This is one of Leonardo's best known drawings. Some experts have identified it as the ancestor of the helicopter. The only drawing accompanying Leonardo's note is the sketch of an aerial screw with a diameter of 5 metres, made of reed, linen cloth and wire, operated presumably by four men who might have stood on the central platform and exerted pressure on the bars in front of them with their hands, so as to make the shaft turn. A machine thus designed would probably never have risen off the ground or been set moving; the idea remains, however, that if an adequate driving force were applied, the machine might have spun in the air and risen off the ground.

Leonardo's Idea

The drawing of the aerial screw was made during Leonardo's first period in Milan and may be dated between 1483 and 1486. It belongs to the first series of machines designed for mechanical flight. The aerial screw differs from the other machines in that it was planned for the study of the propeller's tractive efficiency and not as a real flying machine. In the note accompanying the drawing, Leonardo, in fact, suggests that, by way of example, what he claims can be experimented by taking a thin, wide rod and rotating it fast in the air. This will prove that the arm of the person rotating the rod will be pulled upward towards the rod itself. In the same note, Leonardo suggests making a paper model of a screw and launching it by means of a coil spring wrapped around the base of the screw. The specific mentioning of the screw strengthens the assumption that this model was actually a representation of the windmill game, a toy which was already popular in Leonardo's age. Due to its small size, the toy could be operated by a spring or, better still, by a small rope, the fast unwinding of which turned the screw and made it move upward. This might be the source of the intuition that the same mechanism, larger in size and operated by an adequate driving force, could have risen off the ground.