Aspect Ratio

Aspect ratio of a wing is the ratio of its span 2b to chord c. Consider a cylindrical wing shown in Figure 1.10. Imagine this to be projected on to the plane (xy-plane), which contains the chords of all the sections (this plane is perpendicular to the plane of symmetry (xz-plane) and contains the chord of the wing). The projection in this case is a rectangular area S, say, which is called the plan area of the wing. The plan area is different from the total surface area of the wing. The simplest cylindrical wing would be a rectangular plate, and the plan area would then be half of the total surface area.

The aspect ratio of the cylindrical wing is then defined by:

M=2_b=

c S,

where S — span x chord — 2b x c.

In the case of a wing which is not cylindrical, the plan area is defined as the area of the projection on the plane through the chord of the wing (mean chord) perpendicular to the plane of symmetry, and the aspect ratio is defined as:

(2b)2

S

A representative value of aspect ratio is 6.

Example 1.2

The semi-span of a rectangular wing of planform area 8.4 m2 is 3.5 m. Determine the aspect ratio of the wing.

Solution

Given, S = 8.4 m2 and b = 3.5 m.

The planform area of a wing is S = span x chord. Therefore, the wing chord becomes:

c =

The aspect ratio of the wing is:

Span Chord 2 x 3.5

1.2