Ground effect

Ground effect is the increase in lift and rotor or wing efficiency when the aircraft is very close to the surface. It happens because the airflow and wingtip vortices, or the rotor downwash, are altered by the ground, so less induced drag or less induced flow is produced. In helicopters, this means less power is needed to hover close to the ground than out of ground effect. Pilots use this when assessing take-off and landing performance, but they must expect a higher power demand as soon as the aircraft climbs out of ground effect.