B-29-15-BW 42-6368 Calamity Sue, both from the 486th BG. Several B-29s were to be destroyed in this way over the ensuing months. Although the term "Kamikaze" is often used to refer to the pilots undertaking these attacks, the word was not used by the Japanese military.

B-29s were withdrawn from airfields in China by the end of January 1945. Throughout this prior 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 Islands in the Central Pacific, with the last B-29 combat mission from India flown on 29 March 1945.

The need to use the very difficult air 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 (three on the flat island of Tinian), 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. These 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, more-and-more intense raids were launched regularly until the end of the war. These attacks succeeded in devastating almost all large Japanese cities (with the exception of Kyoto and several others), and they gravely damaged Japan's war industries. Although less publicly appreciated, the aerial-mining program carried out by B-29s against Japanese shipping routes and harbor approaches profoundly degraded Japan's ability to support its population and its army to fight the war.

Perhaps the most famous B-29 is the Enola Gay, which dropped the atomic bomb 'Little Boy' on Hiroshima on 6 August 1945. Bockscar, another B-29, dropped 'Fat Man' on Nagasaki three days later. These two actions, along with the Soviet invasion of Manchuria on 9 August 1945, brought about the Japanese surrender, and the official end of World War II. Both aircraft were handpicked for modification from the assembly line at the Omaha plant that was to become Offutt Air Force Base.

Following the surrender of Japan, VJ Day, B-29s were also used to supply POWs with food and other supplies by dropping barrels of rations on Japanese POW camps.

Although considered for other theaters, and briefly evaluated in England, the B-29 was predominantly used in World War II in the Pacific Theatre. (The use of YB-29-BW 41-36393, the so-named Hobo Queen, one of the service test aircraft flown to RAF Bovingdon Airfield, was thought to be as a "disinformation" program intended to deceive the Germans into believing that the B-29 would be deployed to Europe.) The Hobo Queen even seems to have been featured in a photo in the Nazi newspaper Völkischer Beobachter-the German newspaper's headline showing the photo of the Hobo Queen soon appeared in Boeing factory posters of the era.

Soviet copy

On three occasions during 1944, individual B-29s made emergency landings in Soviet territory after bombing raids on Japanese Manchuria and Japan. In accordance with Soviet neutrality in the Pacific War, the bombers were interned and kept by the Soviets, despite American requests for their return. The Tupolev OKB dismantled and studied them, and Stalin ordered Tupolev and his design bureau to copy the B-29s down to their smallest details, and produce a design ready for quantity production as soon as possible. In 1947, the Soviets debuted both the Tupolev Tu-4 "Bull" copy of the B-29, and the Tupolev Tu-70 transport variant. Similar tail-gunner positions to the B-29 would be incorporated in many later bombers and transports.

Korean Conflict and Postwar Service

The B-29 was used in 1950-53 in the Korean War. At first, the bomber was used in normal strategic day-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 (an aircraft 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 a supply-interdiction 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 notable for dropping the large "Tarzan" radio-controlled bomb in Korea, mostly for demolishing major bridges, like the ones across the Yalu River.

The B-29 was soon made obsolete by the development of the jet engined fighter plane. 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 Superfortress 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.

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, 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.

An example of a later variant of the B-29, the B-50 (which was powered by four 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 and re-designated as KB-29s. 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.

Operators

Survivors

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. The Enola Gay is preserved at the National Air and Space Museum and the Bocks Car is preserved at the U.S. Air Force Museum in Dayton, Ohio.

One B-29 "Fifi" is currently registered as "airworthy", but it is presently grounded due to costly engine problems. In a joint press release, dated 21 January 2008, the Commemorative Air Force and the Cavanaugh Flight Museum, announced a pledge of $1.2M USD to re-engine FiFi.

Specifications (B-29)

See also

References

Notes

Bibliography

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