Inflow

Inflow: The increase in air velocity in front of a propeller produced by its rotation.
In-Line engine: An engine with its cylinders arranged in one or more vertical rows running parallel to the longitudinal axis of the aircraft.

cell system contains an updraught / downdraught core beneath which is the outflow region containing the rain shield and bounded by the downdraught gust front, a flanking line with a dark flat base underneath which is the inflow ...

It also increases angle of attack on all blades by changing the inflow of air. As a result, total rotor lifting force is increased and rate of descent is reduced.

See also: Propeller, Drag, Speed, Power, Lift