Editing Wingtip vortices (section)

== Hazards ==
[[File:Airplane vortex edit.jpg|thumb|right|A [[NASA]] 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 [[Flap (aircraft)|wing flaps]] and landing gear retracted ("heavy, slow and clean").<ref>{{citation |title=Estimation of Wake Vortex Advection and Decay Using Meteorological Sensors and Aircraft Data|first=K.M|last=Butler|publisher=Lincoln Laboratory, MIT|year=1993|url=https://www.ll.mit.edu/mission/aviation/publications/publication-files/atc-reports/Butler_1993_ATC-201_WW-15318.pdf|page=11}}</ref> 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 [[Aileron|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 controller]]s 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.<ref>[http://www.boldmethod.com/learn-to-fly/aerodynamics/avoid-wake-turbulence-during-takeoff-and-landing/ How To Avoid Wake Turbulence During Takeoff And Landing]</ref>

[[Glider (sailplane)|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.<ref>[http://www.soaringsafety.org/learning/towpilot/tpc5.htm Boxing the Wake]</ref>