What is the correct definition of wing aspect ratio?

• A. Span divided by root chord
• B. Span divided by average chord
• C. Wing area divided by wingspan
• D. Chord divided by wingspan

Answer: (B)

Aspect ratio measures how slender the wing is by comparing its span to a characteristic chord length along the span. The correct definition uses the span divided by the average (mean) chord across the wing: AR = b / c̄. This accounts for taper and shape, since c̄ is the average chord along the span; it’s also equivalent to AR = b^2 / S because S = b × c̄. For a rectangular wing, where the chord is constant, this reduces to AR = b / c.

Using root chord would only match AR in a perfectly rectangular wing, not in tapered ones. Wing area divided by wingspan gives the average chord, not AR. Chord divided by wingspan is the reciprocal of AR, not AR.