The Engineering and History of Robert Stephenson's Rocket
by Michael Bailey and John P Glithero
12 March 2001
Michael started the talk by pointing out that Rocket
has been tucked away in museum since 1862. Until the recent work there
was little understanding about the detail of the loco's construction and
engineering history. The Science Museum and NRM invited them to
investigate Rocket - both a tremendous honour and great fun!
Why them? At the Museum of Science and Industry at
Manchester, they headed up the project for the Friends of the Museum to
build the Planet Replica. Following this, they were invited to Nova
Scotia to examine two ancient engines, Samson - a Hackworth design of
1838 and Albion dating from the1850s. The task was to put these into
good order for display. As a result of their investigations, the museum
undertook the restoration and conservation of both engines.
On return to the UK they gave a talk at the NRM on
their work and pointed to Braddyll at the Timothy Hackworth Museum. It
was then in a very delapidated condition, near to being put on the scrap
heap. The loco had been outside since 1875, even being used as a
snowplough for a while. Dame Margaret Weston was at the talk and
invited them to examine the engine and advise on a conservation project.
After submitting their report they were invited to undertake the
restoration. Braddyll is now displayed inside the Soho shed at Shildon
in a colour scheme which has been carefully matched from the paint
remains on the engine. A talk on the project was given at the NRM and so
came the Rocket project.
The opportunity for the investigation arose because
of a two year project to rebuild the transport gallery at the Science
Museum. Rocket had to be removed and, as a consequence, was scheduled
to spend one year in Japan, and another at the NRM in York. It was
during its latter sojourn when the investigation was organised.
Before discussing the investigation, it is worth
putting Rocket into its historical context. George Stephenson's
Locomotion was slow, cumbersome but did the job of hauling coal and
minerals. The requirements of the Liverpool and Manchester Railway were
very different , requiring higher speeds and reliability. The
Stephensons had to get to grips with a radical new engine design, but
the necessary R&D only started when Robert returned for South
America in 1827. Lancashire Witch was the first results of these
experiments, incorporating the novel idea of sprung driving wheels and
inclined cylinders. However he went back to wooden wheels because the
available cast iron was too fragile. Rocket followed on and was
designed to meet the stringent trial requirements which included targets
for haulage and speed. The required speed of 12mph was greatly
exceeded; indeed it reached 36mph after the formal trials. Such was the
pace of locomotive development, however, that Rocket was out of date
almost as soon as the trials were finished. Northumbria, an improved
development of Rocket, was produced for the opening of the LMR in Spring
1830, with the Planet class emerging from the Stephenson's factory
later that year.
It was built in Robert Stephenson's factory at
Newcastle and sent to Liverpool by ship from Carlisle. After the trials
Rocket was extremely popular with the public clamouring for what we
would now call "special" trips. However, its working life was
interrupted by accidents - the first, of course, being the well-known
death of William Huskisson, the MP for Liverpool, during the opening
celebrations. The second accident involved a "footplating" railway
enthusiast , who fell off the tender following an axle break while
Rocket was propelling its train. Rocket was repaired and an opportunity
was taken to fit some improvements including a smokebox. Rocket was
then put on passenger service - after the opening celebrations it had
been relegated to engineering works. Shortly after, Rocket had another
accident in Olive Mount cutting, breaking its driving axle. Further
improvements were then made. A third accident followed while it was on
load to the Wigan branch in 1832, Rocket hitting a loco owned by another
company (this was 150 years before TOCs and Railtrack!).
Rocket was then used in experiments, before being
sold to the Earl of Carlisle for use in connection with his Westmorland
coal mines at Kirkhouse. It only worked here until 1840, when it was put
into store, during which time a lot of its non-ferrous parts were
removed. An abortive plan to restore the loco for the Great Exhibition
was followed by its transfer to the Patent Museum - the predecessor to
the Science Museum.
John then took up the story of the physical
investigation of Rocket. These took place in the main hall of the NRM.
The sessions were organised for each Monday. During the rest of the
week, Michael went round many archives to seek out original
documentation, while John wrote up the results of the investigation.
During the Monday sessions they felt that they were the main displays at
York, fielding many questions from visitors.
Most of the measurements were made with traditional
instruments, rules etc., however a novel technique was devised using
dentists putty for the measurement of the screw threads of the bolts
used on the engine.
The wrought iron bar frame are 1inch thick and,
like many other components, have many redundant holes. Invicta of the
Canterbury & Whitstable Railway provided an extant model of how
the original 38o inclined cylinders of Rocket were fitted to the boiler and frames. When those on Rocket were moved down to 8o,
a buffer was inserted at the front, possibly in an attempt to
strengthen the frames following the Olive Mount accidents. A major
change was necessary to mount the cylinders, via a new sub-frame.
Additional buffers for the Earl of Carlisle were also needed to cope
with the cauldron wagons. A rough shunt during its time at Kirkhouse
was probably the cause of the bend at the front of the frame. There is
also a bend at the footplate end caused by interaction with the tender.
The original firebox disappeared while the engine
was in store at Kirkhouse. This had a jacketed cover in a horseshoe
shape. The backplate was modified to be jacketed probably following one
of the earlier accidents. They exact form of the firebox was not known,
several inaccurate drawings misleading earlier investigators. There is a
footprint on the back of the boiler and there are also clues given by
the water level - which had been raised at some time. Sight glass and
try-cock holes were blocked off, with new ones introduced, illustrating
the raised water level. Originally the level was not much lower than the
regulator so, in the absence of a steam-collecting dome, priming was
likely; a dome was not fitted until November 1830. The early diagrams
misleadingly seem to show a dome, which is now believed to be the front
The wheels now fitted are wooden wagon wheels,
typical of the time. There is a cast iron crank boss and the wheels are
secured to the axle by four keys, using traditional wheelwrights
techniques. There are cracks in the spokes which have been secured with a
reinforcing collar. The current axle, at 4 ins diameter, is not
original - this was only 3½ inch.
The valve gear is a form of slip eccentric and
predates Stephenson's link by 10 years. The driving dogs are attached to
the axle by pinch bolts. The gear shows several fitting marks put on at
different times. One set, comprising a series of dots, can be dated to
the 1862 restoration - this is because it has been assembled
The frame is by no means a precision assembly, being some 5/8
inch out of true. This shows the lack of standardisation in engineering
at the time. The firebox saddle footprint, in the form of holes on the
frame and tube plate, shows that it was also out of true, sticking out
by some 1 inch and twisted. This was because the manufacturers were not
used to working with copper plate of the thickness required to
withstand the boiler pressure. The erection fitters just had to accept
the lean and work round the conflict with the cylinder mounting. The
holes for steam entry into the boiler backplate are also asymmetric. It
also meant that the spacing block feet, which fit the cylinders to the
boiler, also had to be individually fitted to ensure the pistons are
aligned with the wheels. However on the current Rocket exhibit this
alignment is well out of true, especially on the right hand side. This
misalignment comes from the 1860s reassembly when the engine arrived at
the Patent Museum.
A deep groove in the axle was caused by the pinch
bolts of the slip eccentric, probably originating during the move from
Kirkhouse to Newcastle when it was hauled by a locomotive.
In 1862 the engine was in a poor state of repair
and the Patent Office Museum asked the Stephenson Works to undertake
some restoration. While they managed to get the engine into a
presentable form, they also put on some ridiculous additions, e.g. the
chimney with petal top, the steam exhaust, a replica tin firebox. The
Science Museum curator in 1936 stripped away many of these modifications
but added an inappropriate set of trailing wheels and another wrong
chimney! More seriously, he discarded the original supplementary buffers
fitted for its Kirkhouse days.
The result of all these investigations has allowed
Michael and John to produce a diagram showing how Rocket looked when it
was first made. Just to show how short a time Rocket remained in this
state was illustrated by a report to the owners before the Rainhill
trials. The rear trailing wheels had disappeared from the ship when it
arrived at Liverpool so a wagon wheel set of 2ft 8½ inch were
fitted instead of its original 2ft 6 inch. Rocket consequently went
through the trials - and won - with a distinct forward lean!
A report detailing the investigation is available as an NRM publication.
How accurate are the existing replica Rockets?
- Three replicas followed the first "Henry Ford" replica. The current
replica at the NRM has the wrong firebox, wheels and dome. But in
general they are all pretty good representations of the original.
Are the original drawings available? - None
are known. Stephenson employed a draughtsman to make assembly drawings.
But all of these have disappeared over the last century and a half.
How did the maintenance crew clean the boiler tubes? - With difficulty! This was probably part of reason for retrofitting a smokebox.
Is there any evidence of the early experiments made on Rocket? - A blanked off hole at the top of the tube plate seems to be evidence of the experiment of a rotary engine.
Was any allowance made for the expansion of the boiler as it was heated?
- No expansion joints were fitted to allow for temperature or pressure
changes but since the temperature and pressure was not very high, it is
likely that there were no serious problems.
Was any brakegear fitted to the engine? - No
brakes were fitted but the valve-gear eccentric cluster could be moved
into reverse while the engine was in forward motion and so produce a
counter pressure brake. In September 1830 the Directors travelled to
Manchester and on the return a report says that the train was stopped in
70yds for one of the directors to attend to a call of nature! This
shows that braking didn't appear to be too much of a problem.