Bird manoeuvres: turning, landing, braking, and rising
Marginal figures keyed to short 'rules' and 'sciences' of flight, from whirling ascents to broadside braking.
The right margin is filled with small figures of birds in different flight manoeuvres, each keyed to a one-word 'rule' or 'science' beside its note. Leonardo observes that a bird driven by the wind can turn back to make a wedge of the wind's impetus and regain height, and that the impetus of its incident flight can rebound in straight or curved whirling paths until it is spent. Further rules describe landing by lowering the wing on the struck side, braking by turning the wings broadside without a favouring wind, and the whirling motion needed to rise straight up by wing-beats alone, with an opening maxim to 'make of every kind of flight its contrary.'
On this page
Regaining height by turning into the wind
When driven by the wind a bird always declines in oblique motion; to rise again to its first height it turns back, making for itself a wedge out of the wind's own impetus.
Rebounding impetus in whirling paths
The impetus a bird gains in its incident flight can rebound in every direction, whether by straight or curved whirling motion or whatever, until that impetus is spent. The note is headed 'science.'
Landing by lowering a wing
When struck by the wind under its right side and wishing to alight on some place, the bird lowers the wing on that side toward which it wants to settle. The note is headed 'rule.'
Braking by turning the wings broadside
To spend its acquired impetus quickly, a bird turns the full breadth of its wings against the spot where it wishes to stop, and it does this without any favouring wind. The note is headed 'science.'
Rising straight up needs whirling motion
A bird that wishes to rise straight upward without wind, by the beating of its wings alone, requires the whirling motion.
Oblique ascent by frequent wing-beats
But if the bird's motion is in a straight line without a favouring wind, it must be made by frequent beats of the wings, and for that reason the ascent turns out very oblique.