# Dynamometer car
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{{Short description|Type of railroad car}}
{{train topics}}
[[File:North Eastern Railway Dynamometer Car National Railway Museum York Object Number 1975-7050.jpg|thumb|A [North Eastern Railway](/source/North_Eastern_Railway_(United_Kingdom)) dynamometer car on display at the [National Railway Museum](/source/National_Railway_Museum) in York]]
[[File:X32 dynamometer car.jpg|thumb|A [Victorian](/source/Victorian_Railways) and [South Australian Railways](/source/South_Australian_Railways) joint stock dynamometer car (coupled between the locomotive [tender](/source/Tender_(rail)) and the train) being used to record the performance of a [VR X class](/source/Victorian_Railways_X_class) locomotive running on pulverised [brown coal](/source/Lignite)]]
A '''dynamometer car''' is a [railroad](/source/Rail_transport) [maintenance of way](/source/Track_(rail_transport)) car used for measuring various aspects of a [locomotive](/source/locomotive)'s performance. Measurements include [tractive effort](/source/tractive_effort) (pulling force), power, top speed, etc.
==History==
The first [dynamometer](/source/dynamometer) car was probably one built in about 1838 by the "Father of Computing" [Charles Babbage](/source/Charles_Babbage).[{{cite book| author-link= Charles Babbage| title= Passages from the life of a philosopher| publisher= Longman, Green, Longman, Roberts and Green| chapter= XXV. Railways| year= 1994| publication-date= 1864| pages= 328–334| chapter-url= https://archive.org/stream/passagesfromlif00babbgoog#page/n334/mode/1up}}][{{cite journal| author= M. V. Wilkes| author-link= Maurice Wilkes| title= Charles Babbage and his world| journal= Notes and Records of the Royal Society| year=2002 | volume=56| issue=3| pages=353–365| doi= 10.1098/rsnr.2002.0188 | s2cid= 144654303}}][*{{cite journal| author= K. K. Schwarz| author-link= K. K. Schwarz| title= Faraday and Babbage| journal= Notes and Records of the Royal Society| year=2002| volume=56| issue=3| pages=367–381| doi= 10.1098/rsnr.2002.0189| s2cid= 143944611}}] Working for the [Great Western Railway](/source/Great_Western_Railway) of [Great Britain](/source/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 engine's pulling force, a plot of the carriage's path, and the carriage's vertical shake. The work was undertaken to support the Great Western Railway's position in the controversy over standardizing the British [track gauge](/source/track_gauge).
In the United States, the Pennsylvania Railroad began using dynamometer cars in the 1860s.[{{cite book| last1=Hay| first1=William W| title=Railread Engineering| date=1982| publisher=John Wiley & Sons| isbn=0471364002| pages=213–214| url=https://books.google.com/books?id=ygKio-Ks0doC&q=LOCOMOTIVE+dynamometer&pg=PA213| accessdate=17 October 2014| archive-date=25 January 2022| archive-url=https://web.archive.org/web/20220125090139/https://books.google.com/books?id=ygKio-Ks0doC&q=LOCOMOTIVE+dynamometer&pg=PA213| url-status=live}}] The first modern dynamometer car in the United States 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](/source/Janney_coupler) as a scale, directly measuring the force on it. The car would also have a means of measuring the train's speed. 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 gauge](/source/strain_gauge)s.
A LNER dynamometer car was used to record [No 4468 Mallard's](/source/LNER_Class_A4_4468_Mallard) speed record in 1938, and has been preserved at the [National Railway Museum](/source/National_Railway_Museum) in [York](/source/York), England. This was also used for British Railways [1948 Locomotive Exchange Trials](/source/1948_Locomotive_Exchange_Trials) along with two other dynamometer cars, both of which have also survived into preservation.
A car originally belonging to the [Chicago, Burlington and Quincy Railroad](/source/Chicago%2C_Burlington_and_Quincy_Railroad) is preserved at the [National Railroad Museum](/source/National_Railroad_Museum) located in [Green Bay, Wisconsin](/source/Green_Bay%2C_Wisconsin). A car built for the [Chicago, Milwaukee, St. Paul and Pacific Railroad](/source/Chicago%2C_Milwaukee%2C_St._Paul_and_Pacific_Railroad) is preserved at the [Illinois Railway Museum](/source/Illinois_Railway_Museum).[{{cite web |title=Chicago Milwaukee St. Paul & Pacific (Milwaukee Road) X5000 |url=https://www.irm.org/cgi-bin/rsearch.cgi?swork=Chicago+Milwaukee+St.+Paul+&+Pacific+(Milwaukee+Road)=X5000 |website=IRM Roster |publisher=Illinois Railway Museum |access-date=26 June 2022}}]
== Usage ==
While the principal purpose of the dynamometer car was to measure the locomotive's power output, other data were typically collected, such as smoke box data, throttle settings, valve cut-offs, fuel burn rates, and water usage, to determine the locomotive's overall performance and efficiency.
Data would typically be recorded on time-indexed continuous paper recording rolls for the pull and velocity. Power would later be calculated manually from these data for early cars. Some later cars were equipped with a mechanical [integrator](/source/integrator) to directly record power.