What Leonardo da Vinci aircraft concept used a fixed wing and is often called a proto-glider?

Leonardo da Vinci’s glider was a fixed-wing aircraft concept designed to use air currents rather than flapping wings.

Leonardo developed several flying-machine ideas after observing birds, wind, and the structure of wings. One design, associated with studies in the Codex on the Flight of Birds, resembles a hang-glider: the pilot would be supported by a wing framework while seeking lift from moving air.

This makes the design fundamentally different from an ornithopter. An ornithopter attempts powered flapping flight, whereas a glider depends on aerodynamic lift and usually descends gradually unless rising air supports it.

The glider was a theoretical design, not a documented successful aircraft. Leonardo understood important principles of balance and airflow, but the materials, control systems, and launching conditions available in Renaissance Italy limited the chance of practical human flight.