To cover the most amount of distance, or range, with the current fuel load, the drag must be at its minimum. This speed will be slightly higher than that used for endurance, which maximizes the time in the air. A horsepower required curve can be used to identify this speed. In a calm, no-wind scenario, a tangent is drawn from the zero airspeed to the bottom of the horsepower required curve. Where the two intersect is the proper speed for range. This speed will correspond with the lowest total drag as well. If there is a wind, the tangent would be drawn from the headwind or tailwind component.
NOTE: Although they are related, drag is calculated in relation to indicated air speed, whereas range is calculated in relation to true airspeed. The two are shown together to demonstrate that minimum drag is not at the bottom of the horsepower required curve.
Principles of Helicopter Flight, 2nd Edition, pg. 108