Airfols

Airfoil
An airfoil is the shape of a wing or blade (of a propeller, rotor or turbine), or sail.

An airfoil-shaped body moved through a fluid produces an aerodynamic force. The component of thisforce perpendicular to the direction of motion is called lift. The component parallel to the direction of motion is called drag.

There are various terms related to airfoils:

Suction surface.-(a.k.a. upper surface) is generally associated with higher velocity and thus lower static pressure.
Pressure surface.- (a.k.a. lower surface) has a comparatively higher static pressure than the suctionsurface. The pressure gradient between these two surfaces contributes to the lift force generated for a given airfoil.
The geometry of the airfoil is described with a variety of terms. A keycharacteristic of an airfoil is its chord. We thus define the following concepts:

Leading edge.- is the point at the front of the airfoil that has maximum curvature.
Trailing edge.- is defined similarlyas the point of maximum curvature at the rear of the airfoil.
Chord line.- is a straight line connecting the leading and trailing edges of the airfoil. The chord length, or simply chord, , is thelength of the chord line and is the characteristic dimension of the airfoil section.
The shape of the airfoil is defined using the following concepts:
Mean camber line.- is the locus of points midwaybetween the upper and lower surfaces. Its exact shape depends on how the thickness is defined.

Thickness of an airfoil varies along the chord. It may be measured in either of two ways:
Thicknessmeasured perpendicular to the camber line. This is sometimes described as the "American convention“.
Thickness measured perpendicular to the chord line. This is sometimes described as the "Britishconvention".

Finally, important concepts used to describe the airfoil’s behavior when moving through a fluid are:
Aerodynamic center.- which is the chord-wise length about which the pitching moment...