Dornier Do X Do X1

The Treaty of Versailles barred Germany from building aircraft above set speed and range limits, so Claude Dornier put up a purpose-built plant at Altenrhein, on the Swiss side of Lake Constance, and assembled the world's largest flying boat there with money from the German Transport Ministry. The first sketches date from September 1924, formal design work began in late 1925, and construction of airframe number one started in December 1927. Roughly 240,000 work-hours went into it before it was declared finished in June 1929.

The Do X1 was a semi-cantilever monoplane with an all-duralumin hull and wings built from a steel-reinforced duralumin frame, covered in heavy linen and painted with aluminium. Instead of wing floats it carried sponsons, stub wings on the hull sides that steadied the boat on the water and doubled as boarding platforms. Above the wing, six strut-mounted nacelles linked by an auxiliary aerofoil held twelve radial engines in tandem pairs: six tractor propellers and six pushers.

Nobody in the cockpit worked those engines. A flight engineer sat behind twelve throttles and twelve sets of gauges, and the pilot asked him for power through an engine order telegraph, exactly as on a ship of the period — one of many nautical touches, starting with a flight deck that looked like a bridge. Below the passenger deck sat nine watertight compartments, of which seven were enough to keep the boat afloat.

To answer the sceptics, in October 1929 the Flugschiff lifted off Lake Constance with something close to a hundred and seventy people aboard: the crew, factory workers and their families, a handful of journalists, and several stowaways nobody had counted. After a fifty-second take-off run it climbed slowly to about two hundred metres, and passengers were asked to bunch up on one side or the other to help the turns. No aircraft had ever carried so many people at once, and the record stood for twenty years.

The air-cooled radials were this airframe's weak point. They lost power on long runs and could not be turned faster without overheating, so the boat barely cleared four hundred metres above the surface. After around a hundred flights in 1930 the twelve engines were swapped for liquid-cooled Curtiss V-1570 Conquerors and the aircraft was redesignated Do X1a. Every published figure for the type belongs to that second configuration, which is why this entry carries no dimensions of its own.