sin αst

LIST OF ATTACHMENTSBASIS FOR CALCULATIONS
Load case G: Survival wind
In this load case the rotor is spinning and the wind speed is Ve50 equal to 42 m/s, see table
A.2.
It is expected that Cl.max (see (A.12)) will occur on one of the blades due to variations in the
wind direction, creating a root bending moment:
128
(A.18)
This assumes a constant chord length and a triangular lift distribution which is equivalent
to Cl.max at the tip and zero at the root of the blade. Further derivation is available in [5, p.
175].
The shaft is loaded by a thrust force given by
The calculation of the thrust force is based on helicopter theory, where the thrust coeffi-
cient is based on tip-speed rather than wind speed. Its value of 0.17 is found to be near
constant for transient events [45]. The tip-speed ratio �e50 is determined by:
Where �max is the assumed maximum rotational speed of (A.14).
(A.19)
(A.20)
The shaft thrust force is combined with drag forces on the tower and the tail, resulting in a
maximum tower load. The tail is assumed to be perpendicular to the wind and fully ex-
posed. The area of the tower that contributes to drag is considered to be the part above the
upper guy wire attachment.
Drag force on tail:
Where the projected tail area Aproj.tail is 1.04 m 2 and the drag coefficient Cf.tail is 1.5.
Drag force on tower:
M yB
F xS
�
1
Cl.max 6 � Ve50 2 Aproj.B R � 166 N m
2 2
� 0.17BAproj.B� e50 � Ve50 � 12.0 kN
Ftail �
� e50
�
� max � R
V e50
� 6.9
1
Cf.tail 2 � Ve50 2 Aproj.tail � 1.68 kN
1
FT CfT 2 � Ve50 2 �
Aproj.T � 228 N
(A.21)
(A.22)