Floating caused by the phenomenon of ground effect will be most realized during an approach to land when at?

• A. less than the length of the wingspan above the surface
• B. twice the length of the wingspan above the surface
• C. at a higher-than-normal angle of attack
• D. when at touchdown point

Answer: (A)

Floating during an approach to land due to ground effect is most pronounced when the aircraft is at a height less than the wingspan above the surface. Ground effect occurs when an aircraft is close to the ground, typically at an altitude of about one wingspan or less. At this proximity, the wing's airflow interacts with the ground, resulting in increased lift and reduced drag. This effect diminishes as the aircraft ascends, which means that when an aircraft is just above the surface—specifically, less than the length of its wingspan—ground effect will significantly increase the lift, often leading to a condition where the aircraft "floats" longer than expected during the landing phase.

When above the threshold of one wingspan, the influence of ground effect diminishes, making it less pronounced, while at touchdown, the aircraft is in contact with the runway, rendering any floating moot. A higher angle of attack does change the lift characteristics but does not specifically relate to ground effect in the context of floating during an approach. Thus, being at a height less than the wingspan maximally showcases this phenomenon.