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.
Quentin
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.
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?
Our community is FREE to join. To participate you must either login or register for an account.