Great Western Railway Fire Fly class
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 | |