United States Department of Transportation
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Abstract:Davis’ well-known equations for the running resistance of locomotives and cars were first published in this 1926 article. The equations were developed on the basis of extensive experimental tests that had been conducted by leading railway companies over the previous twenty-five years. The study categorizes train resistance into three main types:
1. Constant resistance related to weight per axle, called Journal Resistance. This can be directly determined with acceptable accuracy from the large number of dynamometer tests made at low speeds.
2. Speed-dependent resistance, called Flange Resistance. This cannot be measured directly by any known methods. As a residual, the “B” term comprises all resistances which remain after air resistance and journal resistances have been deducted. Methods of substitution and trial have been used to find values for the B coefficient accurate within the limits of test variations.
3. Resistance proportional to the square of speed, including Air resistance. Air resistance may be calculated with fair accuracy in the case of vestibuled coaches but for freight cars, the method of approximations and substitutions was used to estimate the values.
Experimental methods employed include dynamometer tests, coasting methods, and the analysis of existing data, all conducted under controlled conditions to ensure reliability. The findings reveal distinct differences in resistance characteristics between freight and passenger cars, influenced by their design, weight, and operational context. Customized coefficient values have been recommended for the following specific cases:
• Electric locomotives
• Freight Cars
• Passenger Cars
• Electric M.U. Trains
• Electric Motor (Trolley) Cars
• Gas-Electric Cars
This seminal work has provided an enduring foundation for improved design and operational strategies in railway engineering, and by providing the fundamental framework for modeling train resistive forces, it has clearly facilitated a better understanding of the factors affecting train resistance and performance.
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Content Notes:Public Domain, except where noted in the document. Please cite as Davis, W. J., The Tractive Resistance of Electric Locomotives and Cars, General Electric Review Vol. 29, No. 10., pp. 685-707, October, 1926.
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