Steam Locomotive Designer
Try designing your own steam locomotive. True steam locomotive design
is an art (getting a locomotive that is not too slippery, one that will
fit through clearances, having the correct horsepower for the terrain and
loads it will have to pull, etc.). However, that doesn't prevent us from
having some fun with a few of the important parameters that are used in
steam locomotive design.
This Web page will allow you to specify the parameters that are used to
Effort. As each parameter is changed, the resulting tractive effort
and number of required axles will be computed and displayed.
Live Steam Modelers: While the sliders will not let you specify values in
your ranges, you can still enter any value in the text fields. Remember
to press the "Enter" key after changing a value.
NOTE: Press the <return> key after entering any text.
About Tractive Effort
Tractive effort is a theoretical value based upon the geometry of a
locomotive and is only valid at a speed of 0 (zero). Tractive effort is
sometimes incorrectly called "Tractive Power". Strictly speaking, power is
work per unit of time and is often expressed in units of horsepower, watts,
or joules per second. Tractive effort is simply a measure of the pulling
force of a locomotive. The equation used for computing tractive effort
includes a constant or coefficient. In the USA this coefficient was usually
0.85. Most sources describe this coefficient as the ratio of cylinder
pressure to boiler pressure (15% loss). However a few sources (including Wikipedia) suggest
this term also includes frictional losses. In advertising their roller
bearings on steam locomotives, Timken chose to increase this coefficient to
1.0 to suggest that the use of their roller bearings resulted in no friction
even though roller bearings had no affect on the pressure differential
between the boiler and the cylinders. The use of roller bearings did, of
course, increase drawbar pull because there was less friction to overcome.
Both "tractive effort" and "drawbar pull" are quantities designed to describe
the pulling ability of a locomotive. Both are measured in unit of force.
As mentioned earlier, tractive effort is a theoretical value computed at
a speed of 0. On the other hand, drawbar pull is a real, measured value
that changes with speed and is measured by a dynamometer car.
Below are few examples of existing steam locomotive designs. Try entering
one of these or one of your own.
Boiler Pressure: 300 psi
Driver Diameter: 68 in
Cylinder Diameter: 23.75 in
Piston Stroke: 32 in
Tractive Effort: 135,375 lbs
Nickel Plate Berkshire:|
Boiler Pressure: 245 psi
Driver Diameter: 69 in
Cylinder Diameter: 25 in
Piston Stroke: 34 in
Tractive Effort: 64,135 lbs
NYC J3a Hudson:|
Boiler Pressure: 275 psi
Driver Diameter: 79 in
Cylinder Diameter: 22.5 in
Piston Stroke: 29 in
Tractive Effort: 43,440 lbs