Morning everyone,
So I’ve been looking for about an hour now, but does anybody know the exact reason why the Blomberg ‘Type C’ trucks or A1A Blombergs disappeared on EMDs (aside from the E-units)? I’m asking since I can’t find anything as to why they did.
The center idler (unpowered) axle helped smooth out the ride at high speeds, so was very usefull on passenger engines like E-units. Their only advantage on a freight engine would be if a railroad had light rail or other track issues where having a truck with the center idler helped spread out the weight of the engine. However, motors don’t really add that much to the weight overall, so although a few railroads in that situtation ordered engines with A-1-A trucks instead of B-B, most just bought engines with C-C trucks (three axles, all powered) like SD7s / SD9s.
The reason for A-1-A trucks on E units was the added length and weight of the double engines in an elongated carbody.
bogie_engineer has already described the arrangement at the center axle, and in other posts why mounting the motors ‘inboard’ of the axles improved things like traction-motor cooling and reduced polar moment of inertia.
Of course that arrangement does not help ‘weight transfer’ when the motors torque, so an A-1-A already has an adhesion concern with nose-suspended motors. The truck has cost, weight, and complexity issues vs. the equivalent Bloomberg-designed ‘B’ truck, and the wheel-diameter and -wear restrictions have been mentioned.
Where E units were tried in freight service, another concern emerged: automatic back transition was not installed on many passenger units, and freight engineers accustomed to having the feature on their Fs or GPs could produce interesting flashovers on E8s (say) running TrucTrain and other high-speed service as passenger demand began to wane.
The Flexicoil C truck allowed three motored axles of reasonable size, and could be given lateral accommodation and damping for reasonable high-speed service under the restrictions of the ICC order that came into force 1950 to 1952. While there were some ‘issues’ with passenger versions (I think ‘hollow bolsters’ were one problem) there were few services an FP45 might be used on that would outspeed its trucks.
Thanks for that information @Woke_Hoagland and @wjstix
