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speed of 393 feet per second, or 267 m.p.h. The result is a higher total relative wind, striking the blades at a lower angle of attack. [Figure 16-3] F 

## ROTOR DISC REGIONS 

As with any airfoil, the lift that is created by rotor blades is perpendicular to the relative wind. Because the relative wind on rotor blades in autorotation shifts from a high angle of attack inboard to a lower angle of attack outboard, the lift generated has a higher forward component closer to the hub and a higher vertical com- ponent toward the blade tips. This creates d istinct regions of the rotor disc that create the forces neces- sary for flight in autorotation. [Figure 16-4] The autorotative region, or driving region, creates a total aerodynamic force with a forward component that exceeds all rearward drag forces and keeps the blades spinning. The propeller region, or driven region, gen- erates a total aerodynamic force with a higher vertical component that allows the gyroplane to remain aloft. Near the center of the rotor disc is a stall region where the rotational component of the relative wind is so low that the resulting angle of attack is beyond the stall limit of the airfoil. The stall region creates drag against the direction of rotation that must be overcome by the forward acting forces generated by the driving region. 

## AUTOROTATION IN FORWARD FLIGHT 

As discussed thus far, the aerodynamics of autorotation apply to a gyroplane in a vertical descent. Because gyroplanes are normally operated in forward flight, the component of relative wind striking the rotor blades as a result of forward speed must also be considered. This component has no effect on the aerodynamic principles that cause the blades to autorotate, but causes a shift in the zones of the rotor disc. 

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As a gyroplane moves forward through the air, the for- ward speed of the aircraft is effectively added to the 

