Labels:book | daily | grass | mountain | newspaper | roof | rotogravure | sky | tree | windowpane OCR: Helicopter This famous drawing shows screw proposed by Leonardo to screw -shaped device made power their flight. starched linen stretched over metal frame The linen screw was designed to rotate rapidly, powered someone pedaling beneath Some consider this invention forerunner te the modern helicopter TT 1936 the German engineer Heinrich Focke developed the first practical helicopter Today helicopters use rotary propellers rather than the overa Germar
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