Evolution of Flight

At least 150 million years ago, theropod dinosaurs with feathers on their arms, legs, and tails started to appear. There is still debate about whether the first feathers were ornamental or functional but Archaeopteryx (below) which means Ancient Wing, is generally regarded as the first flying bird.  Flapping flight evolved separately at least four times […]

Wing Bones

 The sketches of four skeletons above show similarities in the arm bones of different types of animals that span a range of more than 200 million years. Each time one of these animals evolved to fly, important parts of the wings were attached to the bones of the hand (shown in green). In each case, the […]

The Engines of Flight

Avian flight muscle is like an engine with a large stroke—developing tension over a much longer relative muscle length than human muscle. This allows a large amplitude wing-flapping motion. Four muscles—two on each side of the chest (the “depressors”)—are the major engines that power the downstroke of a bird’s wings. They form the breast of […]

Taking Off

Birds prefer to take off into the wind—just like aircraft pilots. This way, air moves faster across the wings and generates more lift.   A small increase in airspeed goes a long way — a two-fold speed increase results in 4 times more lift. The lifestyles of many bird species help to provide optimum take off […]

Landing

Birds have perfected the use of stalls and near-stalls as essential techniques for landing. A bird approaching a landing site often changes its orientation with respect to the airflow from a streamlined flight mode to a more upright posture. This increases drag and the bird slows down. It also changes the angle of attack of […]

The Airfoil

  The shape of the curved cross-section that splits the air as it flows over a bird’s wing is called an airfoil. This is clearly visible on the image of the swan (above). It is not a coincidence that early airplanes and birds share the thin curved wing airfoil shapes. Aviation pioneers copied the airfoils […]

Flapping Flight

During flapping flight, the outer part of the wing generates both thrust and lift. The inner wing segment contributes primarily to lift. As the wing tip and primary (outer) feathers sweep forward and downward, the airflow creates a force that is tilted in relation to the wing and the direction of flight. The part of […]

Drag

Many features of a bird’s wing and body have evolved to minimize drag while maximizing lift. Drag is the unwelcome consequence of lift during flight. It is not possible to generate lift without drag—which slows the bird down and causes it to lose altitude. Drag occurs in a number of ways: the gull above is […]

Lift

Lift is a force created by airflow over a wing. It supports the weight of the bird against gravity. Birds do not need to flap to create lift. Lift increases rapidly with increase in speed in a square-law relationship. This is why larger birds may run on the ground before taking off and why large […]