How is the aspect ratio of a wing defined?

• A. Span of a wing divided by its root chord.
• B. Span of a wing divided by its average chord.
• C. Wing area divided by wingspan.
• D. Chord length divided by wingspan.

Answer: (B)

Aspect ratio measures how long and slender a wing is. It is defined as the wingspan divided by the mean geometric (average) chord. The mean chord is the chord length averaged across the span, and for any wing it satisfies AR = b^2 / S because S = b × mean chord, so AR = b / (mean chord) = b^2 / S. This is why spanning divided by the average chord is the correct description.

Using the root chord would ignore taper along the span, and wing area divided by wingspan gives the average chord itself, not the ratio. Chord length divided by wingspan is the reciprocal of the typical AR measure.