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发表于 2011-4-10 02:51:25
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本帖最后由 nkhtonyhk 于 2011-4-10 02:57 编辑 $ r, s9 i8 x3 w" s1 j" d& g! d' h
% x1 {) ~7 @- U; u: i* gRaked 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 efficiency and 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.
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/ a0 Z. g6 j8 Y/ K+ Y4 g& w6 uWhile an equivalent increase in wingspan would be more effective than a winglet of the same length, the bending force becomes a greater factor. A one-foot increase in span has the same bending force as a three-foot winglet, which has the same performance gain as a two-foot wing extension. |
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