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 this force that propels the bird is called “thrust”.
A subtle movement of the wrist during wing recovery changes the angle of the wing to prevent cancelation of the forces created during the downstroke.
Forward flight in helicopters occurs in a similar way. After takeoff, a control input is used to tilt the rotors during part of the rotation so a thrust is generated as well as lift.
Wing flapping also provides both lift and thrust for takeoff. Ducks flushed from the water or ground can rise very quickly using fast powerful wing strokes.
As the wing moves forward, the relative airflow over the wing surface creates a lift force even in stationary air.
LEARN MORE ABOUT FLAPPING FLIGHT
KIDS QUESTION: In the Museum exhibit, we asked: What forces do airplane wings generate?
The answer is: Airplane wings generate lift and drag. Bird wings also generate thrust.
This is a fundamental difference between aircraft flight and bird flight. Aircraft engines are used to generate thrust.