Figure 1.2. Weight Distribution of an 0660
DieselElectric Locomotive.
slip. A locomotive's tractive effort is included in the data
supplied by the manufacturer. The starting tractive effort for some
of the locomotives used by the Army is given in table I along with
other characteristics. The dieselelectric locomotives listed in the
table are designed for both road and switcher service and are
therefore called road switchers. Whenever data on a particular
locomotive are not available, several formulas can be used to
determine its tractive effort depending upon its type. However, for
military planning purposes, a ruleofthumb method for this
determination is adequate. Explanations in this text are confined to
the ruleofthumb method; it is explained in subparagraph b following
an explanation in subparagraph a of the important difference between
starting and continuous tractive effort.
a. Starting and continuous tractive effort. The power of a
locomotive to move itself and the load it is hauling from a stopped
position is called starting tractive effort. Continuous tractive
effort is the effort required to keep a train rolling once it has
been started. The starting and continuous tractive efforts for a
steam locomotive are the same, because it can continue to move
anything it can start. On the other hand, a dieselelectric
locomotive cannot continue to exert maximum power for a prolonged
period without damaging its traction motors; therefore, its
continuous tractive effort is rated at 50 percent of its starting
tractive effort.
b. Ruleofthumb method of determining tractive effort. Starting
tractive effort is directly related to the adhesion between the
driving wheels and the rails. If the power applied to the driving
wheels exceeds the amount of adhesion, the drivers slip. When the
rails are dry, the amount of adhesion is about 30 percent of the
weight on drivers; when the rails are wet, 20 percent. Therefore,
the rule of thumb for determining tractive effort is to average the
two; that is, 25 percent of the weight on drivers of a locomotive is
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