Leonardo da Vinci's studies, drawings, and never-finished inventions involving flight were revolutionary in design to say the least. It is debated whether da Vinci successfully flew using any of his machines, but even if they never left the ground in his time; modern day parachutes and helicopters are very similar to Leonardo's designs from hundreds of years ago. This is interesting because most of his work was not uncovered until the 19th century, after all the machines were reinvented. Leonardo's study of flight started with flapping-wing mechanisms, but after he discovered the futility of human powered and coordinated flight, he turned his eyes to the birds. He studied, watched, and dissected birds and bats, trying to discover what enables them to fly. After his writings on birds his research shifted to glider based flight, rather than further pursuing human powered wings, or the aerial screw (the ancestor of the helicopter).