A century of progress in tractor design
Tuesday, March 4, 2014
Farm tractors have undergone major changes since the early 1900s and, since 1920, the University of Nebraska's test reports have provided invaluable information about their capabilities. Today, they still offer the best source of comparative data available
by RALPH WINFIELD
By the beginning of the last century, steam-powered traction units had been used extensively to operate threshing units and to break prairie sod, but there was no hope of them replacing the teams of horses that were in use for field tillage work in Ontario and elsewhere.
Charles Hart and Charles Parr, two engineering classmates, had started building tractors as early as 1902. It was their sales manager who first introduced the name "tractor" for their massive creation, which looked just like a steam-powered traction unit.
By 1917, almost 260 different tractor companies were building or selling tractors in North America. Some, like the Hart-Parr, were reputable. Others, like the first Ford tractors, were not. They were very unreliable.
Let me explain. The first Ford tractors were not built or endorsed by the Henry Ford with whom we are all familiar. That explains why Henry had to create a new company – Henry Ford & Son – to build his "Fordson Tractor" that was first introduced in 1917 from the factory in Dearborn, Mich.
It was as a result of the worker/labour shortage during the First World War that such a large number of tractor companies existed by 1917. By 1908, public tractor competitions were being held annually in Winnipeg. This was in an attempt to allow tractor manufacturers to show off their tractors in competitions and prove their claims in various brake-horsepower classes.
Comparable competitions followed in Fremont, Neb., from 1913 through 1915. However, the questions of performance and reliability were not being answered satisfactorily during these demonstration days.
Prof. L. W. Chase of the University of Nebraska, who was also serving as the president of the American Society of Agricultural Engineers (ASAE), led the charge to create the Nebraska Tractor Test Bill in the Nebraska legislature. The bill came into effect in 1920, but by then many of the experimental test procedures had already been determined and verified at the University of Nebraska.
The bill made it mandatory for every tractor manufacturer who wished to sell a tractor in Nebraska to submit that model of tractor for testing at the test laboratory in Lincoln, Neb. The company had to pay a fee for the test procedures and agree to public release of the test results.
Official tractor testing started in 1920. Through ASAE, directly from the test lab, and through many agricultural publications, the results became available and were used throughout North America. Because of the wide acceptance of the tests, every tractor manufacturer participated.
The first tractor model tested was: the Waterloo Boy Model N, 12-25, manufactured by the Waterloo Gasoline Engine Co., Waterloo, Iowa. Most of the following tractors were produced by threshing machine companies: Minneapolis Threshing Machine Co., J. I. Case Threshing Machine Co., and the Advance-Rumely Thresher Co.
Virtually all tractor manufacturers complied with the testing program, even though many tractor manufacturers fell by the wayside during the tough marketing times of the 1920s. Thus, many names of the early test runs such as Heider, Emerson-Brantingham, Wisconsin Farm Tractor and Samson are probably tractors that you have never heard about.
Two tests stand out. Test No. 18 was on the Fordson of the Ford Motor Co. The other was Test No. 27 of the Samson Model M. Bill Durant, who was chairman of General Motors, was convinced that GM had to be in the tractor business. He acquired the rights to build the Samson tractor and moved production from California to a new assembly plant in Janesville, Wisc. The economic downturn of the early 1920s took its toll very quickly. The tractor plant was producing Chevrolet cars by 1923 and Bill Durant was building Durant cars elsewhere.
The test procedure and results. Company representatives were allowed to tune the assembly-line tractor after it arrived in Lincoln. From that point on, all adjustments and failures were recorded in the final report.
All drawbar load tests were carried out on a paved track to ensure comparative results. The company representatives had already chosen the weighting (i.e. fluid in tires or number of wheel weights and the gear(s) in which the tractor was to be tested).
An instrument car was attached directly to the tractor drawbar to measure drawbar pull and travel speed. Load car(s) were attached behind to create the variable load required. Two types were used. Initially, a tractor was attached and the engine was operated as an air compressor to create a drag-type load. Later on, electrical generators were designed into the load vehicles. Electrical energy was generated and then dissipated into the air as heat-using resistors.
Two figures (values) were created: one was the maximum drawbar pull and the second one was the maximum drawbar horsepower in the gear stipulated by the manufacturer.
Engine (belt or PTO) horsepower. Initially (1920), all tractors had pulleys to drive threshing machines. Thus, an electrical generator became the chosen device to establish belt horsepower.
The only values that were needed to calculate rotating horsepower were shaft speed and torque. Both of these were easily obtainable using a tachometer for shaft speed and a moment arm attached to a scale to provide a torque value in pounds per foot. It is a force (pounds) at a distance (in feet) from the centre of the rotating generator shaft.
In the early days, from 1920 to 1940, many tractor models were designated by those two horsepower values, drawbar and belt (i.e., 10-20, 12-28, 15-30, etc.). When PTO shafts became a standard feature on farm tractors by the 1940s, the belt horsepower effectively became PTO horsepower.
The 1960s – a time of change. By the early 1960s, many tractors came out with diesel versions, because starting the higher compression engines became easier with newer technology. Manufacturers had moved to direct injection and to 12- and 24-volt electrical systems. Gone were the pup motors used by Caterpillar and John Deere, and the dual fuel system developed by International Harvester to start the engine on gasoline and then switch it over to diesel. Both of these systems worked well, but they were time-consuming for the busy farmer. In Europe, the "hot-bulb" or shell cartridge had been used to start the single-cylinder two-stroke diesel engine tractors.
The other change that occurred in the 1960s was the dropping of PTO shafts on some of the large 4-WD tractors. Some Versatile tractors built in Winnipeg had PTO and three-point hitches as optional equipment. This created a problem for the staff in Nebraska. They had to eliminate the PTO horsepower value for those reports and effectively report "engine brake-horsepower."
The real comparative values. Some very valuable information has resulted from the Nebraska Test data. The term "horsepower hours per gallon" or "Economy" was generated and provides some really useful comparative information. If a PTO was in place, two comparative "Economy" values were obtained.
Let me explain. If a tractor under test at rated PTO speed developed a 140-PTO horsepower and used 20 U.S. gallons of diesel fuel in a two-hour test run, the "horsepower hours per gallon" would be (140 x 2) /20 = 14.0.
What are very interesting are the comparative values over time/fuel type and manufacturer. In the periods before and during the Second World War, when many tractors were fuelled with cheaper distillate fuels, the Economy values ranged from 6.71 up to 12.44. Gasoline fuel gave values from 3.30 up to 13.18. Diesel fuel started at 9.29 and progressed up to 18.64 by 1984. Is it any wonder that diesel fuel has become the tractor fuel of choice over the years?
But let us be realistic. Many significant improvements have been made to diesel engines, and especially the fuel injection systems. The quality of diesel fuel has also improved by better refining processes.
Continuing progress. With the new "Tier 4" emission standards and better transmission systems, we just do not see those plumes of black smoke rising from diesel engines. Some of us remember locating the neighbour's tractor or combine by looking for that plume!
In recent years, we have seen great improvements in transmission systems to increase "Economy" as well. Gone are the days of the three- to six-speed manual transmissions. In those days, you selected the gear that would get you through the tough spot and stayed with it because shifting gears twice during each field pass was just not acceptable.
We have also learned to pull slightly narrower tillage implements at a higher speed to maintain a better "Economy" while passing through the "tough spot" with ease.
It is not hard to remember that having a one-stage power shift to match power better to load was considered to be great technology! Now we have reliable Power Shift and Continuously and Infinite Variable Transmissions (CVTs and IVTs) that we are likely to see more frequently in tractors. Some of this technology is already being used in car transmissions as well.
It should be recognized that the actual horsepower values given for a specific tractor are de-rated about 10 per cent. This ensures that virtually all production tractors of that model should be able to exceed the Nebraska-rated values.
The best source of information we have. For any of you with computer expertise, a Google or other search engine will allow you to enter "Nebraska Test Reports" to access all of the recent test results. The reports provide a wealth of information. You can find out about engine manufacturers and transmission types as well as details about the hydraulic systems.
You can learn many questions to ask tractor salespeople as well about fuel efficiency and wheel/axle loading for the type and size of tillage equipment you plan to use.
Two other acronyms you will need to know: SAE is the Society of Automotive Engineers and OECD is the Organization for Economic Co-operation and Development. The OECD allows some tractors to be rated by Nebraska standards at other locations.
The Nebraska Test Reports might not provide the perfect results but they are the best unbiased/comparative information we have, and they have survived the test of time and are recognized worldwide. Some reports are almost 100 years old! BF
Agricultural engineer Ralph Winfield farms at Belmont in Elgin County.