Editing Boeing B-29 Superfortress (section)

==Design and development==
[[File:Boeing B-29 Superfortress at Davis-Monthan AFB.jpg|thumb|The length of the {{convert|141|ft|m|0|adj=on}} wing span of a Boeing B-29 Superfortress based at [[Davis-Monthan Field]] is vividly illustrated here with the cloud-topped [[Santa Catalina Mountains]] as a contrasting background.]]
[[File:Olive-drab painted B-29 superfortress.jpg|thumb|alt=Two large olive-colored aircraft flying over farmland|YB-29 Superfortresses in flight]]
[[File:Favored by Warm breezes and under a blue Kansas Sky, a vast crowd attends the delivery ceremony on the Boeing-Wichita... - NARA - 196890.jpg|thumb|1000th B-29 delivery ceremony at the Boeing [[Wichita, Kansas|Wichita]] plant in February 1945]]
Boeing began work on long-range bombers in 1938. Boeing's design study for the Model 334 was a pressurized derivative of the [[Boeing B-17 Flying Fortress]] with [[tricycle landing gear|nosewheel undercarriage]]. Although the Air Corps lacked funds to pursue the design, Boeing continued development with its own funds as a private venture.<ref name="Bowers Boeing p318">Bowers 1989, p. 318.</ref> In December 1939, the Air Corps issued a formal [[Specification (technical standard)|specification]] for a so-called "superbomber" that could deliver {{convert|20000|lb|kg|abbr=on}} of bombs to a target {{convert|2667|mi|km|abbr=on}} away, and at a speed of {{convert|400|mph|km/h|abbr=on}}. Boeing's previous private venture studies formed the starting point for its response to the Air Corps formal specification.<ref name="iapr22 p136-7">Willis 2007, pp. 136–137.</ref>

On 29 January 1940, the [[United States Army Air Corps]] issued a request to five major aircraft manufacturers to submit designs for a four-engine [[bomber]] with a range of {{convert|2,000|mi}}.{{sfn|Cate|1953|pp=6-8}} Boeing submitted its Model 345 on 11 May 1940,<ref name="Bowers Boeing p319">Bowers 1989, p. 319.</ref> in competition with designs from [[Consolidated Aircraft]] (the Model 33, which later became the [[Consolidated B-32 Dominator|B-32]]),<ref name="Wegg p91">Wegg 1990, p. 91.</ref> [[Lockheed Corporation|Lockheed]] (the [[Lockheed XB-30]]),<ref name="XB-30">[http://www.nationalmuseum.af.mil/factsheets/factsheet.asp?id=2578 "Factsheet: Lockheed XB-30."] {{webarchive|url=https://web.archive.org/web/20110716073618/http://www.nationalmuseum.af.mil/factsheets/factsheet.asp?id=2578 |date=16 July 2011 }} ''National Museum of the United States Air Force''. Retrieved: 15 November 2010.</ref> and [[Douglas Aircraft Company|Douglas]] (the [[Douglas XB-31]]).<ref name="frnc Doug p713">Francillon 1979, p. 713.</ref> 

Douglas and Lockheed soon abandoned work on their projects, but Boeing received an order on 24 August 1940 for two flying [[prototypes]], which were given the designation XB-29, and an airframe for static testing. The order was revised to add a third flying aircraft on 14 December. Consolidated continued to work on its Model 33, as it was seen by the Air Corps as a backup if there were problems with Boeing's design.<ref name="iapr22 p138">Willis 2007, p. 138.</ref>  These designs were evaluated, and on 6 September orders were placed for two experimental models each from Boeing and Consolidated, which became the Boeing B-29 Superfortress and the Consolidated B-32 Dominator.{{sfn|Cate|1953|pp=6-8}} These were known as very long range (VLR) bombers; the name "Superfortress" was not assigned until March 1944.<ref>{{cite news |url=http://nla.gov.au/nla.news-article75932318 |title=Superfortress |newspaper=[[The Mirror (Western Australia)|The Mirror]] |volume=22 |issue=1139 |location=Western Australia |date=11 March 1944 |access-date=24 August 2023 |page=8 |via=National Library of Australia}}</ref> On 17 May 1941, Boeing received an initial production order for 14 service test aircraft and 250 production bombers;{{sfn|Cate|1953|pp=6-8}}<ref name="Knaack p480">Knaack 1988, p. 480.</ref> this being increased to 500 aircraft in January 1942.<ref name="Bowers Boeing p319"/> 

Manufacturing the B-29 was a complex task that involved four main-assembly factories. There were two Boeing operated plants at [[Renton, Washington]] ([[Boeing Renton Factory]]), and one in [[Wichita, Kansas]] (now [[Spirit AeroSystems]]), a [[Bell Aircraft Corporation|Bell]] plant at [[Marietta, Georgia]], near [[Atlanta]] ("Bell-Atlanta"), and a [[Glenn L. Martin Company|Martin]] plant at [[Bellevue, Nebraska]] ("Martin-Omaha" – [[Offutt Air Force Base|Offutt Field]]).<ref name="Bowers Boeing p319"/><ref name="Bowers Boeing p322">Bowers 1989, p. 322.</ref> Thousands of [[subcontractor]]s were also involved in the project.<ref name="iapr22 p138-9">Willis 2007, pp. 138–139.</ref> The first prototype made its maiden flight from [[Boeing Field]], [[Seattle]], on 21 September 1942.<ref name="Bowers Boeing p322"/> The combined effects of the aircraft's highly advanced design, challenging requirements, immense pressure for production, and hurried development caused setbacks. Unlike the unarmed first prototype,<ref name="RCTp80">Brown 1977, p. 80.</ref> the second was fitted with a Sperry defensive armament system using remote-controlled gun turrets sighted by periscopes. It first flew on 30 December 1942, although the flight was terminated due to a serious engine fire.<ref name="Peacock1 p70-1">Peacock ''Air International'' August 1989, pp. 70–71.</ref>

On 18 February 1943, the second prototype, flying out of Boeing Field in Seattle, experienced an engine fire and crashed.<ref name="Peacock1 p70-1"/> The crash killed Boeing test pilot [[Edmund T. Allen]] and his 10-man crew, 20 workers at the Frye Meat Packing Plant, and a Seattle firefighter.<ref>{{cite web|last1=Banel|first1=Feliks|title=70 Years Ago: Remembering The Crash of Boeing's Superfortress|url=http://kuow.org/post/70-years-ago-remembering-crash-boeing-s-superfortress|website=[[KUOW-FM]]|date=15 February 2013|access-date=2 July 2017}}</ref> 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. AAF-contracted modification centers and its own air depot system struggled to handle the scope of the requirements. Some facilities lacked hangars capable of housing the giant B-29, requiring outdoor work in freezing weather, further delaying necessary modification. By the end of 1943, although almost 100 aircraft had been delivered, only 15 were airworthy.<ref name="iapr22 p144">Willis 2007, p. 144.</ref><ref name="Peacock1 p76">Peacock ''Air International'' August 1989, p. 76.</ref> This prompted an intervention by General [[Henry H. Arnold|Hap Arnold]] to resolve the problem, with production personnel being sent from the factories to the modification centers to speed availability of sufficient aircraft to equip the first [[group (air force unit)|bomb groups]] in what became known as the "[[Battle of Kansas]]". This resulted in 150 aircraft being modified in the five weeks, between 10 March and 15 April 1944.<ref name="Knaack p484">Knaack 1988, p. 484.</ref><ref name="Bowers Boeing p323">Bowers 1989, p. 323.</ref><ref>Herman 2012, pp. 284–346.</ref>

The most common cause of maintenance headaches and catastrophic failures was the engines.<ref name="Knaack p484"/> Although the [[Wright R-3350 Duplex-Cyclone]] [[radial engine]]s later became a trustworthy workhorse in large piston-engined aircraft, early models were beset with dangerous reliability problems. This problem was not fully cured until the aircraft was fitted with the more powerful [[Pratt & Whitney Wasp Major|Pratt & Whitney R-4360 "Wasp Major"]] in the [[Boeing B-29 Superfortress variants#B-29|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 were installed around rubber [[push rod]] fittings to prevent oil loss, thorough [[pre-flight inspection]]s were made to detect unseated valves, and mechanics frequently replaced the uppermost five cylinders (every 25 hours of engine time) and the entire engines (every 75 hours).{{efn|As efforts were made to eradicate the problems a succession of engine models were fitted to B-29s. B-29 production started with the −23, which were all modified to the "war engine" −23A. Other versions were −41 (B-29A), −57, −59.{{cn|date=August 2023}} }}<ref name="Knaack p484"/><ref name="gardiner"/>

Pilots, including the present-day pilots of the [[Commemorative Air Force]]'s ''[[FIFI (aircraft)|Fifi]]'', one of the last two remaining flying B-29s, describe flight after takeoff as being an urgent struggle for airspeed (generally, flight after takeoff should consist of striving for altitude). Radial engines need 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 useful technique was to check the magnetos while already on takeoff roll rather than during a conventional static engine-runup before takeoff.<ref name="gardiner">Gardner, Fred Carl [http://www.oregoncounsel.com/FAAACE/Superfortress.html "A Year in the B-29 Superfortress."] ''Fred Carl Gardner's website'', updated 1 May 2005. Retrieved: 11 April 2009.</ref>
The $3&nbsp;billion cost of design and production (equivalent to ${{formatnum:{{Inflation|US|3|1945|r=0}}}}&nbsp;billion in 2022),{{Inflation-fn|US}} far exceeding the $1.9&nbsp;billion cost of the [[Manhattan Project]], made the B-29 program the most expensive of the war.<ref>{{cite book|title=How the War Was Won|last1=O'Brien|first1=Phillips Payson|date=2015|publisher=Cambridge University Press|isbn=978-1-107-01475-6|edition=1st|pages=47–48}}</ref><ref>{{cite web|url=http://www.pwencycl.kgbudge.com/B/-/B-29_Superfortress.htm|title=B-29 Superfortress, U.S. Heavy Bomber|website=The Pacific War Online Encyclopedia|publisher=Kent G. Budge|access-date=1 April 2018}}</ref> Unit cost was US$639,188<ref>Knaack 1988, p. 486.</ref> (prototype cost $3,392,396.60)<ref>{{cite news |agency=Associated Press |title=Cost of B-29 Bomber Reduced Four-Fifths |newspaper=The San Bernardino Daily Sun |location=San Bernardino, California |date=15 October 1944 |volume=51 |page=2}}</ref>