"The Dornier Do X was the largest, heaviest, and most powerful flying boat in the world when it was produced by the Dornier company of Germany in 1929. First conceived by Dr. Claudius 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 Russian Tupolev ANT-20 Maxim Gorki landplane of a few years later was physically larger, but at 53 metric tons 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.
While the type was popular with the public, a lack of commercial interest and a number of non-fatal accidents prevented more than three examples from being built.
The Do X is 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 aluminum paint.
It was initially powered by twelve 391 kW (524 hp) Siemens-built Bristol Jupiter radial engines (six tractor propellers and six pushers), mounted in six tower nacelles on the wing. The nacelles are joined by an auxiliary wing whose purpose was to stabilize the mountings. The air-cooled Jupiter engines were prone to overheating and proved to only be able to lift the Do X to an altitude of 425 m (1,400 ft). The engines were supervised by an engineer, who also controlled the throttle. The pilot would ask the engineer to adjust the power, in a manner similar to that used on maritime vessels. After completing 103 flights in 1930, the Do X was refitted with 455 kW (610 hp) Curtiss Conqueror water-cooled 12-cylinder inline engines. Only then was it able to reach the altitude of 500 m (1,650 ft) necessary to cross the Atlantic.
Dr. Dornier designed the flying boat to carry 66 passengers on long distance flights or 100 passengers on short flights.
The luxurious passenger accommodation approached the standards of transatlantic liners. On the main deck was a smoking room with its own wet bar, a dining salon, and seating for the 66 passengers which could also be converted to sleeping berths for night flights. Aft of the passenger spaces was an all-electric galley, lavatories, and cargo hold. The cockpit, navigational office, engine control and radio rooms were on the upper deck. The lower deck held fuel tanks and nine watertight compartments, only seven of which were needed to provide full flotation.
Germany's original Do X was turned over to Deutsche Luft Hansa, the national airline at that time, after the financially strapped Dornier Company could no longer operate it. After a successful 1932 tour of German coastal cities, Luft Hansa planned a Do X flight to Vienna, Budapest, and Istanbul for 1933. The voyage ended after nine days when the flying boat's tail section tore off during a botched, over-steep landing on a reservoir lake near the city of Passau. While the fiasco was successfully covered up and the Do X was out of service for three years, during which time it changed hands several times before reappearing in 1936 in Berlin,[clarification needed] where it became the centerpiece of Germany's new aviation museum Deutsche Luftfahrt-Sammlung at Lehrter Bahnhof.
The Do X remained an exhibit until it was destroyed in an RAF air raid during World War II on the night of 23–24 November 1943, by 383 aircraft — 365 Lancasters, 10 Halifaxes, and 8 Mosquitos. Fragments of the torn off tail section are on display at the Dornier Museum in Friedrichshafen. While never a commercial success, the Dornier Do X was the largest heavier-than-air aircraft of its time, a pioneer in demonstrating the potential of an international passenger air service. A successor, the Do-XX, was envisioned by Dornier, but never advanced beyond the design study stage."
