Feather resistance and the flexing of a wing surface
Schematic wings a b and b c; a flexible surface stiffened like card armed with reed spines
This page carries several sketches of birds and wings with three short notes on how feathers resist the air. The first labels two schematic bird figures as showing the modes of feather resistance as the wing comes down. The second, keyed to a and b, states that a flexible resisting surface bends along the line of any air movement, and likens it to sheets stiffened with the sinews from the spines of reeds. The third, keyed to b, c and a, notes that the motion of a b is much greater than that of b c, both downward and backward.
On this page
Modes of feather resistance on the downstroke
The two schematic bird figures are captioned as showing the modes by which the feathers resist as the wing comes down. They introduce the study of how the wing surface meets the air.
Flexible surface a b; card stiffened with reed spines
The resisting surface a b, being flexible, bends along the line of any motion of the air. Leonardo compares it to sheets armed with the sinews from the spines of reeds, an analogy for building an artificial wing.
Motion of a b exceeds b c, down and back
Keyed to the points b, c and a on the wing figure, the note states that the motion of a b is much greater than that of b c. This holds both in the downward stroke and in the backward stroke.