In typical airplanes, lift induced drag can account for the majority of the overall drag. Why don't more aircraft employ methods to reduce this and specifically why not spiroid winglets? From every source I have read on them, they have shown to increase the lift curve slope by a significant margin, allowing for a more efficient wing that results in less induced drag. enter image description here

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    $\begingroup$ Where would one find some of these sources of information? $\endgroup$ – David K Sep 11 '18 at 20:55
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    $\begingroup$ It seems like a pretty complex design compared to current winglets, considering that longer wingspan is better and designers are willing to go with folding wingtips to do it. $\endgroup$ – fooot Sep 11 '18 at 21:42
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    $\begingroup$ There are many winglet questions on the site if you click on the winglet tag. If you read through them you'll find that winglets are usually either a trade-off between aerodynamics and weight, a compromise to keep from having to fully redesign a wing, and sometimes there's an element of gimmick to them. $\endgroup$ – TomMcW Sep 11 '18 at 22:17
  • $\begingroup$ Are you asking about "methods.. such as" spiroid winglets or just spiroids? "Such as" has already been answered. $\endgroup$ – Pilothead Sep 11 '18 at 22:28
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    $\begingroup$ Personally I would note that this is a wingtip device, strictly speaking not a winglet, so personally I don't see this as a duplicate of the other question. $\endgroup$ – Federico Sep 13 '18 at 11:21