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.
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. 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.
Although wing fences over the wing have been known in the UK since 1914, probably due to the RAF's spin research program begun as early as 1912, the invention of the fences is often attributed to German aerodynamicist Liebe of Messerschmitt, with a patent application in 1938.
By 1947, after the introduction of subsonic swept wings, fences independently implemented in the USSR and the US: Lavochkin La-160, Mikoyan MiG-15, Northrop YB-49, McDonnell XF-85. But in the USSR such fences were used more often and for the longest time, they were made large and numerous: from MiG-15 to MiG-25, from Tu-128 to Tu-160, from Su-7 to Su-22.
06 Jun 2016 · The main purpose of the wing fence is to prevent the boundary layer thickening in the wing due to the spanwise flow observed in swept wing, as can be seen below. Image from fuckyeahfluiddynamics.tumblr.com. This is the reason for having wing fence in aircraft such as Mig-25- to avert stall and improve stability.
29 Agu 2019 · Basically, the wing fences stop the spanwise flow, with the result being a new (thinner) boundary layer starts on the other side of the fence. In case of a vortex generator, the VGs basically create a vortex which re-invigorates the boundary layer by mixing free stream air with that of the boundary layer, thereby preventing separation.
28 Nov 2015 · Both vortex generators and wing fences help to reduce this cross flow and delay flow separation on the outer wing at high angle of attack. Vortex generators also help to prevent boundary layer separation past a shock at transsonic speeds when placed close to the leading edge, something a wing fence is incapable of.
03 Jan 2019 · $\begingroup$ Sharklet height is 2.43 meters according to the source above FIGURE-2-2-0-991-004-A01 and FIGURE-2-3-0-991-004-A01 lists the wing tip fence lower tip above ground as W2 = 3.78 and upper tip as W1 = 4.76 - so 0.98 meters....
19 Mar 2023 · On most Caravelles, such as this VI-R, this takes the form of a large inboard fence which wraps around the leading edge of the wing, and a smaller outboard fence which starts significantly behind the leading edge and rises only about half as far from the wing's surface as the inboard fence does:
22 Mei 2017 · I installed my wing fences and in order for the fence to seat correctly on the underside of the wing, I had to create a 2mm deep channel on the bottom wing too. The instructions say to only create the channel for the top part of the fence, but if done this way, my bottom of the fence did not seat against the wing at all.
17 Mei 2008 · Discussion Wing fence for Cessna 210, Ember&Citabria Scratchbuilt Indoor and Micro Models
14 Mar 2014 · A dogtooth is a small, sharp zig-zag break in the leading edge of a wing. It is usually used on a swept wing, but also on straight wings ("Drooped Leading Edge" arrangement), to generate a vortex flow field to prevent separated flow from progressing outboard at high angle of attack. The effect is the same as a wing fence.
21 Agu 2019 · Mine has the groove's in the wings. I also have the original ones and a set of carbon fences. I like the way it looks without but also looking for best flight performance being kinda new to jets. I fly the eflite viper that has no wing fences and it do well. thanks for your input
30 Apr 2018 · In addition to the greater angle of wing sweep and the additional wing fences, the wing of the MiG 17 had a different, thinner profile with a thickness/chord ratio of 1 to 10 or 10%, down from the MiG 15's 11%. This was still relatively much thicker than the 5% wing used on the supersonic McDonnell F4 Phantom.
