The winglets that steer a gliding bird
Bending the wing tip, and the shoulder 'rudders' for banking without flapping
Three notes on how a bird controls its flight without flapping. Leonardo remarks on the bending of the wing tip even when the wing is not being beaten, and describes the 'rudders' at the shoulders of the wings that the bird uses to bank up, down, right or left while gliding over a bed of air. Small sketches at the right show the winglets and the silhouette of a bird with wings outspread.
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Bending of the wing tip without flapping
Leonardo opens with a note on how the tip of the wing bends even when the wing itself is not being beaten. He treats the pliancy of the outer wing as part of the bird's control during a steady glide.
The shoulder rudders steer the glide
The 'rudders' at the shoulders of the wings are needed when the bird glides without flapping and wishes to bank up, down, right or left over a bed of air. To rise it shows the rudder reversed to the wind's blow; to descend it turns the rudder's upper side oblique to the wind; to turn right it presents the right rudder to the wind, and to turn left the left rudder.