Does anyone know (or can speculate) why EMD stopped the tunnel motor design after the SD45T-2? There would only seem to be "pros" in keeping it and no "cons'.
Because with the stretched and increased depth of the radiators on 50-series locomotives they didn't need it. The "Tunnel Motor" design allowed a radiator with increased surface area for greater cooling capacity. EMD was looking for the simplest way to increase cooling capacity without completely modifying the locomotive. When the production SD50s debuted, the stretched frame allowed for more fuel capacity, and it created space for a larger radiator.
Well, there ya go. Thanks.
They designed and catalogued a GP50T, but no one ordered any.
https://cs.trains.com/trn/f/741/t/288317.aspx
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Can't sell any if nobody wants to buy any.
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What tunnels would need tunnel motors for max traffic. Cascade? What else?
The T-2 models were the result of extensive tunnel tests EMD did in the 1968-70 timeframe on the SP to improve tunnel performance of the SD45 cooling system. The tests evaluated water spray on the radiators and elephant ears to draw air in at a lower level while in the tunnel. I was an engineering co-op in that time period and was tasked with analyzing reams of SpeedoMax charts of air and water temperatures. The tests demonstrated a significantly lower air temperature at the walkway level in the tunnels and snowsheds leading to the design of the SD45T-2 low, unobstructed air intakes and cold side radiator fans which push cooler air for more mass flow thru the radiators.
At the same time, the SD45's, especially on the SP, had a horrendous failure rate of the radiators cores. Unique to the 45's were 8 row radiator cores with a 36" width, compared to the 6 row cores of all the other models at the time which were 30" wide. These were all solder bonded cores - the 6 row worked fine but the 8 row would fail in about 2 years at the solder joint between the tubes and the header sheet. So when the -2 series was designed, it was an edict that no 8 row cores would be used, leading to the long radiator sections on the SD45-2 without the flare that the 8 row wider cores required.
As a sidenote, to solve the radiators failures, the SD45X got 8 row cores, but they were mechanically bonded without solder by roller-swaging the tubes into a 5/8" thick header sheet but that required round tubes which were not as efficient at heat transfer as the flat tubes in solder bonded cores. So that loco had a long, flared cooling system with 4 fans to deal with the 4500 BHP of that engine.
The ultimate fix for the radiators came in about 1976 with the development at Harrison Radiator Div. of GM of the flat-round tube radiator with the heavy header sheets with roller swaged tubes that were flat where they pass through the fins for best heat transfer. Eight row 30" wide mechanically bonded radiators became the standard in the 50 series along with taller shutters (30" vs. 24" IIRC) that lowered air flow resistance for better cooling system performance. Starting with the SD80, the flat-round radiators were widened to 45" resulting in the wide flare of current models.
Lower air intakes would have improved the tunnel performance on the 50 series and the Rio Grande was interested in a GP50T but an order never materialized. That model was the same as a standard GP50 but stretched by 3 feet to a length of 62' 2" over coupler pull faces. The fans were still on the roof but the air intakes were dropped to the walkway level starting aft of the air compressor with a curved sheet over the air compressor and equipment rack to direct air to the forward radiator core and fan. The radiators were still in Vee arrangement but flattened somewhat.
There were also layouts made of an SD50T that retained the same length as the SD50 but had a similar intake-radiator-fan arrangement as the GP50T. I don't know what RR if any that was offered to.
Dave
VGN Jess Does anyone know (or can speculate) why EMD stopped the tunnel motor design after the SD45T-2? There would only seem to be "pros" in keeping it and no "cons'.
One con would include the longer length of underframe and it's cost that style cooling system requires which is mostly due to EMD engineering's insistence that a water cooled air compressor is required which in turn requires it be in the engine room to prevent freezing in cold climates. (GE puts their air cooled compressor in the air intake path for the cooling system.) This limits where the air intake can start which is further pushed rearward by the design requirement that the equipment rack not extend over the oil strainer box on the front of the engine so that an engine can be pulled without removing the oil strainer or the water tank.
bogie_engineer One con would include the longer length of underframe and it's cost that style cooling system requires which is mostly due to EMD engineering's insistence that a water cooled air compressor is required which in turn requires it be in the engine room to prevent freezing in cold climates. (GE puts their air cooled compressor in the air intake path for the cooling system.)
One con would include the longer length of underframe and it's cost that style cooling system requires which is mostly due to EMD engineering's insistence that a water cooled air compressor is required which in turn requires it be in the engine room to prevent freezing in cold climates. (GE puts their air cooled compressor in the air intake path for the cooling system.)
FWIW, the EMD compressor setup seems a lot more reliable in Canadian winters. We seem to have way more failed and frozen compressors on GEs in -30 to -40 weather, in particular when the unit is moving backward the compressor is getting the full brunt of the cold wind.
I do wish EMD had switched away from a direct-drive compressor, or at least use a larger one. Even in notch 8 the thing can't keep up sometimes.
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