Forces Affecting Timber Skidding

The research was carried out on the strip road where longitudinal slopes were determined by the leveling method as well as individual distances of the strip road of uniform slope. Skidders were used for carrying out traction tests in downhill and uphill skidding of 9 different loads. Measurement of wheel loads, wheel torques and components of rope force was performed by tensiometric method and remote transferring of measurement signal. According to the results of research, by the increase of longitudinal slope, more tractive force is used for overcoming the terrain slope than for overcoming the traction resistance. In downhill skidding, the horizontal component of the skidder weight (G sinα) acts in the skidder travel direction and hence its value is higher than the traction resistance. Torque distribution depends on the skidder wheel vertical load. In uphill skidding, torques increase proportionally to the vertical component of rope forces and adhesive weight of the skidder. In downhill skidding, the skidder wheel torques are negative, because they are not used for achieving wheel tractive force and instead, the transmission of torque through the transmission system causes skidder´s braking performance. The skidder´s need for braking arises under influence of the horizontal component of the skidder weight (G sinα) that acts in the direction of the skidder travel and under its effect the traction resistances are overcome. It can be concluded that in case of downhill skidding we cannot speak of achieving real tractive force because the skidder pulls the load only by its weight, and the transmittion from engine to wheels is not used for achieving the tractive force.