Locomotives Dimensions - MLW FPA-4
The FPA-4 was the first ALCO/MLW cab unit I drew in 1:18, and my drawings are based on a combination of measurements I made of CN #6765 preserved at Exporail as well as ALCO FA-2 mechanical diagrams.
The center side door, sand hatches and fuel / water tanks are centered between the trucks, and the inner truss structure is also symmetrical between the truck centers. The exact location of the side seam screws varies slightly between units, although the 4" spacing is consistent. Most dimensions are the same between the two sides; the left side is illustrated as that was the side that was accessible for measuring on CN #6765.
Most preserved units have the steam generator piping either removed (units in operation) or modified (CN #6765 at Exporail), so to draw the steam lines, I did an extensive search of older photos of units in operation on CN and VIA, as well as relying on one of my own photos of the steam pipes on a GMD FP9Au; even so, the upper part of the steam pipes are a bit of a stand-in based on what I could decipher from photos.
The drawing illustrates the general appearance of FPA-4's after modifications by CN and VIA, but with the steam lines still intact. Among components with dimensions listed, the front fuel filler, the ladder on the end of the carbody, and the large circular panel on the water tank were absent on the units as-built.
B units were 10" shorter (52' 8") with the length removed between the front coupler and truck, making them symmetrical front-to-back. Two steam generators were located at the front (rather than a single one at the rear); the rooftop hatch over the steam generators was approx. 3" longer than on A units (approx. 75" instead of 72") and was located farther inboard from the end of the carbody. Most of the dimensions and hood components from the front truck rearward were the same between the FPA-4 and FPB-4.
Comparison with FA-2 and FPA-2
The FPA-4 was an evolution of the FPA-2, which was a steam generator-equipped version of the FA-2. Both of the latter models were built by ALCO as well as MLW. Other than the major dimensions (length, truck centers and overall height) almost all the specifications listed in blue above were taken from ALCO FA-2 diagrams.
The heat exchange pipes from the air compressor, previously located on the outside back wall of the carbody on the FA-2 and FPA-2, were moved inside the carbody - which was the reason for the extra air intakes below the radiator shutters on the FPA-4. Although the 251-series engine in the FPA-4 was longer than the 244 engine used in earlier models, the carbody and roof hatch dimensions remained the same. The fuel and water tanks on the FPA-4 were unique compared to other ALCO FA units (although some CN FPA-2 units were rebuilt with similar tanks) and the coupler pockets and draft gear differed from those used in earlier production.
The ALCO FA-2 side view erecting diagram I used for reference listed two overall lengths: 53' 6" between the coupler pulling faces and 54' 0" over the outer edges of the coupler knuckles. This evidently has caused confusion in other diagram sources such as CN, CP and NYC diagram books, which variously list one or the other as the overall length for A-units. As the standard method of measuring length is between the coupler knuckle pulling faces, the correct figure is 53' 6" for both the FA-2 and the FPA-4.