Did you know in 400 AD the Ancient Chinese were playing with a medium sized toy that was hand spun? Well, this was how it worked. It had a string that when it was twisted, all of the energy built up, and when you let go, all of that energy would be released and it would fly out of your hand, and go a few good metres up, and then come back down again. These are now called Chinese tops. This was the first form of helicopter. The Chinese called them 'bamboo dragonflies'.