A traction engine is a steam-powered tractor used to move heavy loads on roads, plough ground or to provide power at a chosen location. The name derives from the Latin tractus, meaning 'drawn', since the prime function of any traction engine is to draw a load behind it. They are sometimes called road locomotives to distinguish them from railway locomotives – that is, steam engines that run on rails. Traction engines tend to be large, robust and powerful, but also heavy, slow, and difficult to manoeuvre. Nevertheless, they revolutionized agriculture and road haulage at a time when the only alternative prime mover was the draught horse. They became popular in industrialised countries from around 1850, when the first self-propelled portable steam engines for agricultural use were developed. Production continued well into the early part of the 20th century, when competition from internal combustion engine-powered tractors saw them fall out of favour, although some continued in commercial use in the United Kingdom well into the 1950s and later. All types of traction engines have now been superseded in commercial use. However, several thousand examples have been preserved worldwide, many in working order. Steam fairs are held throughout the year in the United Kingdom and in other countries, where visitors can experience working traction engines at close hand. Traction engines were cumbersome and ill-suited for crossing soft or heavy ground, so their agricultural use was usually either "on the belt" – powering farm machinery by means of a continuous leather belt driven by the flywheel, a form of power take-off – or in pairs, dragging an implement on a cable from one side of a field to another. However, where soil conditions permitted, direct hauling of implements ("off the drawbar") was preferred; in America, this led to the divergent development of the steam tractor. American designs were far more varied than those of the British, with different boiler positions, wheel numbers and piston placements being used. Additionally American engines often had higher top speeds than those of Britain, as well as the ability to run on straw.
History
The limits of technical knowledge and manufacturing technology meant that practicable road vehicles powered by steam did not start to appear until the early years of the 19th century. In 1841, Ransomes, Sims & Jefferies produced an early traction engine. The design (which was led by a horse to steer it) failed to attract any purchasers. They tried again in 1849, this time without the steering horse, but the machine was under-built for the threshing work it was designed for. Further attempts were made in the second half of the 1850s with Richard Bach of Birmingham, Charles Burrell of Charles Burrell & Sons and Allin Williams all either building or designing road going steam engines. The commercially successful traction engine was developed from an experiment in 1859 when Thomas Aveling modified a Clayton & Shuttleworth portable engine, which had to be hauled from job to job by horses, into a self-propelled one. This alteration was made by fitting a long driving chain between the crankshaft and the rear axle. Aveling is regarded as "the father of the traction engine". Aveling's first engine still required a horse for steering. Other influences were existing vehicles which were the first to be referred to as traction engines such as the Boydell engines manufactured by various companies and those developed for road haulage by Bray. The first half of the 1860s was a period of great experimentation, but by the end of the decade the standard form of the traction engine had evolved and would change little over the next sixty years. As part of these improvements the steering was improved to no longer need a horse, and the drive chain was replaced with gears. In America traction engines fitted with continuous tracks were being used from 1869. Compound engine designs were introduced in 1881. Until the quality of roads improved there was little demand for faster vehicles, and engines were geared accordingly to cope with their use on rough roads and farm tracks. Right through to the first decades of the twentieth century, manufacturers continued to seek a way to reach the economic potential of direct-pull ploughing and, particularly in North America, this led to the American development of the steam tractor. British companies such as Mann's and Garrett developed potentially viable direct ploughing engines; however, market conditions were against them and they failed to gain widespread popularity. These market conditions arose in the wake of the First World War when there was a glut of surplus equipment available as a result of British Government policy. Large numbers of Fowler ploughing engines had been constructed in order to increase the land under tillage during the war and many new light Fordson F tractors had been imported from 1917 onwards.
Decline
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