d vertical flight of six feet in altitude for twenty seconds. British and German engineers were not far behind in the development of the modern helicopter. German engineers were the first to produce an aircraft that utilized two superimposed lifting propellers. However, the real improvements in helicopter design did not occur until the period between WWI and WWII. This is because during this war-torn era the quality and availability of materials improved and engine technology experienced rapid advancement. A Spanish inventor was responsible for solving the instability of manned helicopter flights in the 1930s, “Early manned helicopters were very unstable; some even turned over in mid-air. This problem was solved by a Spanish inventor, Juan de la Cierva. He designed a machine, which he called an autogyro, that was almost impossible to turn over.”
The technology behind the autogyro was never truly successful because the helicopter offered more advantages. For example, the auto
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