Forces of Flight (birds)

Lift, Gliding, Flapping, and Drag comprise the basics of flight for birds (or similar) and demonstrate the aspects that result in differences between natural and man-made aviation. The principle of lift is the same as in aircraft design; air travels across the airfoil (above and below), and the difference in air pressure results in upward force and eventual lift of the aircraft. Gliding is based on the same properties of lift, but allows gliders to obtain both a vertical and forward force from the wings since the lift is generated at 90deg to the air flow (gliders are descending so forces are directed at the underside of the airfoil). Flapping is characterized as the motion of wings similar to lift, but rotated to propel the body forward, creating thrust (which counteracts both the drag and weight of the body). Flapping has two stages: the down-stroke which provides the thrust, and the up-stroke which requires adjustment of the wing position to minimize resistance. During the shift between up- and down-stroke, both wing position and angle of attack change to maximize control over the path and speed of flight. Drag affects the flight through multiple methods (frictional, form, lift-induced), each of which is addressed by wing position, angle of attack, and wing shape.