How the Tractor Trials Wpre Conducted
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THE demonstration of machines entered for the World Agricultural Tractor Trials of 1930, which took place near Wantage last week and is reported elsewhere in this issue, was the culmination of far-reaching tests carried out for some months under the auspices of the Royal Agricultural Society of England and the Institute of Agricultural Engineering, University of Oxford. The official report of these tests and the catalogue of machines taking part in the demonstration is available Ea the price of 1s. from the .Royal Agricultural Society of England, 16, Bedford Square, London,
Arduous Trials.
These trials were carried out on different lines from those followed previously in this country, each machine being submitted to an exacting series of
tests. The market-garden cultivators carried out normal cultivating work during May on crops in the Evesham district, whilst tests of the tractor entrants were performed near Wallingford, where they started on June 2nd. , The complete programme involved about 24 hours' actual working time in each case, and was finished on June 26th. The completion of the programme in so short a time was only made possible by the general efficiency of the machines and by the courtesy of the operators in charge of them.
Only three machines out of 33 tractors and three power-driven market-garden cultivators failed to carry out the full programme. One macliine was withdrawn owing to a change of arrangements on the part of the makers, and two because of mechanical breakdown.
The purpose was not necessarily to determine which tractor is. the best in its class, but simply to show exactly what each machine is capable of doing under normal conditions. Therefore no expression of opinion will be found in the report, which is confined simply to the actual results with notes on points directly connected with them.
The belt tests were taken on an eleetro-dynamometer, whilst fuel consumption during these tests was measured in one of two ways, according to the circumstances. In the first, the tank was filled to a certain known level at the start and refilled to the same level at the finish ; in the second, the tank was disconnected from the carburetter and the last-named connected direct by means of a flexible pipe to a 10-gallon fuel container suspended from a graduated balance.
Drawbar Tests.
In all the drawbar tests the loading of the tractors was effected by one or other of two dynamometer cars. The larger consisted of a chassis on three wheels, the front being employed for steering, whilst the two at the rear were of the ordinary spudded type corresponding to the driving wheels of the tractor, but actually driven around2by the ground as the machine is pulled along. As these wheels revolve they drive an electric generator through -a four-speed gearbox and a final chain drive. With this large machine, 15-40 drawbar horse-power can be dealt with, whilst the smaller car is suitable for 8-25 h.p. Where greater powers had to be dealt with, the two cars were used together.
TestingPower Capabilities.
In arriving at the power exerted by the tractor it was necessary to measure both the drawbar pull of the tractor and the speed at which it was working. The former measurement was made by a pressure unit, consisting of an oil-filled cylinder with a closely .fitting plunger, whilst the actual speed was obtained by timing it over a measured distance, using a stop-watch. For the maximum drawbar-pull tests, however, it was necessary to have a continuous indication of the approximate speed. ,This was effected by a cord, 300 yds. in length, wound on a drum .cm the.dynamometer car. As the tractor pulled the ear along, the cord wound off and revolved a pulley to which was connected an ordinary speed indicator.
'During the whole series of tests of each tractor, a total period of two hours was allowed for stoppages for minor replacements or repairs.
' From the foregoing it will be apparent that the technical side of the trials of the individual machines has been tackled in, a more ambitious manlier than in any similar event preVionsly or ganized in this country. .