FAA Airline Transport Pilot (ATM)Transport Aerodynamics and High-Altitude OperationsMedium
An aircraft is in the flare, descending through a height above the runway approximately equal to one wingspan. Which aerodynamic change is occurring due to ground effect?
- AInduced drag decreases and lift increases for a given angle of attack, tending to cause the aircraft to float
- BThe center of pressure moves forward, producing a strong nose-down pitching moment
- CInduced drag increases and lift decreases, requiring a higher approach speed
- DParasite drag increases sharply due to ground-reflected airflow disturbances
Show answer & explanationAnswer & explanation
Correct answer: A. Induced drag decreases and lift increases for a given angle of attack, tending to cause the aircraft to float
Ground effect restricts the formation of wingtip vortices and downwash near the surface, which reduces induced drag and increases lift for a given angle of attack. This commonly causes the aircraft to float during flare if speed is not properly managed.
Why the other options are wrong
- B. Ground effect tends to produce a nose-up pitching tendency due to reduced downwash on the tail, not nose-down.
- C. This is the opposite of what actually happens in ground effect.
- D. Ground effect primarily affects induced drag, not parasite drag.
Ground Effect
An aerodynamic phenomenon occurring within approximately one wingspan of the ground where downwash and wingtip vortices are restricted, reducing induced drag and increasing lift for a given AOA.
- Occurs within about one wingspan of altitude
- Reduces induced drag, increases lift at same AOA
- Can cause floating during flare and reduced elevator/tail effectiveness
Memory trick: Close to ground, vortices get squashed, wing feels lighter