winglets

[Maximilian_Jenius]

I saw some winglets on a NWA 757 here in LAS the other day. They look pretty effing sweet on the 75s .

Yea...see em here too on NWA 757-200/300's. At first I thought they were EMB-190's. I had to do a double take,was thinkin when NWA get 190's!

 

[caliginousface]

Just because they're attached to the wing doesnt mean they "reduce" wingtip vortices. They just use them to their advantage to reduce drag.

Usually the vortex increases drag by the downwash it produces. By placing the winglet on the tip, it combines with the free airstream which results in somewhat of an angled flow.

By doing this there is a lift vector provided which acts perpindicular to the local airstream therefore producing a vector that is pointed forward.

Just remember that the winglets still produce a parasite drag penalty and added weight to the wing.

So, I'd say your instructor was right!

(how'd I do tgrayson?)

According to the attached photo, do I have the vectors drawn correctly? The red being hte local airstream and the yellow being lift produced by winglets. How does the lift produced by the winglet, perpendicular to the local airstream become a forward pointed vector?

"The winglets increase the spread of the vortices along the TE, creating more lift at the wingtips (figs. 2 and 3). The result is a reduction in induced drag (fig. 4). The maximum benefit of the induced drag reduction depends on the spanwise lift distribution on the wing."

So the spreading of vortices towards the end of the wing lead to a reduction of localized vortice strength allowing more of the wing to produce more lift?

"The 747-400 commercial airplane needed a significant span increase to meet the range requirement. However, structural constraints prevented the total span increase, so a combination of winglet and span increase was used."

I'm slightly confused by explanations given, and have tried reading the wind tunnel test by NASA, but have still not been able to make total sense. Any help would be appreciated.

 

[tgrayson]

According to the attached photo, do I have the vectors drawn correctly?

No, the yellow arrows need to point much more forward.

How does the lift produced by the winglet, perpendicular to the local airstream become a forward pointed vector?

Because the lift generated depends on where the relative wind is coming from. In this case, it's coming from outside the wingtip. Draw a lift vector perpendicular to it.

I'm slightly confused by explanations given, and have tried reading the wind tunnel test by NASA, but have still not been able to make total sense. Any help would be appreciated.

That's because they switch back and forth between two different ways of saying the same thing. Although the winglets do develop lift in the forward direction, when you place these airfoils on top of another wing which is also developing aerodynamic forces, the resulting forces are going to be a combination of the two. Consider that as an airfoil, the winglet will have high pressure on the bottom, low on the top. The high pressure air on the bottom of the main will not experience as much of a pressure difference with the top of the wing, because the high pressure of the winglet separates them. This tends to reduce the intensity of the vortices.

So the idea of the winglets developing lift or the winglets diminishing the vortices is pretty much the same thing.

 

[Olympic]

Winglets do 2 things

Reduce wing tip vorticies and induced drag, thats it!!