Using the IEC Simple Load Model for Small Wind Turbines - Small Wind Turbines: Analysis, Design, and Application - page 184

pre-manufacturing analysis, from finite element or CAD software. Alternatively,
the analysis in Sect. 6.4 for the moment of inertia can be easily modified to give
m B . For the current timber blades with density 550 kg/m 3 , m B = 0.4 kg. The blade
centre of mass, R cog , can be determined in similar fashion, taking note that the hub
end

of the blade is not likely to correspond to zero radius. In this case

R cog = 0.379 m. Thus

DF zB ¼ 2 0 : 4 0 : 379 73 : 30 2 ¼ 1629 : 23 N

ð 9 : 39 Þ

From ( 9.5 ) and ( 9.6 ) respectively:

DM xB ¼ 11 : 32 = 3 þ 2 0 : 4 9 : 81 0 : 379 ¼ 6 : 75 Nm

ð 9 : 40 Þ

and

DM yB ¼ 7 : 11 11 : 32 = 3 ¼ 25 : 55 Nm ð 9 : 41 Þ

Equation 9.7 gives the shaft load as:

DF x shaft ¼ 3 7 : 11 11 : 32
2 0 : 97

¼ 118 : 55 N ð 9 : 42 Þ

From ( 9.8 ), using e r = 0.005 9 0.97 = 0.0049 m, and a measured rotor mass
m r = 3.98 kg,

DM x shaft ¼ 11 : 32 þ 2 3 : 98 9 : 81 0 : 0049 ¼ 11 : 70 Nm ð 9 : 43 Þ

so the assumed eccentricity has little effect in this case. The other shaft moment is
given by ( 9.9 ) using the measured (or designed) length from the rotor to the first
bearing, L rb = 0.026 m,
DM shaft ¼ 2 3 : 98 9 : 81 0 : 026 þ 0 : 97
6

118 : 55 ¼ 21 : 20 Nm ð 9 : 44 Þ

9.4.2 Loads for Case B: Yawing

The blade root bending moment depends on the additional parameters
L rt = 0.218 m, the distance from the rotor to the yaw axis, and J B , the blade
moment of inertia. From the CAD model of the blade, J B = 0.0633 kg m 2 and this
value was confirmed by tests described by Wright [ 5 ]. 34 Note also that J B can be

J B m B R cog ¼ 0 : 4 0 : 379 2 ¼ 0 : 0575 kgm 2 approximated as for the present

rotor. From ( 9.10 ):

34 Note that this value of J for wooden blades is considerable less than for the composite blades
of the same shape considered in Chap. 6 .