Using the IEC Simple Load Model for Small Wind Turbines - Small Wind Turbines: Analysis, Design, and Application - page 189

9.5.2 Equivalent Stress for Case B: Yawing

These calculations are straightforward. For the blade root:

r eq ¼ M yB
W yB

40 : 83
1 : 527 10 4 ¼ 0 : 27 MPa

¼ ð 9 : 60 Þ

from ( 9.45 ). Equation 9.46 gives the maximum stress in the shaft as

r eq ¼ M shaft
W shaft

61 : 81
1 : 534 10 6 ¼ 40 : 29 MPa

¼ ð 9 : 61 Þ

9.5.3 Equivalent Stress for Case C: Yaw Error

Load case C considers only the bending moment on the blades, which is, using
( 9.47 );

r eq ¼ M y
W yB

422 : 82
1 : 527 10 4 ¼ 2 : 77 MPa

¼ ð 9 : 62 Þ

9.5.4 Equivalent Stress for Case D: Maximum Thrust

As for load case C, D only considers a load on the main shaft, with the equivalent
stress level calculated from ( 9.48 );

318 : 25
4 : 909 10 4 ¼ 0 : 65 MPa

r eq ¼ F x shaft
A shaft

¼ ð 9 : 63 Þ

9.5.5 Equivalent Stress for Case E: Maximum Rotational Speed

The loading for this case again considers only one load for both the main shaft and
the blade root. The equivalent stress for the blade root, using the result of Eq. 9.49 ,
is

r eq ¼ F zB
A B

1662 : 48
1 : 46 10 3 ¼ 1 : 14 MPa

¼ ð 9 : 64 Þ