These days, flying saucers are most commonly associated with sci-fi films and conspiracy theories, but in the 1950s, some saw them as the future of aviation.
Documents published by the US National Archives give new information about a craft commissioned by the US air force, which if successfully developed would have achieved speeds of 2,600mph and flown at around 100,000ft.
Details of the proposed craft have been around for years. But the declassified papers include new diagrams and documents that demonstrate the scale of the project's ambition.
The US air force contracted the work to a now-defunct Canadian company, Avro. In one document, Avro envisaged a "top speed potential between Mach 3 and Mach 4, a ceiling of over 100,000ft and a maximum range with allowances of about 1,000 nautical miles". That would have sent the flying saucer spinning into the Earth's stratosphere.
Language in a report labelled "final development summary" was optimistic: "It is concluded that the stabilization and control of the aircraft in the manner proposed – the propulsive jets are used to control the aircraft – is feasible and the aircraft can be designed to have satisfactory handling through the whole flight range from ground cushion take-off to supersonic flight at very high altitude."
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