sin αst

Friction forces and moments
FURLING AND YAW ANALYSIS
(I.13)
The friction force in the bearings is calculated from the sum of the reaction force in the two
bearings, which is:
Using a friction coefficient µs of 0.2, the friction force becomes:
This is recalculated into a frictional resistance moment:
A total frictional resistance moment is calculated by further adding the required starting
(I.14)
(I.15)
(I.16)
torque for the thrust bearing Mst, which is 28.8 Nmm. The calculation, which is documented
in att. 3, uses the following input:
� Bearing load: 997 N
� The number of rotations per minute: 1 rpm
� Friction coefficient in full-film condition: 0.1 µEHL, which corresponds to grease
used as lubrication in the bearing.
Yawing moment
The aerodynamic lift and drag forces on the tail vane will tend to align the rotor with the
wind, whereas the thrust force on the rotor and the above calculated frictional resistance
(I.17)
moment will oppose the tendency. Using principles of equilibrium it is possible to calculate
a steady state yaw offset.
The lift force is perpendicular to the wind direction and the drag is parallel to the wind
direction, which is shown on the free body diagram of the tail vane and the rotor on figure
I.3.
RB Rx.B 2 Ry.B 2
� � � 354 N
Rtot � RA � RB � 721N
Ffr � Rtot s � 144N
Mfr �
Db
Ffr
2
� 6.70Nm
Mfr.tot �
Mst � Mfr � 6.73Nm
205