Keeping balance in gusts: how birds avoid capsizing in wind
Wing beats on curved flight; short tails with broad wings; righting after a gust
Under 'Of flight,' Leonardo sets out rules for a bird's equilibrium in wind: in curved flapping flight it beats the wing on the convex side more, and when a gust strikes the windward wing it would capsize unless the opposite wing drops to catch the wind beyond the center of gravity and restore level. He notes that a wing spread broad and thin is less overturned by a gust, that a bird held obliquely folds its lower wingtip into the shape of a foot to bear its weight, and that short-tailed birds use their broad wings and shoulder-rudders in place of a tail when turning. A closing passage explains that a headwind on the breast would tip the bird backward, which lowering and opening the tail prevents, since more wind strikes below the center of gravity than above. Several small bird studies fill the right margin.
On this page
Rule: more wing-beats on the convex side of a curved flight
The bird flying with a curved motion by beating its wings beats the wing on the convex side of that motion more times, or with a longer stroke, than the wing on its concave side. Leonardo marks this as two conclusions.
Righting the windward wing after a gust, c a b d e n
If the bird raises the windward wing on the side struck by the wind, it would turn upside down unless the opposite wing lowers and catches the wind's percussion beyond the center of gravity, which at once restores it to level with its wingtips equal.
A broad, thin wing is less overturned by wind
That flight will be less overcome by the wind's percussion which spreads itself in a broader and thinner thickness to receive that percussion.
The lower wingtip folds into a foot, b a
This bird cannot fall from b to a. Set to receive the wind obliquely, the outermost part of the lower wing bends greatly and forms the shape of a foot, upon which the bird's weight somewhat sustains itself.
Short-tailed birds steer with broad wings and shoulder-rudders
Birds with a short tail have very broad wings whose breadth supplies the place of a tail, and they make much use of the rudders set in the shoulders of the wings when they wish to turn to some place. The study is lettered a; b.
Opening the tail prevents a backward capsize in a headwind
A bird taking the wind on its front tips backward, raising and stretching its neck skyward; lowering and opening the tail prevents this, because more wind strikes below the center of gravity than above it.