Locomotive Descriptions and Phases - ALCO RSD-12
The ALCO RSD-12 was introduced in 1956 as a replacement for the RSD-5 and as a six-motor version of the concurrent RS-11. It used a 12-cylinder 251-series engine developing 1,800 horsepower.
Visually, the RSD-12 featured a clean-lined carbody, with full-height hood and large vertical radiator intakes at the end with a single large radiator fan. The overall length was increased by 14" compared to the RS-11, with the hood lengthened immediately behind the cab. Early units had a rectangular chickenwire grill over the intercooler intakes covering an air cooling pipe manifold from the air compressor, located about 3/4 of the way along the long hood; this was replaced with a group of three square air filters on later units. The dynamic brakes were located in a raised housing along the center of the roof; units so-equipped had additional air intakes behind the cab (early units) or above the engine compartment doors (later units). A high short hood was initially standard, but many later-production units were built with a low short hood. The hood corners had 45-degree notches for the number boards and classification lights.
Under the frame, the trucks were ALCO's drop-equalized Tri-mount design with unequal axle spacing (5' 7" outboard, 6' 11" inboard) to accommodate the orientation of the traction motors. The "Tri-mount" designation came from the use of a central pivot located just outboard of the middle axle, combined with two sliding bearings on the truck frame between the inner axles; this 3-point support system reduced weight transfer under high tractive effort situations. Most RSD-12's used the later version of this truck with two brake shoes per wheel and two brake cylinders at the upper corners, but SP units used trade-in trucks that had single-shoe brakes and a single central brake cylinder. The fuel tank and air reservoirs were centered between the trucks, with the fuel tank extending out under the air reservoirs and bevelled along the bottom edge.
A total of 171 RSD-12's were built up to 1963. More than half went to Mexico, to Ferrocarril del Pacifico and Ferrocarriles Nacionales de Mexico, along with 10 built by MLW for RFFSA in Brazil. American production went to CO, LSI, NKP, PRR and SP; there was no MLW version sold in Canada. Most remained in service up to the late 1970's or early 1980's; four have been preserved (NKP 329 and three former SP units).
Related models
RS-11
As the RSD-12 was a six-axle version of the RS-11, the two models were very similar and shared most of the same general construction and "phase" details. The underframe on the RSD-12 was lengthened by 14" compared to the RS-11; it used the same walkway height but had slightly higher clearance underneath for the Tri-mount trucks. The underframe construction was substantially heavier, with two 1.75" plates along the bottom and a 1" or 2" plate along the top (compared to a 1" and 0.5" plate on the bottom and a thin plate on the top on the RS-11). The walkway side frame (excluding the top plate) was 1" narrower than on the RS-11, and the air reservoirs were mounted about 2" lower, exposing the top edge of the tanks. The steps and draft gear were largely the same as on the RS-11. The jacking pads above the trucks were in line with the truck pivot pin (22" outboard of the center axle) and included a curved lifting bracket wrapped underneath the top edge of the truck frame.
Above the walkway, all of the 14" length increase over the RS-11 was added immediately behind the cab - about 9.5" between the cab and the first hood seam, and about 4.5" between the seam and the first hood door. All the rest of the short hood, cab and long hood (including the hood-to-pilot distances) was the same as on the RS-11, with the following exceptions:
- The dynamic brake hatch on the roof was 2 feet longer, with 3 instead of 2 bolted panels along the middle (as on the RSD-7 and RSD-15)
- On early units with dynamic brakes, in place of the two widely spaced air intakes behind the cab, there were three unevenly spaced intakes
- In place of the equipment box behind the cab on the conductor's side, there was a curved duct (which remained on later units when the equipment box was removed on concurrent RS-11 production)
RSD-5
The RSD-5 preceded the RSD-12 and used ALCO's earlier carbody design with rounded corners and a lower hood height (most well-known on the RS-2 and RS-3). The RSD-5 had 8" shorter truck centers and was 1' 8" shorter over the pilot plates; the additional length on the RSD-12 was in part due to the clearance required for the outer brake shoes on the trucks.
RSD-7, RSD-15
The RSD-15 was produced at the same time as the RS-11 and RSD-12, but was powered by a 16-cylinder (rather than 12-cylinder) version of the 251 engine rated at 2,400 horsepower. While it shared many general design characteristics with the RSD-12, it was more than 8 feet longer and had notably longer hoods. It was derived from the very similar RSD-7, an earlier model powered by the 244-series engine, which pioneered the general frame and carbody design used in subsequent 251-powered RS and RSD models.
Dimensions
| Model | Overall Length | Length Over Pilots | Truck Centers |
|---|---|---|---|
| RSD-5 | 55' 11 3/4" | 52' 0" | 34' 9" |
| RS-11 | 56' 11 3/4" | 52' 6" | 31' 0" |
| RSD-12 | 58' 1 3/4" | 53' 8" | 35' 5" |
| RSD-7, RSD-15 | 66' 7" | 62' 3" | 43' 6" |
Phases
These phases are of my own making. I compared photos of contemporary RSD-12 and RS-11 units against the phases I had already compiled for the RS-11 - which were in turn based on the RS-11 Roster compiled by David Thompson.
See also RS-11 phases.
| Phase | 1a1 | 1a2 | 1a3 | 1b | 2a | 2b | 3a | 3b |
|---|---|---|---|---|---|---|---|---|
| Dates | 1956-04 - 1956-05 | 1957-02 - 1957-06 | 1957-12 - 1958-04 | 1958-08 | 1958-09 - 1959-10 | 1959-11 - 1961-04 | 1961-02 - 1961-04 | 1961-12 - 1963-10 |
| 45-degree handrail braces | No | Yes | No | |||||
| Air reservoir supports | Attached to U-shaped connector below side sill | Attached to straight connector with a notch in the side sill | ||||||
| Radiator intakes | Narrow frame, 24 shutter vanes with no external clips, control box at top right corner | Wider, bolted frame, 18 shutter vanes with external rod clips, control mechanism at top corner facing the cab | ||||||
| Coupler pocket | Cast | Fabricated (except LSI 1803) | ||||||
| Air intakes behind cab | 3 square intakes (units with dynamic brakes only) | 1 + 2 square intakes with outer frame | Rectangular group of 3 intakes | |||||
| Middle hood air intakes | 3 square intakes above center doors | 3 square intakes with outer frame (units with dynamic brakes only) | 2 narrower rectangular intakes (units with dynamic brakes only) | |||||
| Phase | 1a1 | 1a2 | 1a3 | 1b | 2a | 2b | 3a | 3b |
| Equipment box behind cab | Yes (engineer's side only) | No (except FCP units) | ||||||
| Handrail stanchions | Square, fastened to walkway with L brackets 43" - 54" - 54" - 51" - 51" - 52" - 52" spacing | Cylindrical, fastened directly to walkway 44" - 44" - 44" - 60" - 56" - 52" - 52" spacing | ||||||
| Hood doors | Equal height | Taller engine compartment doors (middle 6) (as on RS-32 and RS-36) | ||||||
| Rear hood intercooler intake | Rectangular chickenwire grill covering air cooling pipe manifold | Narrower rectangular group of 3 intakes | ||||||
| Hand brake wheel | Recessed | Surface-mounted (also appeared on FCP 515-517 in 1961) | ||||||
| Phase | 1a1 | 1a2 | 1a3 | 1b | 2a | 2b | 3a | 3b |
Notes
- The taller hood doors introduced on the RSD-12 in 1961 didn't appear on the RS-11 until the last order of NdeM units in 1963.
- The revised radiator intake design introduced with Phase 1b units was in fact a return to the earlier design used on the RS-2 and MLW RS-10. This was the second time the radiator shutters were reverted, as much of RS-3 production also used a slightly different design.
- There were two styles of draft gear: One similar to earlier ALCO RS-units with several ribs and a flat vertical inner face near the trucks; and and one with a larger casting bolted underneath the coupler shank and an angled inner face near the trucks. From what I can tell, the former was for MF-400 draft gear (or similar) and the latter was for heavier-duty M-380 draft gear. Both were revised when the coupler pocket and striker were changed from cast to fabricated.
- MU connectors were fastened either on the end handrails (typically on earlier units) or on a box on the walkway (typically on later units).
References
ALCO Products Inc. (1959). Operating Manual 1800 hp road switchers models RS-11 and RSD-12.
Peck, D. (1987, September). ALCO's RSD-12. Mainline Modeler, 58.
Norfolk and Western Historical Society. (2019). Archives Database. [RSD-12 database search]. Retrieved November 2023 from https://www.nwhs.org/archivesdb/
Thompson, D. Alco's RS11 - Original Owners. Retrieved January 2018 from http://www.trainweb.org/jaydeet/rs11.htm