Wingtip vortices are created when an aircraft is developing lift. Which condition is present when this occurs?

• A. The aircraft is on the ground
• B. The aircraft is developing lift
• C. The aircraft is in a stall
• D. The aircraft is cruising

Answer: (B)

Wingtip vortices form because the wing creates a pressure difference between its lower and upper surfaces as it generates lift. The air under the wing is pushed outward and downward, creating high pressure, while the air over the wing is at lower pressure. Air tends to spill around the wingtip from the high-pressure region to the low-pressure region, curling behind the aircraft into trailing vortices that sink in the wake. This swirling is produced whenever lift is being generated by the wing, so the presence of wingtip vortices indicates the aircraft is developing lift.

On the ground there isn’t the same lift production, so strong vortices aren’t formed; in a stall the lift is greatly reduced (vortices would be weaker); cruising is a flight condition in which lift is produced, but the key idea is that the vortices come from lift generation.