A locomotive drawbar, or coupler, connects the locomotive to the rail cars that it is pulling. The drawbar pull is the maximum longitudinal force that the locomotive can exert through its drawbar, and is based on characteristics of the locomotive and the rails it travels on. The drawbar pull initiates in the locomotive engine and is transmitted through the drive wheels to the rail.
Instructions
1. Calculate the rolling resistance (RR) of the locomotive by multiplying the gross vehicle weight (GWV) of the locomotive by the coefficient of friction between the wheels and the rail. For steel wheels on steel rails, the coefficient of friction can be conservatively estimated at 0.002. The unit of rolling resistance is either newtons (metric) or pounds (U.S.).
RR = GWV * 0.002
2. Calculate the output torque (OT) of the locomotive by multiplying the vehicle torque (VT) by the gear reduction ratio (GRR). The unit of output torque is either newton-meters (metric) or inch-pounds (U.S.).
OT = VT * GRR
3. Calculate the forward force output (FFO) by dividing the output torque (OT) by the radius of the drive wheel (r). The radius should be measured in meters or inches to match the units of the output torque. The forward force output will have a unit of either newtons (metric) or pounds (U.S.).
FFO = OT / r
4. Calculate the drawbar pull (DP) by subtracting the rolling resistance (RR) from the forward force output (FFO). The unit of drawbar pull is either newtons (metric) or pounds (U.S.).
DP = FFO - RR
Tags: output torque, drawbar pull, either newtons, either newtons metric, force output, forward force