Take the 2-minute tour ×
Aviation Stack Exchange is a question and answer site for aircraft pilots, mechanics, and enthusiasts. It's 100% free, no registration required.

It seems like a lot of the newer airliners have winglets or wing fences. How do they improve aircraft performance?

enter image description here

share|improve this question
4  
Did you read the Wikipedia article? If so, please be more specific about what parts you need help with. There doesn't seem to be much point in somebody rewriting that article as an answer. –  David Richerby Mar 7 at 22:25
    
@DavidRicherby sorry, no I didn't –  flyingfisch Mar 7 at 23:35

3 Answers 3

up vote 15 down vote accepted

they reduce the wingtip vortex and the associated drag by deflecting the air that wants to escape over the tip back down

http://upload.wikimedia.org/wikipedia/commons/thumb/d/d4/737-NG_winglet_effect_%28simplified%29.svg/800px-737-NG_winglet_effect_%28simplified%29.svg.png(source: wikipedia)

share|improve this answer
    
For lots more detail than you ever wanted to know about wingtip vorticies, their induced drag, and wingtip devices to counteract them check out Sighard Hoerner's book Fluid Dynamic Drag. The ZenithAir website also has some more accessible explanations (about 1/3 of the way down under "Wing Tips"). –  voretaq7 Mar 7 at 20:36

Wing generates lift by creating area of higher pressure below and area of lower pressure above.

At the wing tip, some air flows around the tip, reducing the pressure differential and thus the efficiency of the wing. This is called transverse flow. The wing tip reduces this flow, thus improving the efficiency.

The effect of wing tip is actually similar to making the wing a bit longer, but since the wing tip does not produce lift itself, it is less stressed and therefore can be lighter, even though the extension would be about 1/3 shorter for comparable efficiency.

share|improve this answer

Winglets, raked wingtips, fences, sharklets all do the same thing; reduce drag. When the wing is working hard (high AoA), it will produce a lot of this kind of drag since vortecies of all kinds will be stronger. Winglets makes the passage of air from the bottom of the wing to the lower pressure top of the wing more difficult, thus reducing induced drag.

The big manufacturers explored offering winglet retrofit kits to their customers but at the time, it wasn't economical since fuel was so cheap. These days, however, the retrofits pay for themselves fairly quickly even on airplanes wings that have a fairly high aspect ratio. Every 737/757/767 guy that I talk to says they get in the neighbor hood of a 4-6% boost in fuel savings.

On an tangentially related topic, the hump from the satellite internet antennae has a negligible impact on performance, less than 1% according to the few guys that I talked to.

share|improve this answer

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.