GWR 111 The Great Bear

The Great Bear
Official picture of the GWR 4-6-2 No.111 The Great Bear in 1908.
Type and origin Power type Steam Designer G.J. Churchward Builder GWR, Swindon Works Order number Lot 171 Serial number 2279 Build date February 1908 Total produced 1 Rebuilder GWR, Swindon Rebuild date 7 January 1924 Number rebuilt 1
Specifications Configuration: ​  • Whyte 4-6-2  • UIC 2'C1'h4 Gauge 4 ft 8 1⁄2 in (1,435 mm) standard gauge Leading dia. 3 ft 2 in (0.965 m) Driver dia. 6 ft 8.5 in (2.045 m) Trailing dia. 3 ft 8 in (1.118 m) Wheelbase 34 ft 6 in (10.52 m) Length 71 ft 2.025 in (21.69 m) Axle load 20 long tons (20 t; 22 short tons) Adhesive weight 60 long tons (61 t; 67 short tons) Loco weight 97 long tons (99 t; 109 short tons) Tender weight 45.75 long tons (46.48 t; 51.24 short tons) Total weight 142.75 long tons (145.04 t; 159.88 short tons) Tender type 8 wheel bogie Fuel type Coal Fuel capacity 6 long tons (6.1 t; 6.7 short tons) Water cap 3,500 US gal (13,000 l; 2,900 imp gal) Firebox:  • Firegrate area 41.79 sq ft (3.882 m2) Boiler pressure 225 psi (1.551 MPa) Heating surface 3,400.81 sq ft (315.946 m2)  • Tubes and flues 2,697.67 sq ft (250.622 m2)  • Firebox 158.154 sq ft (14.6930 m2) Superheater: ​  • Type Swindon No. 1, Field-tube, 3-row  • Heating area 545 sq ft (50.6 m2) Cylinders 4 Cylinder size 15 in × 26 in (381 mm × 660 mm)
Performance figures Tractive effort 27,800 lbf (124 kN) (at 85% boiler pressure)
Career Operators GWR Class 111 Power class Special Number in class 1 Numbers 111 Official name The Great Bear, renamed Viscount Churchill in 1924 Axle load class Red Locale Great Western Main Line (Paddington - Bristol) First run 4 February 1908 Retired (rebuilt 1924) July 1953 Disposition Rebuilt to GWR 4073 Class

The Great Bear, number 111, was a locomotive of the Great Western Railway. It was the first 4-6-2 (Pacific) locomotive used on a railway in Great Britain, and the only one of that type ever built by the GWR.

There are differing views as to why Churchward and the GWR should have built a pacific locomotive in 1908 when current and future locomotive practice for the railway was centred on the 4-6-0 wheel arrangement. One suggestion is that The Great Bear was built in 1908 to satisfy demands from the directors for the largest locomotive in Britain, and much was made of the locomotive by the GWR's publicity department. However, O. S. Nock was adamant that the design "was entirely due to Churchward, and not to outside influences that pressed the project upon him". Nock regarded the locomotive as "primarily an exercise in boiler design", with Churchward looking forward to a time when his Star Class locomotives could no longer cope with increasing loads.

The front-end layout of the class was the same as that for the Star Class except that Churchward fitted 15 in (380 mm) diameter cylinders, the maximum possible without fouling the rear bogie wheels. However, the design of the boiler was entirely new, and with a barrel of 23 ft (7.010 m) which was exceptionally long both by contemporary and later standards. The main reason why Churchward adopted the 4-6-2 wheel arrangement was to enable him to fit a wide firebox over the trailing wheels. With a firebox surface of 182 sq ft (16.9 m²) this was a 17.5% increase in size compared to the Star Class. It was also built with a Swindon No. 1 superheater.

With the introduction of Great Western Railway Power Classification in 1920, the power classification was "Special" (denoted by a black "+" on the red route availability disc,) although the tractive effort of 27,800 lbf (124,000 N) fell within the range for "D".

In service, the performance of The Great Bear proved to be disappointing and not a significant improvement on existing classes. "The excessive tube and barrel length of 23 feet made for bulk rather than efficiency". Also, the axle boxes of the trailing wheels tended to become overheated due to their proximity to the firebox. Churchward attempted to improve the locomotive's performance by adding a Swindon No. 3 Superheater in 1913 and top-feed apparatus. However, the excellent performance of the Star Class and the advent of the First World War brought a stop to further experimentation without significant improvement.