Wake Vortex Generation

AIM ¶ 7-4-2 — Wake Vortex Generation

AIM 7-4-2 explains how wing pressure differential creates trailing wake vortices. Study guide for pilot students prepping for written tests and checkrides.

In Plain English

Wake turbulence is a byproduct of how wings make lift. Because pressure is lower above the wing and higher below, air spills around the wingtips from the high-pressure side to the low-pressure side. This rollup at the trailing edge produces two counter-rotating cylindrical vortices streaming behind the aircraft.

Key points from AIM 7-4-2:

Lift is created by a pressure differential between the upper and lower wing surfaces.
The airflow rolls up at the rear of the wing, forming swirling masses off the wingtips.
Once rollup is complete, the wake settles into two counter-rotating cylindrical vortices.
Most of the vortex energy is concentrated within a few feet of the core — making the core the most hazardous part.
Winglets improve fuel efficiency (better lift-to-drag ratio) but have a negligible effect on wake turbulence, especially at the slower departure and arrival speeds where wake encounters are most likely.

Understanding vortex generation operationally helps you anticipate where wake will be and why following heavy traffic — even those with winglets — still requires the same separation and avoidance technique.

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AIM Source Text

FAA AIM ¶ 7-4-2

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. FIG 7-4-1 Wake Vortex Generation 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.

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Oral Exam Questions a DPE Might Ask

Q1What causes a wake vortex to form behind an aircraft?

Per AIM 7-4-2, lift is generated by a pressure differential — lower pressure above the wing and higher pressure below. This differential causes airflow to roll up at the rear of the wing, producing two counter-rotating cylindrical vortices trailing from the wingtips.

Q2Where is the energy of a wake vortex concentrated?

Per AIM 7-4-2, most of the wake vortex energy is concentrated within a few feet of the vortex core, making the core itself the most dangerous region of the wake.

Q3Do winglets reduce the wake turbulence an aircraft produces?

Per AIM 7-4-2, no. Winglets are designed primarily to improve the lift-to-drag ratio for fuel efficiency. Studies show they have a negligible effect on wake turbulence generation, particularly at the slower speeds used during departures and arrivals.

Related Paragraphs in Chapter 7

¶ 7-4-1

Wake Turbulence Basics

Wake Turbulence Problem Areas

¶ 7-4-6

Wake Turbulence Avoidance

¶ 7-4-7