Leonardo da Vinci's aerial screw was a helical-blade design intended to rise vertically through the air.
Leonardo drew the machine around 1489, during his studies of flight and air movement. The design shows a large spiral surface made from linen stiffened with reeds and a central mast. Leonardo suggested that if the spiral could be rotated rapidly, it might screw itself upward through the air.
The aerial screw is frequently described as an early ancestor of the helicopter, but it was not a working helicopter. Its proposed human-powered mechanism could not have supplied enough energy to lift the structure and its crew. The drawing is therefore best understood as a conceptual exploration of vertical flight.
The design is also commonly associated with the modern helicopter because of its rotor-like shape. However, powered helicopter flight required later advances in engines, lightweight structures, and rotor control. Leonardo's sketch remains a famous example of Renaissance experimentation with aerodynamics.