Raked wingtips?

Question

How do raked wingtips improve an aircraft's performance?

Answer 1

It isn't clear exactly why, but this is what the patent claims they do:

The relative bluntness of the raked wingtips minimizes boundary-layer separation, drag associated with boundary-layer separation, and premature buffeting of the aircraft during low speed flight.

Answer 2

basically,. it gives more lift without lengthening wing

Answer 3

Didn't you ask this exact question just a few weeks ago?  I know someone did.  You might want to look up that question to see if he got any good answers too.

Answer 4

(from wikipedia.org)

Raked wingtips are a feature on some Boeing airliners, where the tip of the wing has a higher degree of sweep than the rest of the wing. The stated purpose of this additional feature is to improve fuel economy, climb performance and to shorten takeoff field length. It does this in much the same way that winglets do, by increasing the effective aspect ratio of the wing and interrupting harmful wingtip vortices. This decreases the amount of lift-induced drag experienced by the aircraft. In testing by Boeing and NASA, raked wingtips have been shown to reduce drag by as much as 5.5%, as opposed to improvements of 3.5% to 4.5% from conventional winglets.[5] An increase in wingspan is generally more effective than a winglet of the same length, but may present difficulties in ground handling. For this reason, Boeing's short-range 787-3 design currently calls for winglets, instead of the raked wingtips featured on all other 787 variants.

Raked wingtips are or are planned to be employed on:

Boeing 747-8

Boeing 767-400ER

Boeing 777-200LR/-300ER/Freighter

Boeing 787 (except for 787-3 variant)

Boeing P-8 Poseidon

A blended winglet is intended to reduce interference drag at the wing/winglet junction. A sharp interior angle in this region can interact with the boundary layer flow causing a drag inducing vortex, negating some of the benefit of the winglet. The blended winglet is also more aesthetically appealing, and is used on business jets and sailplanes, where individual buyer preference is an important marketing aspect.

Blended winglets have been offered as an aftermarket retrofit for Boeing 737,[1] 757 and Raytheon Hawker 800 with winglets series aircraft by Aviation Partners Inc., and the 737 version is now standard on the Boeing Business Jet derivative. Many operators have retrofitted their fleets with these for the fuel cost savings. Aviation Partners is also developing winglets for the 767-300ER. Airbus tested similar blended winglets designed by Winglet Technology for the A320 series,[10] but determined that their benefits did not warrant further development and reallocated resources from the program to their struggling A380 program.[11]