sin αst

ROTOR
Figure 6.9: Rotor power output at various fixed blade pitch angles. Curve shown for V = 12
m/s and � = 5
On basis of the above graph a fixed pitch angle of 2� is selected. At the rated point, V = 12
m/s and � = 5, the rotor power output is lowered by less than 1% when using an invariant
pitch angle rather the optimum pitch angle of figure 6.8.
A uniform tapering of the chord length is chosen, as it further simplifies the design and
removes a lot of material close to the blade root. The tapering shape is determined from
the slope of a straight line drawn between the span points at 70% and 90%, intersecting
the optimum shape midway at the 80% span point [29, p. 73]. This is illustrated on figure
6.10.
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