What type of rotorcraft did Leonardo da Vinci design as an aerial screw?

Leonardo da Vinci designed a helicopter-like rotorcraft known as the aerial screw.

In a drawing usually dated to about 1489, Leonardo proposed a large helical rotor made from reeds, linen, and wire. He wrote that if the screw-like surface were tightly spun, it might rise into the air by pressing against it. The concept is therefore often called a helicopter, although it was not a practical helicopter by modern engineering standards.

The aerial screw had no engine capable of supplying the required power. Its proposed size and construction also created major structural and aerodynamic problems. Leonardo was exploring a principle of vertical lift rather than presenting a tested aircraft.

The design is often mistakenly described as the first helicopter. It was an important conceptual precursor, but successful powered helicopters appeared only in the 20th century. Leonardo's aerial screw is distinct from his flapping-wing ornithopter studies.