Editing Stephenson's Rocket (section)

== Design ==
[[file:Rocket Verkehrsmuseum Nuernberg 12092010 side view.JPG|thumb|Replica of the ''Rocket'' in its original condition in the [[Nuremberg Transport Museum|Transport Museum]] in [[Nuremberg]] during the exhibition "Adler, Rocket and Co."]]
[[file:Stephenson's Rocket -- colour side elevation drawing (NRM UK SSPL 10301005).tif|thumb|Side elevation of ''Rocket''{{spaces|hair}}]]

The locomotive had a tall 16&nbsp;ft smokestack chimney at the front, a cylindrical boiler in the middle, and a separate [[firebox (steam engine)|firebox]] at the rear.
The large front pair of wooden wheels was driven by two external cylinders set at an angle of 38°. The smaller rear wheels were not coupled to the driving wheels, giving an 0-2-2 [[wheel arrangement]].<ref name="Burton"/> One of the cylinders drove a small 1.25 inch diameter feedwater pump which pumped water from the tender to the boiler, a valve could be adjusted to control the amount of water needed.

=== Driving wheels ===

Stephenson's most visible decision was to use a single pair of driving wheels, with a small carrying axle behind. This was the first [[0-2-2]] and first single driver locomotive.{{efn|Although ''[[Novelty (locomotive)|Novelty]]'' would also bring a 0-2-2 arrangement to Rainhill}}{{sfnp|Snell|1973|p=60}} The use of single drivers gave several advantages. The weight of [[coupling rods]] was avoided and the second axle could be smaller and lightweight, as it only carried a small portion of the weight. ''Rocket'' placed just over {{frac|2|1|2}}&nbsp;tons of its {{frac|4|1|2}}&nbsp;ton total weight onto its driving wheels,<ref>{{cite book|last1=Bailey|first1=Michael R.|last2=Glithero|first2=John P.|title=The Engineering and History of Rocket: A Survey Report|year=2000|publisher=[[Science Museum (London)|Science Museum]] |location=London|isbn=1-900-747-18-9|page=17}}</ref> a higher axle load than ''[[Sans Pareil]]'', even though the [[0-4-0]] was heavier overall at 5&nbsp;ton, and officially disqualified by being over the {{frac|4|1|2}}&nbsp;ton limit.{{sfnp|Snell|1973|p=60}} Early locomotive designers had been concerned that the adhesion of a locomotive's driving wheels would be inadequate, but Stephenson's past experience convinced him that this would not be a problem, particularly with the light trains of the trials contest.

=== Boiler ===
''Rocket'' uses a multi-tubular boiler design. Previous locomotive boilers consisted of a single pipe surrounded by water (though the ''[[Lancashire Witch]]'' did have twin flues). ''Rocket'' had 25 copper{{sfnp|Snell|1973|p=84}} fire-tubes that carried the hot exhaust gas from the firebox, through the wet boiler to the blast pipe and chimney.  This arrangement resulted in a greatly increased surface contact area of hot pipe with boiler water when compared to a [[flued boiler|single large flue]]. Additionally, radiant heating from the enlarged separate firebox helped deliver a further increase in steaming and hence boiler efficiency.

The original innovator of multiple fire-tubes is unclear, between Stephenson and [[Marc Seguin]]. It is known that Seguin visited Stephenson to observe [[Locomotion No 1|''Locomotion'']] and that he also built two multi-tubular locomotives of his own design for the [[Saint-Étienne–Lyon railway]] before ''Rocket''. ''Rocket''{{'}}s boiler was of the more highly developed form, with the separate firebox and a blastpipe for draught, rather than Seguin's cumbersome fans, but ''Rocket'' was not the first multi-tubular boiler, although it remains unclear just whose invention it was.

The benefits of increasing the fire-tube area had also been attempted with [[John Ericsson|Ericsson]] and [[John Braithwaite (engineer)|Braithwaite]]'s ''[[Novelty (locomotive)|Novelty]]'' at Rainhill. Their design though used a single fire-tube, folded in three. This offered an increased surface area, but only at the cost of a proportionately increased length and so poor draught on the fire. Its arrangement also made tube cleaning impractical.

The advantages of the multiple-tube boiler were quickly recognised, even for heavy, slow freight locomotives. By 1830, Stephenson's past employee [[Timothy Hackworth]] had re-designed his [[return-flue boiler|return-flued]] [[Royal George (locomotive)|''Royal George'']] as the return-tubed ''Wilberforce'' class.{{sfnp|Snell|1973|pp=55–56}}

=== Blastpipe ===

''Rocket'' also used a [[blastpipe]], feeding the exhaust steam from the cylinders into the base of the chimney so as to induce a partial vacuum and pull air through the fire. Credit for the invention of the blastpipe is disputed, though Stephenson used it as early as 1814.<ref>{{citation|first=Samuel|last=Smiles|title=The lives of the engineers|volume=3|origyear=1862|date=2010|chapter=ch 5|publisher=BoD – Books on Demand |isbn=9783867412681 |chapter-url=https://books.google.com/books?id=V7rVmJMYQkoC&pg=PP5}}</ref> The blastpipe worked well on the multi-tube boiler of ''Rocket'' but on earlier designs with a single flue through the boiler it had created so much suction that it tended to rip the top off the fire and throw burning cinders out of the chimney, vastly increasing the fuel consumption.<ref name="Burton">{{cite book|author=Burton, Anthony|year=1980|title=The Rainhill Story|publisher=BBC|isbn=0-563-17841-8}}</ref>

=== Cylinders and pistons ===
[[file:Rocket Cylinder.jpg|thumb|A cutaway view of the cylinder and steam valve of the replica Rocket]]

Like the ''Lancashire Witch'', ''Rocket'' had two cylinders set at angle from the horizontal, with the pistons driving a pair of {{convert|4|ft|8.5|in|m}} diameter wheels.<ref>{{citation|first=Michael|last=Bailey|title=The Engineering and History of "Rocket": A Survey Report|year=2000|publisher=National Railway Museum |isbn=9781900747189 |url=https://books.google.com/books?id=hFobmfrIKy0C}}</ref> Most previous designs had the cylinders positioned vertically, which gave the engines an uneven swaying motion as they progressed along the track. Subsequently, ''Rocket'' was modified so that the cylinders were set close to horizontal, a layout that influenced nearly all designs that followed.

Again like the ''Lancashire Witch'', the pistons were connected directly to the driving wheels, an arrangement which is found in subsequent steam locomotives.<ref name=RainhillTrials/>

=== Firebox ===

The firebox was separate from the boiler and was double walled, with a water jacket between them. Stephenson recognised that the hottest part of the boiler, and thus the most effective for evaporating water, was that surrounding the fire itself. This firebox was heated by [[thermal radiation|radiant heat]] from the glowing [[coke (fuel)|coke]], not just [[convection]] from the hot exhaust gas.

Locomotives of ''Rocket''{{'}}s era were fired by [[coke (fuel)|coke]] rather than coal. Local landowners were already familiar with the dark clouds of smoke from coal-fired stationary engines and had imposed regulations on most new railways that locomotives would 'consume their own smoke'.{{sfnp|Snell|1973|p=59}} The smoke from a burning coke fire was much cleaner than that from coal. It was not until 30 years later and the development of the long firebox and [[Firebox (steam engine)#Brick arch|brick arch]] that locomotives would be effectively able to burn coal directly.

''Rocket''{{'}}s first firebox was of copper sheet and of a somewhat rectangular shape from the side.<ref>Richard,&nbsp;Gibbon.&nbsp;Stephenson's Rocket Manual: 1829 Onwards.&nbsp;United Kingdom,&nbsp;Haynes Publishing UK,&nbsp;2016.</ref> The throatplate was of firebrick, possibly the backhead too.{{sfnp|Snell|1973|p=61}} When rebuilt around 1831,{{sfnp|Snell|1973|p=61}} this was replaced by a [[wrought iron]] backhead and throatplate, with a drum wrapper (now missing), presumed to be of copper, between them. This gave a larger internal volume and encouraged better combustion within the firebox, rather than inside the tubes. These early fireboxes formed a separate water space from the boiler drum and were connected by prominent external copper pipes.