Autorotation (Forward Flight)

in Aerodynamics of Flight

Autorotative force in forward flight is produced in exactly the same manner as when the helicopter is descending vertically in still air. However, because forward speed changes the inflow of air up through the rotor disk, all three regions move outboard along the blade span on the retreating side of the disk where AOA is larger. [Figure 2-48] With lower AOA on the advancing side blade, more of the 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; therefore, the size of the driven region on the retreating side is reduced.

Figure 2-48. Blade regions in forward autorotation descent.

Figure 2-48. Blade regions in forward autorotation descent.

Prior to landing from an autorotative descent (or autorotation), the pilot must flare the helicopter in order to decelerate. The pilot initiates the flare by applying aft cyclic. As the helicopter flares back, the airflow patterns change around the blades causing the rpm to increase. Pilots must adjust the collective as necessary to keep the rpm within operating limits.

51l0aN891BL._SX396_BO1,204,203,200_Are you ready to start your journey learning to fly helicopters? Learning to Fly Helicopters, Second Edition, provides details on the technical and practical aspects of rotarywing flight. Written in a conversational style, the book demystifies the art and science of helicopter flying.


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