So, with the F40 thread and the Hybrid thread and a couple other threads all talking about the weight problems with classic framed modern passenger power, I’ve been wondering, why was the A1A wheel arrangment dropped? Wouldn’t it have been cheaper engineering to simply use A1A trucks with a proven design rather then the added cost of the AMD-103 design? Why doesn’t MPI look at A1A to counteract it’s wheight problems? or the F59PHI?
With A1A you could fit larger engines and HEP generators, you would have better ride characteristics, You could run on lighter track. What’s the downside?
I mean sure the old Bloomberg A1A bogey is a little long in the tooth, but there are Still bloomberg B and Flexcoil trucks out there and I would think that bringing it into the modern world would be way lower cost then what the Genesis was.
For that matter, why wasn’t A1A considered for the GP60Ms?
I think a combination of cost, an increase in allowable axle loads and an increase in diesel engine output all did in the A1A truck. You don’t want to have to maintain an extra pair of wheelsets if you don’t have to.
The Genesis design is a good example of how you can build a modern passenger locomotive with good ride quality and packaging on 4 axle trucks.
Interestingly there are some modern “A1A” Passenger units in North America. The Alaska Railroad’s SD70MACs have the ability to switch one of the AC Inverters from traction to HEP for passenger train service. When this feature is selected one traction motor on each truck is cut out, making them “A1A”. For freight the engineer switches the electrical system back to standard CC configuration.It’s a clever way to use the units electrical capacity and have plenty of “hotel power” available without needing an auxiliary genset.
Sure, but how much additional maintence do those trucks really entail? And sure, the genesis is a marvel of engineering, sure, but was it worth the cost in engineering when a more stock design riding on A1As would have been as effective? remember Amtrak’s always being squeezed for money so every dime of expense is fought for. Given that Alaska got the 70 MAC with convertable trucks, it seems like it wouldn’t have been an impossibility.
But even beyond the Genesis, what of MPI? They’re having weight issues with the MPExpress. Couldn’t the A1A truck have allowed them more room to play with to get a better performing engine? Why design something less optimal just to use a 4-axle truck?
MPI may have had weight issues with the MPExpress suburban locomotives, but an A1A truck would have become a cost issue. It would be a non-standard (expensive) design and would have required a totally different frame to allow for the longer wheelbase.
Those equalized A1A trucks have a bazillion parts to them, and getting at the brakeshoes on the ones with the drop equalizers is a big pain. The 4 axle Blomberg has too many parts. The A1A has about double.
I wonder if the patterns for the EMD or AAR style A1As are even around anywhere…
MP got the job done on 4 axles - good enough for the commuter market, anyway.
This isn’t true, on the SD70MACs with HEP you cut out the power to one whole truck, making the locomotive a C-3, rather than an A1A. The SD70MAC has two traction invertors, one for each truck, not three for pairs of axles.
The reason for the disappearance of the A1A truck is related to the need for weight on the powered axles, too much power for too little weight means the wheels will slip. Of course you could limit the power at lower speeds, but US passenger cars are relatively heavy, compared to European designs.
What you say is exactly right for a freight only SD70MAC, but those Alaska SD70MACs might be a special case, since they are “dual mode” need the output of one inverter for HEP. Very clever to go A1A-A1A on one inverter in passenger mode.
Don, shame on you, you have knowledge about locomotives, each invertor is designed to power three axles, you must have some idea of the complications of the additional wiring and serious software changes that would be required to make one of the invertors power 4 axles when in HEP mode, and only 3 motors when in normal mode. The ARR HEP MACs are a cheap and dirty modification to get a combination freight and passenger locomotive. To shift one invertor to HEP just requires software changes to allow them to work at different settings, to allow one to power 4 instead of 3 would require some fancy switchgear and a lot of extra cabling. Remember the front invertor powers the front truck of the locomotive, the rear invertor powers the rear truck. You would need six cables running from the front invertor to the rear truck (three for each motor), and they would only be used when the locomotive is in HEP mode. The invertor that powers either three or 4 axles would have had to be custom designed, and would have cost a great deal of money, and to boot it would be non-standard compared to the rear one and those used in the non-HEP equipped in the ARR fleet. Something like what is proposed would be easy with a GE AC4400CW where you have one invertor per axle, and all 6 invertors are in one compartment adjacent to each other, but in the SD70MAC the invertors are located at each end of the long hood with the engine compartment inbetween. It is totally impractical in a SD70MAC or a SD70ACe. Remember the ARR went through some hoops to get non-Tier II compliant SD70MACs rather than SD70ACes for parts commonality reasons. That is also why the GP49s departed rather than the less fuel efficient GP40-2s.
Don, shame on you, you have knowledge about locomotives, each invertor is designed to power three axles, you must have some idea of the complications of the additional wiring and serious software changes that would be required to make one of the invertors power 4 axles when in HEP mode, and only 3 motors when in normal mode. The ARR HEP MACs are a cheap and dirty modification to get a combination freight and passenger locomotive. To shift one invertor to HEP just requires software changes to allow them to work at different settings, to allow one to power 4 instead of 3 would require some fancy switchgear and a lot of extra cabling. Remember the front invertor powers the front truck of the locomotive, the rear invertor powers the rear truck. You would need six cables running from the front invertor to the rear truck (three for each motor), and they would only be used when the locomotive is in HEP mode. The invertor that powers either three or 4 axles would have had to be custom designed, and would have cost a great deal of money, and to boot it would be non-standard compared to the rear one and those used in the non-HEP equipped in the ARR fleet. Something like what is proposed would be easy with a GE AC4400CW where you have one invertor per axle, and all 6 invertors are in one compartment adjacent to each other, but in the SD70MAC the invertors are located at each end of the long hood with the engine compartment inbetween. It is totally impractical in a SD70MAC or a SD70ACe. Remember the ARR went through some hoops to get non-Tier II compliant SD70MACs rather than SD70ACes for parts commonality reasons. That is also why the GP49s departed rather than the less fuel efficient GP40-2s.
The EMD A1A patterns were scrapped years ago. You are exactly right about the number of parts in both the A1A and the GP swinghanger trucks - no one today would design a truck like that. Too many wearing surfaces that are expensive and difficult to restore during rebuild. Look at the HTCR - no wearing parts to weld up and machine, just change bushings and some bolt-on wearplates and it is back to new condition.
Why are bloombergs so popular still? Why didn’t the HT-B truck on the GP40X become wide spread? I mean, I realize that the HT-B didn’t take off and therefore there are approximately a bazillion Bloomberg B and M trucks to scavange, but still. If they were such a nightmare…
another thing-with A1A’s it was much easier to slide the idler axles when using the independent locomotive brake…lotsa flatspots…idlers lack the traction motors and therefore the rotational inertia that the powered axles have…
I know very little about the HT-B. That’d be a good one for bogie_engr. Hope he chimes in. The Blomberg is a proven design with good ride characteristics (with the leaf spring secondaries, anyway), and it’s easy to do brake shoes and adjust piston travel, but no one would start from scratch today and come up with that design. As long as there are good frame castings floating around, the Blomberg will soldier on. Big steel castings are expensive.