AIM Text
- The creation of a pressure differential over the wing surface generates lift. The lowest pressure occurs over the upper wing surface and the highest pressure under the wing. This pressure differential triggers the roll up of the airflow at the rear of the wing resulting in swirling air masses trailing downstream of the wing tips. After the roll up is completed, the wake consists of two counter-rotating cylindrical vortices. (See FIG 7-4-1.) The wake vortex is formed with most of the energy concentrated within a few feet of the vortex core.
- More aircraft are being manufactured or retrofitted with winglets. There are several types of winglets, but their primary function is to increase fuel efficiency by improving the lift-to-drag ratio. Studies have shown that winglets have a negligible effect on wake turbulence generation, particularly with the slower speeds involved during departures and arrivals.
Source: FAA Aeronautical Information Manual · current edition · paragraph 7-4-2.
The short answer
AIM 7-4-2 is FAA advisory guidance on how wake vortices are generated. It explains that the pressure differential producing lift—lowest pressure over the upper wing, highest underneath—triggers airflow roll-up at the wing tips, forming two counter-rotating cylindrical vortices with most energy concentrated within a few feet of each vortex core.
Research Notes
Common Questions
How are wake vortices actually formed?
AIM 7-4-2 explains lift comes from a pressure differential—lowest over the upper wing surface, highest under the wing. This differential triggers the roll up of airflow at the rear of the wing, creating swirling air masses that become two counter-rotating cylindrical vortices trailing the wing tips.
Do winglets reduce wake turbulence?
Per AIM 7-4-2, winglets primarily increase fuel efficiency by improving the lift-to-drag ratio. Studies have shown winglets have a negligible effect on wake turbulence generation, particularly at the slower speeds involved during departures and arrivals.
Where is the energy of a wake vortex concentrated?
AIM 7-4-2 states the wake vortex is formed with most of the energy concentrated within a few feet of the vortex core, after the roll-up completes into two counter-rotating cylindrical vortices.