"I find that if this instrument in the form of a screw is well made – that is, made of linen cloth, with its pores being plugged using starch – and if it is turned rapidly, this screw will penetrate the air, and it will mount aloft. Take the example of a wide, thin ruler that you turn through the air with fury: you will see your arm being guided along the line of the edge of that board. Let the framing for the above-mentioned cloth be of long, thick canes. A small model of it can be made of paper, so that its post is a thin strip of iron, which is twisted by force, and when it returns
to liberty, it will cause the screw to turn again."
The model is constructed on a fixed circular
base inscribed in a mobile corona, which in turn
is connected to a vertical transmission shaft.
A helicoid structure tapering upward is mounted
on the shaft, connected by braces to the rotating
corona of the base. Leonardo conceived
a structure inspired by the helicoid forms
found in nature, as in the case of maple seeds,
which can fly to great distances rotating about
themselves. Here for the first time the spiral-form
structure, previously used since antiquity in the
field of hydraulics, is applied to flight and air.
In the notes accompanying the drawing, he
specifies the measures for the base (8 Florentine
braccia, about 5 m) and the materials: wood, cord,
and starched linen canvas. The machine could
not have functioned, considering its theoretical
weight and the insufficient energy that would
have been produced by the four men moving it,
at least according to the interpretation provided
by the model’s project designers, Soldatini and
Somenzi, who perhaps went a bit beyond the
elements effectively drawn by Leonardo.
In a study of a small-scale prototype, Leonardo
probably was thinking of a mechanism actuated
by a spring or a cord. He even suggested limiting
the experiment to making a small paper model,
conscious that an actual-size realization would
never have been able to function, primarily
because of the obvious lack of suitable motor.
The model is based on the drawing:
- Manuscript B f. 83 v. (1486-1487)
Paris, Institut de France