Page:EB1922 - Volume 32.djvu/766

740 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 draw- bar, 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 exten- sion to the control apparatus, it can be operated from the imple- ment 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 car- ried 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 por- tion 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 Ib. 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 manu- facturers 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 trac- tor 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 plough- ing 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 (cither 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 3% 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 consump- tion in tractor ploughing varies both with the character and condi- tion of the soil and with the depth of ploughing. The average depth of ploughing at Lincoln was sf inches. The resistance of the soil (drawbar pull) averaged 11-5 Ib. per sq. in. for the heavy clay soil and 9 Ib. 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 Ib. 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. Depart- ment of Agriculture among 400 tractor farmers in the Dakotas con- cerning their experiences in 1917 and 1918. Only one change isi made from the estimate of the department, namely, the assump- tion of a tractor life of seven instead of nine years, which latteri 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.

Two-plough Tracton

Three-plough Tractors

Four-plough | Tractors

First cost. Full working days per year. Acres ploughed per lo-hr. day

$1,050 45 6-3

$1,460

52 8-5

$2,000

64 10-9

Other factors on which the estimate is based are the following: Cost of petrol, $.276 per U.S. gal. ; paraffin, 8.152 per gal. ; lubricat- ing oil, 8.50 per gal.; grease S.io per Ib. ; repairs, 4 % of first cost per j 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 invest- ment). Such items as housing, insurance and taxes are neglected.

Table j. Cost of Tractor Ploughing in the Dakotas ipif-S. (Dollars per acre)

Size of Tractor

Total Cost of Ploughing

Fuel

Oil

Petrol Tractor

Paraffin Tractor

Petrol

Paraffin

Two-plough. Three-plough Four-plough.

2-21

1-975 1-757

I-9I5 1-68 1-462

0-69 0-69 0-69

0-395 0-395 0-395

0-075

0-075 0-075

Other Items

Grease

Re- pairs

Depre- ciation

Man

Labour

Inter- est

Two-plough. Three-plough Four-plough.

O-O2 O-O2 O-O2

0-15 0-13

O-II

o-53 o-49 0-409

0-635 0-47 0-368

o-n

O-IO

0-085

With the data here indicated it is possible to make a close esti-

mate 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 Ib. per sq. inch. In heavier soils the area ploughed per day will be less in substanjially the inverse j ratio of the soil resistance (provided the latter is not excessive). This is borne out by estimates of the ploughing capacities of the l 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 Ib. per sq. in.), and reckoning on the basis of a j lo-hr. instead of an 8-hr, day, the following results are obtained: Two-plough tractor, 4^ ac., three-plough tractor, 5! ac., four-plough tractor, 6 acres.

To the American and Canadian farmer the advantage of the trac- tor 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 Agricul- ture had increased their acreage by purchasing tractors. Anothe 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 con is reduced by I bus. per acre for every day that planting is delayei after May 8. In 1920 the spring was so wet that he was able to won 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 hi tractors, to get his crop in quickly.