by Allen Hazen
Ongoing discussion of duplex designs on the Steam Power forum (cf the "Thoughts on the PRR Q-2" string) got me thinking...
Various radical changes to the T-1 design have been discussed. Counterfactual scenarios are easiest to reason about, however, when they involve only a small change from actual history. So here is a proposal: one basic change, not involving any technological concepts that should have been unfamiliar to steam locomotive designers of the period, that might have made the T-1 a more useful locomotive.
The T-1, as actually designed, had 80-inch drivers. Why? Well, the PRR seems to have decided, back in the late 19th Century (!), that this was the "right" driver size for express passenger engines... and then stuck with it. Could smaller drivers have been used? Well, high speeds and small drivers lead to high r.p.m. Is that a problem?
---maybe high r.p.m. makes adequate lubrication harder. But with roller-bearing journals?
---mainly, I think, it makes balancing harder, leading to stress on the locomotive frame. But by the 1940s, with the use of cast-steel bed-plates, this was much less of an issue.
---And, of course, the whole point of the Duplex drive was to reduce the mass of pistons and rods: surely this would have made the balancing issue LESS pressing-- I would suspect that, for any desired speed, the balance and dynamic augment problems would have been lesser for a Duplex than for a conventional layout, allowing for smaller drivers.
Would smaller drivers have allowed the desired speeds? Recall that the Norfolk & Western J (a non-Duplex 4-8-4) managed 110 m.p.h. with 70-inch drivers. (And that British Rail Class 9F -- a 60-inch drivered 2-10-0 -- was run up to 90 m.p.h. on passenger trains!)
Now, the large drivers gave the T-1 a very long rigid wheelbase: 25"4'. This, all by itself, was a problem for the Pennsylvania Railroad: any PRR power, to be useful on long-distance passenger trains, had to run through Pittsburgh, and the West end of the Pittsburgh station has a very sharp curve leading onto the Allegheny River bridge -- a curve that was problematic for the T-1.
So, what if the T1 had been designed with, say, 70" drivers? I think this would have permitted a 33-inch reduction in driving wheelbase (30 inches just because of the smaller wheels, and 3 inches from the use of shorter-stroke cylinders). This would still have left a long wheelbase-- 16 inches longer than some 80"-drivered 4-8-4 on other railroads-- but might have made operation through Pittsburgh (not to mention a certain famous curve west of Altoona) easier. Without, as far as I can see, any real drawbacks.
Thoughts?
Various radical changes to the T-1 design have been discussed. Counterfactual scenarios are easiest to reason about, however, when they involve only a small change from actual history. So here is a proposal: one basic change, not involving any technological concepts that should have been unfamiliar to steam locomotive designers of the period, that might have made the T-1 a more useful locomotive.
The T-1, as actually designed, had 80-inch drivers. Why? Well, the PRR seems to have decided, back in the late 19th Century (!), that this was the "right" driver size for express passenger engines... and then stuck with it. Could smaller drivers have been used? Well, high speeds and small drivers lead to high r.p.m. Is that a problem?
---maybe high r.p.m. makes adequate lubrication harder. But with roller-bearing journals?
---mainly, I think, it makes balancing harder, leading to stress on the locomotive frame. But by the 1940s, with the use of cast-steel bed-plates, this was much less of an issue.
---And, of course, the whole point of the Duplex drive was to reduce the mass of pistons and rods: surely this would have made the balancing issue LESS pressing-- I would suspect that, for any desired speed, the balance and dynamic augment problems would have been lesser for a Duplex than for a conventional layout, allowing for smaller drivers.
Would smaller drivers have allowed the desired speeds? Recall that the Norfolk & Western J (a non-Duplex 4-8-4) managed 110 m.p.h. with 70-inch drivers. (And that British Rail Class 9F -- a 60-inch drivered 2-10-0 -- was run up to 90 m.p.h. on passenger trains!)
Now, the large drivers gave the T-1 a very long rigid wheelbase: 25"4'. This, all by itself, was a problem for the Pennsylvania Railroad: any PRR power, to be useful on long-distance passenger trains, had to run through Pittsburgh, and the West end of the Pittsburgh station has a very sharp curve leading onto the Allegheny River bridge -- a curve that was problematic for the T-1.
So, what if the T1 had been designed with, say, 70" drivers? I think this would have permitted a 33-inch reduction in driving wheelbase (30 inches just because of the smaller wheels, and 3 inches from the use of shorter-stroke cylinders). This would still have left a long wheelbase-- 16 inches longer than some 80"-drivered 4-8-4 on other railroads-- but might have made operation through Pittsburgh (not to mention a certain famous curve west of Altoona) easier. Without, as far as I can see, any real drawbacks.
Thoughts?