<p>No other aircraft ever combined as many technological advances as the B-29. Designed for a specific strategic task, it later spawned the double-deck Stratocruiser airliner and the KC-97 tanker/transport, and laid the foundations for the super-successful Boeing airliner series. It also provided the Soviet Union with the starting block for the entire Tupolev heavy aircraft lineage.
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<p>It is probable that a detailed analysis of the Soviet 'Blackjack' swing-wing bomber of the 1980s would unearth design features that can be traced right back to the B-29—and the Boeing B-29 Superfortress was started more than three years before the USA entered World War II, in October 1938. In one of his last acts before he was killed in a crash at Burbank, the US Army Air Corps Chief of Staff, General Oscar Westover, had officially established a requirement for a new super-bomber to succeed the Boeing B-17, at a time when the B-17 itself was being denied funds by the Congress. Despite a totally negative reaction from the War Department, procurement chief General Oliver Echols never gave up in his fight to keep the super-bomber alive, and it had the backing of 'Hap' Arnold, Westover's successor. The bomber was to be pressurized to fly very quickly at high altitude: the figures for speed (390 mph; 628 km/h), range (5,333 miles; 8,582 km) and military load were staggering.
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<p>At the Boeing Airplane Company in Seattle there was, at least, experience of large pressurized aircraft, unlike all other companies, but there seemed no way to reconcile the conflicting factors. For most of 1939 the answer seemed to be to fit Pratt & Whitney's slim sleeve-valve liquid-cooled engines inside the wing, but newly hired George Schairer soon pointed out that as the biggest drag item was the wing, the best course was to make the wing as small as possible and not try to put engines inside it. (Thus began a basic philosophy which saw sharp contrast between the Boeing B-47 and the British V-bombers, and has continued to today's Boeing Models 757 and 767.) How does one pressurize a fuselage containing enormous bomb doors? The answer was to make the colossal bomb bays unpressurized and link the front and rear pressure cabins by a sealed tunnel. Chief engineer Wellwood Beall was first to crawl through the mock-up tunnel in January 1940.
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<p>By March 1940 the demands had increased, including 16,000 lb (7,258 kg) of bombs for short-range missions, powered turrets, and far more protection including armor and self-sealing tanks. Weight had already leapt in stages from 48,000 to 85,000 lb (21,773 to 38,556 kg), and with the fresh demands the design finally rounded out at a daunting 120,000 lb (54,432 kg). With just 1,739 sq ft (161.55 m<su>2</su>) of wing, the wing loading was going to be 69 Ib/sq ft (336.9 kg/m<su>2</su>), about double the figure universally taken in 1940 as the desirable limit. Test pilot Eddie Allen was happy that the Boeing Model 345 would be flyable (just) if it had the biggest and most powerful high-lift flaps ever thought of, to reduce take-off and landing speeds to about 160 mph (257 km/h), which was about double the equivalent speed of such familiar machines as the B-17 and Supermarine Spitfire.
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<hi style=hdr1>Funds From USAAC</hi>
<p>As the BEF was rescued from the beaches at Dunkirk the new bomber was designated the B-29, and in August the US Army Air Corps provided funds for two (later three) prototypes. Work was rushed ahead, but nobody knew how to stop guns and propeller mechanisms from freezing at far over 30,000 ft (9,145 m), which Boeing was confident the aircraft could reach. The intense wing loading was all against the designers, but using four monster Wright R-3350 Duplex Cyclones, each with not one but two of General Electric's best turbochargers and driving 16-ft 7-in (5.05-m) Hamilton Standard four-bladed propellers, the propulsion was equal to the task.
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<p>Behind the nose section were two giant bomb bays, from which an electric sequencing system released bombs alternately from front and rear to preserve the center of gravity position. Between the two bays was a ring forming the structural heart of the aircraft and integral with the main wing box, the strongest aircraft part built up to that time. On the wing were four monster nacelles, which Schairer showed to have less drag than engines buried in a bigger wing. After four main gears had been studied, a way was found to fold simple two-wheel gears into the inboard nacelles. Fowler flaps were screwed out electrically to add 21 per cent to area of the wing, fighting a wing loading which by September 1940 reached 71.9 lb/sq ft (351.1 kg/m<su>2</su>) and climbed to a frightening 81.11b/sq ft (396 kg/m<su>2</su>) by the time of the first combat mission.
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<p>Behind the wing the rear pressure cabin had three sighting stations linked to two upper and two lower turrets, each with twin 0.5-in (12.7-mm) machine guns. The electric fire control was normally set so that the top station controlled either or both of the upper turrets, the side stations the lower rear turret, and the bombardier the forward lower turret, but control could be overridden or switched (because gunners could be knocked out in action). In the extreme tail was another gunner driving a turret with two 0.5-in (12.7-mm) guns and a 20-mm cannon.
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<p>In any case, over 2,000 B-29s were to be built before this turret could come into production, because immediately after Pearl Harbor a colossal manufacturing program was organized, involving vast new plants across the nation. Major parts were made in over 60 new factories, the enormous nacelles—each as big as a P-47—coming from a new Cleveland facility operated by the Fisher Body Division of General Motors. Final assembly was organized at three of the world's largest buildings, Boeing at Wichita, Martin at Omaha and Bell at Marietta (today the same building houses the Lockheed Georgia Company). Later, yet another line was set up at Boeing Renton. All this had been organized before the olive-drab XB-29 (41002) had even flown, but from the first flight, on 21 September 1942 (initially using three-bladed propellers), it was clear that the B-29 was going to be a winner. It could so easily have been what test pilots then called 'a dog', and one of the firms delegated to build B-29s was convinced Boeing's figures were far too optimistic and that the whole program was a giant mistake. What made the B-29, by 1942 named Superfortress, now vitally important was that it was obviously going to be the only aircraft with the range to attack Japan.
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<p>To say that the good results of ship 41-002 were a relief would be an understatement. Far more money ($3 billion) had been invested in the B-29 program long before its wheels left the ground than in any other project in the history of any nation. At the same time the technical snags were severe, and they multiplied. Many, such as powerplant fires and runaway propellers, were highly dangerous, and three months into the flight program the prototypes had logged just 31 of the 180 hours scheduled.
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<p>Even when the Superfortresses trickled and then poured off the lines, they were so complex that nobody in uniform fully understood them. All went to a modification center at Salina, Kansas, where over 9,900 faults in the first 175, urgently needed for the new 20th Bomb Wing, were bulldozed right by a task force of 600 men in 'The Battle of Kansas'. Sheer manpower and the USA's mighty industrial power forced the obstacles out of the way, and the B-29s not only began racking up the hours but their baffled crews gradually learned how to manage them, how to fly straight and level in a goldfish bowl without continuously using instruments, and above all how to get something faintly resembling the published range with heavy bomb loads. Air miles per pound of fuel were improved by exactly 100 per cent between January and March 1944. And the complex systems grew reliable in the ultra-cold of 33,000 ft (10,060 m).
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<p>On 5 June 1944 the first combat mission was flown from Kharagpur, India, to Bangkok; the worst problem was an unexpected tropical storm. On 15 June the first of the raids on Japan was mounted, from Chengtu (one of many newly bulldozed B-29 strips in China) to the Yawata steel works. The specially created 20th Air Force grew in muscle, and in October 1944 the first B-29s arrived on newly laid runways on the Marianas islands of Tinian, Saipan and Guam, just taken from the enemy. The numbers grew swiftly as the mighty plants back home poured out B-29s and B-29As with 12 in (30 cm) more span and the four-gun front turret, while Bell added 311 B-29Bs with all armament stripped except that in the tail, making a considerable difference in reduced weight and complexity. The B-29B was made possible by the patchy fighter opposition, and many Superfortresses were similarly stripped in the field.
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<p>Moreover, the commander of the XXI Bomber Command, Major General Curtis LeMay, boldly decided to bomb Tokyo by night from low level, with a full load of incendiaries. There were many reasons for this, but the chief ones were that it promised much greater bomb loads and the elimination of bombing errors attributable to jetstream winds. This policy, totally at variance with the idea of high-altitude day formations, resulted in the greatest firestorms the world has ever seen, and the biggest casualties ever caused by air attack. They were far greater than the 75,000 of Hiroshima, hit by the 20-kT 'Little Boy' atom bomb dropped on 6 August 1945 from Colonel Paul Tibbetts' B-29 'Enola Gay', or the 35,000 of Nagasaki hit by the 20-kT 'Fat Man' dropped on 9 August from 'Bock's Car'. The war ended five days later.
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<hi style=hdr1>Many Modifications</hi>
<p>Only by the incredibly bold decision to go into the biggest multi-company production program ever organized long before the first flight, did the B-29 manage to make so large a contribution to World War II. By VJ-Day more than 2,000 were actually with combat crews, and although 5,000-plus were cancelled days later the manufacturing program was slowed progressively, and did not close until May 1946, by which time 3,960 B-29s had been built. Hundreds were modified for different tasks, and many were launched on new careers as air/sea rescue aircraft, turbojet testbeds or tankers, which kept them busy for another decade or more. Back in 1942 Boeing had begun to work on the Model 367 transport version with a much larger upper lobe to a 'double bubble' fuselage, the first XC-97 flying on 15 November 1944.
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<p>A B-29A (42-093845) was flown with the 28-cylinder Pratt & Whitney R-4360 Wasp Major engine in early 1944 as the XB-44, and the 3,000-hp (2,238-kW) engine made such a difference that other changes were made, including a wing made of 75ST aluminum alloy giving much greater strength with 650 lb (295 kg) less weight, and a taller vertical tail. There were many systems changes, and the propellers were made reversible. Various other improved bomber versions were cancelled but the XB-44/B-29D was continued and became the B-50.
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<p>The XB-39 was a single B-29 powered by V-3420-11 engines, and the F-13 designation covered photo-reconnaissance variants, later being redesignated FB-29 in 1945 and RB-29 in 1948. These were used on early reconnaissance flights to monitor the Soviet Union after the end of the war.
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<p>In the 1950s hundreds of B-29s kept flying, almost all modified for different roles (CB-29—transport, DB-29—drone director, EB-29—mother-ship for XF-85 parasite fighter, GB-29—mothership for X-planes, KB-29—aerial refueling tanker, QB-29—radio-controlled drone, SB-29—rescue version with air-droppable lifeboat, TB-29—unarmed crew trainer and WB-29—weather reconnaissance platform). Bomber B-29s were widely used in the Korean War, where its gunners made the Superfortress the second highest scoring type in aerial combat behind the Sabre. The Navy acquired four under the P2B designation.
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<p>A remarkable postscript to the B-29 story was provided by the Soviet Union. When USAAF B-29s force-landed in Soviet-held territory during operations against Japan, Tupolev engineers were set to work copying the aircraft. Not only did the Soviets produce a lkarge number of Tu-4 'Bull' bomber copies, the technology gleaned from the B-29 provided the inspiration for subsequent Tupolev designs such as the Tu-16 'Badger' and Tu-95 'Bear'. No doubt some features of Boeing's mighty Superfortress can be found in the Tu-160 'Blackjack' supersonic bomber of today.
<item><hi format=bold>Performance:</hi> maximum speed 358 mph (576 km/h) at 25,000 ft (7,620 m);cruising speed 230 mph (370 km/h); service ceiling 31,850 ft (9,710 m); range 3,250 miles (5,230 m)
<item><hi format=bold>Weights:</hi> empty 70,140 Ib (31,815 kg); maximum take-off 124,000 lb (56,245 kg)
<item><hi format=bold>Dimensions:</hi> span 141 ft 3 in (43.05 m); length 99 ft 0 in (30.18 m); height 29 ft 7 in (9.02 m); wing area 1,736 sq ft (161.27 m<su>2</su>)
<item><hi format=bold>Armament:</hi> two 0.5-in (12.7-mm) guns each of four remotely controlled power-operated turrets, and three 0.5-in (12.7-mm) guns or two 0.5-in (12.7-mm) guns and one 20-mm cannon in the tail turret, plus a bomb load of up to 20,000 lb (9,072 kg)
