In the late 1480s, Leonardo sketched an aerial screw: a screw that bites the air.

Its spiral sail of linen, stiffened with starch, had a radius of about 5 m.

A 75 kg person weighs 735.75 N: that is the thrust the sail must make.

The sail sweeps about 78.5 m² and pushes the air down at about 2 m/s.

Momentum theory gives the ideal power: about 1.45 kW to lift 75 kg.

Leonardo wrote that it must turn quickly enough to lift the structure.

The ideal figure is a lower bound: a real screw needs more power.

It stayed a drawing. The idea of lift from a spinning surface came back centuries later.