Boeing B-29 Superfortress Design and development Boeing began work on pressurized long-range bombers in 1938, in response to a United States Army Air Corps request. Boeing's design study for the Model 334 was a pressurized derivative of the Boeing B-17 Flying Fortress with nosewheel undercarriage. Although the Air Corps did not have money to pursue the design, Boeing continued development with its own funds as a private venture. The Air Corps issued a formal specification for a so-called "superbomber", capable of delivering 20,000 lb (9,100 kg) of bombs to a target 2,667 mi (4,290 km) away and capable of flying at a speed of 400 mph (640 km/h) in December 1939. It featured a pressurized cabin, all dual wheeled, tricycle landing gears, and a remote, electronic fire-control system that controlled four machine gun turrets. Boeing received an initial production order for 14 service test aircraft and 250 production bombers in May 1941, this being increased to 500 aircraft in January 1942. The first prototype made its maiden flight from Boeing Field, Seattle on 21 September 1942 Manufacturing the B-29 was a complex task. It involved four main-assembly factories: a pair of Boeing operated plants at Renton, Washington (Boeing Renton), and Wichita, Kansas (now Spirit AeroSystems), a Bell plant at Marietta, Georgia ("Bell-Atlanta"), and aMartin plant at Omaha, Nebraska ("Martin-Omaha" - Offutt Field). B-29 Superfortress General characteristics Crew: 11 (Pilot, Co-pilot, Bombardier, Flight Engineer, Navigator, Radio Operator, Radar Observer, Right Gunner, Left Gunner, Central Fire Control, Tail Gunner) Length: 99 ft 0 in (30.18 m) Wingspan: 141 ft 3 in (43.06 m) Height: 27 ft 9 in (8.45 m) Wing area: 1,736 sq ft (161.3 m²) Aspect ratio: 11.50:1 Empty weight: 74,500 lb (33,800 kg) Loaded weight: 120,000 lb (54,000 kg) Max. takeoff weight: 133,500 lb (60,560 kg) ; 135,000 lb plus combat load Powerplant: 4 × Wright R-3350 -23 and 23A Duplex-Cyclone turbosupercharged radial engines, 2,200 hp (1,640 kW) each Zero-lift drag coefficient: 0.0241 Drag area: 41.16 ft² (3.82 m²) Performance Maximum speed: 357 mph (310 knots, 574 km/h) Cruise speed: 220 mph (190 knots, 350 km/h) Stall speed: 105 mph (91 knots, 170 km/h) Range: 3,250 mi (2,820 nmi, 5,230 km) Ferry range: 5,600 mi (4,900 nmi, 9,000 km,[75]) Service ceiling: 31850 ft [24] (9,710 m) Rate of climb: 900 ft/min (4.6 m/s) Wing loading: 69.12 lb/sqft (337 kg/m²) Power/mass: 0.073 hp/lb (121 W/kg) Lift-to-drag ratio: 16.8 Armament Guns: eight or 10× .50 in (12.7 mm) Browning M2/ANs in remote-controlled turrets.[76] (omitted from Silverplate B-29s) 2× .50 BMG and 1× 20 mm M2 cannon in tail position (the cannon was later removed)[N 11] Bombs: 20,000 lb (9,000 kg) standard loadout The nose and the cockpit were pressurized, between fore and aft pressurized sections was a long tunnel over the two bomb bays so as not to interrupt pressurization during bombing. 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 . Cockpit General Electric Central Fire Control system B-29 Guns The revolutionary General Electric Central Fire Control system on the B-29 directed four remotely controlled turrets armed with two .50 Browning M2 machine guns each. There were five interconnected sighting stations located in the nose and tail positions and three Plexiglas blisters in the central fuselag. Five General Electric analog computers (one dedicated to each sight) increased the weapons' accuracy by compensating for factors such as airspeed, lead, gravity, temperature and humidity. The computers also allowed a single gunner to operate two or more turrets (including tail guns) simultaneously. The gunner in the upper position acted as fire control officer, managing the distribution of turrets among the other gunners during combat The tail position initially had two .50 Browning machine guns and a single M2 20 mm cannon. Later aircraft had the 20 mm cannon removed,[30]and sometimes replaced by a third machine gun. Battle of Kansas The combined effects of the aircraft's highly advanced design, challenging requirements, and immense pressure for production, hurried development and caused setbacks. Changes to the production craft came so often and so fast that in early 1944, B-29s flew from the production lines directly to modification depots for extensive rebuilds to incorporate the latest changes. the B-29 project was unprecedented in Aviation history: from inception, to drawing board and mass production took three years, at a time when such a design should have taken five years just to become a prototype. Instead the engineering design, production and testing were being undertaken simultaneously, with all of the expected and unexpected problems. at the end of 1943, although almost 100 aircraft had been delivered, only 15 were airworthy. The basic design of the B-29 was sound, but significant shortcuts had been taken in the rush to get it into service, causing numerous defects and quality problems. o The biggest headaches were caused by the new R-3350 engines, which were constantly overheating. the uppermost five cylinders (every 25 hours of engine time) and the entire engines (every 75 hours). This problem was not fully cured until the aircraft was fitted 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. o Other problems arose with defective pressure seals around the cockpit windows and sighting blisters, which needed precise fitting to avoid leakage. o Also causing problems were the sighting systems (four analog computers) for the remote controlled defensive armament, as well as the turrets themselves. o Then came electrical failures, caused by faulty Cannon plugs, which supplied connections throughout the ten miles (16 km) of wiring in each B-29. o Sub-standard glass in the cockpit transparencies meant the pilots had problems due to the distortion. o A minor "beef-up" was found to be needed on the wing structures o When General Arnold visited the Wichita Plant on 11 January 1944 he wanted 175 combat ready B-29s for the XX Bomber Command. As he was shown around the assembly lines he picked out the 175th fuselage section and signed it commenting: "This is the plane I want. I want it before the First of March. When he discovered two months later that no B-29s were actually combat ready, and that some had been sitting waiting for parts for two months or more Arnold was livid. o This prompted an intervention by General Hap Arnold to resolve the problem, with production personnel being sent from the factories to the modification centers to speed modification of sufficient aircraft to equip the first Bomb Groups in what became known as the "Battle of Kansas". This resulted in 150 aircraft being modified in the six weeks between 10 March and 15 April 1944. Specialist USAAF ground crew and technicians were called in from all over the country and 600 workers were pulled from the Wichita assembly lines. Subcontractors were told to stop all work on non-B-29 components until they had fulfilled their commitments o With the thermometer often reading below zero the 1,200 technicians who had gathered at the Wichita factory and the Modification Centers were being asked to modify each bomber inside and out. Firstly the wings needed to have some of the plating removed, the required "beef-ups" were added then each piece of skin riveted back in place. At the same time the cowl flaps, which controlled airflow through and around the troublesome engines, were being modified. Each piece of glass installed in the nose had to be pulled out and replaced with new distortion free panes. After that the pressurization had to be rechecked: 75 B-29s in total needed new glass. Internally every electrical plug had to be removed, disassembled and resoldered - a total of 586,000 connections in completed aircraft, plus those on the assembly lines and in wiring harnesses ready for installation. A lot of the work was being done in the middle of the frequent snow- storms: it was so cold crews could only work for 20 minutes at a time, with most of the jobs requiring delicate handling Operational history In September 1941, the Army Air Forces plans for war against Germany and Japan proposed basing the B-29 in Egypt for operations against Germany as British airbases were likely to be overcrowded. Air Force planning throughout 1942 and early 1943 continued to have the B-29 deployed initially against Germany, only transferring to the Pacific after the end of the war in Europe. By the end of 1943, however, plans had changed, partly due to production delays, and the B-29 was dedicated to the Pacific Theater. Operational history China A new plan implemented at the direction of President Franklin D. Roosevelt as a promise to China, called Operation Matterhorn, deployed the B-29 units 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. Keep China in the war holding down Japanese forces. The Twentieth Air Force was formed in April 1944 to oversee all B-29 operations.