D. M. Xu, R. N. Yong et A. M.O. Mohamed

p. 7–19

Résumé
EN : A vehicle mobility model has been developed using energy principles and a quasi-static moving boundary displacement method. For a given condition of both tyre and terrain characteristics, the model calculates the contact length, the slip rate, the traction efficiency and the drawbar pull. The effect of tread configuration is also included in calculating the slip rate. A numerical example is given to demonstrate the capability of the new developed mode. The model's predictions are also compared with the experimental results in the laboratory tests and a good agreement is obtained.

Hooshang Sobhany et W. B. Stuart

p. 21–24

Résumé
EN : A project, "Logging System Evaluation", was initiated by the Iranian Forest Service and Teheran University in 1988. The objective is to develop a quantitative basis for job layout and planning, operations management, and forest management. Initial work is focusing on transportation functions, the largest single cost component. A brief discussion of harvesting conditions in the Caspian forest is followed by the results of initial investigations of rubber-tired skidding.

Eldon Olsen, Stephen Pilkerton, John Garland et John Sessions

p. 25–32

Résumé
EN : During June 1989, researchers from the Forest Engineering Department at Oregon State University evaluated the feasibility of using the computer program BUCK® to aid the Hahn Harvester operator in determining the best bucking cuts.The computer was able to increase the total value by 7.5%. This is about US $6.40 per tree for the 38-cm [15-in] diameter trees we processed. This increase was from improved log quality and increased scaling volume when Scribner rules were used. The computer solution cuts roughly 16% more logs. The computer solution increased the volume in the best export sort by 8%.The computer solution could increase the total value by 19.6% if more accurate tree quality information were sent to the computer before the bucking cuts were made.

Rolf Björheden

p. 33–39

Résumé
EN : In this paper, a proposal for a system of basic time concepts is presented. The lack of uniformity of time concepts was identified by the group preparing this proposal as the single most important obstacle when trying to make international comparisons of time study reports. The aim of the proposal is to set standards for scientific presentations so that international comparisons and analyses of results are simplified. The proposal is not aimed at defining a terminology for practical time study, nor does it contain suggestions on what methods to use (or not to use). It simply contains a number of basic concepts for time measurement of work that should always serve as a basis for any study claiming international significance.It is the suggestion of the 'terminology team' that study results should either be published using the terms defined by the proposal or in such a way that a transformation into the proposed concepts is possible.

Andrew F. Howard

p. 41–45

Résumé
EN : Interest charges are an important component of owning and operating costs for logging equipment. Methods commonly employed by researchers and practitioners ignore the difference between interest on borrowed money and proprietary capital invested. Correct formulas for computing interest charges are given and a comparative study between historic methods and the appropriate computations is presented.