What is ground effect?

Ground effect refers to the increased lift and decreased drag experienced by an aircraft when it is flying close to the ground, typically within a distance equal to the wingspan of the aircraft. This phenomenon occurs due to the interference between the aircraft's wingtip vortices and the ground. When an aircraft is near the ground, the vortices tend to be contained closer to the wings and do not have the same strength as when the aircraft is at a higher altitude, leading to a reduction in induced drag and an increase in lift.

This effect is particularly important during takeoff and landing phases, as it allows the aircraft to generate lift more efficiently and can result in a smoother transition as it approaches the runway. Understanding ground effect is crucial for pilots when managing their approach and landing techniques, as it can influence the aircraft's performance near the ground.

The other choices do not accurately describe this concept; they either reference conditions that do not pertain to ground proximity, such as aerodynamic efficiency at high altitudes or changes in weight, or confuse the relationship between altitude and aerodynamic effects.