Wingtip vortices

When a wing generates aerodynamic lift, it results in a region of downwash between the two vortices. Three-dimensional lift and the occurrence of wingtip vortices can be approached with the concept of horseshoe vortex and described accurately with the Lanchester–Prandtl theory. In this view, the trailing vortex is a continuation of the wing-bound vortex inherent to the lift generation. == Effects and mitigation ==

and wingtip devices Wingtip vortices are associated with induced drag, an unavoidable consequence of three-dimensional lift generation. The rotary motion of the air within the shed wingtip vortices (sometimes described as a "leakage") reduces the effective angle of attack of the air on the wing. The lifting-line theory describes the shedding of trailing vortices as span-wise changes in lift distribution. For a given wing span and surface, minimal induced drag is obtained with an elliptical lift distribution. For a given lift distribution and wing planform area, induced drag is reduced with increasing aspect ratio. As a consequence, aircraft for which a high lift-to-drag ratio is desirable, such as gliders or long-range airliners, typically have high aspect ratio wings. Such wings however have disadvantages with respect to structural constraints and maneuverability, as evidenced by combat and aerobatic planes which usually feature short, stubby wings despite the efficiency losses. Another method of reducing induced drag is the use of winglets, as seen on most modern airliners. Winglets increase the effective aspect ratio of the wing, changing the pattern and magnitude of the vorticity in the vortex pattern. A reduction is achieved in the kinetic energy in the circular air flow, which reduces the amount of fuel expended to perform work upon the spinning air. After NASA became concerned about the increasing density of air traffic potentially causing vortex related accidents at airports, an experiment by NASA Ames Research Center wind tunnel testing with a 747 model found that the configuration of the flaps could be changed on existing aircraft to break the vortex into three smaller and less disturbing vortexes. This primarily involved changing the settings of the outboard flaps, and could theoretically be retrofitted to existing aircraft. == Visibility of vortices ==

s of an F/A-18 The cores of the vortices can sometimes be visible when the water present in them condenses from gas (vapor) to liquid. This water can sometimes even freeze, forming ice particles. Condensation of water vapor in wing tip vortices is most common on aircraft flying at high angles of attack, such as fighter aircraft in high g maneuvers, or airliners taking off and landing on humid days. Aerodynamic condensation and freezing The cores of vortices spin at very high speed and are regions of very low pressure. To first approximation, these low-pressure regions form with little exchange of heat with the neighboring regions (i.e., adiabatically), so the local temperature in the low-pressure regions drops, too. If it drops below the local dew point, there results a condensation of water vapor present in the cores of wingtip vortices, making them visible. == Formation flight ==

in V formation One theory on migrating bird flight states that many larger bird species fly in a V formation so that all but the leader bird can take advantage of the upwash part of the wingtip vortex of the bird ahead. Albion Bowers, a NASA scientist ( ret. ), has stated on yt videos that they have the vortex form at 75% of halfspan, & they cross their wings ( bird ahead, bird behind ) at this point, showing exactly that they are taking advantage of this: each bird flies in the outboard-upwash of the bird ahead. == Hazards ==

study on wingtip vortices, illustrating the size of the vortices produced. Wingtip vortices can pose a hazard to aircraft, especially during the landing and takeoff phases of flight. The intensity or strength of the vortex is a function of aircraft size, speed, and configuration (flap setting, etc.). The strongest vortices are produced by heavy aircraft, flying slowly, with wing flaps and landing gear retracted ("heavy, slow and clean"). Large jet aircraft can generate vortices that can persist for many minutes, drifting with the wind. The hazardous aspects of wingtip vortices are most often discussed in the context of wake turbulence. If a light aircraft immediately follows a heavy aircraft, wake turbulence from the heavy aircraft can roll the light aircraft faster than can be resisted by use of ailerons. At low altitudes, in particular during takeoff and landing, this can lead to an upset from which recovery is not possible. ("Light" and "heavy" are relative terms, and even smaller jets have been rolled by this effect.) Air traffic controllers attempt to ensure an adequate separation between departing and arriving aircraft by issuing wake turbulence warnings to pilots. In general, to avoid vortices an aircraft is safer if its takeoff is before the rotation point of the airplane that took off before it. However care must be taken to stay upwind (or otherwise away) from any vortices that were generated by the previous aircraft. On landing behind an airplane the aircraft should stay above the earlier one's flight path and touch down further along the runway. Glider pilots routinely practice flying in wingtip vortices when they do a maneuver called "boxing the wake". This involves descending from the higher to lower position behind a tow plane. This is followed by making a rectangular figure by holding the glider at high and low points away from the towing plane before coming back up through the vortices. (For safety this is not done below 1500 feet above the ground, and usually with an instructor present.) Given the relatively slow speeds and lightness of both aircraft the procedure is safe but does instill a sense of how strong and where the turbulence is located. == Gallery ==

Image:EA-6B Prowler from VAQ-138.jpg|An EA-6 Prowler with condensation in the cores of its wingtip vortices and also on the top of its wings. Image:DehavillandCC-115Buffalo12.JPG|Vortices form at the ends of propeller blades, as seen on this DHC-5 Buffalo. Image:Wingtip condensation.jpg|The core of the vortex trailing from the tip of the flap of a commercial airplane with landing flap extended. Image:Cessna 182 model-wingtip-vortex.jpg|Wingtip vortices from a Cessna 182 wind tunnel model. Image:C17-Vortex.JPG|Wingtip vortices shown in flare smoke left behind a C-17 Globemaster III. Also known as smoke angels. file:MV-22B Osprey (USMC) 008.jpg|The MV-22 Osprey tiltrotor has a high disk loading, producing visible blade tip vortices. File:Euler tip vortex.png|Euler computation of a steady tip vortex. Contour colours and isosurface reveal vorticity. File:Model in Vortex Facility - GPN-2000-001288.jpg|A Boeing 747 model has just passed through a stationary sheet of smoke, which is showing its trailing vortices, at the Vortex Facility at the Langley Research Center. == See also ==