according to the dictionary of aeronautical terms 2nd edition, published by asa in the late 80's early 90's. ground effect is an increase in lift of an aerodynamic flying machine (airplane or helicopter) flying very near the ground. this additional lift is caused by a distortion of the airflow that produces an increased angle of attack. grond effect disappears when the flying machine is about a half a wingspan or half rotor span above the ground.