Bird as Swimmer; Banking, Soaring, and the Wing's Rudder
Steering likened to swimming, and the sharp edge that sets the wing-bone into the wind
Leonardo likens a bird steering with its wings and tail to a swimmer steering with arms and legs, giving compass-point examples of how unequal strokes turn the body. He describes the sudden circular turn produced by throwing one wing edgewise toward the tail, and how a bird soars upward in a spiral to windward without beating its wings before gliding back over the spot it wants. Three lettered figures of the wing's "rudder" (a b, b a, d c, f e) show how its sharp edge sets the wing-bone into or above the wind; the last note breaks off unfinished.
On this page
Bird's wings and tail likened to a swimmer's limbs
The bird does the same office in air with wings and tail as a swimmer does in water with arms and legs. Even strokes toward the east drive him east; a longer northern stroke sends him north-east (greco), a longer right-arm stroke south-east (scirocco).
A banking turn from one wing thrown edgewise
The impetus of one wing thrown edgewise toward the tail gives the bird a sudden circular motion, following the thrust of that wing.
Soaring in a spiral to windward without beating the wings
Circling upward to windward without beating its wings, the bird is carried by the wind out of the region it wants. It then turns its brow to the oncoming wind and, entering obliquely beneath it, descends somewhat until it lies above the place to which it wishes to return.
The sharp edge of the wing's rudder (a b, b a, d c, f e)
The cutting edge a of the wings' rudder, or the thick finger of the bird's hand b a, is what sets the wing-bone below or above the wind. Were the bone round rather than sharp-edged, the wing could not suddenly enter the wind at need; the note breaks off with wind f e striking from below.