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Monday, November 30, 2009

How much weight can a train pull?

: how much weight can a train pull

Why: A train track runs right through the middle of Memphis, which is kind of annoying. A train drove by me and Joel the other night.

Answer: A shitton:
Since gravity and horsepower are constants, there is a simple formula used to calculate how much horsepower will be needed to move a given amount of tonnage up a grade, called the "Rolling Train Resistance Formula". It is as follows: take the horsepower per ton (HPT), multiply by twelve, divide by the percentage of the grade, and that will tell you the speed you will make. Expressed another way, HPT x 12 / %G = S.

The locomotives are indeed putting out a lot of horsepower. On US railroads a typical diesel-electric road locomotive develops between 3,000 and 6,000 horsepower each. But this applies to the diesel engine itself, or prime mover, which powers the main alternator, companion alternator and auxilliary generator.

The main alternator supplies electricity for the axle hung traction motors, which are what does the actual pulling. "Tractive Effort", or torque, is the name of the game, and the electric motor is king in this realm. A simple rule of thumb is that the locomotive will convert approximately 25% of its weight into tractive effort. Again, most locos in the US are in the neighborhood of 410,000 lbs., they produce about 105,000 ft/lbs of torque. To compare, the production model of the 429 Hemi, gasoline powered automobile engine, was the highest producer of torque at 405 ft/lbs.

As far as getting the power to the rail, the weight of the locomotive is where it gets its traction. When 200+ tons occupies twelve points on the rail, each not much bigger than a silver dollar, it "hooks up" pretty good. In instances where extra traction is needed, such as at starting or on wet rail, sand is applied in front of the drive wheels for extra grip.
Source: A retired locomotive engineer on Yahoo! Answers

The More You Know: Thomas the Tank Engine first appeared in 1946 in the book Thomas the Tank Engine as a station pilot, whose job was to shunt coaches for the bigger engines. He longed for more important jobs such as pulling the express train like Gordon, but his inexperience prevented this. Eventually he was responsible for rescuing James the Red Engine after an accident, and the Fat Controller (then known as the Fat Director) decided that he was a Really Useful Engine, and ready for his own branch line. He has remained in charge of this line ever since.

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