Rotor downwash limits helicopter hover-taxiing near parked light aircraft. The result is a region of downwash behind the aircraft, between the two vortices. A smaller (1/15th-scale) model with a powered rotor was used for downwash investigations. They were concerned that the strong propeller downwash would make it difficult to operate. This permits a lower downwash velocity for a given amount of thrust. The downwash at any given station is a function of the entire shed vortex system. This is caused by the downwash pattern associated with swept/tapered wings. The Kutta condition explains the existence of downwash at the trailing edge of the wing. However, the downwash is purely a function of the circulation only.