sin αst

Figure 6.8: Optimum blade chord and blade pitch as a function of the non-dimensionalised
blade radius
Note that no chord length or pitch angle is specified for the part of the blade that is closest
to the hub. This is due to the first element of each blade being left out in the BEM calcula-
tions, which underlie the optimum blade calculations. Further explanation can be found in
appendix C.
On figure 6.8 it is shown that the blade design for optimum power production has an in-
creasingly large chord and pitch angle when approaching the blade root. This hyperbolic
ROTOR
contour of the theoretical optimal shape makes the fabrication of the blade difficult and the
design is therefore modified for ease of manufacturing using the optimum blade shape as a
guideline. An invariant pitch angle is chosen, as a twisted blade will complicate the manu-
facturing process. Figure 6.9 shows the rotor power output at V = 12 m/s as a function of a
fixed pitch angle.
49