1. The earliest references for vertical flight have come from China. Since around 400 BC, Chinese children have played with bamboo flying toys. The bamboo-copter is spun by rolling a stick attached to a rotor. The spinning creates lift, and the toy flies when released. The 4th-century AD Daoist book Baopuzi by Ge Hong ("Master who Embraces Simplicity") reportedly describes some of the ideas inherent to rotary wing aircraft.