What does "ground effect" refer to?

"Ground effect" refers to the aerodynamic phenomenon that occurs when an aircraft is flying close to a surface, typically in the range of about one wingspan from the ground. In this situation, the airflow around the wings is altered due to the proximity to the ground, which leads to two key effects: the increased lift and decreased drag.

As the aircraft approaches the ground, the air pressure under the wings increases due to the reduced space for airflow. This increase in pressure results in enhanced lift, allowing the aircraft to maintain or gain altitude more easily than it would at a greater height. Concurrently, this change in airflow patterns also results in a reduction of induced drag, which is the drag caused by the generation of lift.

Understanding ground effect is crucial for pilots, particularly during takeoff and landing phases, as it can influence the aircraft's performance and control. It allows for smoother landings and takeoffs, but pilots must be mindful of the effects as they may lead to unexpected behaviors if not correctly anticipated.