The Planet and Samson Locomotives: Their Design and Development

By Anthony Dawson

Robert Stephenson’s Planet class locomotive was the first true design of mainline express passenger locomotive. Delivered less than a year after Rocket it was one of the most successful early locomotive designs. Planet set the mold for British locomotive design for more than the next century featuring a multi tubular boiler; inside cylinders; crank axle; and the first use of proper frames.

The Planet class, and its 0-4-0 Samson derivative, found use across Britain with examples being supplied to railways in London and Glasgow. The Planet class proved popular in Europe too with examples being first exported and then built in France. Two were exported to Austria, and the first locomotive to steam in Russia was based on the design. Planet and Samson also crossed the Atlantic with more examples being built in the United States than in Europe.

A working replica of the revolutionary design was built in Manchester in 1992: the first mainline express passenger steam locomotive to be built in Britain since the 1960s.

This book outlines the technical design of the Planet and Samson locomotive, and charts the careers of the class members at home and abroad.

• Language: English
• Publisher: Pen and Sword
• Release date: Aug 17, 2023
• ISBN: 9781399092654

Anthony Dawson

Anthony Dawson is an archaeologist and historian who has made a special study of the history of the British army in the nineteenth century. He spent two years as a post-graduate research student at the University of Leeds where he gained an MRes. As well as writing articles on the subject in magazines and journals, he has published Napoleonic Artillery, French Infantry of the Crimean War and Letters from the Light Brigade: The British Cavalry in the Crimean War.

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INTRODUCTION

Concept and Design

Robert Stephenson’s Planet and subsequent Samson class of locomotives were the first main line express passenger and goods locomotives, representing a step change in locomotive design that was both revolutionary and evolutionary. The Planet design is categorised through a 2-2-0 wheel arrangement; the use of inside cylinders; crank axle; and outside ‘sandwich’ frames. It was a popular and successful design. As Dr Michael Bailey has stated, the delivery of Planet in October 1830 was the culmination of:

‘An extraordinary period of research and development by Robert Stephenson and his close colleagues in the 33 months between January 1828 and September 1830.’¹

Planet represents the first ‘modern’ locomotive, and incorporated design features that would become standard on locomotives for the next 130 years.² These included the use of:

•A boiler with an inner firebox as part of the boiler shell.

•A proper smokebox containing a blast pipe.

•A steam dome, steam riser, and internal steam pipe.

•Cylinders set low down at the front of the locomotive, working a cranked driving axle.

•The use of a proper frame.

•The use of leaf springs, horns, and horn guides.

The origin of the Planet design goes back to December 1827, when Robert Stephenson returned from South America. In a letter to Michael Longridge he wrote that:

‘since I came down from London I have been talking a great deal to my father about endeavouring to reduce the size and ugliness of our locomotive engines, by applying the engine either side of the boiler, or beneath it entirely somewhat similarly to Gurney’s steam coach [author’s emphasis].’³

Goldsworthy Gurney (1793–1875) was a London-based engineer and inventor who had essayed a series of steam road coaches. In 1826 he had established a steam carriage manufactory, and planned to operate a series of steam road coaches between London, Bristol and Bath. Gurney had obtained three different patents for his steam road coaches (1825, 1827 and 1829). It was his design of 1827 that contained the germ for the idea of the layout of Planet; in fact, the basic design of the two are virtually identical. In this design Gurney utilised horizontal cylinders mounted at the front of the carriage that drove a crank axle at the rear. The whole was supported on a strong wooden frame reinforced with wrought iron. The slide valves were operated using a form of gab valve gear. There were two fixed eccentrics, the eccentric rods terminating in an X-gab that could be raised or lowered from pins on a rocking shaft that worked the valve spindles. This meant the engine could be reversed easily using a single lever. Unusually, Stephenson did not emulate this form of valve gear on Planet, preferring a version based on that used on Rocket.

Robert Stephenson, the ‘Mozart of Railways’, was only twenty when appointed managing director of Robert Stephenson & Co., and had only just turned twenty-six when Rocket won the Rainhill Trials.

Gurney’s 1829 ‘steam Drag’ was a light four-wheel vehicle with a pair of small, steerable, leading wheels and large-diameter driving wheels at the rear. Instead of carrying passengers on board, the ‘steam Drag’ was a road locomotive, hauling a conventional road coach behind; the Duke of Wellington’s carriage was hauled around the yard of Hounslow Cavalry Barracks on 12 August 1829 in such a manner. These road locomotives were also adapted to rail use and two were tried on the Hirwaun plateway in South Wales in March 1830. They were fitted with iron wheels and their light weight mitigated against damaging the brittle cast-iron track, but ultimately proved to be of little use, ‘rearing up like restive horses’ from the weight hitched behind.⁴

Elevation and plan of Goldsworthy Gurney’s ‘Steam Drag’, the design of which was the inspiration for the layout of Planet.

The Design Team

Planet was on the drawing board in July 1830, showing that Stephenson and his team at Forth Street were putting ideas on paper at the same time that Northumbrian was being constructed. In addition to Stephenson, the management team included Harris Dickinson and William Hutchinson (1792–1883) the works manager, who was appointed to that position at the end of 1825. In fact, three brothers Hutchinson were employed at Forth Street: Ralph Hutchinson, who was a fitter, and Edward, who later moved to Liverpool to work on other early railway projects. Ralph assisted in the construction of Rocket and was ‘invested with the management of it’ at the Rainhill Trials, assisted by Mark Wakefield (an apprentice at Robert Stephenson & Co.) and Robert Hope, who acted as fireman. Alexander Fyfe (1790–1848) was described in his obituary as ‘chief designer and draughtsman’ at Robert Stephenson & Co., and ‘made all the improvements in Stephenson’s time’, which also included taking on a leading technical role in the design of Planet. He later found employment as one of two locomotive foremen on the Liverpool & Manchester Railway. The ‘very capable’ George Phipps (1807–1888) was, from May 1828, employed as a draughtsman. In old age he recalled drawing out Rocket, full size, on the works floor in chalk and assisting in her design, suggesting he may have had a similar involvement with Planet. Indeed, Phipps supplied a drawing of Planet for inclusion in the 1831 edition of Nicholas Wood’s Treatise on Railroads. This triumvirate of Stephenson, Phipps and Hutchinson quickly became a close-knit team that made rapid progress in locomotive development.

Original working drawing for Planet, dated July 1830, showing the germ of the idea of the Planet class. Curiously, the stated scale and written dimensions don’t agree: the driving wheels being scaled at 6ft diameter, but dimensioned as 5ft. (SSPL)

One of the crucial factors for locomotive development after the Rainhill Trials of October 1829 was that there were long stretches of the Liverpool & Manchester Railway main line upon which designs could be tested. Robert Stephenson & Co. had no test facilities of its own, which meant running-in and performance trials could only be carried out once a particular locomotive had been delivered. Each locomotive manufactured and sold was in effect a dynamic prototype, with Robert Stephenson & Co. remaining in close contact with the customer in order to learn about the performance of each locomotive and each component thereof. This meant between January and October 1830, the period between the delivery of the first of Rocket’s sisters and Planet, that locomotive development progressed rapidly thanks to the ability to test locomotives over long distances and at various speeds and loads on the L&M. Data collected by the group of ‘Resident Engineers’ – both of them Stephenson men – John Dixon and William Allcard was relayed to Stephenson and his design team in Newcastle, a process that continued after the delivery of Planet in October 1830 to assess long-term reliability and component performance, with many lessons regarding fireboxes, boiler tubes, wheels and axles being learned on the way, albeit sadly as the result of nasty accidents.

In order to adopt a layout ‘similar to Gurney’s steam coach’, Stephenson and his team had to redesign the locomotive. Earlier locomotives had either vertical or inclined cylinders driving to outside crank pins. Frames and bearings were inside the wheels, and often somewhat flimsy. The Forth Street team took their own experience of locomotives and married it to the successful layout of Gurney, who used inside, horizontal cylinders at the front end; a crank axle toward the rear; and a substantial outside wooden frame.

Frames

A locomotive’s frame fulfils several functions. It is the main structural component to which other elements (boiler, horn guides, springs) are attached; it distributes the weight of these components; it contains and transmits the train load. The frames also keep the locomotive all ‘of a piece’ when traversing curves in the track.

The initial concept drawing (ROB3/2/22) dated July 1830 for Planet shows a very unusual-looking locomotive indeed, with the main frame carried beneath the driving axle and above the leading axle – but this did not prevent Clement Stretton from stating Planet was indeed built thusly. The drawing itself is curious as the scaled dimensions don’t agree with those written on the drawing: driving wheels are drawn with a scale of 6ft but dimensioned as 5ft. The leading wheels are 2ft 6ins with the driving axle springs carried beneath the frame and those for the leading wheels above. The cylinders are mounted horizontally, level with the top of the frame, meaning that the boiler is necessarily high pitched to accommodate the crank throws. This concept drawing shows the cross-heads guided and supported by elongated wrought-iron slide bars similar to those used by Gurney on his steam drag. The four slide bars are shown as being supported from the piston rod glands, probably a very weak arrangement, hence no doubt the adoption of four inside frames, which not only carried the slide bars but also provided additional support for the crank axle. A second, albeit undated, drawing shows a more familiar form of Planet with the frame carried above both axles and a lower-pitched boiler the cylinders being carried level with the top of the frame.

Undated General Arrangement drawing for Planet, ‘No. 10 L’Pool Locomotive. Mr Stephenson’s, combining all the basic features of the Planet design. (After Warren, 1923)

General arrangement drawings for Planet-type locomotives supplied by Robert Stephenson & Co. to Fenton, Murray & Jackson of Leeds, clearly showing the outside ‘Sandwich Frame’ and four inner frames between the firebox and cylinders. (After Warren, 1923)

Hitherto Stephenson locomotives had used wrought-iron bar frames, formed from wrought-iron bars forge welded together. The frame of Planet was a departure from this tradition and was probably inspired by the Gurney steam drag. Planet utilised a wooden outside frame that carried outside bearings for the driving and carrying wheels. In order to support the crank axle, an internal frame was provided, strongly reminiscent of Gurney practice. Here, Gurney supported the crank axle on either side of the crank throw; on Gurney’s steam drag this meant there were three points of support, while on Stephenson’s Planet there were six. These four internal frame members also supported the slide bars. While this provided maximum support for the crank axle, it would also have increased the rolling friction of the crank axle as with the technology of the time it would have been difficult to perfectly align all six bearings.

Boiler

The boiler design was an evolutionary part of the Planet concept, and it copied that already successfully used by Northumbrian and Majestic. Northumbrian had been delivered with the prototype of the first ‘modern’ locomotive boiler. It incorporated the firebox within the boiler barrel at one end, and a proper smokebox at the opposite end. The boiler had a steam dome and steam riser to help prevent priming and an internal steam pipe to improve thermal efficiency. The boiler for Planet was specified to be the same as that of Northumbrian but ‘only 3ft diameter and 6ft 6ins long … Plate to be ordered ¼ thick stiff’.⁵

Due to the increasing cost of copper, fireboxes were initially made from iron but this was found to wear out rapidly. Boiler tubes were copper but they too wore out rapidly due to the scouring effect of abrasive coke particles. Similarly, there were also problems with water circulation due to too many tubes being crammed into the boiler, a problem not helped due to using dirty feed water, which led to the deposition of sludge and scale that caused tubes to overheat.

At the front of the boiler was a proper, air-tight, smokebox containing a blast pipe; this was very long and reached into the base of the chimney. Access was gained through unbolting a large oval plate: heavy and cumbersome (a two-man lift) but this was the only means of ensuring that the smokebox was airtight to maintain a good vacuum to help the fire draw.

Cylinders

Although Richard Trevithick’s locomotives had used horizontal cylinders, the fear that the weight of a piston in a horizontal cylinder would wear it oval led to the use of vertical cylinders by early locomotive designers. From Blenkinsop and Murray onwards, vertical cylinders were preferred, which often necessitated the use of a geared or indirect drive between the piston rod and the wheels. The first locomotive to use direct drive was Timothy Hackworth’s Royal George, albeit with vertical, inverted, cylinders. The first Stephenson locomotive with direct drive was Lancashire Witch. Crucially, she used inclined cylinders: this meant that both axles could be sprung. Vertical cylinders meant springing of the driven wheels was difficult as any springs would absorb most of the thrust of the piston. Furthermore, the cylinders would have to have a larger swept area than usual to accommodate the vertical movement of the cylinder. Finally, vertical cylinders damaged the track through a phenomenon known as ‘hammer blow’, something mitigated through using inclined cylinders. The cylinders of Lancashire Witch and indeed Rocket were inclined at 39 degrees, but they became progressively lower to an almost horizontal position with Northumbrian. Moving the cylinders to a truly horizontal position, as utilised by Gurney in his steam road coaches, was a logical step. Adopting inside cylinders meant that the thrust of the pistons was closer to the locomotive’s centreline, which would help reduce a phenomenon known as ‘hunting’ where the piston thrust would shift the locomotive from one side of the rail to the other on each stroke, and thus reduce damage to the track and wheels and produce a smoother ride. Furthermore, horizontal cylinders with the piston rod aligned with the crank axle also reduced mechanical losses, making the locomotive more efficient with less power going to waste. Thus, Planet’s general arrangement with horizontal inside cylinders would have made the locomotive far more stable, powerful, and kinder to the track than locomotives hitherto. In coming to this conclusion, there had been:

‘Repeated conversations … between Mr Stephenson … Mr Hutchinson, and [Phipps] with respect to the saving of fuel that would be affected by placing the cylinders within the smokebox; they also had the desire to fix the cylinders in a horizontal position … [so] that the vertical motion of the springs should be eliminated from the cylinders, and this naturally led to the horizontal arrangement.’⁶

One contemporary newspaper, the Manchester Guardian, concluded that:

‘Mr Stephenson … determined to try the effect of placing the cylinders beneath the boiler, and communicate the power to the wheels by means of two cranks in the axle … This plan was reduced to practice in the construction of the Planet, and its consequences were immediately apparent in the steadiness of motion, and the very great working power of that engine … We believe it was estimated that her effective power was nearly one-third greater than that of other engines of equal size, but made on the old principle.’⁷

By placing the cylinders beneath the smokebox, Stephenson also increased their thermal efficiency, helping to reduce the formation of condensation by keeping them warm.

Crank Axle

The use of a cranked driving axle was not new in 1830; earlier road coaches, such as that of Trevithick, had used them. George Stephenson had proposed using a cranked axle and coupling rods on his patent locomotive of 1815; Braithwaite & Ericsson’s Novelty (1829) had a cranked driving axle, so too William IV and Queen Adelaide (1830), although in each case they used vertical cylinders. The very public success of the Gurney steam drag probably inspired more than just Robert Stephenson to be attracted to its general arrangement as both Edward Bury (1794–1858) and his partner James Kennedy (1797–1886), and Timothy Hackworth (1786–1850), built locomotives almost contemporaneously with Planet. This, however, led to subsequent controversy over which of these engineers had the idea first and was the first to put it into practice. In fact, a bitter James Kennedy accused Robert Stephenson of stealing the idea from himself:

‘The late Mr George Stephenson had told both Mr Bury and Mr Kennedy, after having seen the Liverpool engine … that his son, the present Robert Stephenson, had taken a fancy to the plan of the Liverpool engine, and intended to make, immediately, a small engine on the same principle.’⁸

In countering this claim, Robert Stephenson replied:

‘Planet … had been made … and constructed under my direction, without any reference or knowledge of the Liverpool … Neither was there any analogy between the two machines, for the Planet had a multi-tubular boiler, the fire being urged by a blast-pipe, and the cylinders, which were nearly as horizontal as their position would permit, were fixed between the frames … with the cylinders in the smoke box a cranked axle was indispensable, and there was not anything new in its use in locomotives.’⁹

Timothy Hackworth also utilised a crank axle in his 0-4-0 Globe, the layout of which was the opposite of Planet: near-horizontal cylinders were carried at the firebox end of the boiler with the crank axle at the leading end, the wheels being coupled with outside rods. Globe did not use a multi-tubular boiler and instead used a single large-diameter flue tube with water-filled cross-tubes arranged in a spiral formation. However, they soon furred up due to sediment in the water and were impossible to clean out. Lacking capacity of his own, Globe was ordered at Stephenson’s Forth Street works in March 1830; the Stockton & Darlington ‘finding the wheels, axles … and boiler plates for the body of the boiler.’ Due to pressure on the Stephenson team, Globe was not delivered until 4 October 1830, a month after Planet. While Globe was a one-off, her general layout was apparently influential in the United States, with locomotives built by the West Point Foundry Association such as the West Point and others sharing the same basic layout.

Timothy Hackworth’s headed notepaper depicting his Globe of 1830, which used a crank axle and inside cylinders, albeit reversed from Stephenson’s Planet. It also used a cross-tube boiler. (After Young, 1923) Bury & Kennedy’s Liverpool was probably the first