sin αst

YAW AND FURLING
80
8.2 Furling system
Over-speed and power output control is needed to prevent the wind turbine from captur-
ing excessively high wind speeds that may overload mechanical and electrical compo-
nents. Among commonly used control mechanisms are stall control and furling control.
The present design uses a gravity-controlled furling system as shown on figure 8.6. This
furling mechanism is advantageous compared to other types of furling systems in that it
does not require counterweights or springs.
Figure 8.6: Top view of the furling and yaw system. Top: Normal operation. Bottom: Furled
operation
The simple appearing furling control mechanism is based on an eccentric positioning of
the rotor and the tail vane with respect to the yaw axis.
At wind speeds up to 14 m/s the tail vane properly orients the wind turbine, as described
in section 8.2. At higher wind speeds the tail vane remains approximately aligned with
the wind direction, while the increasing thrust force on the rotor creates a yawing mo-
ment, due to the lateral offset of the rotor, which tends to turn the rotor out of the wind in
the horizontal plane.