It occurs to me that steam loco size hit the wall due to limitations of the physical plant. Northerns and 2-10-4’s were about all most roads could handle and even articulateds were about as big as they could be.
I wonder where we are with respect to diesels and what might be next. Have 6 wheel trucks on current 6,000 hp units reached the limits? The newest are using computerized traction control and advanced truck designs to avoid slipping and I suspect axle loading can’t go too much higher. Is something like an SD95 with a single prime mover and an advanced version of the 8 wheel DDA40x Centenial truck far off? Or would something more like the Baldwin Centipede or GG1 be a better alternative?
I would think that 6000 HP on six axles may be a ceiling for more reasons than weight and adhesion limits. The reliability issue is one. 6000 HP all by itself can handle a lot of trains and a locomotive failure can cause real problems if all that HP is in one unit. Another reason might be the inflexibility caused by a pool of 6000 HP units. Something that big is not suited for a lot of jobs because it’s an awfully expensive way to work a mine run, transfer job or local freight.
Articulated wheelbases, even if every axle is powered like GN’s W-1 electrics, are overly complex and more difficult to maintain. They may reduce axle loadings, but at extra expense.
You could get pretty whacky and wild with loco design. EMD was messing around with a bolsterless, radial B+B configuration on the rear of a BN SD45 a decade ago, or so. So, based on that, how about an 8,000 HP, 8 axle AC loco? Or, maybe you put 3 B+Bs under it and do a 12,000 HP 12 axle AC loco. Power could come from a gas turbine, or better yet, a fuel cell.
But, what would you pull with these whacky locos? Right now, a pair of ACs can just about break the knuckles on grade C draft equipment and 3 of them can do the same to grade E. So, for monster locomotives, you either need stronger frt cars or distributed power. If you go the distributed power route, then why not go for smaller HP&TE chunks - e.g. 2000 HP 2 axle locos and sprinkle them throughout the train. You could transition to lower tare wt. equipment if this was the case and trains could be any size and length you’d care to build.
With present wheel slip control technology, 1000 hp per drive axle is on the edge control.
While the bean counter types love the economies of single engine trains they really have not looked at the down side of single engine trains. The first and most significant down side is when the engine fails…the train is dead…right where it sit…PERIOD. With multiple engine trains, unless the engine fails on the ruling grade of the territory, the train is able to limp to a location of operational safety (a siding or a location in multiple track territory where a dead train can be more easily passed). With a single engine train there is no ability to limp.
The second drawback of single engine trains in todays world, is that the ‘Wide Body’ cab configurations cannot be safely operated backwards in line of road operations. With the end of the Steam Engine era and the rise of the Road Switcher type of locomotive, the railroads eliminated most of the turning facilities that existed for steam engines. In today’s world single engine, wide body, trains that terminate at locations without turning facilities have prevented the use of that engine in the return direction, at least as a lead engine on a consist.
The devil is in the details when it comes to single engine operations.
And one step further: small diesel engines on the platforms of container cars or in the trucks and cabs at the ends will give you John Kneilings integral train (and no locomotive [:(]).
Gensets could evolve into these entegrated trains with the big engines getting close to the limits of drawbar pull. Gensets have small power packages that could be distributed evenly through out a train and reducing in train forces. Right now they are only switchers, but deisel electrics were once just switchers.
But then again if you had sugested 6000hp units on 6 axles instead of 8 axles, it wouldn’t have seemed likely. Perhaps drawbar strength will yet get stronger and wheel slip technoligy even better and therefore single units bigger. There will probably always be a need for bigger trains.
I recall back in the 60’s, Trains had an article about an Austrian light weight, high-adhesion locomotive that toured around the US. Might that type of loco be an area for further development?
Because you don’t want to drag around any extra weight if you don’t need it. Two AC traction motor powered axles would provide just about the right amount of TE to go with 2000 HP for typical intermodal and road freight operation.
Could an effective 2000 HP two axle locomotive be built? Keeping the weight down would be a real challenge. And, how would such a beast ride and track? It’s outside the scope of current practice, so it certainly is no slam dunk. You COULD go with 4 axles, but only 2 powered ala AC traction subway cars.
I would agree that the bean counters certainly play a role and I’m guessing a single diesel prime mover is more efficient than two having half the horsepower, at least that was the justifdication given on a recent Discovery Channel program for using a very large single power plant in Container ships. I’m not sure how far it’s practical to go, but we did have the 8500 HP gas turbines some years ago.
To anyone’s knowledge did they/do they ever use one ac6000 or sd90mach on an each end of a coal train? I agree that the single engine would be a problem in the case of a break down or failure, but on a tandem set of ac4400s if one went the train would almost be dead on tracks wouldn’t it?
If one AC44 fails on the ruling grade of a territory the train will stall., howver, territories are made of more than the ruling grade…in those less severe territories the train can still proceed…proceed to a point when it can be more conviently worked around until adequate power is secured to move it to destination. When a single engine train has it’s engine fail…it can’t go anywhere. Other trains or engines are necessary to move the ‘dead’ train to a place of operational safety.