An airfoil is any surface which provides aerodynamic force when it is subjected to a moving flow of air. This includes the wings of an aircraft, used to generate lift. Further, the term usually refers to the shape of the wing or revolving blade, as seen in the cross-section. Therefore, an aircraft’s wings, horizontal stabilizers, vertical stabilizers, propellers, fans, compressors, and turbines are all considered airfoils. All of these components are related to the term “angle of attack,” as airfoils are designed to efficiently create lift when subject to an angle of attack against a moving fluid.
The difference in pressure distribution on the wing’s surface, explained by Bernoulli’s Principle, is the interaction of airstreams around the airfoil, which ultimately creates lift. An airfoil should be designed with a greater curvature on the upper side, in order to allow the air to accelerate as it passes over it. By doing so, the speed of air over the airfoil results in a decrease in pressure (Bernoulli’s Principle), contributing to total lift. The other interaction of airflow that contributes to total lift is the downward-backward stream of air that is created by the top surface. According to Newton’s Third law of motion, this should create an opposite, upward reaction of the airfoil.
Some terms that are related to an airfoil are: mean camber line, chord line, chord, maximum thickness, aerodynamic center, and center of pressure. The mean camber line refers to an imaginary line drawn midway between the upper and lower surface of an airfoil. The chord line is another imaginary line that is drawn connecting the leading and trailing edges of an airfoil, meeting at the two ends of the mean chamber line. Chord is the term used to refer to the length of the chord line. Maximum thickness is the position of the maximum thickness expressed as a percentage of the chord. The aerodynamic center is the position on the chord where the pitching movement is independent of the lift coefficient and angle of attack. Lastly, the center of pressure is the location on the chord at which the pitching movement is zero.