Wing fences, also known as boundary layer fences and potential fences are fixed aerodynamic devices attached to aircraft wings. Often seen on swept-wing aircraft, wing fences are flat plates fixed to the upper surfaces parallel to the wing chord and in line with the free stream airflow, typically wrapping around the leading edge. By obstructing span-wise airflow along the wing, they prevent the entire wing from stalling at once, as opposed to wingtip devices, which increase aerodynamic efficiency by seeking to recover wing vortex energy.
Three wing fences are installed on the wing of a Tu-95
As a swept-wing aircraft slows toward the stall speed of the wing, the angle of the leading edge forces some of the airflow sidewise, toward the wing tip. This process is progressive: airflow near the middle of the wing is affected not only by the leading edge angle, but also the spanwise airflow from the wing root. At the wing tip the airflow can end up being almost all spanwise, as opposed to front-to-back over the wing, meaning that the effective airspeed drops well below the stall. Because the geometry of swept wings typically places the wingtips of an aircraft aft of its center of gravity, lift generated at the wingtips tends to create a nose-down pitching moment. When the wingtips stall, both the lift and the associated nose-down pitching moment rapidly diminish. The loss of the nose-down pitching moment leaves the previously balanced aircraft with a net nose-up pitching moment. This forces the nose of the aircraft up, increasing the angle of attack and leading to stall over a greater portion of the wing. The result is a rapid and powerful pitch-up followed by a complete stall, a difficult situation for a pilot to recover from.[1] The "Sabre dance" (which caused many F-100 Super Sabres to crash) is a notable example of this behavior.
Wing fences delay, or eliminate, these effects by preventing the spanwise flow from moving too far along the wing and gaining speed. When meeting the fence, the air is directed back over the wing surface. Similar solutions included a notch or dogtooth in the leading edge, as seen on the Avro Arrow, or the use of slats, as on the earlier versions of the F-86. Slats can act as fences directly, in the form of their actuators, but also reduce the problem by improving the angle of attack response of the wing and moving the stall point to a lower speed.[1]
^ abHurt, H. H. Jr., "NAVAIR 00-80T-80, Aerodynamics for Naval Aviators". Naval Air Systems Command, 1965, p. 86. at faa.gov
^(in German)DE 700625 "Vorrichtung zum Verhindern der Ausbreitung von Strömungsstörungen an Flugzeugflügeln" filed on September 27, 1938.
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Wing Vortex Devices at aerospaceweb.org
January 27, 2023
wing, fence, this, article, needs, additional, citations, verification, please, help, improve, this, article, adding, citations, reliable, sources, unsourced, material, challenged, removed, find, sources, news, newspapers, books, scholar, jstor, april, 2011, l. This article needs additional citations for verification Please help improve this article by adding citations to reliable sources Unsourced material may be challenged and removed Find sources Wing fence news newspapers books scholar JSTOR April 2011 Learn how and when to remove this template message Wing fences also known as boundary layer fences and potential fences are fixed aerodynamic devices attached to aircraft wings Often seen on swept wing aircraft wing fences are flat plates fixed to the upper surfaces parallel to the wing chord and in line with the free stream airflow typically wrapping around the leading edge By obstructing span wise airflow along the wing they prevent the entire wing from stalling at once as opposed to wingtip devices which increase aerodynamic efficiency by seeking to recover wing vortex energy Three wing fences are installed on the wing of a Tu 95 The MiG 17 included prominent wing fences Close up of the wing fences of a Sukhoi Su 22 This plane was used by Former East German Air Force and retired after German unification As a swept wing aircraft slows toward the stall speed of the wing the angle of the leading edge forces some of the airflow sidewise toward the wing tip This process is progressive airflow near the middle of the wing is affected not only by the leading edge angle but also the spanwise airflow from the wing root At the wing tip the airflow can end up being almost all spanwise as opposed to front to back over the wing meaning that the effective airspeed drops well below the stall Because the geometry of swept wings typically places the wingtips of an aircraft aft of its center of gravity lift generated at the wingtips tends to create a nose down pitching moment When the wingtips stall both the lift and the associated nose down pitching moment rapidly diminish The loss of the nose down pitching moment leaves the previously balanced aircraft with a net nose up pitching moment This forces the nose of the aircraft up increasing the angle of attack and leading to stall over a greater portion of the wing The result is a rapid and powerful pitch up followed by a complete stall a difficult situation for a pilot to recover from 1 The Sabre dance which caused many F 100 Super Sabres to crash is a notable example of this behavior Wing fences delay or eliminate these effects by preventing the spanwise flow from moving too far along the wing and gaining speed When meeting the fence the air is directed back over the wing surface Similar solutions included a notch or dogtooth in the leading edge as seen on the Avro Arrow or the use of slats as on the earlier versions of the F 86 Slats can act as fences directly in the form of their actuators but also reduce the problem by improving the angle of attack response of the wing and moving the stall point to a lower speed 1 Wolfgang Liebe who is generally credited with inventing wing fences filed a patent 2 for it in 1938 while working on the Messerschmitt Bf 109B After World War II Soviet military aircraft designers became known for their habit of using wing fences using them on aircraft as varied as Mikoyan MiG 15 Mikoyan MiG 17 Mikoyan MiG 19 Mikoyan MiG 21 Mikoyan MiG 25 Mikoyan MiG 31 Tupolev Tu 128 Tupolev Tu 95 Tupolev Tu 160 in swept wing mode and Tupolev Tu 22Ms See also EditVortilon a similar device mounted on the underside of the wing Boeing 727 Sud Aviation Caravelle De Havilland Canada DHC 6 Twin Otter BAE Systems Hawk Baade 152References Edit a b Hurt H H Jr NAVAIR 00 80T 80 Aerodynamics for Naval Aviators Naval Air Systems Command 1965 p 86 at faa gov in German DE 700625 Vorrichtung zum Verhindern der Ausbreitung von Stromungsstorungen an Flugzeugflugeln filed on September 27 1938 External links Edit Wikimedia Commons has media related to Wing fences Essay on wing fences PDF Archived from the original PDF on 2006 02 11 at B2streamlines com Wing Vortex Devices at aerospaceweb org Retrieved from https en wikipedia org w index php title Wing fence amp oldid 1077444915, wikipedia, wiki, book, books, library,
