FAA Sport Pilot Airplane (SPA)Aircraft Performance and SystemsMedium
On short final, a pilot reduces power to idle just before touchdown, but the airplane seems to float and resists settling onto the runway. Which phenomenon best explains this?
- AIncreased induced drag from ground effect
- BDecreased induced drag from ground effect
- CIncreased downwash angle from wingtip vortices
- DIncreased parasite drag from ground effect
Show answer & explanationAnswer & explanation
Correct answer: B. Decreased induced drag from ground effect
Within about one wingspan of the surface, ground effect reduces the wingtip vortices and downwash, decreasing induced drag and increasing lift efficiency, causing the airplane to float longer before touchdown.
Why the other options are wrong
- A. Ground effect decreases induced drag, not increases it.
- C. Ground effect actually reduces the downwash angle, not increases it.
- D. Parasite drag is largely unaffected by ground effect.
Ground Effect
A reduction in induced drag and change in airflow pattern that occurs when an airplane flies within approximately one wingspan of the surface.
- Reduces induced drag and downwash
- Can cause floating during landing flare
- Can cause premature liftoff at too-low airspeed during takeoff
Memory trick: Close to ground, drag goes down, float goes up.