On Birds: Hovering Against the Wind and Wing Position

A bird hovers motionless when wind-lift equals its weight

Let bird m stand in the wind a b d c; the wind strikes beneath the obliquity of wing n f, forming a wedge that would raise it up and backward, but for the contrary power of its weight, which desires to descend down and forward along the obliquity g h. Because equal powers only resist and do not overcome one another, the bird neither rises nor falls but stays fixed in its place.

Wings held level give the greatest stability against capsizing

If the bird lowers its wings toward level, it becomes more stable upon the air and sustains itself with less difficulty, since keeping the wings at the position of equality spans a greater space. Holding the wings high is safer against turning upside down than holding them low, though it banks less easily to right or left.

Banking by the tail-rudder; the more-spread wing resists descent

When the bird dips to the right by the rudder of the tail, resistance increases because that wing embraces more air than the other and at once descends back to level. This makes wings-high a good expedient for descending with a straight, simple obliquity, whereas wings held below the body would flip it upside down, since the more-extended wing embraces more air and resists the oblique descent more than the other.

Uccello contro vento, con:

Doppia figura d'uccello, con:

Figura analoga, con:

Uccello ad ali abbassate e inclinate:

Bird against the wind, with:

Double figure of a bird, with:

Analogous figure, with:

Bird with wings lowered and inclined:

On Birds: Hovering Against the Wind and Wing Position

On this page

A bird hovers motionless when wind-lift equals its weight

Wings held level give the greatest stability against capsizing

Banking by the tail-rudder; the more-spread wing resists descent