Flapping
When a bird flaps, as opposed to gliding, its wings continue to develop lift as before, but the lift is rotated forward to provide thrust, which counteracts drag and increases its speed, which has the effect of also increasing lift to counteract its weight, allowing it to maintain height or to climb. Flapping involves two stages: the down-stroke, which provides the majority of the thrust, and the up-stroke, which can also (depending on the bird's wings) provide some thrust. At each up-stroke the wing is slightly folded inwards to reduce upward resistance. Birds change the angle of attack between the up-stroke and the down-stroke of their wings. During the down-stroke the angle of attack is increased, and is decreased during the up-stroke.
Read more about this topic: Bird Flight, Basic Mechanics of Bird Flight
Famous quotes containing the word flapping:
“I was awakened at midnight by some heavy, low-flying bird, probably a loon, flapping by close over my head, along the shore. So, turning the other side of my half-clad body to the fire, I sought slumber again.”
—Henry David Thoreau (1817–1862)
“Amidst the dust, and the falling things, and the flapping scenery, Cincinnatus made his way in that direction where, to judge by the voices, stood beings akin to him.”
—Vladimir Nabokov (1899–1977)