Editing Wingtip device (section)

==== Raked wingtip ====

Raked wingtips, where the tip has a greater [[wing sweep]] than the rest of the wing, are featured on some [[Boeing Commercial Airplanes]] to improve [[fuel efficiency]], takeoff and climb performance. Like winglets, they increase the effective [[wing aspect ratio]] and diminish [[wingtip vortices]], decreasing lift-induced drag. In testing by Boeing and NASA, they reduce drag by as much as 5.5%, compared to 3.5% to 4.5% for conventional winglets.<ref name="bca_aero_17_wingtip_devices" />  While an increase in span would be more effective than a same-length winglet, its [[bending moment]] is greater.  A {{cvt|3|ft|cm}} winglet gives the performance gain of a {{cvt|2|ft|cm}} span increase but has the bending force of a {{cvt|1|ft|cm}} span increase.<ref name="airspace">{{cite web |url= https://www.airspacemag.com/flight-today/how-things-work-winglets-2468375/ |title= How Things Work: Winglets |work= Air & Space Magazine |date= September 2001 |author= George C. Larson |publisher= Smithsonian}}</ref>
[[File:Anh-2-15222236062661656996940.jpg|thumb|The [[Boeing 787 Dreamliner]] is an example of raked wingtips utilization.]]
Raked wingtips offer several weight-reduction advantages relative to simply extending the conventional main [[wingspan]]. At high load-factor structural design conditions, the smaller [[Chord (aeronautics)|chords]] of the wingtip are subjected to less load, and they result in less induced loading on the outboard main wing. Additionally, the leading-edge [[Swept wing|sweep]] results in the [[Center of pressure (fluid mechanics)|center of pressure]] being located farther aft than for simple extensions of the span of conventional main wings. At high load factors, this relative aft location of the center of pressure causes the raked wingtip to be twisted more leading-edge down, reducing the bending moment on the inboard wing. However, the relative aft-movement of the center of pressure accentuates [[Aeroelasticity#Flutter|flutter]].<ref>{{Cite web|last=Herrick|first=Larry|date=June 12, 1998 |title=Blunt Leading-Edge Raked Wingtips|url=https://patentimages.storage.googleapis.com/71/cf/0d/66512395e96100/US6089502.pdf|access-date=2021-12-06|website=Google Patents}}</ref>

Raked wingtips are installed on the [[Boeing 767]]-400ER (first flight on October 9, 1999), all generations of [[Boeing 777]] (June 12, 1994) including the upcoming [[Boeing 777X|777X]], the 737-derived [[Boeing P-8 Poseidon]] (25 April 2009), all variants of the [[Boeing 787]] (December 15, 2009) (the cancelled [[Boeing 787#787-3|Boeing 787-3]] would have had a {{cvt|51.7|m|ft|order=flip}} wingspan to fit in [[ICAO#Aerodrome Reference Code|ICAO Aerodrome Reference Code]] D, as its wingspan was decreased by using blended winglets instead of raked wingtips <ref>{{cite web |url= http://www.aci-na.org/static/entransit/Gen.%20Rich%20Breuhaus.pdf |title= 787 Dreamliner: A New Airplane for a New World |author= Rich Breuhaus |date= 20 May 2008 |publisher= Boeing |work= ACI-NA Commissioners Conference |access-date= 2019-01-06 |archive-url= https://web.archive.org/web/20170307045010/http://www.aci-na.org/static/entransit/Gen.%20Rich%20Breuhaus.pdf |archive-date= 2017-03-07 |url-status= dead }}</ref>), and the [[Boeing 747-8]] (February 8, 2010). The Embraer [[E-jet E2]] and [[Embraer C-390 Millennium|C-390 Millennium]] wings also have raked wingtips.