C&0's dynamometer car

On June 4, 1930, the C&O received a dynamometer car built to its specifications by the Standard Steel Car Company, with on-board test equipment developed and installed by the Baldwin Locomotive Works.

The car cost $82,267.07; a very expensive piece of equipment in the terms of its day. It was in this period that the testing of locomotives had reached a high degree of sophistication, and the dynamometer car had been developed for this use.

Ralph Johnson, writing in Baldwin Locomotives, the Baldwin Works' company magazine, said that the final question to be answered by the dynamometer car was "... to determine how much can be accomplished in the actual drawing of a load by the mechanical means available, and the most economical use of these means."

Up until the period following the First World War most locomotive tests had been done in stationary test plants, such as the one at Purdue University, where a locomotive was placed on what was essentially a "treadmill:" where it could be operated at all speeds, and its wheels simply turning rollers mounted beneath them. However useful this type of testing was, it failed to consider the peculiar characteristics of a particular railway line such as grade, curvature, wind and journal resistance, etc.

To better determine the output of or work performed by a locomotive its efficiency and capacity had to be accurately measured under actual operating conditions. The dynamometer car was therefore developed to measure the actual pulling forces, and the resistance to these forces, encountered with a locomotive in actual service on a train of known weight and configuration.

The dynamometer itself was simply a spring weighing device "in which the actual force necessary to extend the spring can be read by means of a calibration in pounds ... for power or weight. The modern railway dynamometer consists of a `weighing head,' which connects the drawbar through a properly proportioned lever to pistons operating on the hydraulic principle. These then transfer through special diaphragms the variations due to compressive action set up by the movement of the drawbar." [Johnson, Baldwin Locomotives, January 1927]

The dynamometer car was used to do a number of jobs: First, to determine tonnage ratings for various types of locomotives over various divisions or sections of a railway, which helped decide on pusher districts and the types of locomotives to be used on various classes of trains. It was also used to determine the most economical use of available locomotives, to determine how local conditions of one type or another might affect train operation, and finally to compare various locomotive types in order to build up data that could be used in designing new locomotives. It is in this latter capacity that the dynamometer cars did their best known work.

The June 27, 1925, issue of Railway Review, one of the several trade journals of the era, stated: "No railroad can be said to have a locomotive policy unless it has a busy dynamometer car. No railroad can distribute its power intelligently or say it is making a real record of fuel economy without one."

The car itself almost always had an outward appearance like that of a passenger train car, usually with the addition of a cupola and even bay windows from which test personnel could observe the train and engine. The car usually had living accommodations for the test personnel, including a kitchen and sleeping berths. The C&O car's living areas occupied over half the car. Two double berths (and an upper berth in the working area), as well as a bunk for the cook, a shower, and restroom facilities were provided. The machinery and working area occupied the remainder of the car, with the main instrumentation table facing the end of the car where the actual dynamometer apparatus was installed. The cupola was located above the instrumentation and machinery area. A wide express-style sliding door was located on each side of the working area so that supplies and machinery could be taken in and out as needed.

In the C&O's car the recording paper was 24 inches wide, with stainless steel pens recording the data. A roller revolved every mile and sounded an alarm so that the operator could watch for the mile post and annotate it on the graph paper. A special clock marked the passage of each minute on the graph as well..

In the era of the 1920s, when it was making so many decisions about the improvement of locomotives, the C&O often borrowed the dynamometer car owned by Baldwin, and after the Nickel Plate Road acquired a car in 1924, it was used. By 1930 the C&O wanted its own, for more frequent use in testing, which eventually led to the last great development of the steam locomotive, including the H-8 2-6-6-6, K-4 2-8-4, J-3 and J-3a 4-8-4s, and L-2/L-2a Hudsons.

In actual use the dynamometer car would almost always be seen coupled directly behind the locomotive on a freight train of some type. Occasionally passenger locomotives were tested as well, so the modeler wanting to use a dynamometer car model could use it in either service.