Editing Wingtip device (section)

== Physics ==

When a conventional [[wing]] generates lift, it also experiences [[lift-induced drag]]. Higher pressure air under the wing flows to the lower pressure surface on top at the wingtip, which results in a vortex caused by the forward motion of the aircraft. [[Erich Trefftz|Trefftz]]-plane theory shows that increasing the height of the lifting system will decrease induced drag. A vertical fin or winglet will reduce induced drag if it is placed anywhere along the wing off-center of the aircraft, but it is most effective when it is placed at the wingtip.<ref name="McLean Boeing" />