Helicopter
Helicopter was invented in the early part of the twentieth century, but the idea of a helicopter was born almost five hundred years back. The person who thought of such a machine was the great genius of the 15th century, Leonardo da Vinci (who else!). While he is famous for his paintings (such as Mona Lisa and the Last Supper) and sculptures, few people are aware that Leonardo was also a great inventor.
The idea of the helicopter came to Leonardo from windmills. He noted that the blades of the windmill rotate because of the wind, and generate energy. He figured that if he could make a "windmill in reverse", it could be put to some use. To try out his idea he fitted a clock spring inside a small toy with blades, or propellers. The idea worked, but there was no way it could be used.
It took another five hundred years before the technology was developed enough for a real helicopter.
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