The wetted aspect ratio is a good indication of the aerodynamic efficiency of an aircraft. It is a better measure than the aspect ratio

Aspect ratio (wing)

In aerodynamics, the aspect ratio of a wing is essentially the ratio of its length to its breadth . A high aspect ratio indicates long, narrow wings, whereas a low aspect ratio indicates short, stubby wings....

. It is defined as:


where is span and is the wetted surface (the entire surface area of the airframe exposed to airflow) of the whole aircraft in contrast to the wing area used for the definition of the aspect ratio.

A good example of this is the Boeing B-47 and Avro Vulcan

Avro Vulcan

The Avro Vulcan, sometimes referred to as the Hawker Siddeley Vulcan, was a jet-powered delta wing strategic bomber, operated by the Royal Air Force from 1956 until 1984. Aircraft manufacturer A V Roe & Co designed the Vulcan in response to Specification B.35/46. Of the three V bombers produced,...

. Both aircraft have very similar performance although they are radically different. The B-47 has a high aspect ratio wing, while the Avro Vulcan is a low aspect ratio blended wing body

Blended wing body

Blended Wing Body aircraft have a flattened and airfoil shaped body, which produces most of the lift, the wings contributing the balance. The body form is composed of distinct and separate wing structures, though the wings are smoothly blended into the body...

. They have, however, a very similar wetted aspect ratio.