engleski

Critical slope in downhill timber skidding

Skidder’s ability to extract timber is defined by: 1) basic dimensional features of the vehicle, 2) the ability to overcome obstacles during movement, 3) traction performance and 4) environmental soundness. Traction performance depends on the ground conditions (soil bearing capacity) and the total effect of all forces on the vehicle. In downhill skidding, skidder is under great influence of parallel component of forces, adhesion weight and slope, which combined result in negative traction force, torque and thrust force. When the horizontal component of rope force is equal to zero i.e. the moment when the weight of the load and resistance to traction are in equilibrium, the slope angle α, is a function of load mass distribution factor and skidding factor. This is a »turning point« that can be defined as a critical slope because the load starts to push the vehicle downhill which results in negative horizontal component of rope force. Depending on skidder Ecotrac 120V point of gravity, load mass distribution factor, skidding factor and previous research, five different loads were analyzed (1 to 5 tones) in order to define the critical slope angle for each of them. Critical slope for downhill skidding of 1 tone timber is on longitudinal slope of –26%, for 2 tone timber on –30%, 3 tone timber on –34%, 4 tone timber on –38% and for 5 tone timber on –43% of terrain longitudinal slope. Even though skidding is possible on even greater slope angles, the most important in downhill skidding, is to avoid blocking of the wheels, which will lead to a complete vehicle slippage and driver must be constantly aware of that fact. When load pushes the vehicle down the slope, due to the constant thrust of the timber at the back end of a skidder, one can conclude that such performance in a due time will result in fatigue of the material and early damage to the vehicle as well as the negative influence on psycho-physical state of the driver.

Skider ; privlačenje drva niz nagib terena ; sila u vučnome užetu ; granični nagib terena.

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