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A traction engine is a steam engine 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 steam locomotive – 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 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 All types of traction engines have now been superseded in commercial use.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.
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 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.
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 (although imports were subject to taxes of up to 33%). 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 (equivalent to around £9000 today, 2024) 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 engines were constructed during the 1930s, although many continued in commercial use for many years while there remained experienced enginemen available to drive them.
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 (non-self moving), 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.
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.
The winding drum was either mounted horizontally (below the boiler), vertically (to one side), or even concentrically, so that it encircled the boiler. The majority were underslung (horizontal), however, and necessitated the use of an extra-long boiler to allow enough space for the drum to fit between the front and back wheels. These designs were the largest and longest traction engines to be built.
Mostly the ploughing engines worked in pairs, one on each side of the field, with the wire rope from each machine fastened to the implement to be hauled. The two drivers communicated by signals using the engine whistles. The engines in the pairs differed slightly with one designed to feed the cable out on the left side and the other on the right. Occasionally an alternative system was used where the plough was pulled between a single engine and an anchor.
A variety of implements were constructed for use with ploughing engines. The most common were the balance plough and the cultivator – ploughing and cultivating being the most physically demanding jobs to do on an arable farm. Other implements could include a mole drainer, used to create an underground drainage channel or pipe, or a dredger bucket for dredging rivers or moats. The engines were frequently provided with a 'spud tray' on the front axle, to store the 'spuds' which would be fitted to the wheels when travelling across claggy ground.
Ploughing engines were rare in the US; ploughs were usually hauled directly by an agricultural engine or steam tractor.
Production took place outside the UK with Kemna Bau of Germany producing ploughing engines.
Peak use in Britain was during World War 1 with a bit over 600 pairs as the country attempted to increase food production. Use of ploughing engines declined in the 1920s as internal combustion engine powered tractors took over. John Fowler & Co. stopped producing of ploughing engines in 1935 . Low prices in the aftermath of World War 2 meant a few farmers purchased them and continued to use them into the 1950s. As late as 1998 few engines in preservation were taking the occasional commercial job dredging lakes.
They were popular in the timber trade in the UK, although variations were also designed for general light road haulage and showman's use.
The most popular of these designs was probably the Garrett 4CD, meaning 4 nominal horse power compound. Garrett Steam Tractors & Rollers, R. A. Whitehead, 1999
The characteristic features of these engines are very large rear driving wheels fitted with solid rubber Tire, three-speed gearing (most traction engine types have only two gears), rear suspension, and belly tanks to provide a greater range between the stops needed to replenish water. All these features are to improve the ride and performance of the engine, which were used for journeys of hundreds of miles. Most road locomotives are fitted with a winch drum on the back axle. This can be used by removing the driving pins from the rear wheels, allowing the drive train to power the winch drum instead of the wheels.
James Boydell worked with the British steam traction engine manufacturer Charles Burrell & Sons to produce road haulage engines from 1856 that used his dreadnaught wheels which were particularly suited to bad roads or off-road use.
One place where road locomotives found a significant amount of use was in hauling timber from where it was felled to timber yards. Once the timber had been moved to a road the road movements were carried out hauling the trunks on . In France road locomotives were used to move mail in the 1880s.
A number of road locomotives are fitted with a crane boom on the front. The boom pivot is mounted on the front axle assembly and a small winch is mounted on an extension to the smokebox in front of the chimney, the cable passing over a sheave at the top of the boom arm. The winch is powered by bevel gears on a shaft driven directly from the engine, with some form of clutch providing raise/lower control. These road locomotives can be used to load a trailer as well as to haul it to a new location. They are often referred to as 'crane engines'.
A particularly distinctive form of road locomotive was the showman's engine. These were operated by travelling showmen both to tow fairground equipment and to power it when set up, either directly or by running a generator. These could be highly decorated and formed part of the spectacle of the fair. Some were fitted with a small crane that could be used when assembling the ride. About 400 were built with 107 surviving into preservation.
The poor state of the roads and the larger distances involved meant road locomotives (including showman's engines) were less used in the US.
Some traction engines were designed to be convertible: the same basic machine could be fitted with either standard Tire tread road wheels, or else smooth rolls – the changeover between the two being achieved in less than half a day.
The overtype had a steam engine mounted on top of a fire-tube boiler, in a similar manner to a traction engine. The front of an overtype steam wagon bears a close family resemblance to traction engines, and manufacturers who made both may well have been able to use some common parts.
The undertype had the steam engine mounted under the boiler, usually between the frames of the chassis. The boiler was usually mounted well forward and was often a vertical and/or water tube type.
Steam wagons were the dominant form of powered road traction for commercial haulage in the early part of the twentieth century, although they were a largely British phenomenon, with few manufacturers outside Great Britain. Competition from internal-combustion-powered vehicles and adverse legislation meant that few remained in commercial use beyond the Second World War.
Model steam traction engines are manufactured by several companies, notably Mamod and Wilesco. Larger scale model engines are popular for model engineers to construct, either as a supplied kit of parts or machined from raw materials.
A small number of full size traction engines have been built in modern times. In 2018 an enthusiast group in the United States completed a new Case Corporation 150, built using original manufacturing documents.
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