And just to expand on one amazing facet of the B-29:
Of course one of the huge problems, never fully solved, was to find engines powerful enough to power such a large plane, at high altitudes, at high speeds.
More engines would be the obvious answer but for each engine added to an aircraft (or ship for that matter), the efficiency drops considerably. So four engines was really the practical limit in WWII. Today, the largest Boeings used by US air carriers (passenger service) actually have two engines, all to increase efficiency (Boeing 777).
Technology at that time allowed 2,000 HP from an aircraft engine readily enough, and 2,500 HP with a little tweaking and straining. But Boeing was looking for well over 3,000 HP, which was not only not readily available but even when power levels such as that were reached, the engines were unreliable and subject to catastrophic failure, which brought more than one B-29 down.
During the design phase, Boeing actually gave a great deal of consideration to a very unusual, unproven British engine. It was odd in several ways, not the least of which was it was an "H" engine, or a double plane, horizontally opposed engine of two banks of 12 cylinders each, for a total of 24 cylinders. It was also a sleeve valved engine, something that never gained much traction in the US although very common in the UK at that time. In the end, Boeing abandoned the British Napier Sabre engine and instead went with a Wright cyclone engine, a much more conventional air- cooled, dual row, radial engine that was a proven design although not at the power levels Boeing was looking for for the B-29. So they 'stretched its legs' and squeezed more power out of it, finally reaching 3,500 HP but at the same time making the engine temperamental and subject to catching on fire, something that plagued all B-29's during WWII. Meanwhile, the Napier Sabre went on to be used in some of the fastest British (and anywhere in the world) fighters and eventually produce a record holding output nearing 5,000 HP. The head of the B-29 project later stated he was sorry he had not held out and gone with the Napier engines in the first place.
And as a final footnote: eventually the B-29, long after WWII, would be fitted with Pratt and Whitney Wasp Major engines ( four rows of 9 cylinders to make a 28 cylinder engine, truly massive), they never did escape the engine problems that plagued such a high power output device from a conventional piston engine. Eventually gas turbine or 'turbo- props' would solve the problems but true reliability was never reached with US piston engines operating well above the 3,500 HP level.
Brian
