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The reference for locomotives and railcars

Great Western Railway Fire Fly class

Great Britain 1840 62 produced
Replica in April 2011 at Didcot Tony Hisgett CC BY 2.0

Daniel Gooch used the Star class, more precisely the “North Star” locomotive developed by Robert Stephenson, as a basis for the design a new broad-gauge express locomotive. He stayed with the 2-2-2 wheel arrangement and a driving wheel diameter of seven feet, but installed a larger boiler.

In the years 1840 to 1842, seven manufacturers made a total of 62 locomotives. The names of the locomotives did not follow a uniform scheme. In addition to names that began with “Fire”, there were also those which came from Greek mythology or from animals. From 1865 they were counted to the Priam class.

“Fire Fly” is said to have traveled the nearly 31 miles from Twyford to London Paddington in 1840 at an average of 50 mph, which was a record at the time. Later, the locomotives were fitted with new cylinders which were 16 by 20 inches instead of 15 by 18 inches. The withdrawals took place between 1864 and 1879. A working replica of “Fire Fly” was completed in 2005.

Technical data

General

Property as built rebuilt
Built 1840-1842
Manufacturers Jones, Turner and Evans, Sharp, Roberts & Co., Fenton, Murray and Jackson, G. and J. Rennie, R. B. Longridge and Company, Stothert, Slaughter & Co., Nasmyth, Gaskell and Company
Wheel arrangement 2-2-2 (Jenny Lind)
Gauge 2,140 mm (GWR broad gauge)

Dimensions and weights

Property as built rebuilt
Wheelbase 4.01 m
Total wheelbase 6.20 m
Service mass 24.6 t
Adhesion mass 11.8 t
Rigid wheelbase 4.01 m
Axle load 11.8 t
Water capacity 8,184 l
Fuel capacity 1.7 t (coal)

Boiler

Property as built rebuilt
Grate area 1.245 m²
Firebox surface 9.012 m²
Tube heating surface 68.005 m²
Evaporative heating surface 77.017 m²
Total heating surface 77.0 m²

Power plant

Property as built rebuilt
Driver diameter 2,134 mm
Boiler pressure 3.4 bar
Expansion type simple expansion
Cylinders two, 381 x 457 mm two, 406 x 508 mm

Power

Property as built rebuilt
Power source steam
Estimated power 112 kW (152 PS)
Top speed 93 km/h 98 km/h
Starting effort 9.1 kN 11.5 kN

Calculated values

Property as built rebuilt
Factor of adhesion 1 : 12.74 1 : 10.08
Optimal speed 76 km/h 60 km/h
Power-to-weight ratio 4.6 kW/t
Heating Surface Equivalent 122.1 m²
Cylinder volume/HSE 1 : 853.97 1 : 1,079.59
Adhesive weight/Total 1 : 2.08
Tractive force/Heating surface 1 : 2.47 1 : 3.12
Grate area/Heating surface 1 : 61.86
Firebox/Tube surface 1 : 7.55
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