Chicago, Rock Island & Pacific (Rock Island) class M-50
One of the first railroads in the USA to purchase the 4-8-2 “Mountain” wheel arrangement was the Rock Island. In 1913, however, only the two prototypes of the M-50 class were initially delivered. They had square cylinder dimensions measuring 28 by 28 inches and drivers measuring 69 inches or 1,753 mm in diameter.
The First World War had to pass before series production came about. Between 1920 and 1924, 80 more M-50 were built in several batches, some of which were fired with coal and some with oil. They also had larger drivers of 74 inches or 1,880 mm, a larger firebox thanks to thermic syphons and a boiler pressure of 200 instead of 180 psi. Some of the coal-fired machines later received a stoker.
In 1941 seven were sold to the St. Louis Southwestern and rebuilt there. The Rock Island also rebuilt 18 of its locomotives to the M-50a. They got roller bearings on all axles, lighter connecting and coupling rods, disc drivers, a boiler pressure of 220 psi and two inch smaller cylinders that were cast in one piece along with the front frame.
Technical data
General
| Property | prototypes | production | rebuilt M-50a |
|---|---|---|---|
| Built | 1913 | 1920-1924 | 1941-1944 |
| Manufacturers | ALCO | Silvis | |
| Wheel arrangement | 4-8-2 (Mountain) | ||
| Gauge | 1,435 mm (Standard gauge) | ||
Dimensions and weights
| Property | prototypes | production | rebuilt M-50a |
|---|---|---|---|
| Wheelbase | 11.86 m | 12.88 m | 12.83 m |
| Total wheelbase | 21.40 m | 26.92 m | 26.77 m |
| Service mass | 151 t | 171.5 t | 171.7 t |
| Adhesion mass | 101.6 t | 115.8 t | 115 t |
| Total mass | 223.8 t | 259.5 t | 327.5 t |
| Rigid wheelbase | 5.49 m | 6.05 m | |
| Axle load | 25.4 t | 28.9 t | 28.7 t |
| Water capacity | 32,176 l | 37,854 l | 75,708 l |
| Fuel capacity | 12.7 t (coal) | 14.5 t (coal) | 18,927 l (oil) |
Boiler
| Property | prototypes | production | rebuilt M-50a |
|---|---|---|---|
| Grate area | 5.825 m² | 5.853 m² | |
| Firebox surface | 28.986 m² | 36.883 m² | 34.188 m² |
| Tube heating surface | 353.496 m² | 398.369 m² | 378.023 m² |
| Evaporative heating surface | 382.482 m² | 435.251 m² | 412.211 m² |
| Superheater surface | 87.701 m² | 111.112 m² | 118.544 m² |
| Total heating surface | 470.2 m² | 546.4 m² | 530.8 m² |
Power plant
| Property | prototypes | production | rebuilt M-50a |
|---|---|---|---|
| Driver diameter | 1,753 mm | 1,880 mm | |
| Boiler pressure | 12.4 bar | 13.8 bar | 15.2 bar |
| Expansion type | simple expansion | ||
| Cylinders | two, 711 x 711 mm | two, 660 x 711 mm | |
Power
| Property | prototypes | production | rebuilt M-50a |
|---|---|---|---|
| Power source | steam | ||
| Estimated power | 2,088 kW (2,839 PS) | 2,461 kW (3,346 PS) | 2,610 kW (3,549 PS) |
| Starting effort | 216.5 kN | 224.3 kN | 212.8 kN |
Calculated values
| Property | prototypes | production | rebuilt M-50a |
|---|---|---|---|
| Factor of adhesion | 1 : 4.60 | 1 : 5.06 | 1 : 5.30 |
| Optimal speed | 60 km/h | 68 km/h | 76 km/h |
| Power-to-weight ratio | 13.8 kW/t | 14.4 kW/t | 15.2 kW/t |
| Heating Surface Equivalent | 702.8 m² | 841.9 m² | 820.2 m² |
| Cylinder volume/HSE | 1 : 804.00 | 1 : 671.18 | 1 : 594.00 |
| Adhesive weight/Total | 1 : 1.49 | 1 : 1.48 | 1 : 1.49 |
| Tractive force/Heating surface | 1 : 9.62 | 1 : 8.58 | 1 : 8.37 |
| Grate area/Heating surface | 1 : 80.72 | 1 : 93.35 | 1 : 90.68 |
| Firebox/Tube surface | 1 : 12.20 | 1 : 10.80 | 1 : 11.06 |
| Total/Superheater | 1 : 4.36 | 1 : 3.92 | 1 : 3.48 |
