A distinct trend I've noticed is that in typical American and British practice, the axle loadings of unpowered axles were often much lower than the powered axles, often less than half the weight compared to powered both for leading and trailing independent axles. Yet in continental Europe, the story is quite different, with the overall axle loading on the bogie often far larger than the driving wheels independently. Europe seems to have much heavier locomotives proportional to their wheel arrangement compared to the US and UK.
Is there a reason for this difference in design in different places? And was there a real reason for the US and UK to have such conservative weights on unpowered wheels aside from adhesive reasons?
Also, I think this should be moved to the steam subforum.
ShroomZedA distinct trend I've noticed is that in typical American and British practice, the axle loadings of unpowered axles were often much lower than the powered axles, often less than half the weight compared to powered both for leading and trailing independent axles. Yet in continental Europe, the story is quite different, with the overall axle loading on the bogie often far larger than the driving wheels independently. Europe seems to have much heavier locomotives proportional to their wheel arrangement compared to the US and UK. Is there a reason for this difference in design in different places? And was there a real reason for the US and UK to have such conservative weights on unpowered wheels aside from adhesive reasons? Also, I think this should be moved to the steam subforum.
What defines how much tonnage a steam locomotive can haul - Weight on Drivers.
US practice has always been about maximizing weight on drivers so as to increase the hauling power of the locomotive. Leading and trailing trucks may be needed for stability at speed reasons, but weight on drivers is the key to hauling more train.
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BaltACD ShroomZed A distinct trend I've noticed is that in typical American and British practice, the axle loadings of unpowered axles were often much lower than the powered axles, often less than half the weight compared to powered both for leading and trailing independent axles. Yet in continental Europe, the story is quite different, with the overall axle loading on the bogie often far larger than the driving wheels independently. Europe seems to have much heavier locomotives proportional to their wheel arrangement compared to the US and UK. Is there a reason for this difference in design in different places? And was there a real reason for the US and UK to have such conservative weights on unpowered wheels aside from adhesive reasons? Also, I think this should be moved to the steam subforum. What defines how much tonnage a steam locomotive can haul - Weight on Drivers. US practice has always been about maximizing weight on drivers so as to increase the hauling power of the locomotive. Leading and trailing trucks may be needed for stability at speed reasons, but weight on drivers is the key to hauling more train.
ShroomZed A distinct trend I've noticed is that in typical American and British practice, the axle loadings of unpowered axles were often much lower than the powered axles, often less than half the weight compared to powered both for leading and trailing independent axles. Yet in continental Europe, the story is quite different, with the overall axle loading on the bogie often far larger than the driving wheels independently. Europe seems to have much heavier locomotives proportional to their wheel arrangement compared to the US and UK. Is there a reason for this difference in design in different places? And was there a real reason for the US and UK to have such conservative weights on unpowered wheels aside from adhesive reasons? Also, I think this should be moved to the steam subforum.
I'm definitely aware of the practice of placing as much weight on the drivers as possible as a general steam locomotive staple, but I'm just taken aback by how much proportional weight the Europeans placed on their carrying wheels.
I thought there was a certain point where bogies and trucks can become overloaded and begin to have worse performance. If so, I wonder what the general standard was to how much of a locomotive's weight was considered safe to place on a nonpowered truck.
I have no comprehension of the European practices, and no explanation of them.
Everybody has a theory and plan right up until the first punch is thrown. US theory and practice has always been about hauling maximum tonnage.
The right person to discuss this with will be Juniatha, but you'll need to PM Wayne and get him to see if she'll send him an answer to PM to you. She no longer comments on the open forum.
My decidedly less valuable impression is that an important determinant of locomotive axle load would come from the relevant influence of the 'civil engineering' and permanent-way on railroad management or ownership. This either to save money on the cost of the trackwork and grade, as in some European cases, or to simplify alignment and preserve what might be heavy investment in low-grade and compensated-curve routes as sen in Britain.
There are other interesting effects on design: three that come to mind being adoption of tapered loading, Stroudley's optimization of lead-driver interaction in curves, and the detail design of Golsdorf's Austrian 2-6-4. I'm sure you are aware of the timeless topic of whether American-style equalization is "preferable" to careful individual axle springing and damping arrangements...
Weight on drivers is best determined relative to service and expected driver tire wear -- neither too much not too little. This in turn puts constraints on the detail design of the steam-generation system and other construction of the locomotive as a whole, and then on efficient guiding of the locomotive trucks, and then on 'best' locations of axles for weight bearing. In my opinion, which might be wrong, it is better to have lead and trailing trucks equalized with at least the nearest adjacent driver pair for best overall performance, even if the peak axle load rises at times.
A couple of 'continental' engines have peculiar truck loading, notably the Thuile locomotive -- it is inexplicable by me why that licomotive has a six-wheel truck. Note that 242 A1, somewhat similar to the production PRR T1s, has the trailing truck wheels so close together as to be almost the moral equivalent of a big Delta single... with dubious loading of the rail as a continuous beam as a result. But remember to look carefully at the truck axles and pivot point with the Bissel formula in mind...
The lead truck has the sole purpose of guiding the locomotive. It only needs enough weight to allow it to do that function. In fact, the weight of the lead truck itself may be sufficient.
The trailing truck, on the other hand, exists to carry some portion of the weight of the firebox, etc. Early steamers were able to carry that weight on the drivers, but a boilers grew, (and with such features as the Wooten firebox), there came the need for that trailing truck.
The goal would still be to keep as much weight on the drivers as possible.
Some trailing trucks had a small steam engine within, used only for starting a train after which the gears disengaged. I believe that was also done with some tender trucks.
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