translational lift

The additional lift (or rotor thrust) obtained through air speed because of the increased efficiency of the rotor system, whether it is when transitioning from a hover into forward flight or when hovering in a wind. During a hover, the rotors are lifting in a downward-moving column of air; the lift increases as the helicopter starts moving forward out of the descending column of air it created while hovering. With an increase in forward speed to about 12 to 15 knots, the rotor becomes more efficient and produces a dramatic increase in the lift compared to while hovering.
When hovering in calm conditions, a given induced flow passes at right angle to the rotor disk. In case of any wind, the induced flow perpendicular to the disk becomes smaller.
The downward vortex is beginning to dissipate and induced flow down through the rear of rotor disk is more horizontal than at hover.
At slow speeds the perpendicular flow is substantial, but as airspeed increases it lessens while the horizontal component increases. At high speeds, the horizontal flow component is very large and would only reduce if the disk inclination becomes greater.

Aviation dictionary. 2014.

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