What is the definition of "Ground Effect"?

The definition of "Ground Effect" correctly refers to the phenomenon where increased lift and reduced drag occur when an aircraft, including helicopters, is operating close to the ground. This effect is primarily due to the interaction between the aircraft's rotor system and the surface below. When a helicopter hovers or flies at low altitudes, the ground serves as a barrier that limits the downwash of air created by the rotor blades. This compression of air increases the efficiency of the rotor system, enhancing lift while simultaneously reducing induced drag.

Understanding Ground Effect is crucial for pilots, especially during takeoff and landing phases, as it impacts flight performance and handling characteristics. By recognizing how this effect influences lift and drag, pilots can make more informed decisions about altitude management and maneuvering.

The other options do not accurately describe Ground Effect. For instance, thermal currents relate to different lift-generating processes, and the reduced lift scenario does not align with what happens during Ground Effect. Similarly, increased drag at low altitudes does not characterize Ground Effect, further emphasizing why the correct definition focuses on the beneficial increase in lift and reduction in drag while close to the ground.