The Wing Mechanism: Foot and Hand Row and Feather the Wing
A hand-and-foot linkage lowers, raises, and turns the wing edge-on; a cross-reference to sheet 19
The sheet is dominated by a large drawing of the flying machine's wing with its screw-and-lever mechanism, together with several detail sketches of the linkage. The accompanying note, keyed with letters (b, a, hand, K, o, d, foot c, h, g), explains that when the feet lower the wing h, the hand at b raises lever K so the wing rows backward, and when the feet raise the wing, the hand at a pulls lever g up so the wing turns edge-on and does not impede the bird's motion against the air. Leonardo cross-refers to sheet 19 of the codex, where the cause is demonstrated.
On this page
Foot-and-hand linkage that rows and feathers the wing (b, a, K, g, h)
When the feet lower the wing h, the hand at b raises the lever K, and the wing rows backward. When the feet raise the wing, the hand at a pulls the lever g upward, turning the wing edge-on so it slices the air instead of striking it.
Turning the wing edge-on to preserve forward motion
By raising the wing edgewise as it lifts, the mechanism keeps the wing from impeding the bird's motion against the air. This lets forward impetus continue during the recovery stroke.
Cross-reference to sheet 19
Leonardo notes that the cause of this action is demonstrated on sheet 19 of the codex. The remark ties this page to his fuller mechanical argument elsewhere in the book.