Tractors

"TRACTORS. - The petrol tractor for agricultural and kindred purposes is a development of the steam traction engine, widely used for operating grain threshers and to a small extent for ploughing. Steam ploughs were used toward the end of the 19th century on the large ranches of the north-western section of the United States, in Canada and in Egypt. Their usefulness was limited, however, owing to their great weight, which resulted in the packing of the soil and in rather inefficient operation. When the weight of the petrol engine was greatly reduced by motor-car engineers, about 1900, the idea of substituting that type for the heavy steam plant naturally suggested itself.

The first petrol tractors seem to have been those built by the Huber Mfg. Co., of Marion, 0., in 1898. These were not successful and only 30 were completed. In 1901 the Hart-Parr Mfg. Co., of Charles City, Ia., engaged in the manufacture of petrol tractors, and, although this company met with many difficulties, it was successful and, after 19 years of continuous manufacture, produced in 1920 5,000 tractors. There are two general types of agricultural tractor, the wheeled and the crawler, or caterpillar, types. The crawler type, in which the weight is spread over a large supporting surface on the ground, can pass over marshy land where the wheeled tractor would be mired, and when used for pulling barrows, seeders and other implements over ploughed ground, does not pack the soil as a wheeled tractor would. Early technical development was chiefly toward large tractors, designed to operate from 6 to 12 plough bottoms, because the only farmers who then took an interest in tractors were the owners of large ranches in western America. The largest producers of petrol tractors in the United States between 1905 and 1913 were manufacturers whose main line was general agricultural machinery and steam traction engines, such as the International Harvester Co., the J. I. Case T. M. Co., and Emerson-Brantingham Co. The large petrol tractors of that period were crude in design and very heavy; their frames were built up of heavy rolled channels, and they had driving wheels of enormous diameter. Their great weight naturally rendered them inefficient, for a large proportion of the engine power was consumed in moving the tractor itself. The oil-pull tractor shown in fig. r is characteristic of tractors of that period.

FIG. I.

Agricultural Tractors. - Tractors are usually rated in terms of the number of 14-in. plough bottoms which they will pull. In 1920, of loo models on the American market capable of pulling two or more bottoms, 20 were two-plough tractors; 42 three-plough; 17 fourplough and the rest were capable of pulling five or more ploughs. Table 1 shows the production of tractors in the United States each year from 1909 to 1920.

Table z. Tractor Production in the United States. According to a statement issued by the Ministry of Transport, there were Io,161 agricultural tractors in the United Kingdom in 1921. Of the tractors produced in the United States 14,8J4 were exported in 1917, 3 6 ,35 1 in 1918, 19,693 in 1919, and 29,143 (valued at $30,850,O00) in 1920. It will be seen from the above table that a slump in tractor production occurred in 1913. It was in 1912 that the business in the large tractors of 6-to 12-plough capacities reached its zenith, and thereafter it declined rapidly. The first popular small tractor, the Bull, was brought out the following year, and in 1914, no fewer than 3,000 tractors of this make were sold. Although smaller, it was still of the same crude design as the larger machines, with exposed gears, plain bearings and similar features. About 1916 a number of engineers with motor-car experience entered the tractor field, and as a result of their efforts tractor design was greatly improved. Before 1920 many farm tractors were designed to use paraffin as fuel, because paraffin was considerably cheaper than petrol, and the conditions of engine operation on a tractor (constant speed and steady, heavy load) made it comparatively easy to burn paraffin with a moderate degree of success. Petrol, however, proved much more satisfactory in the average engine, and when in 1919 the price of paraffin advanced sharply, tractor users generally turned to petrol. The consumption of petrol in gallons per acre is less, there is less difficulty in cold weather and the oil in the crank case does not lose its lubricating value so quickly. For the sake of economical manufacture many of the earlier small tractors were made with only three wheels, but the buying public did not approve of this feature of construction, and the typical 1920 wheeled tractor had four wheels, two in front steering and two in the rear for driving. The Twin City 12-20 H.P. tractor shown FIG. 2.

in fig. 2 is a good example of the lighter tractors based on motorcar practice. The following is a composite description of a 1920 model three-plough tractor, the features mentioned being those found on the greatest number of models of this capacity; there was a four-cylinder, four-stroke vertical engine at the front, of about 44-in. bore by 6-in. stroke, adapted to burn either petrol or paraffin. Ignition was by a high-tension magneto with impulse starter. (The latter device consisted of a spring attachment for magnetos specially developed for use on tractors, which made it unnecessary to " spin " the heavy engines in order to generate a spark in the magneto.) The carburetor was fitted with an air cleaner, which prevented gritty dust from getting into the engine and rapidly wearing out the cylinder barrels. These air cleaners usually acted on the centrifugal principle, but in the lava-ash districts on the Pacific coast it was necessary to employ air washers, owing to the lightness of the dust. Behind the engine there was a friction clutch, and then came the change-speed gear, which gave two forward speeds and one reverse. The higher forward speed was for regular use in ploughing and the lower for emergencies, for ploughing up steep inclines, in heavy soil, etc. Then there was a further reduction by gears to the rear axle. The engine speed was limited by a governor to about Boo revolutions per minute, and as the ploughing speed was about 24 m.p.h., with 48-in. driving wheels, a reduction of roughly 40 to I had to be provided between engine crankshaft and rear axle or rear wheels. In the early tractors the final drive was through exposed bull gears directly on the driving wheels, but the typical 1920 tractor had all its gearing enclosed and protected from dust and mud, which is an important feature in a machine FIG. 3.

operating in the fields during the wet season as well as when the soil is dry and dusty. The wheelbase of the tractor was 96 in. and its weight about 5,000 pounds. The wheels were built up of rolled rims and flat spokes riveted to the hubs and rims. The driving wheels were provided with angle-iron lugs to increase the traction, and the front wheels with central skid rings to make the steering more positive. The front axle was swivelled to the frame at the middle, to permit the wheels to accommodate themselves to uneven ground. In addition to the pivot joint a spring could be used between the axle and the frame at the front to relieve shocks. These 1920 tractors were provided with a belt pulley for operating threshing machines, wood saws, silo fillers, etc. It was customary to apply a double horse-power rating; for instance, a three-plough tractor was often rated as a 12-25 H.P. machine. This signified that the tractor could develop 25 H.P. on the belt and 12 H.P. on the drawbar, the difference of 13 H.P. being required for moving the tractor itself over the field. In 1917 the Society of Automotive Engineers standardized tractor belt speed at 2,600 ft. p.m. and the drawbar height at 17 inches. Another class of wheeled tractor, having only two wheels, is exemplified by the Moline Universal illustrated in fig. 3. This is intended for cultivating as well as for ploughing and similar work, and has the necessary clearance to pass over plants 2 ft. or more high. Another feature is that, by means of an extension to the control apparatus, it can be operated from the implement drawn, thus dispensing with the need for an extra man in operating a self-binder, for instance. The crawling tractor had one or two continuous-chain tracks on which it ran and which it carried with it. That portion of the chain track in contact with the ground had transverse projecting bars or depressions which caused it to grip the ground firmly, while the upper side of the lower portion of the chain formed a smooth track on which rolled idler wheels carried on the frame of the tractor. The power from the engine was transmitted through a suitable reduction gear to a pair of toothed wheels which engaged with teeth or rollers on the inner side of the track and, when power was applied by letting in the clutch, the tractor rolled ahead on the track and the track at the same time rolled forward. The power was applied to the two chain wheels through a differential gear, and in order to steer a tractor of this kind, one track was held stationary by means of a brake on the shaft of its chain wheel, while all the power was applied to the other chain wheel. The Cletrack tractor shown in fig. 4 was one of FIG. 4.

the smallest tractors of this type. Much of the development work in connexion with crawler tractors was done in California, where the Holt, the Best and the Yuba, all tractors made in large sizes, originated. The Holt, which is called a Caterpillar, became the prototype for the " tanks " which played such an important part in the World War. In 1920 many of these large crawler tractors were used for other than agricultural purposes-for example, in oil-fields, in lumbering and in road-building; and the city of New York that year purchased a large number for use in clearing the streets of snow. The lumbering or logging work done was mainly in swampy districts where previously it had been impossible to work with horses except in winter when the ground was frozen, whereas the crawler tractor made logging in such districts possible the year round. The weight on the track of a crawler tractor of the 1920 type was as low as 5 lb. per sq. in., and such a tractor could go into boggy places. where no wheeled vehicle could follow.

In 1919 the Legislature of the state of Nebraska passed a law providing that thereafter no tractor should be sold in that state until the manufacturer had first submitted a sample tractor for trial to the Agricultural Engineering Department of the university of Nebraska and the tractor had satisfactorily met the test required. The manufacturer must also satisfy the state authorities that he is maintaining an adequate supply of repair parts within the state. This legislation was the result of complaints of farmers that manufacturers were overrating their tractors. The result was that, during a period when 66 tractors were tested, the makers of 8 were compelled to increase their rated engine speed, 13 lowered their horse-power rating, 14 changed some part and 4 withdrew.

Cost of Tractor Ploughing.-The three chief items of cost in tractor ploughing are fuel, depreciation and labour. At the tractor trials held at Lincoln, England, in the autumn of 1919, the fuel consumption per ac. averaged almost exactly 4 imp. gal. for ploughing in heavy clay soil, and 3 gal. for ploughing on cliff lands. In the corn belt of the United States, where the soil is comparatively light, it has been customary to reckon on a fuel consumption (either petrol or paraffin) of 2.5 U.S. gal. (2 imp. gal.) per acre. On the other hand, in a bulletin of the U.S. Department of Agriculture on " The Gas Tractor in Eastern Farming," a fuel consumption of 32 U.S. gal. per ac. is made the basis of cost calculations of the eastern section, and in the tractor trials held at Harrisburg, Pa., in 1919 the average fuel consumption of all tractors using paraffin worked out at 3.28 U.S. gal. (2.62 imp. gal.) per acre. The fuel consumption in tractor ploughing varies both with the character and condition of the soil and with the depth of ploughing. The average depth of ploughing at Lincoln was 54 inches. The resistance of the soil (drawbar pull) averaged II 5 lb. per sq. in. for the heavy clay soil and 9 lb. per sq. in. for the cliff land. In the corn belt of the United States the soil resistance generally varies between 5.5 and 7 lb. per sq. in., and this explains the low fuel consumption in ploughing there. The estimate here given of the cost of ploughing one acre is based on the results of an inquiry by the U.S. Department of Agriculture among 400 tractor farmers in the Dakotas concerning their experiences in 1917 and 1918. Only one change is made from the estimate of the department, namely, the assumption of a tractor life of seven instead of nine years, which latter figure is admittedly too high. The answers to the questionnaire yielded the averages shown in Table 2. Table 2. Average Cost and Performance of Tractor Ploughing in the Dakotas. Other factors on which the estimate is based are the following Cost of petrol, $.276 per U.S. gal.; paraffin, $.152 per gal.; lubricating oil, $.50 per gal.; grease 8.'0 per lb.; repairs, 4% of first cost per year; depreciation on a 7-year basis; man labour at $4.00 per day; interest at 6% on the average investment (one-half of total investment). Such items as housing, insurance and taxes are neglected.

Table 3. Cost of Tractor Ploughing in the Dakotas 1917-8. (Dollars per acre) With the data here indicated it is possible to make a close estimate of the cost of tractor ploughing under different conditions, as all the basic costs are given. The average soil resistance in the Dakotas may be assumed to be 8 lb. per sq. inch. In heavier soils the area ploughed per day will be less in substantially the inverse ratio of the soil resistance (provided the latter is not excessive). This is borne out by estimates of the ploughing capacities of the tractors which competed in the Lincoln trials of 1919, made by the judges of the event. Averaging the estimates for heavy clay soil (soil resistance 11 5 lb. per sq. in.), and reckoning on the basis of a to-hr. instead of an 8-hr. day, the following results are obtained: Two-plough tractor, 42 ac., three-plough tractor, 51ac., four-plough tractor, 61 acres.

To the American and Canadian farmer the advantage of the tractor is not so much that it reduces the cost of ploughing as compared with horses, as that it enables one man to work a much greater acreage. Approximately one-third of several hundred tractor farmers in Illinois circularized by the U.S. Department of Agriculture had increased their acreage by purchasing tractors. Another great advantage is that the tractor permits work to be done quickly when the weather is favourable. For instance, a southern Illinois farmer estimates that in his neighbourhood the yield of Indian corn is reduced by I bus. per acre for every day that planting is delayed after May 8. In 1920 the spring was so wet that he was able to work in the field only the first day and the last day of April, not a day in between; but when the weather turned he was able, owing to his tractors, to get his crop in quickly.

Power farming has proved particularly advantageous in the wheat belt of Kansas. For the best yield the land must be ploughed in Aug., when the temperature is often above too') F. in the shade and very little work can be accomplished with horses. The tractor works as efficiently at this temperature as in winter. Moreover, the tractor can be used also for threshing, and the old practice of contract threshing has been largely superseded by the plan of four or five farmers owning a small threshing machine cooperatively and helping each other thresh their grain, each using his own tractor as the motive power. A three-plough tractor is generally recommended for a 20x36 in. grain separator. Sometimes it is necessary to get a crop into the ground very quickly, and, with a double shift of operators, tractors can then be operated continuously day and night.

Interest in farm tractors increased greatly in Europe during and following the World War. In 1919 and 1920 tractor trials were held at Lincoln, England, the first under the auspices of the Society of Motor Manufacturers and Traders and the second under that of the Royal Agricultural Society. The French Government in 1920 paid a bonus of 25% on the purchase price of tractors of domestic manufacture and 10% on tractors of foreign manufacture. During the war the British, French and Italian Governments contracted for large numbers of farm tractors in the United States. In 1919 there was an international tractor demonstration and test at Sabyholrn, Denmark, in which Danish, Swedish, German, British and American tractors were entered. Several demonstrations were also held in France in the years immediately following the World War; French engineers paid particular attention to tractors for use in vineyards, which must be very narrow. Those for use in orchards, on which a number of American manufacturers specialize, must be very low. A somewhat distinct type is the garden tractor for the cultivation of row crops and general work in market gardening. The Beeman, the first model of this type, was put on the market in 1915, and in 1919 about half a dozen other tractors of this type were brought out. For rubber-tired road tractors, see Motor Vehicles; for artillery tractors, see Artillery.

BIBLIOGRAPHY

Barsch, Motorpfluge (1919); Page, The Modern Gas Tractor (1917); Sherwood, The Farm Tractor Handbook (1919); Society of Motor Manufacturers and Traders, Report on the Tractor Trials held at Lincoln (London, 1919, 1920); U.S. Department of Agriculture, The Gas Tractor in Eastern Farming (1918), Tractor Experience in Illinois (1918) and The Farm Tractor in the Dakotas (1919). (P. M. H.)

Categories: TOW-TRI