PPRuNe Forums - Winglets..are they usefull?

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Quote:

Originally Posted by SCaro

Raked wing tips: I would say the 777 is years behind on that. We had them on gliders more than a decade ago. Just look at a Discus.

Since then computer design and materials have advanced to the point where the simple nature of the glider technology can be scaled up to the demands of an airliner.

If you want to see what an ideal wing would look like if it were possible to forget wingspan and strength limitations... look at the wandering albatross. That wing has been developed over aeons to provide the best lift/drag ratio possible. The new raked wigtips bear similarities that can't be ignored.

I always wondered why eaglesa nd the like don't have the same finely pointed wingtips. Apparently the rounded wingtips with the feathers that separate and fan out at the wingtip are best able to identify the rising air of a thermal.

Quote:

Originally Posted by philleas fogg

What i can recall from my limited knowledge of aerodynamics, wiglets help reduce wing tip vortices and thereby cruise drag. How come Boeing went for winglets on the 747 and BBJs, but not the 777?

Well Boeing says they give a fuel saving of 3-5%.
They give better performance capability.

But most of all, they LOOK GOOD.

A quick search on the NASA Technical Reports Server yields a few interesting looking documents. Here's the shortcut: http://ntrs.nasa.gov/index.cgi?metho...words=winglets

The 757/767 has super critical elements in it's wing design as well. Obviously the best technology of the day has been surpassed with the 777 as after- market winglets are now available for the 757. Here's a good read about supercritical wing technology.

http://oea.larc.nasa.gov/PAIS/Concep...rcritical.html

From an after-market winglet manufacturer on the benefits...

"Aviation Partners Boeing expects to Performance Enhance the majority of the 600 plus existing fleet of 757-200s with revolutionary Blended Winglet Technology. Operator benefits include: a block fuel improvement of up to 5%, approximately 200 nautical miles of additional range or up to 10,000 lbs. of incremental payload capability, improved second segment climb, enhanced operational flexibility (such as trading improved fuel burn for faster cruise speeds), improved takeoff performance out of high, hot, or obstacle limited airports, reduced engine maintenance costs, enhanced aesthetic appeal, increased aircraft residual value, and a range of environmental benefits that will equate to an economic payback period of less than 3 years for most operators."

Having just arrived in the states via Newark, it would appear that Continental think they are a good idea; every 757 I could see (and that was quite a few!) had retrofitted winglets on.