The aerial screw

This is one of Leonardo da Vinci's most famous drawings, generally considered to be the ancestor of the modern helicopter.
This aerial screw with a radius of 4.8 metres is made of linen stretched around metal wire. The screw is turned either by men who push the bars by walking around the central shaft, or by the rapid unwinding of a cable around the shaft.
Leonardo commented: "It seems to me that this screw device is well made with the linen sheet and the seams sealed with starch and if the rotating movement is fast enough, the screw will become the male element and the air the female element, and the machine will be able to take flight".