BNSF 6628 is ES44C4 six-axle road locomotive. Built by General Electric in August of 2009, it is one of over 1,200 ES44C4's that BNSF keeps on its roster. These units are used on every possible train type, with the obvious exception of locals.
The ES44C4 is based on the familiar Evolution series chassis and body, with a few major differences. The GEVO (GE EVOlution) 12 cylinder prime mover outputs enough power to allow the traction motors to deliver 4400 HP to the wheels. However, unlike all the other ES44 models, it only has four traction motors and not six. The center axle on each truck is completely un-powered. The C4 uses an A-1-A truck arrangement, meaning that the outer two axles are powered, but the center is an idler. The main spotting feature of a C4 are the extra "brake" cylinders the cause the center axle to lift slightly off the rail, thereby transferring more weight to the powered axles to increase traction.
In theory this arrangement is supposed to be a cost-saving measure as maintaining and replacing traction motors is very expensive. Less traction motors on a locomotive means there is less to maintain. Transferring weight from the center axle to the outer axles is supposed to make up for the loss of tractive power from two less traction motors. In practice though there are mixed feelings on these locomotives. Some engineers like them because they ride much better than other Evolution series locomotives, but many engineers despise them because they feel that the locomotive can't pull anything. Love it or hate it, the A-1-A truck arrangement is here to stay on the BNSF for the foreseeable future.
Other spotting features include a different arrangement of screens on the radiator section, a dynamic brake "blister" on the conductor's side behind the cab, and much wider stanchions than other GE's.
The model 6628 is a MTH offering, moderately modified to better reflect the prototype. I shot the prototype in 2014 as it pulled a ballast train through town. I redid all the piping on the sideframes, added all the piping and cabling under the sill, added all the necessary fuel tank details, added scale coupler pockets, new MU cables and hoses, new grabs in various places, tinted the windows, and Sergent couplers. I installed a Railpro module and dual sugar cube speakers in the fuel tank.
Weathering was done by shooting the model with Dullcote, then fading the orange and black separately using thinned acrylics. The bulk of the weathering was spent on the underframe, using almost exclusively acrylics. Raw umber was my main choice, with some burnt sienna and burnt umber mixed in here and there to get various effects. The pilots received similar treatment. The prototype had some sort of a turbo failure with the after-effects leaking through the body seams. The oil and grime had run across the walkway and had dribbled down the fuel tank. I replicated this the best I could using oils and powders. MTH makes a decent starting point for the C4, though the weakest area are the handrails and stanchions. I chose to leave them as is until I come up with a better solution.