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Great Western Railway No. 111 “The Great Bear”
Great Britain | 1908 | only one produced
Railway and Locomotive Engineering, April 1908

Although the GWR had concentrated on the 4-6-0 wheel arrangement for high-value traffic since the turn of the century and the Star class seemed to be sufficient for express traffic for a long time, George Jackson Churchward designed a Pacific locomotive. One can only speculate about the reason for the development of “The Great Bear”, whether the largest locomotive in Great Britain was to be built simply for advertising purposes or Churchward personally had the construction carried out in order to be able to carry out tests with a particularly large boiler.

For the first time in Great Britain, the choice of wheel arrangement fell on the 4-6-2 (Pacific) in order to be able to accommodate a wide firebox over the trailing axle. At 23 feet, the boiler barrel reached an extreme length that was hardly reached by other locomotives later on. At 15 inches, the diameter of the four cylinders was chosen so large that it was just possible to maintain the loading gauge and allow the bogie to move freely. The outer cylinders were at the level of the rear axle of the bogie and drove the second coupled axle, while the inner cylinders were at the level of the bogie pivot and drove the first coupled axle

Schematic drawing with dimensions
Schematic drawing with dimensions
Locomotive Magazine, February 1908

The number 111 was the largest steam locomotive in Great Britain at the time and, despite the sixth axle, achieved an axle load of 20.8 tons. At the time, the only GWR route capable of handling such heavy loads was the Great Western Main Line from London-Paddington to Bristol. Despite the very limited usability, the one-off had great value for the public perception of the GWR.

From a technical point of view, however, the locomotive was anything but a success because the evaporation capacity was limited. This can be attributed to the fact that the heating surface of the firebox was very small compared to the heating surface of the smoke tubes. Here the tube heating area was 18 times the firebox heating area, while this ratio was in the 11 to 13 range for most Pacifics. Thus, relatively little direct radiant heat could be absorbed by the firebox, while the smoke tubes, which were too long, were inherently problematic and had more surface area than would have been necessary to absorb the heat from the smoke. For this reason, brick archescombustion chambers or thermosiphons were built into the combustion chambers elsewhere to increase the direct heating area.

The “The Great Bear” remained in service, but suddenly lost importance in 1923 with the introduction of the more powerful Castle class. A year later it was decommissioned. As late as September 1924 some parts of the locomotive were used in the manufacture of a Castle class example. This also got the number plate of 111, but was given the name “Viscount Churchill”.

General
Built1908
ManufacturerSwindon
Axle config4-6-2 (Pacific) 
Gauge4 ft 8 1/2 in (Standard gauge)
Dimensions and Weights
Length71 ft 2 in
Wheelbase34 ft 6 in
Fixed wheelbase14 ft
Total wheelbase61 ft 0 1/2 in
Service weight217,840 lbs
Adhesive weight137,424 lbs
Total weight320,320 lbs
Axle load45,808 lbs
Water capacity4,203 us gal
Fuel capacity13,440 lbs (coal)
Power
Power sourcesteam
Estimated power1,700 hp (1,268 kW)
Optimal speed39 mph
Starting effort27,797 lbf
Power Plant
Driver diameter80.5 in
Boiler pressure225 psi
Expansion typesimple
Cylindersfour, 15 x 26 in
Boiler
Grate area41.8 sq ft
Firebox area158.2 sq ft
Tube heating area2,676.8 sq ft
Evaporative heating area2,835 sq ft
Superheater area545 sq ft
Total heating area3,380 sq ft
Calculated Values
steam locomotive
express
George Jackson Churchward
last changed: 06/2022
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