Expert: Paul Soderman - 11/16/2006

Question
When the first super-long haul jets came (1980's)in I noticed that they had vertical fins flicked up at the end of the wings. Now more and more modern planes have these - but not all. Some small jets have them, some big passenger liners long and short haul, but not all. Firstly, what is their purpose? Secondly, in serving this purpose, why aren't they adopted universally?

Many thanks in advance

Answer
Hi Chris
The vertical fins are called winglets.  Winglets are designed to reduced aircraft induced drag by modifiying the vortex distribution in the tip area, which reduces the wing downwash, which reduces induced drag.  The winglet lift is slightly in the aircraft thrust direction, so some of the winglet drag is negated.  And of course, the wing span is less than the wing would have to be for the same induced drag, so airport congestion is reduced.  A nice aerodynamic improvement, thanks to the research of Whitcomb, a NASA engineer.

I assume winglets are not universally accepted because there are a lot of aircraft in service that are based on old designs that predate the winglet popularity.  Or, perhaps some designers feel that the extra weight and complexity do not justify the drag reduction.  Not all aircraft companies are as innovative as others.

Paul