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Dynamometer car

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Title: Dynamometer car  
Author: World Heritage Encyclopedia
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Subject: Charles Babbage, List of railway vehicles, Maintenance of way equipment, NER Class T3, 2-6-6-6
Collection: Charles Babbage, Dynamometers, Maintenance of Way Equipment
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Dynamometer car

North Eastern Railway Dynamometer Car at the National Railway Museum in York
Victorian and South Australian Railways joint stock Dynamometer Car (coupled between the locomotive tender and the train) being used to record the performance of a VR X class locomotive running on pulverised brown coal.

A dynamometer car is a railroad maintenance of way car used for measuring various aspects of a locomotive's performance. Measurements include tractive effort (pulling force), power, top speed, etc.


  • History 1
  • Usage 2
  • Power calculations 3
  • References 4
  • External links 5


The first dynamometer car was probably one built in about 1838 by the "Father of Computing" Charles Babbage.[1][2][3] Working for the Great Western Railway of Great Britain, he equipped a passenger carriage to be placed between an engine and train and record data on a continuously moving roll of paper. The recorded data included the pulling force of the engine, a plot of the path of the carriage and the vertical shake of the carriage. The work was undertaken to help support the position of the Great Western Railway in the controversy over standardizing the British rail gauge.

In the United States, the Pennsylvania Railroad began using dynamometer cars in the 1860s.[4] The first modern dynamometer car in the US was built in 1874 by P.H. Dudley for the New York Central Railroad.

The early cars used a system of springs and mechanical linkages to effectively use the front coupler on the car as a scale and directly measure the force on the coupler. The car would also have a means to measure the speed of the train. Later versions used a hydraulic cylinder and line to transmit the force to the recording device.

Modern dynamometer cars typically use electronic solid state measuring devices and instrumentation such as strain gauges.

The dynamometer car used to record No 4468 Mallard's speed record is preserved at the National Railway Museum in York, England.

A car originally belonging to the Chicago, Burlington and Quincy Railroad, is preserved at the National Railroad Museum located in Green Bay, Wisconsin.


While the principal purpose of the dynamometer car was to measure the power output of locomotive, other data was typically collected such as smoke box data, throttle settings and valve cut offs, fuel burn rates, and water usage to determine the overall performance and efficiency of the locomotive.

Data would typically be recorded on time indexed continuous recording rolls for the pull and velocity. Power would later be manually calculated from this data on early cars. Some later cars were equipped with a mechanical integrator to directly record the power.[4]

A separate use for the car was to test a particular rail route to rate it for tonnage based on a run with a dynamometer car and recording the effect of the grades and curvature on the capacity and resulting power requirements for that line.[4]

Power calculations

The operating principle of the dynamometer car is based on the basic formula for power being equal to force times distance over time.

P = \frac{F\cdot d}{t}

This formula can be reduced to power equals force times velocity:

P = F\cdot\frac{d}{t}=F\cdot V

In other words, the instantaneous power output of the locomotive can be calculated by measuring the pull on the coupler and multiplying by the current speed.

P =50,000 lb\cdot \frac{30 mi}{hr}\cdot\frac{5280 ft}{mi}\cdot\frac{hr}{3600 s}=2,200,000\frac{ft\cdot lb}{s}

Converting to horse power gives:

P =2,200,000\frac{ft\cdot lb}{s}\cdot\frac{1 hp}{550 ft\cdot lb/s}=4,000 hp


  1. ^ "XXV. Railways". Passages from the life of a philosopher. Longman, Green, Longman, Roberts and Green. 1864. pp. 328–334. 
  2. ^  
  3. ^ * 
  4. ^ a b c Hay, William W (1982). Railread Engineering. John Wiley & Sons. pp. 213–214.  

External links

  • Testing a Locomotive — Comprehensive details of how a dynamometer car is used for performance testing
  • Rail Training & Test Cars photos of some prototype cars.
  • Carriages of LNWR: 6-wheeled Dynamometer Car
  • Laboratory on Wheels Details (including publicity article from February 1951) of the Victorian & South Australian Railways' dynamometer car
  • Esoteric Test Equipment
  • Norfolk & Western dynamometer car drawings
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