Wing Geometry

A cut through the wing perpendicular to the leading and trailing edges will show the cross-section of the wing. This side view (profile) is called an 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 leading to trailing edge of the airfoil 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 Line.

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. Often you will see these values divided by the chord length to produce a non-dimensional or "percent" type of number.

Airfoils can come with all kinds of combinations of camber and thickness distributions. NACA (the precursor of NASA) established a method of designating classes of airfoils and then wind tunnel tested the airfoils in order to provide lift coefficients and drag coefficients for designers.

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.

Wing 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. A negative Dihedral angle is called Anhedral.