Both the EMD E-units and ALCO PA’s had A1A trucks. The Great Northern used E7’s on the Empire Builder, but withdrew them in favor of passenger F’s.
Do the readers think that the E’s and PA’s would have been a better mountain locomotive with a C-C truck? If my memory serves me correctly, the UP and MILW (for their UP pool locomotives) ordered their E’s with dynamic braking as per UP specs.
Ed Burns of Anoka, MN
Happily retired NP-BN-BNSF Clerk from Northtown and an ATCS host.
The prevelant answer will be that passenger trains did not need the C-C or three axel power.
The reason that the E’s went to A1A -A1A from B-B, was that the locomotive weight was getting too high for four axles. The EMD A1A trucks were laid out symmetrically, which was not possible with a three motor C truck. One other reason for sticking with two motors per truck on the E’s, was that each engine powered a single truck. Transitioning between series and parallel motor connections was easier with just two motors as opposed to three motors. This was not the same issue with the single engine PA, but Alco’s first foray into passenger power was the dual engine DL-109, which had the same issues with transition as the E units.
It was simpler to use re-geared F units for mountain use than converting E’s to C-C’s.
I think a lot of the reason EMD went from the B-B configuration of their earliest passenger engines like the TA was that the idler axle allowed for a smoother ride at high speed. E units were great on relatively flat terrain like NYC’s water level route or CB&Q’s prairie lines, but not in the mountains. Later when the FT was introduced, it had the ability to have a steam generator in the B unit so it could be used on passenger trains.
FWIW, although hardly thought of a passenger engine, GM’s SD’s could be ordered with steam generators too. The Missabe had two SD-9’s with boilers that could pull (and heat) passenger cars if needed to pinch-hit for the road’s RDC. In the seventies, they were leased to Amtrak for a time and used on Amtrak trains between the Twin Cities and Duluth-Superior.
I would guess the main reason the GN withdrew E7’s from the Builer is the minimum continuous speed of a 92 mph geared unit was about 31 mph per an E7 operating manual I have. The minimum continuous speed of the F3 greared for 89 mph was about 21 mph. Perhaps the GN discovered it was more economical to run 3 unit F3’s at a slower speed than to run three or more E7’s at 31 mph in the mountains.
The UP seems to have had a different idea and stuck with E units and used helpers where necessary. Later they just added more E units.
Well, first of all a center- axle motor could not be added to the Blomberg AiA-A1A truck used ongthe E’s.
There was not nough room, and it a cooling duct for the other motors was already occupied that soace in the forem of a holloe area in thew truck.
So, a new truck would have to be developed pretty rapidly. EMD I don’t think produced an actual “C” truck until the advent of the SD9 in 1952. I don’t know whether Alco produced an RSD3.
The E8 and E9 locomotives, and their little brother F7 and F9’s respectively, had larger traction motors, heavier insulation, and mechanical /automatic cooloing systems,compaired with the E6/E7, and the F3.
The older models simply did not have either the electrical nor the cooling capacity for mountain railraoding.
The Alco PA had the electrical capacity, but it , as well as the FM Erie-Builts, had insufficient cooling capacity, and the PA’s 244 engine had weak cranshafts.
So, at that time, I do not think that there was a suitable “C” truck available.’ The key word is “suitable.”.
The GG-1 electric used C trucks, but to give good tracing qualities, the wheel arrrangemebt wa
s 2-C + C-2, and an unusual frame configuration that was very independently flexible, and very heavy as the pulling went trough the underframe anf trucks, and not the carbody.
Fast forward to Amrak’s SDP40-F, and it’s alleged tendency to derail at speed, and the fact that the F40 and the P42 and all the other locos built specifically for passenger service are B-B’s.
Conclusion(from Trains and other sources): The E’s were already very heavy… The extra axle was to reduce the axle load, and to provide a safe ride at high speed. It did that job well. but the E was already costly to produce, with 2 prime movers…
I think that if UP’s E8 and E9 locos did not make it in the mountains they wold have gone to F7’s and F9’s. There would have been n
You meant the SD-7, which was introduced in 1952. The SD-9 came a year or two later. I worked at EMD in the summer of 1952 and both the GP-9 and the SD-9 were in the design stage. Both were incremental improvements, with better and simpler electricals than the -7 models, but not radically different. HP up from 1500 to 1750. But the F-7, GP-7, and SD-7 could be “tweaked” to 1600 HP, and I understand some railroads did.