A vertical cut through the wing parallel to
flight's direction (plan view) will show the cross-section of the
wing. This side view (profile) is called Airfoil, and it has
some geometry definitions of its own as shown on the picture below.
The longest straight line that can be drawn from the Airfoil's
leading edge to trailing edge is called the Chord Line. The
Chord Line cuts the airfoil into an upper surface and a lower
surface. If we plot the points that lie halfway between the upper and
lower surfaces, we obtain a curve called the Mean Camber
For a symmetric airfoil (upper surface the same shape
as the lower surface) the Mean Camber Line will fall on top of the
Chord Line. But in most cases, these are two separate lines. The
maximum distance between these two lines is called the Camber,
which is a measure of the curvature of the airfoil (high camber
means high curvature). The maximum distance between the upper and lower surfaces is called the
Thickness. Both the Thickness
and the Camber are expressed as a percentage of Chord.
Airfoils can come with all kinds of combinations of camber and
Aspect Ratio is a measure of
how long and slender a wing is from tip to tip. The Aspect Ratio of
a wing is defined to be the square of the span divided by the wing
area and is given the symbol AR.
The formula is simplified
for a rectangular wing, as being the ratio of the span to the chord
length as shown on the figure below.
Dihedral refers to the angle of wing panels as seen in the
aircraft's front view. Dihedral is added to the wings for roll
stability; a wing with some Dihedral will naturally return to its
original position if it is subject to a briefly slight roll
displacement. Most large airliner wings are designed with Dihedral. On the contrary the highly
maneuverable fighter planes have no
Dihedral. In fact, some fighter aircraft have the wing tips lower
than the roots, giving the aircraft a high roll rate.
Dihedral angle is called Anhedral.