The above PRR T1 curves are based on the results from the Altoona test plant. They definitely do not reflect dynamometer car tests. They measure drawbar pull and drawbar HP at the rear of the locomotive, not the rear of the tender. Consequently, the results are much higher than conventional DBHP and DB pull readings, and they are not comparable with the WM test results. They reflect indicated HP developed in the cylinders less machinery resistance. They do not include rolling resistance or air resistance of the locomotive and tender, both of which become significant as speed increases.

For example, the T1 developed about 6,600 indicated HP at the cylinders, 5,700 DBHP at the rear of the locomotive and 4,100 DBHP at the rear of the tender, all at 100 mph. These figures also appear in Vernon Smith’s book, One Man’s Locomotives.

Also, the graphs are based on an evaporation rate of 100,000 lbs/hr, a high, but actually obtained and sustained figure during some of the Altoona tests. The WM graphs are likely nowhere near this, although both the 4-8-4 and 4-6-6-4 could likely produce this much steam per hour if pushed a bit. They both had large boilers.

More to the point, the WM K2 4-6-2 would probably develop its peak DBHP at about 40 mph, but I would be very surprised if it were greater than 2,000 or so. I don't have enough data to do an estimate, but 202 is lighter than a USRA light Pacific, so it's probably smaller in all dimensions.

This may be of help : http://www.alphabetroute.com/wm/1954sd.php

That will help, thanks!! Amazing, WM info hiden under Alphabet Route.

The above PRR T1 curves are based on the results from the Altoona test plant. They definitely do not reflect dynamometer car tests. They measure drawbar pull and drawbar HP at the rear of the locomotive, not the rear of the tender. Consequently, the results are much higher than conventional DBHP and DB pull readings, and they are not comparable with the WM test results. They reflect indicated HP developed in the cylinders less machinery resistance. They do not include rolling resistance or air resistance of the locomotive and tender, both of which become significant as speed increases.

Agreed that the tests are different and result in a different measure of peak power.

However, I assume that the T-1, would have a LOWER power curve, but one with he same basic shape and developing peak power at a relatively high speed.

I'm still convinced that for today's largely pedestrian low-speed operations, a low-drivered freight engine developing peak power at 20-30mph is the way to go.

Let me consider a specific project where alternatives existed. I'll surely ride the B&M 3713 when it runs; marvel at it, but will be expecting a diesel assist if it rains and its got 8 heavyweights up the grade. but if I had a "do-over", unlimited funds and was suddenly appointed Sec of Int, I'd push to restore the IC 790 (especially given the emphasis on yard operations) or if "big power" is necessary, the NKP 759. It will never run at its intended design speed in excursion service. Now of course, the interpretive value of a real passenger engine is another matter-I just favor mechanical considerations.

I have to agree with you on that point.I would think in the long run it would be less expensive and more practical to rebuild the 790 for that particular job. I'd love to see the B&M engine run,but highballing at 70 (where is where she is in her element) instead of slogging along ant 20-30MPH.I think some have fallen into the trap Class Ones did with some of their steam, but for different reasons.

Superheater - You're correct. The PRR T1's DBHP curves (measured at the rear of the tender) would have a similar shape to the LDBHP curve, but at a lower level and lower speed. For example, during N&W dynamometer tests with PRR T1 5511 (yes it actually happened in June 1948) the T1's peak DBHP was 4,600 at about 55-60 mph, with a more normal evaporation rate around 80,000 to 85,000 lbs/hr.

In the FWIW category, based on the locomotive diagram, WM 202 would probably produce a little over 1,700 DBHP at 35-40 mph.

For mainline excursions, I'd suggest that we've seen two types of locomotives that are almost ideal for that service recently - NKP 765/PM 1225 and Milw 261. These are medium size locomotives, not excessively large in any dimension, weights on driving axles are reasonable. They can dig in at lower speeds well enough (765 has the advantage at lower speeds) and can run with the best of them at any normal track speed.

I'd also suggest that for a go-anywhere loco, look no further than a USRA light 2-8-2 (NKP 587 as an example). This loco would have lower driver axle loadings, adequate low speed dig, and could still kick up its heels at 45-50 mph when required.

The main problem I see with something like a heavy 2-8-0 or 2-10-0 (WM types listed above) is that they tend to have high driver axle loadings (70,000+ IIRC), and will start to pound the rails at even moderate speeds. Sometimes an excursion run needs to get out of the way. Freights can move fairly rapidly today.

"For example, during N&W dynamometer tests with PRR T1 5511 (yes it actually happened in June 1948) the T1's peak DBHP was 4,600 at about 55-60 mph, with a more normal evaporation rate around 80,000 to 85,000 lbs/hr."
What was that occasion? I have read the PRR tested an N&W A class; then went and built duplex locomotives-never knew the N&W tested PRR. I'm guessing the test results weren't satifactory and that's what caused them to build the extra J's?

Back to my original point thought. Its harder and harder to get on a mainline to have a freight to get away from. If you are going to get into a rebuild.. well, you know..

Superheater - At the risk of being accused of hijacking this thread, I'll try to answer your question as briefly as possible.

The N&W test of the PRR T1 was published in the Summer 2009 issue of PRRT&HS magazine, The Keystone (Vol.42, #2). It was also published in the N&WHS magazine, The Arrow, Nov/Dec 2006. PRRT&HS sells single back issues, NWHS only sells an entire year as a group. Disclaimer - this is not an unbiased recommendation, I wrote the articles.

Here's a thumbnail sketch of pgs 52 to 66:

PRR was rapidly dieselizing its passenger service and wanted to sell the T1's to a railroad that still used steam in 1948. N&W was partly owned by PRR and was a natural choice.

The T1 was not built for N&W's grades, so it didn't fare very well in the tests on Christiansburg mountain. It was able to handle the equivalent of a 13-car train, but not as fast as the J. In maximum tonnage tests the T1 successfully handled a 1,220 ton train and the J a 1,758-ton train, both at about 25 mph. The reason was the J's low speed tractive effort superiority.

In other tests between Petersburg and Suffolk, the T1 did better. Tests were run with a 21-car passenger train. Coal and water usage were measured to determine which locomotive was the most economical to operated in three different speed bands. In 65 mph max speed tests, the J used less coal and water per unit of output than the T1. In the 75 mph max speed tests the results were mixed. In the 85 mph max speed tests, the T1 used less coal and water per unit of output for all tests. It also covered 30% of the distance between the two end points at 85 mph or better. The J covered 12%. The reason was the T1's high speed horsepower capability.

You can see that both locomotives did what they were designed to do for their respective railroads. Neither was ideally suited for the other.

N&W correctly concluded that the T1 did not have sufficient capacity in the speed ranges that its passenger service operated.

I doubt N&W seriously considered the T1 for purchase, even before the tests.

A quick correction regarding 765's supposed advantage. 1225 has 1" larger nominal diameter cylinders (26x34) versus 765 (25x34). So standard tractive effort for 1225 is 69,350 lbf versus 64,100 lbf for 765. I say nominal and standard because the Advisory Mechanical Committee Standard Maintenance or Equipment Instructions allow reboring cylinders to 3/4" oversize before bushing replacement and of course tires do wear. 1225's cylinders were at 26.415" when we manufactured piston rings in the '80s and the tires are worn to around 68-1/2" so tractive effort is higher on both counts. The tire diameter as built and as used in both tractive effort calculations is 69" but was increased to 70" on the PM berkshires following WWII. This may have coincided with merger plans with the C&O or it may have been an independent attempt at a speed increase. The main was cross counterbalanced at the same time.

The boilers on the 1225 and 765 are so similar that I don't think they have any bearing on performance differences. Maybe one 2-1/4" tube and a fraction of an inch on mudring width. There may be more differences between PM berkshire classes.
What might have some effect is valve events and roller bearings. PM never owned a roller bearing axle on a steam locomotive. Both the earlier Alco NKP berkshires and the Lima PM berkshires were built with 1/16" exhaust clearance. At some point NKP changed to line in line exhaust. I don't know if 765 was built that way or modified later.

The point of this digression is that 765's advantage over 1225 is not tractive effort, nor is it likely to be peak horsepower, given equal boiler capacity and pressure. I would expect the advantage of 765 to be a higher speed at peak horsepower, but even there it wouldn't be more than a few mph.

I agree that AMC berkshires make good medium speed excursion engines, but they have limitations. The fact that they were designed as freight haulers means that wheels, rods, and counterbalance were not "state of the art", but "good enough". The long piston stroke means high piston speeds as well. They are not speedsters. 79 mph would probably be more vibration than most would want to take. 90 mph would be bouncing the drivers down the rails.

Now to the theme of the thread. If you operate your own tourist railroad, the speed of operation is probably governed by track condition. The difference between class II at 30mph and class III at 60 mph is surface and annual rail detector car operation with the comitment to fix any defects found. This just doesn't make sense for a one hour tourist ride. The upshot is that I agree that small drivered power is a better match for a tourist operation. However, many "small" freight engines have far more tractive effort than a tourist operation usually requires. Perhaps what is needed is an analysis of the horsepower needed to operate the line at the desired speed and then assuring that power chosen can provide adequate tractive effort at that speed. As always, some reserve to avoid beating the engine to should be included.

Andrew Adams

I looked at the graph and the first thought that popped up what how it shows how nicely Strasburg's big steamers are matched to their operation.

Bob

There was some fascinating in cab footage shot of 261 on The New River Train. Hearing the hogger talk about running a locomotive not designed for the route is insightful. 261 was giving all she had, but with larger drivers and smaller pistons then then Berks she was operating outside of her potential. What with 30 cars on a mountainous curvy terrain.