Editing Swept wing (section)

=== Forward sweep ===
{{Main|Forward-swept wing}}
[[File:PSU Blanik.JPG|thumb|[[LET L-13]] two-seat [[Glider aircraft|glider]] showing forward swept wing]]
[[File:Grumman-X29-InFlight.jpg|thumb|[[Grumman X-29]] experimental aircraft, an extreme example of a forward swept wing]]

Sweeping a wing forward has approximately the same effect as rearward in terms of drag reduction, but has other advantages in terms of low-speed handling where tip stall problems simply go away. In this case the low-speed air flows towards the fuselage, which acts as a very large wing fence. Additionally, wings are generally larger at the root anyway, which allows them to have better low-speed lift.

However, this arrangement also has serious stability problems. The rearmost section of the wing will stall first causing a pitch-up moment pushing the aircraft further into stall similar to a swept back wing design. Thus swept-forward wings are unstable in a fashion similar to the low-speed problems of a conventional swept wing. However unlike swept back wings, the tips on a forward swept design will stall last, maintaining roll control.

Forward-swept wings can also experience dangerous flexing effects compared to aft-swept wings that can negate the tip stall advantage if the wing is not sufficiently stiff. In aft-swept designs, when the airplane maneuvers at high [[load factor (aerodynamics)|load factor]] the wing loading and geometry twists the wing in such a way as to create washout (tip twists leading edge down). This reduces the angle of attack at the tip, thus reducing the bending moment on the wing, as well as somewhat reducing the chance of tip stall.<ref>[https://web.archive.org/web/20110712214258/http://www.homebuiltairplanes.com/forums/hangar-flying/1247-forward-swept-wings.html#post6578 "Forward swept wings."] ''Homebuiltairplanes.'' Retrieved: August 1, 2011.</ref>  However, the same effect on forward-swept wings produces a wash-in effect that increases the angle of attack promoting tip stall.

Small amounts of sweep do not cause serious problems, and had been used on a variety of aircraft to move the spar into a convenient location, as on the [[Junkers Ju 287]] or [[HFB 320 Hansa Jet]].<ref name = "aopa 2017">Bedell, Peter A. [https://www.aopa.org/news-and-media/all-news/2017/february/pilot/turbine-quick-look-hansa-jet "Quick Look: Hansa Jet: The ‘German LearJet’ was forward thinking, yet doomed."] ''aopa.org'', 1 February 2017.</ref><ref>Sweetman, Bill. [https://aviationweek.com/blog/junkers-ju287-technology-surprise-1945-style "Junkers Ju287 Technology Surprise, 1945-Style."] ''Aviation Week'', 1 September 1914.</ref> However, larger sweep suitable for high-speed aircraft, like fighters, was generally impossible until the introduction of [[fly by wire (flight control)|fly by wire]] systems that could react quickly enough to damp out these instabilities. The [[Grumman X-29]] was an experimental technology demonstration project designed to test the forward swept wing for enhanced maneuverability during the 1980s.<ref>Green 1970, pp. 493–496.</ref><ref name=AIS_X-Planes>{{cite web |url=http://www.ais.org/~schnars/aero/x-planes.htm |title=The X-Planes: From X-1 to X-34 |website=AIS.org |editor-first=Andreas |editor-last=Gehrs-Pahl |year=1995 |access-date=1 September 2009}}</ref> The [[Sukhoi Su-47]] ''Berkut'' is another notable demonstrator aircraft implementing this technology to achieve high levels of agility.<ref name=JAWA00-01>Jackson 2000, pp. 457–458.</ref> To date, no highly swept-forward design has entered production.