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Raked Wingtips ....  
User currently offlineYodobashi From United Kingdom, joined Sep 2007, 237 posts, RR: 3
Posted (4 years 8 months 2 weeks 4 days 13 hours ago) and read 4015 times:

Hi folks,

As far as I understand, winglets and raked wingtips help to reduce drag, stopping the airflow from the top and bottom of the wings colliding at the wingtip and causing drag.

I shot the following picture from a Singapore B777-300ER wing whilst in the climb out of Singapore. The condensation on the upper wing seems to stop short of the wingtip about where the raked wing starts.

Does anyone know is this just coincidence, or does this show how the raked wing stops the airflow on the top of the wing from reaching the wingtip itself?

http://www.pbase.com/image/120774328.jpg

Any info would be greatly appreciated.


"The World is a book, and those who do not travel read only a page"
4 replies: All unread, jump to last
 
User currently offlineTdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 79
Reply 1, posted (4 years 8 months 2 weeks 4 days 9 hours ago) and read 3951 times:



Quoting Yodobashi (Thread starter):
As far as I understand, winglets and raked wingtips help to reduce drag

Yes.

Quoting Yodobashi (Thread starter):
stopping the airflow from the top and bottom of the wings colliding at the wingtip and causing drag.

Not really. The reduce, but do not eliminate, the airflow around the end of the wing. Most of their effect (in terms of drag) actually happens fairly far from the tip itself.

Quoting Yodobashi (Thread starter):
The condensation on the upper wing seems to stop short of the wingtip about where the raked wing starts.

Does anyone know is this just coincidence, or does this show how the raked wing stops the airflow on the top of the wing from reaching the wingtip itself?

It's not a coincidence, but it's not a because the tip is stopping the airflow either. The condensation is caused by the pressure drop over the wing's upper surface...the amount of condensation is, roughly, a measure of the lift being generated at that wing station. The lift on all wings (regardless of winglet/raked tip/normal tip) goes to zero at the tip, so the upper surface condensation will also disappear at the tip. How close it gets to the tip depends, a lot, on how much lift the wing is generating, the atmospheric conditions at the time, and the wing shape.

Tom.


User currently offlineVikkyvik From United States of America, joined Jul 2003, 10024 posts, RR: 26
Reply 2, posted (4 years 8 months 2 weeks 4 days 2 hours ago) and read 3874 times:
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Couple photos to illustrate Tom's point:


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Click here for bigger photo!

Photo © Ronald J Stella



Notice in the next two photos, the condensation basically spans the flap span. The portion of the wing that has flaps is generating far more lift than the tip, when the flaps are extended. You also get a powerful vortex off of the end of the flaps. These effects are generally best noticed on landing, as you're at a high flap setting.


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Click here for bigger photo!

Photo © Tim De Groot - AirTeamImages
View Large View Medium
Click here for bigger photo!

Photo © Andrew Hunt - AirTeamImages




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User currently offlineBMI727 From United States of America, joined Feb 2009, 15742 posts, RR: 27
Reply 3, posted (4 years 8 months 2 weeks 4 days 1 hour ago) and read 3853 times:

I don't have a lot to add here, the other two mostly covered it.

Quoting Tdscanuck (Reply 1):
The condensation is caused by the pressure drop over the wing's upper surface...the amount of condensation is, roughly, a measure of the lift being generated at that wing station.

The condensation forms in lower pressure areas and on a wing, the areas with the lowest pressure (above the wing) create the most lift. This effect also appears as the shock collars in transonic flight and in some engines, if the conditions are right.



Why do Aerospace Engineering students have to turn things in on time?
User currently offlineYodobashi From United Kingdom, joined Sep 2007, 237 posts, RR: 3
Reply 4, posted (4 years 8 months 2 weeks 3 days 15 hours ago) and read 3780 times:

Gentlemen,

Many thanks for your replies, I think I am now a little wiser as the reasons for the effects pictured.

Thanks again!

 Smile



"The World is a book, and those who do not travel read only a page"
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