The key to flight is to master the air. That starts even earlier with the Chinese, who invent the kite. It proves that a heavier-than-air object can fly by producing lift. Enter Leonardo da Vinci, who deduces that humans are unlikely to be able to generate the forces required to fly like a bird. So, he imagines a machine flapping its wings. Unfortunately, he never gets one to work. To find out why requires modern analysis. At MIT in California, scientists explain that we now know that the flapping of wings is only one part of flight.