Bamboo-copter (竹蜻蜓 "bamboo dragonfly")'s a Chinese children's toy invented around 400 BC . It essentially consists of a propeller on a stick, and rolling the stick in the right direction spins the propeller, causing the toy to "take off" when it's let go of. This toy made its way to Europe and's depicted in a 1463 European painting. "Bao Pu Zi" (抱樸子) was a 4th century book in China that described some of the ideas in a rotary wing aircraft. In the USA,… (More on Bamboo-copter)