Fol. 9v

It is here that Leonardo arrives one step away from solving the problem of flight. This page Codex consigns to history the first scientific intuition about the relationship between the phenomenon of flight and the profile of the wing, in birds as well as in flying machines. Leonardo understands that it is the pressure of air flows exerted on the wings that allows the kite to ascend or descend. Only one final intuition is missing to complete the study of aerodynamics, that is, the difference in pressures between the upper and lower parts of the wings, determined by the configuration of the wing itself.

«Il taglio "a" del timone delle ali, o il dito grosso della mano dell'uccello "b" "a" è quello che mette immediatamente l'omero dell'ala sotto, o sopra il vento. E se l'omero stesso non fosse sottilmente tagliente, l'ala non potrebbe rapidamente entrare sotto o sopra il vento»
(The shape a of the rudder of the wings, or the thumb of the hand of the bird [alula] b a, is what immediately positions the humerus of the wing below or above the wind. If the humerus itself were not slightly cutting, the wing could not enter rapidly below or above the wind.)

NOTE. For each page of Leonardo’s Codex we provide a brief summary, with the quotation of one that page’s most significant passages edited in modern Italian, with an English translation.

translation by Kim Williams