What is an Airfoil?

For an aircraft the primary source of lift is the wing. The lift from the tail is used to control the attitude of the aircraft so it does not contribute to carrying the weight. The primary relation in the computation of lift (consider level flight) is

The wing can be considered a 3D airfoil [ the airfoil represents a 2D wing ] or the cross section of the wing

There are several airfoils that have been designed over the years (access the airfoil data base using the link on the right to get an idea). New airfoils continue to be designed even today. It is not difficult to design airfoils as several computer programs exist that allow efficient airfoil design. For low speed general aviation aircrafts, the airfoils can be designed with confidence using only compter programs - without any wind tunnel testing. Different performance requirements can be handled by different airfoil shapes.

The 3D lift coefficient is a strong function of the operating angle of attack and the airfoil (2D or infinite) aerodynamic coefficients

The typical airfoil description parameters:

LE: leading edge of airfoil

TE: Trailing edge

Chord: c (line from the LE to TE)

x_u : upper surface of airfoil defition - mathematical curve

x_l : lower surface of airfoil defition - mathematical curve

(Note airfoil definition is normalizedwith respect to chord)

Aerodynamic calculations are based on relative wind (V_rel)

α_g= geometric angle of attack: (angle between relative wind and chord line)

α_a = absolute angle of attack :( angle between relative wind and the zero lift line)

The angle between the the the absolute angle and geometric angle is the angle at which lift is zero (Typically negative in most cambered airfoils)