It was the largest, heaviest, and most powerful flying boat in the world when it was produced. First conceived by Claude Dornier in 1924, planning started in late 1925 and after over 240,000 work-hours it was completed in June 1929. During the years between the two World Wars, only the Soviet Tupolev ANT-20 Maksim Gorki landplane of a few years later was physically larger, but at 53 metric tonnes maximum takeoff weight it was not as heavy as the Do X's 56 tonnes. The Do X was financed by the German Transport Ministry and in order to circumvent conditions of the Treaty of Versailles, which forbade any aircraft exceeding set speed and range limits to be built by Germany after World War I, a specially designed plant was built at Altenrhein, on the Swiss portion of Lake Constance. The type was popular with the public, but a lack of commercial interest and a number of non-fatal accidents prevented more than three examples from being built. The Do X was a semi-cantilever monoplane. The Do X had an all-duralumin hull, with wings composed of a steel-reinforced duralumin framework covered in heavy linen fabric, covered with aluminium paint. It was initially powered by twelve 391 kW (524 hp) Siemens-built Bristol Jupiter radial engines in tandem mountings (i.e. a "push-pull" configuration), with six tractor propellers and six pushers mounted in six strut-mounted nacelles above the wing. The nacelles were joined by an auxiliary wing whose purpose was to stabilise the mountings. The air-cooled Jupiter engines were prone to overheating and could barely lift the Do X to an altitude of 425 m (1,400 ft). The engines were supervised by a flight engineer, who also controlled the 12 throttles and monitored the 12 sets of engine gauges. The pilot would ask the engineer to adjust the power setting, in a manner similar to the system used on maritime vessels, i.e. an engine order telegraph. Indeed, many aspects of the aircraft echoed nautical arrangements of the time, including the flight deck, which bore a strong resemblance to the bridge of a vessel. After completing 103 flights in 1930, the Do X was refitted with 455 kW (610 hp) Curtiss V-1570 "Conqueror" water-cooled V-12 engines. Only then was it able to reach the altitude of 500 m (1,650 ft) necessary to cross the Atlantic. Dornier designed the flying boat to carry 66 passengers on long-distance flights or 100 passengers on short flights. For more details of the design, operation and final fate of the Do X, click here.
