Flight of birds: reflected winds and steering with the tail
Curved oblique flight is safer than straight; a bird lowers a tail-horn to hold its course in a crosswind.
This page of Notebook E continues Leonardo's study of the flight of birds (De volatili), arguing that curved oblique flight into the wind is safer than straight oblique flight and that a bird cannot regain height after descending without beating its wings or a favouring wind. A short section headed 'Of reflected winds' considers how wind striking a wall bounces back to meet a bird gliding into it, illustrated by a complex of walls drawn in section at the lower right. A marginal figure shows a bird countering a crosswind by lowering the right horn of its tail to hold a straight northward course, and a small bird is sketched at the upper right.
On this page
Curved flight into the wind is safer than straight oblique flight
A bird declining with straight obliquity against the oncoming wind always has its rebounding motion higher than its incident motion. The curved obliquity seen when birds fly into the wind, with incident and rebounding motion, is much safer than the same motions made in a straight oblique line. Leonardo adds that a bird cannot regain its first height after descending without beating its wings or a favouring wind.
Reflected wind deflected off a wall
A bird pushed by the wind without beating its wings meets a wall set against it; as that wall deflects the wind, the bird immediately runs into the reflected wind bouncing back. The idea is worked out with a complex of walls drawn in section.
Steering against a crosswind with the tail
If a bird flying northward above the wind is pushed eastward, it lowers the right horn of its tail so that horn catches the wind's blow more than the left one. In this way it keeps its straight northward course without disturbing the equal spread of its wings that holds it aloft. The labels a - m n key the marginal figure.