The greatest vortex strength occurs when the generating aircraft is

• A. Heavy, clean, and slow
• B. Light, clean, and slow
• C. Heavy, dirty, and fast
• D. Light, dirty, and fast

Answer: (A)

Vortex strength comes from the amount of lift the wing is producing. The more lift, the stronger the wingtip vortices. Heavier airplanes must generate more lift to stay in level flight, so they create stronger vortices. Flying slower increases the lift coefficient needed to hold altitude, which also boosts the lift and the resulting vortices. Keeping the aircraft in a clean configuration (no flaps, gear retracted) ensures you’re not adding extra lift devices that change the wake in a way that would reduce the coherent, strong wingtip vortices. Put together, the strongest wake is behind a heavy, clean, and slow aircraft.