AIM

4/20/23

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Wake Turbulence

Section 4. Wake Turbulence

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1. General

a.

Every aircraft generates wake turbulence while in flight. Wake turbulence is a function of an aircraft

producing lift, resulting in the formation of two counter

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rotating vortices trailing behind the aircraft.

b.

Wake turbulence from the generating aircraft can affect encountering aircraft due to the strength, duration,

and direction of the vortices. Wake turbulence can impose rolling moments exceeding the roll

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control authority

of encountering aircraft, causing possible injury to occupants and damage to aircraft. Pilots should always be
aware of the possibility of a wake turbulence encounter when flying through the wake of another aircraft, and
adjust the flight path accordingly.

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2. Vortex Generation

a.

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

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rotating cylindrical vortices. (See FIG 7

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1.) The wake

vortex is formed with most of the energy concentrated within a few feet of the vortex core.

FIG 7

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1

Wake Vortex Generation

b.

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

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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.

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3. Vortex Strength

a.

Weight, speed, wingspan, and shape of the generating aircraft’s wing all govern the strength of the vortex.

The vortex characteristics of any given aircraft can also be changed by extension of flaps or other wing
configuring devices. However, the vortex strength from an aircraft increases proportionately to an increase in
operating weight or a decrease in aircraft speed. Since the turbulence from a “dirty” aircraft configuration hastens
wake decay, the greatest vortex strength occurs when the generating aircraft is HEAVY, CLEAN, and SLOW.

b. Induced Roll