sin αst

YAW AND FURLING
As shown on figure 8.7 the furling axis is tilted compared to the yaw axis. This inclination
causes the tail vane to rise during the furling action, thus creating an increase in the po-
tential energy of the tail vane.
Figure 8.7: Raising tail vane. Top: Normal operation. Bottom: Furled operation with inclined
tail vane.
The instantaneous position of the furled rotor is a balance between the gravity force on
the tail vane and the thrust force on the rotor. Equilibrium of the system is established
under stationary conditions when the torque around the yaw axis balances the gravity
torque around the furling axis. When the wind speed decreases below the critical value of
14 m/s, the rotor is automatically recovered from the furled position and realigned with
the wind direction by the restoring moment provided by gravity.
Appendix I.2 verifies the overall functionality of the furling mechanism by confirming
that furling is initiated at a wind speed of 14 m/s (equivalent to a thrust force of 872 N).
The power production beyond the onset of furling is not analysed in the present project,
as it is beyond the limitations of the BEM theory described in appendix B.1.
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