Airfoil
An object that produces a useful aerodynamic reaction when moved through the air. An airfoil is the shape of a cross-section of a wing, control surface or rotor blade.
It can be symmetrical by having the top and bottom surfaces identical, or unsymmetrical by having more curvature on the top or bottom.
AIRFOIL TERMINOLOGY
* Aerodynamic center : The point on the chord line about which the moment coefficient is constant with changes in angle of attack. Also, the point where all changes to lift effectively occur.
* Angle of attack : The angle between the chord line and the resultant relative wind.
* Angle of incidence : The angle between the chord line and the path of rotation.
* Bernoulli's law : States that in a flow of incompressible fluid, the sum of the static and dynamic pressures remain constant if gravity and friction are disregarded.
* Boundary layer : The slow moving or stagnant air next to the surface of an airfoil. It is usually about as thick as a playing card but can be up to a quarter of an inch at or near the trailing edge of an airfoil.
* Center of pressure : The poing along the chord line through which all aerodynamic forces act.
* Chord line : A straight line that connects the leading and trailing edges of an airfoil.
* Drag : The force that opposses the motion of an airfoil. It is parallel to but opposite relative wind.
* Flight path velocity (FPV) : The speed and direction of the airfoil as it passes through the air.
* Induced velocity (flow) : The air vector perpendicular to the path of rotation produced because the wing or rotor is generating lift.
* Lift : The force perpendicular to the relative wind.
* Relative wind : Air in motion with respect to an airfoil. It is equal to and opposite the FPV.
* Resultant relative wind : Airflow from rotation that is modified by the induced velocity.
* Rotational relative wind : Relative wind produced by the rotation of the rotor blades of an aircraft.
