Private Pilot License (PPL) Aerodynamics Practice Exam

Under what conditions is the greatest strength of a vortex produced?

1. Light, dirty (flaps down), fast

2. Heavy, clean (flaps up), slow

3. Heavy, dirty (flaps down), fast

4. Light, clean (flaps up), slow

The correct answer is: Heavy, clean (flaps up), slow

The greatest strength of a vortex is produced under conditions where the aircraft is heavy, clean (with flaps up), and flying at a slower speed. A heavy aircraft generates stronger vortices due to the increased lift required to support its weight. This is because more lift creates greater differences in pressure between the upper and lower surfaces of the wing, which is essential for vortex formation. When the aircraft is clean, meaning the flaps are up and any surface protrusions or additional drag factors are minimized, the airflow remains more streamlined over the wings. This streamlined flow is critical for forming well-defined and powerful vortices. In contrast, deploying flaps increases the angle of attack, leading to increased drag and disrupting the airflow, which diminishes vortex strength. Flying at a slower speed also contributes to stronger vortices. As the aircraft moves slower, lift is maintained at lower speeds via a higher angle of attack. The higher angle of attack increases circulation around the wing, thereby enhancing vortex strength. In summary, the combination of being heavy, maintaining a clean configuration, and flying at a slower speed creates optimal conditions for producing significant and strong wake turbulence, which is characterized by the strength of the vortices generated at the wingtips.