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Origin of the Airfoil.
The origin of airfoil was inspired by the question: How do birds fly? An one author states, "birds are exquisitely designed (or adapted) for flight"" (Knight, 2002, p. 103). There are many technical inventions human borrowed from nature, and the airfoil is one of them. In the late 19th century scientists observed birds' ability to glide without wing movement and loss of altitude, and made a conclusion that some force was produced by their wings. After further investigation they discovered that "A bird's wing is curved along the top, a crucial aspect of its construction. As air passes over the leading edge of the wing, it divides, and because of the curve, the air on top must travel a greater distance before meeting the air that followed across the bottom" (Knight, 2002, p. 104). This effect produces different pressures over and under the wing of a bird, and creates a lift. The birds' wings, in profile, look exactly like a modern airfoil, and scientists took this design and made it their own. Then airfoil was developed and it became more complicated and varied, but the original idea was adopted from a bird's wing. .
Definition and Overview of the Airfoil.
According to the Fuller (1996) "The aerodynamic lift on an object moving through air is defined as the upward force on the object that opposes the downward force of gravity on the object. This lift force results from the difference between the pressure acting upward on the bottom of the object and the pressure acting downward on the top of the object"" (p. 31). By this definition a motionless profile cannot produce any force. In order to begin producing lift, the profile must begin to move in the air or liquid. In this case the airfoil is influenced by several forces. These forces are weight of the profile (downward), drag, which is braking force (against the motion), thrust, which usually provided by the engines (forward), and lift, which is produced by profile capacity (upward).
