Autorotation (Forward Flight)

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Autorotative force in forward flight is produced in exactly the same manner as when the helicopter is descending vertically in still air. However, because for-ward speed changes the inflow of air up through the rotor disc, all three regions move outboard along the blade span on the retreating side of the disc where angle of attack is larger, as shown in figure 3-23. With lower angles of attack on the advancing side blade, more of that blade falls in the driven region. On the retreating side, more of the blade is in the stall region. A small section near the root experiences a reversed flow, there-fore the size of the driven region on the retreating side is reduced.

Figure 3-23. Blade regions in forward autorotation descent.