Page 17 - Understanding Flight

CH01_Anderson PFS2 7/25/01 8:55 AM Page 4

4 CHAPTER ONE

Trailing edge

Wing

Leading Airfoil
edge
Fig. 1.3. The wing and airfoil.

Chord line
Camber line

Relative wind Angle of attack

Fig. 1.4. Airfoil nomenclature.

leading edge with the trailing edge. The chord is used for determining
the geometric angle of attack (discussed below) and for determining
the area of a wing.
The mean camber line is the line an equal distance from the upper
and lower surfaces of the wing. The camber is the curvature of the
mean camber line. A wing that has an airfoil with a great deal of
curvature in its mean camber line is said to be a highly cambered
wing. A symmetric airfoil has no camber.
An airfoil with lift also has an angle of attack, as shown in the
figure. The relative wind is the direction of the wind at some
distance from the wing. It is parallel to and opposite to the direction
of motion of the wing. The velocity of the relative wind is equal to
the speed of the wing. In aeronautics the geometric angle of attack is
defined as the angle between the mean chord of the airfoil and the
direction of the relative wind.