texasflyer
Posts: 77
Joined: Sun Jun 06, 2004 7:38 am

How Winglets Help

Wed Sep 08, 2004 3:01 pm

I'm not a huge expert on the technical issues of winglets, but I did notice that my Southwest flight in clouds was a lot smoother. I also heard it can help with fuel consumption. And finally if they are so good why doesn't every airliner coming out of the factories have them.
We confide in our strength, without boasting of it; we respect that of others, without fearing it. Thomas Jefferson
 
deltaflyertoo
Posts: 1479
Joined: Tue Nov 14, 2000 3:18 pm

RE: How Winglets Help

Wed Sep 08, 2004 4:51 pm

The way the winglets work is this:

When an airplane wing takes flight, there is higher pressure below the wing than above it, creating lift. The faster the wing travels, the higher the pressure below than above, more lift. Now these 2 pressure differences remain seperated. Until you get to the wing tip. It is there that the higher pressure below the wing, mingles w/ the low pressure above. This part of the wing is not the most efficient and does not contribute to the overall lift of the a/c. W/ these 2 pressure points mingling, there becomes drag. So the winglets work to keep these 2 areas seperate, minimize drag and minimize excess fuel burn to compensate for the drag.

Now the winglets only work the best on very long haul flights when the wing is traveling at its maximum speed at high altitudes where these pressure points meet. Therefore we seem them on long haul a/c such as the 747-400, Airbuses, etc.

SOME airlines feel that the extra cost of adding the winglets don't offset the cost of fuel savings. This will remain to be seen at SW where these winglets add extra weight and may not always be on transcon flights.
 
FredT
Posts: 2166
Joined: Thu Feb 07, 2002 9:51 pm

RE: How Winglets Help

Sun Sep 12, 2004 11:05 pm

If you do a forum search, you will find a lot.

As that is probably the most boring answer you can receive on here, here's a quick rundown:

Low pressure on top, high pressure above. That's how lift is generated. This will, however, tend to push air around the tip of the wing from the bottom to the top. This means a loss in efficiency, as some of the pressure is used to push the air around the wingtip instead of lifting the aircraft.

This air going around the wingtip is what sets up the wingtip vortices.

This flow of air around the wingtip combined with the airspeed sets up a flow of air above the tip of the wing which goes slightly inwards. The wingtip is right in the middle of this flow. It is built like a small wing in itself, using this airflow to generate lift. Had the airstream been going straight aft, this lift would point straight in towards the fuselage. However, the airstream goes inwards too. This means the lift generated by the winglet points slightly forward, thus reducing the drag on the aircraft.

However, they also generate some parasite drag. In some flight conditions, this drag may be more than the drag reduction achieved. Thus, for some flight profiles, winglets aren't saving you any fuel at all. They do make great spots for displaying the company logo though...

New aircraft are typically not equipped with winglets as they are effectively an aerodynamical band-aid. If you can design a new wing, you are better off just increasing the span of the wing (if there is enough room on the ramp). However, lengthening an existing wing design is tricky as it changes the loads on the wing significantly. A winglet is a lot better in this respect as it tends to reduce aerodynamic loads rather than increase them.

Regards,
Fred
I thought I was doing good trying to avoid those airport hotels... and look at me now.
 
QantasA332
Posts: 1473
Joined: Sat Dec 13, 2003 5:47 pm

RE: How Winglets Help

Mon Sep 13, 2004 7:13 am

Thanks, Fred, for giving Qantas-"The Winglet Man"-A332 a break from answering this time...  Big grin

One thing I want to clear up, though, is the conditions of flight where winglets are most effective and least effective. Deltaflyertoo suggested above that winglets are most effective at higher speeds - that's not the case. Vortex strength and thus winglet effectiveness is highest at low speeds and high altitudes. Accordingly, winglets are least effective at high speeds and low altitudes. Period.

The reason why many long-haul aircraft have winglets doesn't really follow those lines, then, as you can see. Rather, the effectiveness simply becomes tied to flight length - that is, on longer flights, you understandably see more of a savings and therefore winglets are more 'effective' in that sense.

Cheers,
QantasA332
 
waketurbulence
Posts: 1264
Joined: Sun Apr 18, 2004 12:33 pm

RE: How Winglets Help

Mon Sep 13, 2004 10:19 am

"And finally if they are so good why doesn't every airliner coming out of the factories have them."

I think that Airbus has put them on all series of a/c coming off the line, they are not the Boeing type winglets but rather the wingtip fences. As for Boeing, the 727 adv can get winglets added, the 737NG and BBJ also have the option. The 747-400 has them, the 757 will eventually have them. No on the 767 except the -400 with raked tips, and from what I hear the 777 had such an efficient wing that it didn't really need it, although the 200ER and 300 have the raked wingtips to help performance. So most of Boeing's a/c either have them installed of as an option. Many airlines just can't afford a set for their planes, and it adds weight as well. Hope that helps.
-Matt
 
vikkyvik
Posts: 11799
Joined: Thu Jul 31, 2003 1:58 pm

RE: How Winglets Help

Mon Sep 13, 2004 11:03 am

WakeTurbulence,
Not to nitpick, but:

"No on the 767 except the -400 with raked tips, and from what I hear the 777 had such an efficient wing that it didn't really need it, although the 200ER and 300 have the raked wingtips to help performance."

The 777-200LR and -300ER have the raked wingtips. 777-200/200ER/300 do not. I'm sure that's what you meant though.  Smile

The wingtip vortices create induced drag, or drag due to lift. This component of drag is decreased as wingspan is increased, though parasite drag (caused by friction) may be increased.

~Vik
I'm watching Jeopardy. The category is worst Madonna songs. "This one from 1987 is terrible".
 
waketurbulence
Posts: 1264
Joined: Sun Apr 18, 2004 12:33 pm

RE: How Winglets Help

Mon Sep 13, 2004 11:41 am

No, nitpicking is necessary if the info is wrong. Thanks for the correction, I rushed through the explanation and didn't make it clear enough. Thanks for the clarification.
-Matt

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