Cable-towed vehicles for harvesting small timber on steep terrain

This study explored the potential of cable-towed vehicles for harvesting prebunched small timber on steep terrain. Two types of cable-towed vehicles, a cable-towed arch and a self-towed vehicle equipped with a winch, were included in the study. Computer modeling and simulation techniques were used to compare their mechanical and economic performances with a conventional running skyline system as a basis. The results from computer modeling indicated that both cable-towed vehicle systems have the potential to reduce cable tension requirement and equipment size, which in turn reduces forces applied to anchors. Harvesting costs for the cable-towed vehicles can be reduced by approximately 25% compared to the conventional running skyline system, with greater benefits on less steep terrain and/or at lower deflection.; A computer model was developed to predict the towing force required to pull the rigid or pneumatic-tired wheels of a single-axled vehicle over an idealized obstacle. Scale models were tested for three wheel types: rigid, rimless spoke wheel and pneumatic tires. For the rigid wheels, the results from both models were in good agreement. For the pneumatic tires, the computer model tended to underestimate the towing force compared to the scale model. The tests with the scale model showed that rimless spoke wheels are able to traverse obstacles that are theoretically not possible for a rigid wheel, but towing force requirements are relatively high for small obstacles. The results from both models indicated that use of low pressure pneumatic tires can improve the obstacle performance of cable-towed vehicles, but only to a limited degree.; An experimental vehicle was built to test steering methods and to evaluate sideslope drift problems for the cable-towed vehicles. Four steering schemes were tested: (a) articulated steering; (b) front wheel steering only; (c) independent front and rear steering; and (d) leading end steering. The leading end steering scheme (i.e. front wheel steering for traveling forward and rear wheel steering for travel in reverse) was found to give the best performance for the wheeled cable-towed vehicles because of its ease of control and conformity to the desired trajectory.