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This question already has an answer here:

If all winglets serve the same purpose (to reduce vortex drag), why do different aircraft have different winglets? This question is not trying to get a comparison of the development of winglets/wingtips, with other aircraft components, as the question of @Manu H is.

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marked as duplicate by Federico, Simon, FreeMan, Erich, fooot May 18 '15 at 15:17

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

  • $\begingroup$ @Federico, the questions do seem similar. However, they are addressing two different things. $\endgroup$ – Madhav Sudarshan May 16 '15 at 14:25
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Winglet design is driven more by marketing than by engineering, so every aircraft brand tries to cultivate their own, supposedly better, shape.

A study by Nita and Scholz (PDF!), Chapter 6 gives a good overview over recent winglet studies. A raked tip performs better, and if winglets could point downwards, they also could do better. As they are, they give only 28% to 38% drag reduction of an equivalent span increase.

Raked wingtip of the Boeing 777-300

Raked wingtip of the Boeing 777-300

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  • $\begingroup$ Thanks! This is great. I take it the newer split winglets don't really include the benefits of a downward-pointing winglet, since they primarily point upwards? $\endgroup$ – egid May 17 '15 at 17:23
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    $\begingroup$ @egid: A downward pointing winglet is only slightly better, and with the limited size cannot effect drag much. Theoretically, a variable-geometry winglet which can be folded up for landing would capture the benefit, but would work best when stopped halfway in the transition from pointing upward to pointing downward ;-) $\endgroup$ – Peter Kämpf May 17 '15 at 19:33

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