hmmm...Kozzie musings......hmmmmmm.....

[M636C]

Sorry, my simplified description of the Krauss-Helmholtz was directed at indicating its effect on the running gear clearances rather than being a technical description. Both leading and leading coupled axles are carried in the main frames in arrangements indeed similar to lateral motion axleboxes, and the beam connections to both axles are by pivots on what are essentially "cannon boxes". There were preloaded spring lateral motion arrangements at the K-H pivot as well, as in a conventional leading bogie.

The amazing thing about these trucks was that the Germans put them on their War Locomotives classes 52 and 42, on which everything was supposedly simplified for wartime production.

I suspect the US builders viewed them with suspicion as being "not invented here", but they would have been interesting on Berkshires and the larger wheeled Texas types, like the ATSF 5001 class.

I'll look up Chapelon's book and get back to you on 242A1

Peter

[Overmod]

All this correct, of course, from my extremely sketchy knowledge of Czech steam.

There's a bit more to a K-H bogie than the pivoted beam! Since the leading axle articulates sideways, it requires a pivot on the beam to keep the rodwork aligned 'on quarter', and also pivots (mere clearance WON'T cut it!) in the forward side rods so they can move laterally with the shifting axle without binding under load. There also needs to be some sort of fixed guide in the main locomotive frame for the leading axle's bearings which is capable of taking the rod loadings on the front drivers, yet allow the controlled lateral motion required by the bogie.

I would note that implementing this kind of system on a modern American locomotive with lateral-motion axleboxes ought to be quite simple, at least in principle; I'd like to see informed opinions about why late American Berks in particular didn't try this approach with lateral-motion control.

Likewise -- what WERE Chapelon's reasons for using a four-wheel trailer on 242 A1?

[M636C]

The 486.0 4-8-2s were built by Skoda in December 1933 and the 486.1 2-8-4s by CKD late the same year, formally entering service in April 1934.

The 486.1 inside cylinder drove on the second axle, but the outside cylinders drove on the third axle. It did have a Krauss-Helmholtz truck connecting the two leading axles. I think you have a more complex idea of the K-H truck than the reality. The "truck" is really just a beam under the axles, with a pivot under the cylinders (in the case of the 486.1).
Slezak's "CSD Dampflokomotiven" (1969) has scale drawings of the 486.0 and 486.1 on the front endpapers. Surprisingly the smokebox, barrel and firebox on both locomotives are almost identical in dimensions, although the 2-8-4 has a vertical throatplate while that on the 4-8-2 is angled back to clear the trailing drivers. This might explain the small difference in grate areas! I think the number of axles was determined by the weight and axle load, and they were willing to try both options. The Austrians had just built a 2-8-4, and the CSD had Golsdorf 2-6-4s in service themselves.

I'm not sure what you mean about 242A1's boiler. The basic boiler was modified by Chapelon, but it was to the same external dimensions as it had been when built, and that loco was a 4-8-2, 241-101. Chapelon added the new two axle trailing truck.

The three cylinder compound (a "Smith" or "Chapelon" compound) was class 476, a smaller slower and lighter loco (you can say all that just from the class), with 1624mm drivers rather than 1830mm. Only three were built (against 147 equivalent 475.1 two cylinder locos) and they were all rebuilt as two cylinder locomotives. One was given to the USSR (after conversion). These were said to run roughly because the power in the outside low pressure cylinders was less than expected.

The largest local 2-10-0 in Czeckoslovakia, the 556.0, was basically the German 52 chassis with a boiler from the 475.1 4-8-2. This was really useful, and they built 510, many more than all the 4-8-2s combined.This is the only Czech steam loco class I've seen, in 1975 in Gmund, Austria.

Peter

[Overmod]

Not attempting to second-guess Czech designers (who I understand were competent):

I believe the competition you describe was in 1932, and the nominal reason was that the existing 4-6-2 locomotives were becoming incapable of handling heavier trains on some of the grades. One might suspect, then, that a 4-8-2 design would be adequate if the grate area were sufficient to support the additional cylinder capacity. Be interesting to compare the 4-cylinder Norwegian 2-8-4s of slightly later vintage (1935).

There is nowhere near a 'reasonable' difference in the grate areas between these two locomotives that would justify a four-wheel trailing truck (instead of a two-wheel version). At the same time, we might presume that the 2-8-4 would have a shorter boiler, a shorter smokebox, or both compared with the 'equivalent' 4-8-2 (I have no pictures to confirm this) and that might affect the steaming capability. Without a Krauss-Helmholtz or similar arrangement -- which I would find somewhat difficult to arrange correctly on a three-cylinder engine with all three rods driving on the second axle -- an early-Thirties two-wheel lead truck would almost certainly be ill-suited to express passenger working at the speed (110kph) involved; it would also in all probability be less well suited to controlling the lateral motion of even a three-cylinder engine at high power (which may explain the cylinder 'derating' conducted later, perhaps better than a hypothesis that the boiler was somehow defective in steam raising capability)

Postwar improvements on the Czech 4-8-2s were interesting, including Kylchap nozzles (with consultation by Andre the Giant himself!), circulator syphons and arch tubes, rocking grates, etc. My opinion is that a two-wheel truck was quite sufficient to support all the boiler that these classes of engine required; I can find no indication that Czech designers even with close input from Chapelon thought it either necessary or desirable to use the sort of boiler characteristic of, say, 242 A1.

Now, "Super Power" in Eastern Europe would have been applicable to freight, not passenger -- and in Czechoslovakia as in Germany the 2-10-0 appears to have dominated operations. There is an interesting note in the literature regarding one of the other Czech three-cylinder classes, with Chapelon-style compounding -- it was optimal in continuous heavy-steam-consumption operation, but not so economical in what was called 'typical' Czech running, which involved (as in most American practice) frequent power changes. My guess is that the extra driver axle proved more "useful" than a bigger grate.

[M636C]

Guys,

The 38" wheels come with the load capacity, they are the AAR standard for G type (6.5"x12") bearings. My understanding was that the larger wheel diameter increased the contact area with the rail and reduced rail stress and wear. These are called "125 ton" trucks, that being the car capacity.

I spent most of 1975 until 1978 investigating the tracking performance of these trucks as applied to ore cars, 10.36 m long cars loaded up to 140 tonnes gross.

We were concerned about wear in tangent track areas as well as curves. My conclusions were that the state of longitudinal force in the train was quite important. Many of our problems occurred in dips where there was briefly no traction or buffing forces in the train, allowing the cars to "dance about" if disturbed by minor irregularities in the track. The trains ran about 140 cars in those days. Now they run about 330, but with a pair of DP units at the head of each.

I should get back to the original thread topic.

To start, to make sense of what I'm saying we have to define the Czech steam locomotive classification. They used three digits (as was common in Central Europe) but with specific meanings:

First number = number of coupled axles.
Second number= add three, multiply by 10, get max speed in km/h.
Third number= add ten, get axle load in tonnes.

The Czech locos I alluded to earlier were classes 486.0 and 486.1, which were 4-8-2 and 2-8-4 locomotives for passenger work, each with three cylinders 550mm x 680mm, and with coupled wheels 1830mm diameter (close to 6'). The boiler pressure was 16 kgf/sq cm for both. The 2-8-4 was heavier, 107.5 tonnes and had a 5 sq m grate, while the 4-8-2 had a 4.83 sq m grate and weighed 102.3 tonnes. Three 2-8-4s and eight 4-8-2s were built.

As should be clear, any road that includes the axle load as part of the classification is worried about weight, and weight distribution was very important. There were previous passenger locomotives with 2-6-4 and 4-6-2 wheel arrangements, trying to balance locomotive weights on even lighter tracks.

The 4-8-2 "won" and forty two more 486.0 were built, but were reclassified 498.0, as more speed and higher axle loads were now permitted. Fifteen more class 498.1, slightly modernised were also built. All these locomotives used double return cranks on the left side to drive the centre valve.

A slightly smaller two cylinder locomotive, 4-8-2 class 475.1 had 147 units built (plus another 25 sent to North Korea).

So in Czech conditions, the 4-8-2 "won" on closely matched designs with similar dimensions. In fact, the 2-8-4 was found to be uneconomical and had the cylinders reduced to 500mm diameter - so much for "Super Power" in Central Europe!

Peter

[Overmod]

The added wheel size on modern freight cars is almost certainly for longer wheel life (and perhaps lower bearing speed) rather than higher weight-bearing capacity. Using taller wheels in the middle might be an attempt at equalizing wear on a given set so that all the wheels would 'wear out' at the same time -- this seems reasonable to me.

I don't think that in this general range of diameters there's much real difference in tracking characteristics. [If you get smaller -- down to 28" -- the wheels are turning more quickly, and wear faster, especially at higher permitted loadings; if you get substantially bigger the wheels begin to exert more gyroscopic moment (think "flywheels") at high rotational speeds, which can affect tracking.]

My understanding of the large pilot wheels on some of the Western engines is that it's related to the frame and cylinder-block height relative to the railhead. As you get taller and taller drivers, there's more available room, and e.g. to reduce wheel wear for a given axle loading you have more room for larger wheels. You can also carry the pilot truck frame up a bit closer to the frame, and hence perhaps make it, or the locomotive frame, a bit less heavy than it would otherwise be. Note that the permitted swing and lateral excursion of the lead truck is going to affect how large the wheels can be in many cases; the rear pair in particular can't foul any part of the crosshead assembly, rodwork, or valve gear...

Large *trailing* wheels can be for a different reason, of course: they help make booster engines run better.

[Anonymous]

Regarding articulated cars, after reading this thread I spotted how 'all purpose spine cars' are articulated and it is quite a bit different from newer cars. Another difference I've noticed some time ago on double-stack well cars is 38" wheels in the middle with 33" wheels at the ends. I've assumed this is because of the extra weight, but are there other reasons??? Does wheel size also affect tracking??

Going back to steam, some of the Super Power Northerns, Hudsons, etc., had fairly large pilot wheels, IIRC late UP Northerns were ~40" and of course most passenger cars had larger wheels than freight. Were the large pilot wheels for speed, weight, or both???

[Kozzie]

QUOTE: Originally posted by Overmod

Let me see if I can be a bit clearer this time:

2-8-4 and 4-8-2 are from different evolutionary families: Think of the 4-8-2 as evolving from the Pacific (by getting one more driver) and the 2-8-4 as evolving from the Mikado (by getting a much bigger firebox with extra bearer). They're different. Still more different, continuing this analogy, is a comparison between a 4-10-2 and a 2-10-4.

The point of what I was going after with 2-8-2s is that you do NOT go from 2-8-2 to 4-8-2 evolutionarily -- nobody needs a 'more stable' Mikado, they need an eight-wheeled freight locomotive with more available power. Hence the concentration on the back end, and (in original SuperPower form) not that much emphasis on high speed vs. better running at typical slower speeds -- hence the combination of lightweight rodwork with a relatively primitive Bissel truck. Completely different thinking was going on, most of the time, when 4-8-2s were designed -- here you were making an eight-drivered engine out of something that started out with fewer drivers, rather than expanding something that already had eight drivers...

Now, it's non-trivial to get to a 'different kind of 4-8-4' by expanding capacity of the two initial locomotive types: A more capable boiler on the 4-8-2 can be gotten by using a four-wheel trailing truck, or a 'more stable' express version of the 2-8-4 can be achieved with the four-wheel leading truck. The first would be optimized as a 'passenger' engine, the latter as a fast freight engine. Eventually you get a convergence like one of the later ATSF 4-8-4 classes, with 80" drivers, big cylinders, bigger boiler, and reasonable stability.

Now, an interesting comparison -- which I think has, in fact, been suggested elsewhere -- would be to look at a NKP S-3 vs. one of the later NYC Mohawks. What might make this suggestive and sweet is that we're about to have a running example of the S-3 (#765) and Mohawk 3001 in Elkhart is supposedly in restorable condition, so in theory a reasonable physical test could be arranged...

Does this make what I'm saying any clearer?

Overmod [:)] Thanks for that - I understand better now. Thanks for your patience.
A classic case of "horses for courses" [;)] [:)]

Dave

[mudchicken]

QUOTE: Originally posted by M.W. Hemphill

Overmod: Here's what my track engineer friend sent me (now if I could just get him to participate directly):

I’m not going to get into this too deeply, but the wear under consideration is minimal – not the dramatic gauge corner you see in the body of a curve. Mostly, it’s a slight rounding of the gauge corner, but still more pronounced than you’d find in tangent track. It won’t be apparent on broad curves.

As to causes, I can only report what I’ve observed. While most freight car trucks steer reasonably well, there are the “bad actors” in the fleet, which generally show up under heavily loaded cars (since the steering moment is a function of friction, which is a function of the vertical force on the center plate). Slewing (“lozenging”) of the truck is also a factor, but less, I think, that the steering issue. And the force (measured at the flange) required for truck rotation will probably be quite high under any circumstances, though I can’t give you exact numbers without the coefficient of friction of the center plate liners. One poster (presumably a mechanical department guy) implies that car trucks rotate freely. Yes, but only in a relative sense. But I wouldn’t expect any less from a mechanical department guy! I don’t believe that the polar moment of inertia of the car as a whole has much to do with the instant case.

Still not convinced? Go stand out just beyond the end a relatively sharp curve (not a sweeping curve on the prairie) and just listen to the squeal of some of the trucks after they’ve exited the body of a curve. This is a sound you don’t hear on long stretches of tangent track when everything is behaving normally. (Don’t get me into a discussion of spirals, here, since they are often executed incorrectly in the field, particularly on the sharp curves which are of concern in the particular discussion).

That being said, the person who discussed articulated cars brings up an interesting point. The side bearings (a proprietary ASF design?) of the early cars were, as I recall, blamed for a series of rail rollover derailments. After much testing, what was discovered was that the cars act as if they had one leading truck and five trailing trucks going one direction. Going the other direction, the car acted as if it had five leading trucks and one trailing truck. The cause was the fact that the side bearings of one well “sat” on top of the side bearings of the adjacent well, which contacted the truck side bearings. The side bearing arrangement, that is, which bearing was on the “bottom” in relation to the direction of travel, was consistent along the length of the car. Don’t know how, or if, this has been resolved, though I would assume modifications have been made.

AMEN! & Kudos to the silent track engineer! (especially on the parenthetical on spirals! - So many folks on the track side do not understand what a track liner does or how it operates....getting folks to line track to a surveyed solution is almost unheard of anymore and reliance on a machine solution curve is standard.....)

[Overmod]

Modelcar: To my knowledge, no centipede was made with blind wheels. In my opinion it would have been nearly impossible to get a tender like this to track straight without the lateral composite springs; conventional lateral-motion boxes with coils would have suffered induced oscillation almost no matter how much damping you could apply to them, since very small perturbations off center would result in considerable flange contact, but much more absolute excursion relative to the frame would be required in curve following...

Apparently the pedestal axles were quite flexible. I suspect Steve Lee and the Heritage team could give you all the operating experience and opinions you might need about how these tenders operate in service.

I'm still hoping to hear what kind of wear the exiting '100 feet' suffers, particularly whether it shows periodic effects or is continuous. I do not really think that sway would result in substantial amounts of this kind of wear, as it would manifest more as tread loading than gauge loading, and tread loading is a rolling contact. However, I do agree it can be a substantial effect, particularly in cars with long-period 'slosh' -- I've seen tank cars on KCS in Shreveport creaking and rocking on their bolster springing 20 minutes or more after coming to a standstill, and that was after slow-speed operation.

Peter -- I'm not convinced this is either a centerplate lubrication or lozenging issue per se, although I would rapidly agree that instrumented testing to determine both factors can, and should, be undertaken (e.g. by FRA). I think mudchicken is onto something with its being an artifact of particular MOW practices.

I'm not sure that the wear would be 'only' on the inside rail, because you'd have effective 'scrubbing' of both axles, the inside tread on one and the outside tread on the other doing the 'dragging' -- remember this is on tangent track outside the curve and/or transition, as I understood Mark to say.

I wonder whether some of the effect is related to the mismatch between the line followed by the truck center and the line between the coupler-face points through which draft vector force is observed. Especially with stretched hydraulic underframes, the 'swing' coming out of curves is considerably outboard of the arc followed by the center pivots. No guiding force is applied to the truck frame, and ideally the matched coning of the railhead and tread does the truck-frame steering... and thence, the 'cornering force' that actually turns the car. But the only way that cornering force can be communicated to the carbody is via the truck pivots... which do no axle guiding, only bolster guiding.

I think that the rate of 'car rotation' will have been steadily decreasing as the car traverses the exit transition spiral -- that being one of the points of having a spiral -- and I think by the time you're out of the curve any residual rotational acceleration (around the vertical axis at the car's centroid) would be very slight compared to the absolute centripetal accelerations that perform the 'cone' centering action. I'd be much more concerned with hunting, and of course lozenging is often encountered during 'hunting season'!

[jchnhtfd]

mudchicken -- I wonder, too, just how much of that excess wear on the leadout from a curve is related to simple sway on the cars -- particularly things like double stacks and covered hoppers -- as they come back to level (we hope) -- which they have to do, unless you happen to be going at exactly the balancing speed for the superelevation... also maybe from the fact that the whole car is rotating around its centre (not obvious, but it is) and that rotation has to be stopped, which requires extra force on the lead truck inside flanges and the back truck outside flanges...
just musing...

[Modelcar]

....With the mention of centipede tender wheel arrangements....in above conversation and mentioning..."This permitted each axle to float laterally -- there were no restricting pedestals -- or horn plates", did this have anything to do with helping the long line of "rigid" wheel arrangement around a curve...and or did some of the tender wheels remain flangeless....?

[M636C]

Guys,

What did US lead bogies use for side control. Most English sources talk about the French De Glehn bogie with pre-compressed springs as the optimum arrangement, obtained in the UK with the French four cylinder compounds in the first decade of the Twentieth century.

With regard to curve wear, if the problem was with centre plates, wouldn't the extended wear be on the inside of the curve, because the truck would remain in the curved postion.

If the wear is on the outside rail, it must be caused by excess "lozenging", allowing the axles to take up a counter-curving angle of attack.

In Czechoslovakia in the 1930s, prototype locomotives were built with similar dimensions but with 2-8-4 and 4-8-2 wheel arrangements. The 2-8-4s remained as prototypes, but the 4-8-2s entered production. So in a way, they answered Dave's question - the 4-8-2 was superior with other things being equal.

Peter

[mudchicken]

QUOTE: Originally posted by M.W. Hemphill

Interesting -- a track engineer I was talking to on Saturday noted that curve wear extends 100 feet or so beyond the end of the curve as the trucks on ordinary cars take a while to recognize that they are no longer in a curve.

(1) Try center-bound trucks on any cars, but especially stack cars (lubrication of the center plates remains an issue)
(2) Some of that wear is the doglegs left behind by conventional track lining equipment and the cars in sway reacting to the doglegs.[}:)][}:)][}:)]

[Overmod]

Let me see if I can be a bit clearer this time:

2-8-4 and 4-8-2 are from different evolutionary families: Think of the 4-8-2 as evolving from the Pacific (by getting one more driver) and the 2-8-4 as evolving from the Mikado (by getting a much bigger firebox with extra bearer). They're different. Still more different, continuing this analogy, is a comparison between a 4-10-2 and a 2-10-4.

The point of what I was going after with 2-8-2s is that you do NOT go from 2-8-2 to 4-8-2 evolutionarily -- nobody needs a 'more stable' Mikado, they need an eight-wheeled freight locomotive with more available power. Hence the concentration on the back end, and (in original SuperPower form) not that much emphasis on high speed vs. better running at typical slower speeds -- hence the combination of lightweight rodwork with a relatively primitive Bissel truck. Completely different thinking was going on, most of the time, when 4-8-2s were designed -- here you were making an eight-drivered engine out of something that started out with fewer drivers, rather than expanding something that already had eight drivers...

Now, it's non-trivial to get to a 'different kind of 4-8-4' by expanding capacity of the two initial locomotive types: A more capable boiler on the 4-8-2 can be gotten by using a four-wheel trailing truck, or a 'more stable' express version of the 2-8-4 can be achieved with the four-wheel leading truck. The first would be optimized as a 'passenger' engine, the latter as a fast freight engine. Eventually you get a convergence like one of the later ATSF 4-8-4 classes, with 80" drivers, big cylinders, bigger boiler, and reasonable stability.

Now, an interesting comparison -- which I think has, in fact, been suggested elsewhere -- would be to look at a NKP S-3 vs. one of the later NYC Mohawks. What might make this suggestive and sweet is that we're about to have a running example of the S-3 (#765) and Mohawk 3001 in Elkhart is supposedly in restorable condition, so in theory a reasonable physical test could be arranged...

Does this make what I'm saying any clearer?

[Kozzie]

Overmod

I think I have understood most of what you said.

But in your paragraph you compare 2-8-2 with 4-8-2...
First of all: the 'proper' comparison would be 2-8-4 to 4-8-4, as the firebox (at least in American practice) is a much more important constituent than the lead truck arrangement. It's usually unfair to compare a 2-8-2 to a 4-8-2, as the former is generally purpose-built as a low-drivered general-purpose freight engine, while the latter is normally either a passenger engine....."

but I was trying to compare 2-8-4 with 4-8-2...or is that what you meant???

Dave

[Overmod]

Mark -- how much of this did he say was 'slow return' (or inertia) and how much was induced oscillation? Any mention of the KIND of wear he was talking about (e.g., gauge corner vs. tread profile)? And to what extent is the issue induced, exacerbated, or driven by worn wheel-tread or railhead profiling?

I had not thought that (with modern lubricants) there was any substantial impediment to truck rotation around the pivot. I have not, however, looked at this issue since legal axle loadings increased -- and there may well be nonlinear effects showing up now.

Do you have an easy way to check the recent material on the 'stick' solid flange lubricators or the railhead-lubrication systems to see what they might believe are driving causes of the exit-wear problem?

[Overmod]

Well now, that would depend on a variety of things, like how fast you intended to run, how long your turntable was, how high-quality was your trackwork (and how well are the various compensations on curves, grades, spirals, pointwork, etc. done), and what kind of suspension you were prepared to use.

First of all: the 'proper' comparison would be 2-8-4 to 4-8-4, as the firebox (at least in American practice) is a much more important constituent than the lead truck arrangement. It's usually unfair to compare a 2-8-2 to a 4-8-2, as the former is generally purpose-built as a low-drivered general-purpose freight engine, while the latter is normally either a passenger engine (think "bigger Pacific" or a dual-service locomotive running at higher speed. A 2-8-4 can be (and often was) a high-speed locomotive.

And of course the "historical" answer to your question is rather obviously displayed by the relative prevalence of the 4-8-4 wheel arrangement, across a wide range of different roads with different operating philosophies. If there has to be one 'classic' wheel arrangement for heavy steam power, that's it. But if I understand your question correctly, you're asking whether there's a way to make a two-wheel lead truck 'better' -- and my opinion is yes.

A fundamental problem with 'conventional' four-wheel lead trucks is that you generally need a longer piston rod, crosshead, and main rod than you would if there were no space required for a wheel between the cylinder and the first driver. You also want to minimize your rigid and overall wheelbase, and have as much of the engine weight available for traction as you can arrange.

The 'traditional' American two-wheel lead truck had frankly lousy guiding and suspension characteristics -- much worse than pin-guided four-wheel lead truck acting as the forward 'leg' of tripod equalization. In Europe you found things like Krauss-Helmholtz bogies (which combined the pony axle with the first driver axle in a common frame) -- don't expect such a thing to last particularly long in American service! Interestingly enough, however, there were some experiments right at the ragged last edge of steam that made two-wheel tracking at least the potential equal of a conventional four-wheel truck -- and possibly better.

You need to be familiar with the suspension under pedestal (aka centipede) tenders to understand what those experiments involve. Note that the lateral stability and 'restoring force on deflection' that a leading wheelset must exhibit is ideally not linear -- you want tight response for small oscillations off center (so you damp out hunting) but somewhat quieter and slower response for slightly larger oscillations ( to give good curve entry without higher flange wear) and then progressively harder force with increasing deflection (to give faster restoring force coming out of curves). Some modern approaches to the question of overbalance on steam locomotives (cf. the Norfolk & Western J-class 4-8-4) used very tight lateral compliance on lead and trailing truck to keep the locomotive steady on both tangent and curved track, but this exacted a price: the locomotive was more prone to (and often did) derail on poorly-surfaced or curved track.

Now, a centipede tender has a very long apparently rigid wheelbase -- as long as some 10-coupled locomotives. Yet these tenders were known for good flexibility and tracking -- better than tenders of equal capacity riding on pivoted trucks, in many cases. This was accomplished by providing lateral guidance and restoring force via horizontal composite shear springs -- like sandwiches of rubber and metal plates -- between the journal boxes and the lower spring bearers. This permitted each centipede axle to float laterally -- there were no restricting pedestals or 'horn plates' -- with very good damping and progressive restoring force, and very little 'dead center' play. Suspension and equalization were relatively unaffected. One manufacturer of these springs used the trade name "Fabreeka."

N&W, observing the good performance of this kind of arrangement, experimented with putting Fabreeka springs into two-wheel lead trucks. I have not seen firsthand reports of the testing, but I strongly suspect that with proper revision of the lateral weight-bearing guidance of a two-wheel truck frame and with a Fabreeka or chevron spring providing small-displacement lateral compliance for the leading axle, there would be no particular stability issue up to reasonably high speeds (and perhaps even extremely high speeds). As an additional benefit, such a truck would be inherently dynamically stable when running in reverse (something that is manifestly not true for most designs of pin-guided lead trucks in reverse at high speeds!)

For almost all railroads using steam locomotives, a relatively low-drivered Berkshire would be all the locomotive needed, in a smaller and lighter package than an equivalent 4-8-4, and the shorter frame would allow a larger tender to be carried for a given turntable or stall length. Plenty of room for boosters on the trailing truck, too, if improvements in slow-speed starting are wanted... it's a bit dicier to use a high-speed or highly-powered booster on a single-axle Delta truck than on a four-wheel truck.

I'm open to arguments about the relative need for four-wheel trucks on even moderately heavy power -- there are strong arguments, for example, that NYC's Mohawks were 'better' engines than Hudsons in just about all practical services, even with only a two-wheel trailing truck. (Of course, no Mohawk was anything near the locomotive a Niagara was, but that's *different*!) It would be interesting to see what could be done with a high-speed version of a Mikado -- might even be possible to make the thing fully bidirectional.

But I have to confess that I still like 4-8-4s better than either of the 'contenders' you mention...

[Kozzie]

After reading the article in Sept issue of Trains Mag (yes, we get them much later down here[:(]) about "beefed up" steam locos, I got wondering about certain wheel arrangements....[;)]hmmm.... Especially comparing 2-8-4 with 4-8-2....keeping other things (like height of driving wheels etc etc) the same, would the 4-8-2 arrangement be superior, you reckon, with a two axle truck maybe tracking better up the front than a single axle? [:)]

Dave
(Kozzie)