Leonardo da Vinci's Helicopter
The "aerial screw" (1483) was one of the Leonardo da Vinci's prototypes for flying machines and an early precursor of the modern helicopter. The flight mechanism designed for this machine, first documented by da Vinci, relies on creating human powered vertical lift by expelling compressed air downward. In principle this could lift the device off the ground, but unfortunately, humans cannot produce and sustain the required power to lift themselves against the force of gravity. The necessary light materials and engines were only produced around 1900 and the first helicopter (helico-spiral, ptero- wing) to fly came in the 1940s.
 J. G. Leishman. "A History of Helicopter Flight." (Aug 25, 2000) http://www.researchgate.net/publication/267682216_A_History_of_Helicopter_Flight.