Traction engine
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 All types of traction engines have now been superseded in commercial use.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 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
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 failed to attract any purchasers. They tried again in 1849, this time without the steering horse, but the machine was under-built for threshing work it was designed for. Further attempts were made in the second half 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
Road steam disappeared through restrictions and charges that drove up their operating costs. Through 1921, steam tractors had demonstrated clear economic advantages over horse power for heavy hauling and short journeys. However, petrol lorries were starting to show better efficiency and could be purchased cheaply as war surplus; on a busy route a 3-ton petrol lorry could save about £100 per month compared to its steam equivalent, in spite of restrictive speed limits and relatively high fuel prices and maintenance costs.Throughout the 1920s and 1930s there were tighter restrictions on road steam haulage, including speed, smoke and vapour limits and a 'wetted tax', where the tax due was proportional to the size of the wetted area of the boiler; this made steam engines less competitive against domestically produced internal combustion engined units. As a result of the Salter Report on road funding, an 'axle weight tax' was introduced in 1933 in order to charge commercial motor vehicles more for the costs of maintaining the road system and to do away with the perception that the free use of roads was subsidising the competitors of rail freight. The tax was payable by all road hauliers in proportion to the axle load and was particularly restrictive on steam propulsion, which was heavier than its petrol equivalent.
Initially, imported oil was taxed much more than British-produced coal, but in 1934 Oliver Stanley, the Minister for Transport, reduced taxes on fuel oils while raising the Road Fund charge on road locomotives to £100 per year provoking protests by engine manufacturers, hauliers, showmen and the coal industry. This was at a time of high unemployment in the mining industry, when the steam haulage business represented a market of 950,000 tons of coal annually. The tax was devastating to the businesses of heavy hauliers and showmen and precipitated the scrapping of many engines.
The last new UK-built traction engine was sold in 1944, although many continued in commercial use for many years while there remained experienced enginemen available to drive them. Commercial used continued until 1992 with a William Foster & Co. engine being used to power a saw mill. Engines already in preservation continued to take the occasional commercial jobs until at least 1998.
Preservation
Perhaps the first organisation to take a general interest in traction engine preservation was the Road Locomotive Society formed in 1937.From the 1950s, the 'preservation movement' started to build as enthusiasts realised that traction engines were in danger of dying out. Many of the remaining engines were bought by enthusiasts, and restored to working order. Traction engine rallies began, initially as races between engine owners and their charges, later developing into the significant tourist attractions that take place in many locations each year.
The Traction Engine Register records the details of traction engines, steam road rollers, steam wagons, steam fire engines and portable engines that are known to survive in the United Kingdom and Irish Republic. It recorded 2,851 self moving engines and wagons, 687 portable engines, 160 steam fire engines existing in 2016. A new edition of the Register is planned in 2020. It was previously estimated in May 2011 by an unknown source that over 2,000 traction engines have been preserved. This figure may include engines preserved elsewhere in the world, particularly the US, Canada, Australia and New Zealand, but if so, is an underestimate. Comprehensive information on past UK manufacturers and their production is recorded by the Road Locomotive Society based in the UK.
Operation
Although the first traction engines employed a chain drive, it is more typical for large gears to be used to transfer the drive from the crankshaft to the rear axle.The machines typically have two large powered wheels at the back and two smaller wheels for steering at the front. However, some traction engines used a four-wheel-drive variation, and some experimented with an early form of caterpillar track.