Figure 2.5. Symmetrical and Asymmetrical Airfoils.
2.6. ANGLE OF ATTACK
The angle of attack is the angle at which an airfoil passes through the air. This angle is measured
between the chord of the airfoil and the relative wind, as shown in figure 2.6. The chord is an imaginary
line from the leading edge to the trailing edge of an airfoil. Increasing the angle of attack deflects the
airstream and causes an upward pressure on the underside of the airfoil. This in turn increases the speed
of the airflow over the topside of the airfoil. As air-flow-speed increases, pressure on the foil's top side
is further reduced. The upward pressure on the foil's underside and pressure reduction on the top side
combine to furnish lift.