Calculating the Aspect Ratio of a Wing or Flying Surface

The Aspect Ratio is the ratio of wingspan to average wing chord.

Average wing chord for a tapered wing is the root chord plus the tip chord divided by two.  For a constant chord wing, the average chord is the chord anywhere along the wing panel.

Why Aspect Ratio is Important

• The Aspect Ratio of a wing is an indicator of the aircraft's roll response.

  All else being equal, high aspect ratio wings (narrow chord to span) will have a slower roll response than a low aspect ratio wing.

• The Aspect Ratio of a flying surface largely determines the lift to drag ratio of the surface.

  High aspect ratio wings, such as on sailplanes, are more efficient and have a higher lift to drag ratio.

• High aspect ratio wings are more easily broken and are less tolerant of poor engineering, poor building and flight outside design parameters.

To Calculate the Aspect Ratio

There are two ways to calculate the Aspect Ratio of a flight surface.

Method 1

Divide the wing span by the average wing chord.  For example, if the root chord is 12" and the tip chord is 8", then the average chord is 10" assuming a straight tapered wing.

Let's say the wing span is 50".  Divide the span by the average chord to determine the aspect ratio:

50" ÷ 10" = 5:1 aspect ratio

Method 2

Square the wing span and divide by the wing area.  This is helpful for wings where determining the average chord would be difficult such as elliptical wings.

50² ÷ 500 = 2500 ÷ 500 = 5:1 aspect ratio

You can also trace this information backwards to find the average chord of a wing.  Simply divide the wing area by the wing span.

500 ÷ 50 = 10" average chord

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Copyright © 2003 Paul K. Johnson