All you mechanical engineers out there, dust off your slide rules and consider this: The knock on the PRR T-1 was that it was slippery, especially at high speeds. So why couldn’t they connect the number two and three axles with inside drive rods? Then they would have a four cylinder 4-8-4. It’s slippery tendencies would be controlled by the more stable rear wheels, PRR trains would run even faster, the diesel would be vanquished and all would be well in the world. OK, maybe the diesels would have won, but it would have been a better fight![(-D]
The T-1 was designed and BUILT specificially to preserve the track.
By seperating the sets of drivers, better high speed was acheived without the intense pounding onto the track everytime the side rods came down.
The design was successful and further improved with the rebuild to a 4-6-4-4.
Engineers did find it to be a bit slippery which was pretty scary at times.
So. The theory behind the 2-10-4 or 4-8-4 is that the large sets of wheels and rods beat the track to death. The seperation of the drives and possibly additional power achieved from a second pair of cylinders may have alot to do with it’s success.
Keep in mind there was no room for inside drive rods. Not to mention a mechanical nightmare. It was actually better that each set of drives did thier own power to the track and they would sometimes phase in and out from each other so. there it is.
The ACE 3000 would have had its middle drivers connected that way. A great article on this is “Did we scrap steam too soon” in the June 1974 Trains. Were both pairs of drivers on the T-1 of the same diameter ? Was the T-1 quartered on the proper side or on the PRR side ?
The divided drive of the T1 (no hyphen, it was the PRR) was supposed to eliminate problems expected with extremely powerful 4-8-4s caused by high piston thrusts and dynamic augment of one set of drivers.
These problems did not manifest themselves with powerful 4-8-4s, so there was no actual need to divide up the power at the cost of an extra set of cylinders and valve gear.
PRR’s Q1 4-6-4-4 was not an outgrowth of the T1, and was not successful. The Q2 4-4-6-4 was moderately more successful but was more slippery than the J1 2-10-4s. The Q2 was tested on N&W’s Scioto Division against performance records of N&W’s Class A 2-6-6-4s and did not come close to equalling the A in heavy tonnage service, even though it was heavier.
Old Timer
Good that you say this half in jest. The T-1 came out in 1945. I think the epitaph for steam was written in 1939, with GM’s FT diesels. In the diesel RR execs looked beyond just a change in hardware technology. They saw it as an opportunity to restructure their workforces drastically. Once they started getting diesels they was no turning back. Instead of having to cross-train their maintenance staff and crews on both steam and diesel and having to maintain separate maintenance facilities, they rushed to get rid of steam totally. Eventually they even got rid of the firemen. I look at the T-1 as a gallant but futile attempt to keep steam viable.
I had never heard that they were slippery at high speeds, but they were a bear to get started and up to speed with a train of any length. The idea of coupling the second and third drivers would somewhat reduce the tendency to slip, the coupling would need to be made to keep the front and rear pistons at 45 degrees from each other so as to make the power as smooth as possible over the entire rotation.
Robert Le Massena argued in “The Big Engines” in June 1968 TRAINS that steam locomotive development in the United States peaked in 1937. Development after that date was held back by World War II and the transition to diesels. The design of the T1, Q2 and S1 were part of a lot of last-ditch designs to hold back the diesel. Many were foiled by their own complexity in an attempt to incorporate too many advances in one design.
Even were such internal rods an improvement over the uncoupled design, in terms of performance on the rails, maintenance costs alone would have made them an unsupportable nightmare. Compare locomotives which did have internal rods – three-cylinder machines like U.P.'s Nines or S.P’s Overlands. Even though the Nines lasted almost to the end of steam (1954-55), they remained a maintenance headache, going only about 25,000 miles between shoppings toward the end. The Challengers which replaced them (and did last to the end of steam – 1962) could go ten times that distance between shoppings.
Also, the third rod of a Nine is unbelievably difficult to get at – why do you think a steam locomotive remains the only one of man’s machines with its working parts on the outside?
Finally, it was not just maintenance costs which killed steam. Diesels eventually became thermally more efficient – a greater percentage of their energy output is converted to work – and with the development of MU connections, crew costs became drastically reduced as well. On a steam locomotive, there really was no substitute for the men in the cab; two cabs meant four men – who all had to be paid.
We have to remember that the T1 had an integrally cast one piece engine bed or frame.
It would have been impossible to fit internal rods on that account alone. Actually, all high speed divided drive locomotives had a tendency to be slippery. I have a video showing the front unit of UP’s Challenger slipping like mad on Altamont Pass while the rear unit remained stable. UP engineers were much more comfortable with the Big Boys as they were beautifully balanced and almost never slipped. The Q2 slipped too if the engineer was ham-handed with it . Both T1 and Q2 were successful if they were in good working order and skillfully handled but the Pennsy guys were just accustomed to much simpler and more robust motive power and the diesel onslaught didn’t allow time for extensive modifications.
Numerous 3-cylinder engines - engines with a middle rod and crank axle - were built with cast engine beds. It would not be impossible to couple the two engine units on a T1 in this manner, as you assert. It would be complex, difficult to maintain, and possibly negate the whole divide drive concept, but it could be done.
A more plausable “pie-in-the-sky” fix for the PRR T1 would be a large sprocket on axles 2 & 3 and a chain drive. Most of these components are available. You’ll fine one set on each side of the larger bulldozers. (Grousers not required).
All these pipe dreams not withstanding, there are two advantages of the diesels which the steam locomotive cannot touch: Steam locomotives cannout MU & steam locomotives have no dynamic brakes.
To wccobb: Have you also been reading “Articulated Locomotives”? The sprocket and chain drive arrangement sounds like it was borrowed from a Schwartzkopf locomotive. Most of those were on light narrow-gauge operations, though.
I rode behind a T1 in July 1947 on the “American” enroute from New York to St Louis. There wa no slippage that I noticed while i was in the diner having breakfast or any other time. But we rolled along at a fast pace even though the train was a long one made up of heavyweight cars. There were few opportunities to catch a look at the front of the train even from the last car because of the lack of curves. But a T1 at speed was a sight worth waiting for.
Sentinel in the UK also used chain drives on a range of locomotives and railcars, some of which were large-ish standard-gauge designs. For an example of a large, heavyweight standard-gauge steam loco with chain drive, see Bulleid’s “Leader” class 0-6-6-0 built for the Southern Railway in the UK.
The PRR T1 is NOT an articulated locomotive. Thus, axles 2 & 3 will remain rigidly “in line” at all times, one of the basic requirements for a successful chain drive.
The starting TE of a PRR T1 is given as 58,300 lbs on PRR tracing D-437564. The Tractive force of PRR T1 No. 6110 was given as 65,000 lbs (Baldwin Locomotives magazine, December 1942, p.5)
The drawbar pull of a Caterpillar D11R is in excess of 330,000 lbs (current Caterpillar web site). That’s 165,000 lbs on each track and it is the track which takes the force from the drive train (sprocket) through the shoes & grousers to the ground.
Read that: one track (drive chain) from a Caterpillar D11R can “absorb” all the “power” from 2.5 PRR T1 locomotives.
Even the most casual glance at the several photographs of the T1’s cast frame in the Baldwin Locomotives magazine is suficient to clarify that there is no linkage possible between axles 2 & 3. (We may be very confident that could it have been done, the guys of PRR woulda done it !!!)
The next “nutty-railfan” assignment: design MU capabilities into the PRR T1 and install dynamic brakes.
Steam locomotives were built with an equivalent to dynamic brake, known variously as Le Chatelier counter-pressure brakes, repression brakes, or water brakes. Commonly fitted to locomotives for steeply-graded mountain lines or rack and adhesion lines, examples may still be seen in service today.
http://www.smrailwayhobbies.co.nz/tr%20abt%20railway%20loco.jpg
The vertical brass pipe behind the chimney is one of the two brake exhaust pipes.
All the best,
Mark.
As designed and built, no, there isn’t. If the requirement was to have coupled the 2nd and 3rd axles with rods, there is no technical reason that a cast bed couldn’t have been designed and built to accomodate this feature. As I noted before, GSC produced a number of cast beds for three-cylinder locos with a crank axle. The same problems apply to that design, and were successfully overcome.
GSC were capable of casting an engine bed with integral saddle, cylinders, cylinder back covers, steam passages, air reservoirs, slide bar brackets, motion brackets and air compressor brackets - I seriously doubt that making provision for rods and crank axles would have been beyond them. I don’t know whether you’ve ever seen a GSC cast bed “in the flesh” ? I worked for six years on the rebuilding of a steam loco with one, and I can tell you that they are an amazing example of advanced foundry work.
It could have been done, and was.
http://www.chapelon.net/cgi-bin/i/pics/plm151a_1.jpg
http://www.chapelon.net/cgi-bin/i/pics/plm151a.gif
I’m equally confident that the Pennsy did not couple the two engine units for the reasons outlined in previous replies - the intent of the divided drive concept was to reduce piston thrust and reciprocating /rotating mass, thereby reducing dynamic augment. Read Ralph P. Johnson’s various papers and articles for a better insight into the divided drive concept and it’s aims. Coupling the two engine units would compromise these aims.
[quote]
QUOTE: The next “nutty-railfan” assignment: design MU capabilities into the PRR T1 and instal
wccob,
If you look at the graph for the drawbar pull of the D11R, the 330,000lbs is extrapolated back to 0 mph. If you extrapolate an AC4400’s power back to 1 mph it equals 1,600,000 lbs of pull.
Unless Caterpillar has found a way to bend the laws of physics, this represents an adhesion of 143% since the D11R only weighs 230,000 lbs fully operational.
The 0 mph pull of 330,000 lbs is not realistic because the dozer will spin its treads before this figure is reached. I’ve heard this called “digging coffins” because if the operator doesn’t stop, the dozer will dig trenches deep enough to bottom itself out. Another dozer will then have to pull it out. It’s similar to why the AC4400 never produces 1,600,000 lbs TE at 1mph; it runs out of adhesion way before that.
If you look down the page, you will see the D11R has a maximum operational pull of 148,500 lbs with a single tooth ripper.
Not to nit-pick, but your comment about the drive train of the D11R “absorbing the power of 2.5 PRR T1s” is not exactly true either.
Drawbar pull is a force, not power. Power is a force over a time interval. If you look at the D11R’s drawbar graph, it’s drawbar pull at 7 mph is zero! 0lbs pull = 0 HP. At 7 mph, the T1 hasn’t even started to rev up.
The D11R does have more low speed pull than a T1, but it has much less total power. The drive train on a T1, however must be built to withstand 5,000 to 6,000 maximum horsepower, so any chain/belt drive would have to be engineered to that specification, not the D11R’s lower power.
One piece of the puzzle is that engineers “cured” the T1 high speed slip problem by running with somewhat reduced throttle and later cutoff.
Think about it. For efficient use of steam, and you have to make good use of steam at high speed, not just for fuel saving but because your boiler will run out, you need wide open throttle so as much as boiler pressure gets to the cylinder, and you need maximum expansion (early cutoff). The T1 poppet-valve gear should have been quite capable for controlling cutoff.
Also think that your cylinders are set up so that at low speed start, you are running very late cutoff (full steam pressure through the full piston stroke), and the wide-open throttle steam pressure should be barely enough to slip the wheels so you get enough cylinder area and steam pressure to get max starting tractivie effort.
One of the things that happens as you increase speed is that the maximum tractive effort declines somewhat. If you are running at high speed full throttle, early cutoff, you are getting a pulse of high piston force that tapers off as the steam expands.
Could it be that at high speeds, full throttle, early cutoff for efficient high-speed running, and with the light rods, that they were getting a bump in tractive effort with each piston stroke that was causing the wheels to break free in a slip? Could it be that cutting back on the throttle and delaying the cutoff produced a somewhat lower and more even peak thrust of tractive effort?
I also read the Champelon was always at war with his locomotive crews for not running wide open throttle and properly hooking up the gear – he criticized crews for wasting fuel by using the throttle to control power. Maybe the crews knew what they were doing and the limitations of highly-expansive working in high speed operation.
If anyone wants to see how complicated a three cylinder steam locomotive is, you can visit the Franklin Institute in Philadelphia, Pa. I suspect that Baldwin Locomotive Works donated the engine because they could not find any customers to buy it. It is a 4-10-2.