Just based on the video (i.e. if we didn’t know where it was shot), I see no way to prove that it’s upgrade at all.
The UP chart claims the climb is compensated-- i.e. the actual grade on each curve is reduced below 0.7% to make the total resistance equivalent to 0.7% on straight track. To estimate the curve resistance they used some simple formula, which may be about right for all we know.
Fictitious is the operative word here, because I’m agreeing with feltonhill that the UP Challenger was a 4,600 -4,700 HP locomotive at best. I’m basing that on its boiler size and the experience of the Western Maryland Railroad with their Challenger locomotives. The WM M2 Challengers had larger boilers than the UP version, yet the WM found out that their huge J-1 Class Potomac 4-8-4s produced more HP above 35mph.
Interesting. 5 8-40CW’s are good for 18,000 HP at the drawbar vs. 4,600 to 4,700 HP for the Challenger. The 8-40CW powered train would have around 2.3 HP per ton vs. 0.6 HP per ton for the Challenger pulled train. Even a mild grade like Archer would have slowed that train right down, and forget about having any acceleration away from a stop or slow signal. Pretty much explains why you always see intermodal trains loaded with horsepower.
For Comparison, and because you mentioned and I had not see it; I looked it up and linked it here;
http://www.youtube.com/watch?v=pl-QVxHIq6o
Edit:
http://www.youtube.com/watch?v=so7-Fu2psjc&feature=related
Here is a video of the 1218 in Apr 87. What is amazing is the size of the passenger train (I’m guessing; about 20 or so cars), Maybe some one can get a better count. Anyway there is a segment of the 1218 slipping on Christianburg Hill near Arthur,Va. Slipped 3 times in starting that train on the grade…Anyone provide what percentage that grade is? Thanks!
It seems you have copied the same URL. ?
-Crandell
Your link was incorrect. Perhaps you meant this link:
http://www.youtube.com/watch?v=zV8rA3UE-lc&feature=related
Actually that isn’t two Class Ys. It is a Class Y 2-8-8-2, a Class A 2-6-6-4, and a third Class Y pushing the rear. Enjoy.
Hey feltonhill, any idea where this was filmed at? Also, can you estimate the weight of the train based on the capacity of the N&W coal cars at that time?
Most of the action was filmed on Blue Ridge grade east of Boaz (the natives tell me it’s pronounced boze, not bow-az) siding near Vinton, VA. The sample on youtube was made as the train approached “photographers bridge” about halfway up the hill. The bridge is long gone and the area has grown over considerably since 1957. I just bought the DVD in Roanoke last weekend, and it’s probably one of the best I’ve ever seen.
A train weight of about 11,000 to 12,000 trailing tons sticks in my mind if three loco’s were used, but I’m not sure.
While there is a mathematical approximation between horsepower and tractive effort, it does not hold in real life actual performance.
Tractive Effort, more correctly known as Starting Tractive Effort, does not remain constant, but immediately drops off for most engines after about 10 mph.
Locomotive horsepower curves are bell shaped, and for steamers, generally increasing as speed increases (and different from diesel horsepower curves).
That’s why diesels can start a train they cannot keep moving on some grades (and stall), and steamers can pull more train than they can start (helpers were used on long trains on the PRR just to get them rolling).
The Union Pacific 4-12-2 produced 4917 horsepower at 37 mph as originally tested during 1926.
The Union Pacific Challenger was designed to exceed that power output and run as fast as 90 mph.
Kratville in The Challenger Locomotives says they were designing for about 5500 horsepower. IIRC, the actual drawbar horsepower was said to be in the 5200 horsepower range.
Starting tractive effort was not important to the Union Pacific**.** Instead, horsepower at speed was–and they really wanted high speed, because they were in a race with Santa Fe and others to see who could move freight the fastest.
John
Also–today’s diesels are using computerized wheelslip control to maintain a much more constant (and higher) rate of adhesion between the steel wheel and the rail than what steam power could achieve. As much as I love steam power, there is no real comparison to today’s diesels. They’re just different animals.
Also–it was customary on the old railroad plans to quote degrees of curvature. This really had to be degrees of central angle, and not the civil engineering definition of degree of curve.
As already pointed out above, the math just doesn’t work out–those old track charts are stating degrees of central angle.
John (civil engineer)
UP 4-12-2 - The formulas
Tractive Effort x speed/375 = Indicated HP
and
Drawbar Pull x Speed/375 = Drawbar HP
aren’t estimates. They are mathematical relationships. TE and DB Pull may be estimates, but the formulas are accurate if the input variables are accurate. If this isn’t the case I’d like to see an example. I’ve been working with locomotive performance for over 40 years, and I’ve never seen a case there these two relationships were proved incorrect.
Also, what kind of horsepower are you referring to, indicated or drawbar.? With steam locos, using the word horsepower without an adjective doesn’t mean much. Kratville refers to 5,400 maximum cylinder HP for the 3900s (p127) which is the same as indicated HP, so he’s specific as far as type of HP. The estimate I gave earlier of about 4,700 DBHP at 40 mph also showed 5,500 IHP at the same speed. That’s one of the reasons I felt OK in posting it because it tied into Kratville’s figure.
The formulas might be correct, but I think someone above was taking starting tractive effort and attempting to convert it to maximum horsepower, which you cannot do. Also, in the real world, and as you indicated in your comments regarding indicated horsepower at the cylinders versus drawbar horsepower, there are other variables and losses that come into play. If the engine wasn’t being fired correctly, or wasn’t working flat out at the maximum output, you get misleading data.
I agree–without having the actual tractive effort curve value for a given speed, you cannot calculate drawbar horsepower correctly.
I sold both volumes of the 4-12-2 books by Kratville and Bush, so I no longer have those curves for that engine–but at 37 mph, tractive effort has fallen off considerably from the peak.
I don’t believe Kratville gives the tractive effort curve of a Challenger–at least not in my 1980 edition of his book.
John
Y6B in compound mode:
152206 pounds TE X say 5 mph divided by 375 = 2094 horsepower
Just sounds a bit low to me. Is it correct? Maybe, but I honestly have no idea.
I’m well out of my depth, but I always understood HP as being a force moving, but also sustaining, the mass at a given speed. Tractive effort is more related to torque applied somewhere along the drivetrain, say at the axles, or a driveshaft. Low speeds are where the torque comes into play, but it falls off rapidly as a HP curve climbs, and that would necessarily mean a steam locomotive develops its useful HP at speeds, often in excess of 40 mph. So, I wouldn’t expect a Y to be producing much more than 1500-2000 hp below 6-8 mph.
-Crandell
And it would be lower still at 1 mph.
“Horsepower” doesn’t have any independent existence-- the force-times-speed-div-by-375 formula defines it. You measure force and calculate horsepower.
A Y6b if held in simple operation at 5 mph will develop about 155,000 lbs drawbar pull based on curves developed from road tests. At this, reading, about 2,070 DBHP is being developed. So your figure is about right. However, the DBHP curve rapidly increased to 3,200 at 10 mph, 5,200 at 20 mph and a max of 5,500 at 25 mph. These latter figures are in compound operation.
In compound operation at 5 mph, the Y6b (and the improved Y5/Y6’s) developed about 130,000 lbs DB pull, or 1,700 DBHP
Starting TE of a Y6b was about 166,000 lbs to as high as 170,000 lbs under the right conditions. For some reason, N&W never changed the rated STE from the 152,206-lb figure.
This is diverging from the point, but I am amazed at this comparatively small engine. If current HO models are accurately rendered, it was much smaller an engine than an H-8 or a Yellowstone, for example, but it out-performed them in terms of brute traction at start-up.
-Crandell
A bit off topic, but wouldn’t the indicated HP be calculated from the PV diagram traced out by a cylinder indicator?
Tractive Effort X speed/375 would be a measure of drawbar HP, provided that tractive effort is measured at some drawbar. Indicated HP is indeed defined as the “fatness” of the cylinder indicator curve. Indicated HP is always greater than drawbar HP because of the friction losses in the cylinders, valves, valve gear, rod bearings, wheel bearings, and even the aerodynamic drag of the locomotive.
The indicated HP is some measure of the thermodynamic efficiency of the engine, that is the efficiency of turning steam at the operating pressure and superheat temperature into mechanical work at the piston faces. Indicated HP does not take into account the efficiency of combustion or the efficiency of heat transfer in turning coal into steam, and it does not take into account the mechanical friction losses downstream of the piston faces.
You are correct, in terms of boiler the Y6b is smaller than the 2-6-6-6 or 2-8-8-4 locomotives. It is basically a large 4-8-4 boiler sitting on a lot more driving wheels. It was designed for low speed lugging power, and it did that very well. The 2-6-6-6s and 2-8-8-4s hit their power peak above 40 mph and were best suited for moving heavy tonnage at those speeds. They were two different animals designed for different assignments.
With the 2-8-8-4s, one could make an argument that the DM&IR did not utilize them to their fullest extent (e.g. lugging around ore trains at relatively slow speed) while the B&O did (not only in coal service, but full use in high speed general merchandise trains and high speed express service). The 2-8-8-4 was the perfect locomotive for the B&O’s high speed main lines, while the DM&IR might have been better served with a version of the Y6b.
TE x Speed/375 is not a measure of DBHP. It’s a measure of Indicated or cylinder HP. Tractive effort is not measured at the drawbar. Drawbar pull is measured at the rear of the tender. This is where the dynamometer car is located during road tests. Therefore, DBHP is calculated from tractive effort/force less the machinery resistance of the locomotive minus the rolling resistance of the locomotive and tender minus the air resistance of the locomotive. IHP is measured by indicator diagrams taken from measurements at the cylinders and converted to IHP by use of a planimeter.
This agrees in large part with earlier posts.