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). http://en.wikipedia.org/wiki/Boeing_B-29wikipedia "Design and Development." Thanks for looking! Jeremy CREDITS: Bryce 6.1, Poser 6.0, PSP 5.0. Aircraft: Was a Net freebie that I got so long ago I no longer remember where I got it.