Dornier Do X

Claude Dornier conceived the Do X in 1924, planning started in late 1925, and the aircraft was finished in June 1929 after more than 240,000 work-hours. Because the Treaty of Versailles barred Germany from building aircraft above set speed and range limits, the programme was financed by the German Transport Ministry but a purpose-built plant was erected at Altenrhein, on the Swiss shore of Lake Constance. What emerged was a semi-cantilever monoplane with an all-duralumin hull and wings of steel-reinforced duralumin framework covered in heavy linen and aluminium paint. Its 56-tonne maximum takeoff weight put it beyond every contemporary: only the Soviet Tupolev ANT-20 Maksim Gorki of a few years later was physically larger, and it stopped at 53 tonnes.

The powerplant was both the Do X's most striking feature and its weakness. Twelve 391 kW Bristol Jupiter radials built under licence by Siemens were mounted in tandem push-pull pairs on six strut-mounted nacelles above the wing, six tractors and six pushers, joined by an auxiliary wing that steadied the mountings. Air-cooled, they overheated and could barely lift the boat to 425 metres; a flight engineer worked the twelve throttles and watched the twelve sets of gauges while the pilot passed power requests to him through an engine order telegraph of the kind used aboard ships. After 103 flights in 1930 they were replaced by water-cooled 455 kW Curtiss V-1570 Conqueror V-12s, and only then could the aircraft reach the 500 metres needed to cross the Atlantic. The accommodation matched an ocean liner: three decks, a smoking room with its own bar, a dining salon and seats convertible into berths for the 66 passengers of long flights, up to 100 on short ones.

On 12 July 1929 the Flugschiff, or flying ship, made its first test flight with a crew of fourteen. To silence sceptics, on its seventieth test flight on 21 October it carried 169 people aboard, 150 of them passengers, ten aircrew and nine stowaways, setting a world record for people carried on a single flight that stood for twenty years. On 3 November 1930 it left Friedrichshafen under Friedrich Christiansen bound for New York; the journey stalled at Lisbon on 29 November, when a tarpaulin touching a hot exhaust pipe started a fire that consumed most of the left wing. Repaired after six weeks in the harbour, it worked its way down the African coast, reached Cape Verde on 5 June 1931, crossed to Natal in Brazil and arrived in New York on 27 August 1931, almost ten months after departure. It left again on 21 May 1932 via Newfoundland and the Azores and touched down on 24 May at the Müggelsee in Berlin before a crowd of 200,000.

The other two aircraft, ordered by the Italian state airline SANA, were the X2 Umberto Maddalena and the X3 Alessandro Guidoni, slightly larger and powered by Fiat A-22R V12s; they entered service in August 1931 and May 1932, but the Italian air force requisitioned them for prestige flights, officer training cruises and aeronaval manoeuvres before breaking them up in 1937. The German original passed to Deutsche Luft Hansa once Dornier could no longer afford to operate it; an overly steep landing on a reservoir near Passau tore off its tail section in 1933 and kept it out of service for three years. It ended as the centrepiece of Germany's aviation museum at the Lehrter station in Berlin, where a Royal Air Force air raid destroyed it on the night of 23 to 24 November 1943. It was never a commercial success, yet it showed that international passenger air service was within reach.