First road carriages
Trevithick was able to translate his steam engines from stationary machines to mobile ones because his boiler was a cylindrical vessel with internal heating. Older boilers relied on external heat sources and were in effect pot or kettle boilers. He wasn't the first engineer to build a self-propelled vehicle but he was the first to show the possibilities of steam travel as a practical mode of transport rather than a curiosity.
In 1769 Nicholas-Joseph Cugnot (1725-1804), a French military engineer, designed a three-wheeled oak tractor — fardier à vapeur — or steam dray based on earlier small-scale models. It was intended to replace horses for pulling heavy artillery and could carry four people while moving at walking pace. It had a rounded copper boiler suspended forward of the single front wheel, which was used for drive and steering, and had to stop every 15-20 minutes for a boiler top-up. It carried no reserves of water or fuel (wood).
Cugnot produced an improved version in 1770 that could operate non-stop for 75 minutes. It had rack-and-pinion steering and was powered by two pistons connected by a rocking beam. The reciprocating motion was converted to rotary motion to turn the wheels, though the tractive force produced was small. With most of the weight at the front, the vehicle was unstable and it crashed into a wall. A third one, built a year later, is on display at the Conservatoire National des Arts et Métiers in Paris.
William Murdock (or Murdoch, 1754-1839), a Scottish engineer working for Boulton & Watt in Cornwall, had been experimenting with model steam carriages in his spare time. In 1784 he built a working prototype, followed by several larger models. They too had three wheels, with the drive applied to the rear pair and a vertical cylinder inside the boiler. In an 1815 letter to James Watt junior, Murdock's son John (1790-1862) says that a working model using "strong steam and no vacuum" built in the summer of 1792 was shown to Trevithick and his cousin Andrew Vivian "about two years after".
Murdock set out for London in 1795 intending to apply for a patent but was waylaid by Matthew Boulton who made it clear that Boulton & Watt was aware of his activities and would oppose his carriage just as fiercely as it had Hornblower's engine. Murdock abandoned full-scale trials and turned his attention to using coal gas for lighting. In 2000 a large replica of the 1784 Murdock Flyer was placed on Tolgus roundabout in Redruth.
While Trevithick was aware of Murdock's work on steam carriages, it is not clear how much he knew of the details, and his own steam vehicle looked very different from Murdock's — it was the first to have four wheels.
In 1800 it was thought that a heavy steam engine driving on smooth wheels would not be able to propel itself, that the wheels would spin on the spot or skid. By driving a chaise (without its horse) uphill using manual force to turn the wheels, Trevithick and his mentor Davies Gilbert proved that the friction between the wheel rims and the road is sufficient to ensure good road holding.
Construction of Trevithick's first travelling engine began around November 1800 at the Tuckingmill works owned by his brother-in-law John Tyack in Eastern Lane, Camborne. The vehicle was assembled there from components manufactured in various locations, for a total cost of parts of around £70.
The vehicle weighed over 1.5 tonnes and the engine worked at a pressure of 414kN per sq m (60psi). The single cylinder was set vertically in one end of the boiler, with the furnace and chimney at the other end. The internal flue tube was U-shaped to increase the heating surface and the boiler was equipped with a safety valve.
Its first run was at dusk on Christmas Eve 1801, when it was said to travel from the smithy up "Camborne Hill" (Beacon Hill) to the beacon. It's more likely that it completed only the initial part of the journey, along Tehidy Road, as night was falling and it was raining, which tended to cool the boiler.
Nevertheless, it apparently carried some eight people up a slope of 1 in 20, stopping to turn round when the incline was 1 in 15 as it was short of steam. This was the first time that people had travelled under mechanical power in Britain. A wall plaque erected on 19th July 1919 in Tehidy Road commemorates the momentous event.
On Christmas Day Trevithick and Vivian set out again in the first road carriage, this time visiting the Vivian family home at Crane Manor about 1.5km from Tyack's workshop. It was on this successful journey that an elderly lady, Mrs Paul, called the machine a "walking, puffing devil". And the name stuck.
The next trip for the Puffing Devil
was on 28th December 1801 to Tehidy House, some 4km distant, where Trevithick and Vivian were to join Francis Basset (created Baron de Dunstanville in 1796 and Baron Basset in 1797) and his family and guests, Gilbert among them. The carriage never arrived — before a third of the journey was completed, while Trevithick was attending to the engine and Vivian steering, they hit a gully in the road and the Puffing Devil
overturned. It was soon righted by willing onlookers and pushed into the grounds of Knapp's Hotel on Tehidy Road. Writing in 1830, Gilbert described what happened next.
"The Travelling engine was replaced in a building and Trevithick and Vivian and the others determined on supporting their spirits by dining at the inn. They did so and forgot to extinguish the Fire that evaporated the water and then heating the Boiler red hot, communicated fire to the wooden machinery and everything capable of burning was consumed." In a letter of 1839 Gilbert commented further that the "Parties adjourned to the Hotel, & comforted their Hearts with a Roast Goose & proper drinks".
Undeterred by the loss, Trevithick and Vivian decided to patent their ideas and build more mobile engines. Their patent No.2599 granted on 26th March 1802 describes the construction of steam engines to drive carriages and for other purposes.
In a logical development of his early models of 1797, the by now 30-year-old Trevithick envisaged something quite different from the existing stationary engines and the railway locomotives that would follow — an engine that could not only perform various tasks but also could drive under its own power to the place where it was required.
The patent shows three types of engine. The first is a portable high pressure one with a cast iron globe boiler (its underside indented for a fireplace) that may be worked either using an air pump to condense the exhaust steam or as a puffer using a plunger pole to force water into the boiler.
The second is also portable and high pressure but has a wrought iron cylindrical boiler with flat end plates and operates with one or two cylinders. The third is a locomotive engine and carriage for road use, very different from the 1801 engine, having a cylindrical wrought iron boiler and single horizontal cylinder with a split piston rod. It has a crankshaft and flywheel, with gear wheels to increase the power of the cylinder.
Trevithick had found that directing exhaust steam into the chimney, via a 'blast pipe', gave more energy to the fire than blowing on it with bellows, though neither bellows nor blast pipe are detailed in the patent. However, the blast pipe was a feature of subsequent puffer (non-condensing) engines and helped overcome the problem of travelling engines running out of steam.
While Trevithick and Vivian were in London securing their patent, it was recommended to them that a steam-powered road carriage for the city would be profitable. London then had a population of just over a million, with its industrial heartland surrounded by farms and market gardens supplying fresh food. The limiting factor on expansion was the length of time it took to bring perishable foods like milk from outlying areas to the centre. The more quickly foodstuffs could be transported over greater distances, the more the city could grow. Faster travel would also mean better lines of communication for business between London and other towns and cities.
Work began on another road carriage, with the wrought iron boiler, cylinder and cast iron parts made at Harvey & Co, supervised by William West, another of Trevithick's brothers-in-law. It was assembled at the Tuckingmill smithy and road tested in late 1802 or early 1803, apparently observed by future Member of Parliament, Michael Williams. The trials showed that larger wheels would be required to prevent the rims cutting into the road surface or being caught in potholes.
The engine was shipped to London from Falmouth, arriving at William Felton's coach building works at 36 Leather Lane, Holborn in London, in April 1803. Felton made a new carriage capable of carrying up to eight people, which was two more than a standard stagecoach. It had a steerable front wheel moved with a tiller by the driver who sat outside the passenger pod, and two large driving wheels at the rear.
The engine was mounted between the back wheels, just behind the axle and below the coach body, tended by an engineman standing on a step. It was said to be "about the size of an orchestra drum" and weighed some 305kg. The single cylinder was set into the boiler horizontally, with the piston working at 50 strokes per minute.
West stayed in London for five months to oversee the assembly of carriage and engine, with Trevithick and Vivian visiting at intervals while lodging at 1 Southampton Street in the Strand. The total cost of the steam carriage and engine was about £207.
At a trial very early one summer morning, when the streets were clear of horse-drawn vehicles and pedestrians, the carriage travelled along Tottenham Court Road and City Road, through Oxford Street and back to the coach builder. On another occasion, Vivian steered the carriage from Leather Lane along Gray's Inn Lane to Lord's Cricket Ground, on to Paddington and back again by way of Islington — a round trip of some 16km. It ran at a speed of 13-14km/hour on the flat. The London road trials showed up defects in the firebox design. The motion of the carriage tended to shake the fire bars loose and burning coals dropped into the ash pan.
Though the carriage was reportedly seen by "tens of thousands" of spectators during the London trials
, the partnership of Trevithick, Vivian and West received no orders for the new vehicle. With money running out and more interest being shown in Trevithick's other engines, the steam carriage was abandoned. The coach body was sold and the engine transferred to a hoop iron rolling mill, where it worked for many years as a stationary engine.
Trevithick had invented two different engines that signalled the beginnings of the rail locomotive and modern motor vehicles. He would go on to make more locomotives but his ideas for travelling engines were ultimately to prove way ahead of the times.
portrait of Richard Trevithick Institution of Civil Engineers