Until the nineteenth century, Leonardo da Vinci was generally known only as a painter.  Little or nothing of his sculpture or engineering works survived, and his notebooks, the only surviving evidence of his insatiable curiosity and fertile mind regarding science and technology, were long hidden away, dispersed in private hands.  It was only after 1800 that the record of his intellectual and technical accomplishments, the thousands of pages of writings and drawings that we collectively refer to today as Leonardo’s codices, began to surface, be studied, and published.  With the rediscovery of the Leonardo codices, the artist who painted the Mona Lisa and The Last Supper was recast as the Renaissance visionary who saw the modern world before it was realized.

Among the many subjects Leonardo studied, the possibility of human mechanical flight held particular fascination.  He produced more than 35,000 words and 500 sketches dealing with flying machines, the nature of air, and bird flight.  These investigations of flight are scattered throughout the many da Vinci codices and manuscript collections, but he did produce one short codex almost entirely on the subject in 1505-1506, the Codice sul volo degli uccelli (Codex on the Flight of Birds).

Leonardo’s interest in flight appears to have stemmed from his extensive work on military technology which he performed in the employ of the Milanese court.  He filled many notebooks with countless sketches of weapons, military machines, and fortifications.  They included a giant crossbow, a tank, and a submarine, to name just a few.  However, as far as it is known, none of these inventions were ever built.  Leonardo’s focus on military technology and tactics lead him to the idea of aerial reconnaissance.  Once engaged with the notion of a flying machine, it became an obsession.

Given his close observance and use of nature as a foundation for many of his ideas, emulating natural flight was an obvious place to begin.  Most of Leonardo’s aeronautical designs were ornithopters, machines that employed flapping wings to generate both lift and propulsion.  He sketched such flying machines with the pilot prone, standing vertically, using arms, using legs.  He drew detailed sketches of flapping wing mechanisms and means for actuating them.  Imaginative as these designs were, the fundamental barrier to an ornithopter is the demonstrably limited muscle power and endurance of humans compared to birds.  Leonardo could never have overcome this basic fact of human physiology.

Interestingly, most of these avian mimicking designs predated Leonardo’s serious study of bird flight, which we find in the Codex on the Flight of Birds, begun in 1505.  In this work, compiled during the same period as the Mona Lisa was painted, we see some of the ideas and observations by Leonardo about flight that were more forward looking than his better known earlier ornithopter drawings.  In the Codex, da Vinci discusses the crucial concept of the relationship between the center of gravity and the center of lifting pressure on a bird’s wing.  He explains the behavior of birds as they ascend against the wind, foreshadowing the modern concept of a stall.  He demonstrates a rudimentary understanding of the relationship between a curved wing section and lift.  He grasps the concept of air as a fluid, a foundation of the science of aerodynamics.  Leonardo makes insightful observations of gliding flight by birds and the way in which they balance themselves with their wings and tail, just as the Wright brothers would do as they evolved their first aeronautical designs.  He comments on the pilot’s position in a potential flying machine and how control could be achieved by shifting the body weight, precisely as the early glider pioneers of the late nineteenth century would do.  He notes the importance of lightweight structures that aircraft would require.  He even hints at the force Newton would later define as gravity.

In less than 20 pages of notes and drawings, the Codex on the Flight of Birds outlines a number of observations and beginning concepts that would find a place in the development of a successful airplane in the early twentieth century.  Leonardo never abandoned his preoccupation with flapping wing designs, and did not develop the insights he recorded in the Codex on the Flight of Birds in any practical way.  Nonetheless, centuries before any real progress toward a practical flying machine was achieved, the seeds of the ideas that would lead to humans spreading their wings germinated in the mind of da Vinci.  In aeronautics, as with so many of the subjects he studied, he strode where no one had before.  Leonardo lived a fifteenth century life, but a vision of the modern world spread before his mind’s eye.

Leonardo da Vinci’s Codex on the Flight of Birds will be on display at the Smithsonian’s National Air and Space Museum from September 13—October 22, 2013, in The Wright Brothers & The Invention of the Aerial Age gallery.