BEAUSABRE It's impossible in theory - steam locomotives, by their nature, have a narrow range of speeds at which top horsepower is produced (they're always in one gear - 1st on a switcher or drag freight engine, 4th on a MILW class F7 4-6-4 on the Hiawatha). It ramps up to a peak, then falls off. No steam engine ever built could produce the same HP at 20 and 60 mph. It's inherent to the nature of reciprocating steam and one reason diesels took over, with transition and proper gearing, the same design could serve as a helper (F3's with 45 mph gearing on Horseshoe Curve on the PRR) and an express locomotive (F3's with 102 mph gearing on the ATSF). Rather than paying for custom designed small batches (steam builders were job shops), you could enjoy the benefits of the economies of scale of designs built in the hundreds or thousands (lookin' at you GP7 and GP9) due to mass production. "The fixed geometry of any steamer's drive means the maximum power and efficiency occurs within a narrow band of RPM or speed. Although a thoroughly accepted characteristic, this narrow band severely limited the flexibility of assigning locomotives to trains." Anerican Steam Locomotives page 320 by Withun. So no 0-6-0's with a 40mph max power speed range. From page 321 "The diesel's horsepower and efficiency reach maximum quickly - around 8 mph - and stay high as speed increases. Horsepower does not begin to fall off until 40 to 60 mph, depending on axle gearing...To a railroad manager, the diesel is the dream locomotive becuase it maximizes productivity regardless of speed."
It's impossible in theory - steam locomotives, by their nature, have a narrow range of speeds at which top horsepower is produced (they're always in one gear - 1st on a switcher or drag freight engine, 4th on a MILW class F7 4-6-4 on the Hiawatha). It ramps up to a peak, then falls off. No steam engine ever built could produce the same HP at 20 and 60 mph. It's inherent to the nature of reciprocating steam and one reason diesels took over, with transition and proper gearing, the same design could serve as a helper (F3's with 45 mph gearing on Horseshoe Curve on the PRR) and an express locomotive (F3's with 102 mph gearing on the ATSF). Rather than paying for custom designed small batches (steam builders were job shops), you could enjoy the benefits of the economies of scale of designs built in the hundreds or thousands (lookin' at you GP7 and GP9) due to mass production. "The fixed geometry of any steamer's drive means the maximum power and efficiency occurs within a narrow band of RPM or speed. Although a thoroughly accepted characteristic, this narrow band severely limited the flexibility of assigning locomotives to trains." Anerican Steam Locomotives page 320 by Withun. So no 0-6-0's with a 40mph max power speed range. From page 321 "The diesel's horsepower and efficiency reach maximum quickly - around 8 mph - and stay high as speed increases. Horsepower does not begin to fall off until 40 to 60 mph, depending on axle gearing...To a railroad manager, the diesel is the dream locomotive becuase it maximizes productivity regardless of speed."
Fair points. I would just say that the drawbar horsepower shown on the UP graph for the 51" drivered 0-6-0 looks fairly reasonable, rising to a maximum at about 23 mph and falling off after that. Railroads made considerable use of calculations for horsepower and drawbar pull, and I think that's what was done in the case of the 0-6-0 here. And I wouldn't infer too much out of the fact that the graphs go up to 60 mph on several low-driver types. It's a little like assuming the car can go as fast as the speedometer reads.
Yes, I had noticed that the horsepower curves for most types appeared to be based on theoretical models and not actual dynamometer drawbar test data (who would go to the trouble of testing an 0-6-0 switcher in that manner?). The comprehensive test reports on 4-8-4's, 4-6-6-4's, and 4-8-8-4's contains a level of instrumentation for temperatures and pressures that approaches a PRR steam locomotive road test, and which had never before been seen for these large UP types.
timzDid you see https://utahrails.net/flebbe-papers/UP_Horsepower-Curves-and-Tonnage-Ratings-Charts.pdf ? Says a 51-inch driver 0-6-0 has as much cylinder horsepower at 60 mph as at 20 mph. But thanks for the mention -- need to look them over.
Says a 51-inch driver 0-6-0 has as much cylinder horsepower at 60 mph as at 20 mph.
But thanks for the mention -- need to look them over.
I feature that is calculated theory. I can't imagine a 0-6-0 switcher being able to attain 60 MPH.
Never too old to have a happy childhood!
Did you see https://utahrails.net/flebbe-papers/UP_Horsepower-Curves-and-Tonnage-Ratings-Charts.pdf ?
A number of 1940s and 50s Union Pacific test reports and test-related documents were recently posted on the Utah Rails website. They were papers from the collection of Paul Flebbe, the Union Pacific Engineer of Road Tests in the late 1940s, when the railroad was still evaluating steam locomotive performance. I came across this link on Facebook yesterday and haven't gone through everything, but it is quite a new discovery for those interested in steam locomotive engineering and test data. Not much technical test data on modern UP steam locomotive types has ever been published.
https://utahrails.net/flebbe-papers/
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