Wing and tail as the bird's rudders in flight
Twisting the spread tail toward a contracted wing, and two 'rudders' in the wing's humerus
Written inverted on the sheet, these notes continue Leonardo's study of how a bird controls its course in the air. The upper passage explains that when one wing cannot spread again as freely as the other, the bird opens and twists its tail toward the contracted side to convert circular flight back into straight motion. The lower note, keyed to the letter a, describes two 'rudders' seated in the humerus of each wing that drive the bird up and down without any change of the wings, while the tail-rudder governs sideways movement. A small bird with outspread wings is sketched in the left margin.
On this page
Twisting the spread tail to leave circular for straight flight
If the wing drawn in toward the body cannot widen again with the required ease, the bird spreads its tail and twists it open toward the side where that wing is contracted. Doing so, the bird flies in a straight line and abandons the circular motion.
Two rudders (a) in the humerus of each wing
Keyed to the letter a, the note states that there are two rudders in the humerus of the wings of every bird. Without any change of the wings themselves they can produce various up-and-down motions, whereas in sideways movements only the tail-rudder is engaged.
Bird in flight sketched from above
A small bird is drawn with its wings fully outspread, seen from above, in a rapid pen sketch. It illustrates the wing-and-tail control discussed in the surrounding notes.