Wake Turbulence

What is Wake Turbulence?

Wake turbulence is the disturbed airflow left behind an aircraft, primarily caused by wingtip vortices. These vortices form as high-pressure air from beneath the wing spills around the tip into the low-pressure region above, creating rotating tubes of air that trail behind the wingtips. The strength of these vortices is directly related to the aircraft's weight, speed, wing aspect ratio, and angle of attack.

Causes and Influencing Parameters

• Aircraft Weight: Heavier aircraft generate stronger vortices.
• Speed: Slow speeds (high angle of attack) produce more intense wake turbulence.
• Wing Configuration: Clean wings (flaps retracted) result in stronger vortices. Deploying flaps or slats can weaken the primary vortex by creating secondary vortices.
• Aspect Ratio: Wings with a lower aspect ratio (short and wide) tend to produce stronger vortices than high aspect ratio (long and narrow) wings.

Distribution and Duration

Wake turbulence begins as the aircraft rotates for takeoff and ends when the nosewheel touches down. The vortices descend and drift outward from the runway, influenced by wind. In calm conditions, they can linger and remain hazardous for several minutes. Light crosswinds (3–10 knots) are particularly dangerous, as they can keep a vortex over the runway, increasing risk for following aircraft.

Hazards and Effects

• Roll Hazard: The most dangerous effect is a sudden, uncontrollable roll if one wing of a following aircraft enters a vortex, especially for lighter aircraft.
• Buffet and Stall: Encountering a vortex can lead to pre-stall buffet or even a full aerodynamic stall, particularly if the aircraft is already at a high angle of attack.
• Loss of Control: Light aircraft are especially vulnerable and may lose control authority completely during a severe encounter.

Wake Turbulence Avoidance

• Separation Standards: Minimum separation times and distances are enforced, especially behind heavy or super category aircraft.
• Operational Awareness: Pilots should remain vigilant for wake turbulence symptoms, especially in light wind or crosswind conditions, and adjust their approach or takeoff path if necessary.

Energy Loss and Drag

Wake turbulence is a direct result of induced drag, representing energy lost from the wing to the surrounding air. The stronger the vortices, the greater the induced drag and energy loss, impacting aircraft performance and efficiency.