South African class FD
After the single 2-6-2+2-6-2 Modified Fairlie of class FC of the South African Railways, Colonel F.R. Collins specified a somewhat heavier variant that was again to be built by North British. The four locomotives were delivered in 1925 and were called class FD. They had direct competition from the class GD Garratt that had the same wheel arrangement.
In service it was found that the long rigid frame produced some problems. These included huge side overhangs when running through curves and oscillations of the water and coal tanks at speed. Also the pivot bearings had to support considerably higher weights due to the supplies being on the main frame. So ultimately the GD Garratts were more successful with 14 built. All FD locomotives were scrapped in 1949.
Technical data
General
- Built
- 1925
- Manufacturers
- North British
- Wheel arrangement
- 2-6-2+2-6-2T (Modified Fairlie)
- Gauge
- 1,067 mm (Cape gauge)
Dimensions and weights
- Length
- 20.01 m
- Wheelbase
- 17.86 m
- Service mass
- 115.9 t
- Adhesion mass
- 74 t
- Rigid wheelbase
- 2.59 m
- Axle load
- 12.6 t
- Water capacity
- 17,277 l
- Fuel capacity
- 5.1 t (coal)
Boiler
- Grate area
- 3.8 m²
- Firebox surface
- 16.5 m²
- Tube heating surface
- 144.186 m²
- Evaporative heating surface
- 160.685 m²
- Superheater surface
- 34.467 m²
- Total heating surface
- 195.2 m²
Power plant
- Driver diameter
- 1,168 mm
- Boiler pressure
- 12.4 bar
- Expansion type
- simple expansion
- Cylinders
- four, 381 x 610 mm
Power
- Power source
- steam
- Estimated power
- 969 kW (1,317 PS)
- Starting effort
- 159.8 kN
Calculated values
- Factor of adhesion
- 1 : 4.54
- Optimal speed
- 37 km/h
- Power-to-weight ratio
- 8.4 kW/t
- Heating Surface Equivalent
- 312.1 m²
- Cylinder volume/HSE
- 1 : 890.68
- Adhesive weight/Total
- 1 : 1.57
- Tractive force/Heating surface
- 1 : 17.10
- Grate area/Heating surface
- 1 : 51.36
- Firebox/Tube surface
- 1 : 8.74
- Total/Superheater
- 1 : 4.66
