Leonardo designed a curious apparatus that would have allowed a man to glide in the air, driven by the force of the wind. The device is a sphere obtained from the intersection of three concentric circumferences having the same diameter, realized using reeds and lightweight fabric. At the center, a series of movable rings of different sizes form a Cardan suspension similar to the mechanism used for holding nautical compasses level.
The project assumed the pilot would operate in a standing position at the interior of the smallest of the circumferences, free to rotate in all directions. The machine, which Leonardo called la ventola, or “the fan,” was to be positioned upon a hilltop, so that, when driven by the wind, it would be transported according to the direction of the air currents. Despite the movements of the sphere, the pilot ought to have been able to remain continuously standing, meaning in the vertical position with respect to the ground.