My narrow knowledge tells me that I've only seen (on models) leaf spring trucks on steam loco tenders and cabooses. I'm assuming a leaf spring gives a smoother ride, but there must be quite a difference in the spring strength between a tender and a caboose, given the difference in weight. So in the day of arch bar trucks, for instance, why wouldn't the shipper using a reefer want a similar smooth ride? But I'm guessing that a leaf sprung arch bar truck never saw the underside of a reefer. Thoughts?Thanx,Ross PINYAN - Irvine, Calif.
There is little mystery here. The leaf springs work nicely in cars where the weight changes little if at all in service, for example in cabooses or the bolster springing in a 'Blomberg' truck. You may want to look forward at the experimentation with true high-speed three-piece trucks starting in the late '40s, some of which involved leaf springs. Nests of coils with 'snubbing' action is a far more flexible approach over a range of car types to be accommodated by one set of parts, and addition of elastomer blocks (think of them a bit like 'rubber car spring 2.0') adds suitable damping where required (you seldom see the need for things like hydraulic dampers on three-piece trucks although earlier designs such as Chrysler's explicitly had them).
cowcatcherrider My narrow knowledge tells me that I've only seen (on models) leaf spring trucks on steam loco tenders and cabooses. I'm assuming a leaf spring gives a smoother ride, but there must be quite a difference in the spring strength between a tender and a caboose, given the difference in weight. So in the day of arch bar trucks, for instance, why wouldn't the shipper using a reefer want a similar smooth ride? But I'm guessing that a leaf sprung arch bar truck never saw the underside of a reefer. Thoughts?Thanx,Ross PINYAN - Irvine, Calif.
The action of the leaf springs caused the leafs to slide in relation to each other as the spring flexed. So in effect, leaf springs have moving parts. The leafs sliding against each other as the spring flexes causes friction, which dampens the spring rebounding action. So they act as shock absorbers used on motor vehicles in addition to just flexing to absorb shock loading from rough track.
Whereas, coil springs only have the one coil that compresses and rebounds. When this is set into motion by hitting a bump in the track, the coil spring reacts by repeating the bounce several times in diminshing fashion. It would be like removing the shock absorbers from your car and driving it. Leaf springs, with their friction between the leafs, dampen out that rebound typical of plain coil springs.
There are many design variables in car trucks and several of them are related to dampening out the bounce of pure coil springs. One method is to use more than one diameter of coil springs. The different coils have differing spring rates, and this is intended to thwart the tendency for a coil spring to freely rebound in a repeating bounce fashion. This is why you see smaller diameter coil springs nested inside of the larger coil spings that are plainly visible on freight car trucks.
EuclidI would not assume that leaf springs were not used in reefer trucks. There was a genre of trucks known as "swing motion" trucks...
Note that 'swing motion' and 'swing hanger' trucks are two potentially different things, and they control the lateral component of ride more than vertical secondary suspension.
A major issue with any truck involving a separate bolster is that if the springs break or dislocate there is an immediate and catastrophic effect usually leading to derailment.
This type of truck was intended for a smoother ride and was widely used on cattle cars...
... with sets of elliptical leaf spring sets mounted with their length parallel with the swinging spring plank. The leaf spring sets were naturally stable in accommodating the oscillating spring plank...
The action of the leaf springs caused the individual leaves to slide in relation to each other as the spring flexed. So in effect, leaf springs have moving parts. The leaves sliding against each other as the spring flexes causes friction, which dampens the spring rebounding action. So they act as shock absorbers used on motor vehicles in addition to just flexing to absorb shock loading from rough track.
As an amusing aside, the most expensive Nova ever built took pride in the fact that Teflon sheets were provided between the leaves of its primitive rear suspension. This kept noise down and ride pretty good... but required as you'd expect good sudpension damping, more than the stock 'shock absorbers' would happily provide.
Meanwhile on the PRR T1s the limits of good modern leaf-spring self-damping were encountered pretty early, and not too happily. PRR and/or Baldwin tinkered with this later than 1947, finally using resonance-breaking snubber spring rate at the tied ends of the equalization.
There are many design variables in car trucks and several of them are related to dampening out the bounce of pure coil springs. One method is to use more than one diameter of coil springs. The different coils have differing spring rates...
There is another consideration here, which was comparatively less seen in olden days: springs wound for variable spring rate on compression. You used to see this often in heavy American automobiles, where part of the spring that compressed in initial short excursion from ride height would be comparatively soft, but once these were compressed the effective rate of the spring would rise, possibly becoming very stiff indeed just as the suspension travel got to the bumpstops.
In a typical three-piece truck there isn't really enough spring travel to accommodate more than a little variable-rate winding unless the springs are carefully designed and consistently made. Hence you see trucks on some coal trains that involve elastomer pads (which can have even more indefinite spring rate and inherent damping than even high-friction leaf springs do) to support some of the loaded weight resiliently while retaining decent travel and riding for what is often low-tare equipment.
Overmod,
Wow, you provided a lot of info... much appreciated. Now I'll take a chance and put my surplus (leaf spring) arch bar caboose trucks on an HO wooden reefer kit that's nearing completion; and see if any rivit counters notice.
If leaf springs work best on equipment with a fairly constant weight why would they be used on steam locomotive tenders? The empty and loaded weight of a tender would vary significantly.
Mark Vinski
mvlandswIf leaf springs work best on equipment with a fairly constant weight why would they be used on steam locomotive tenders? The empty and loaded weight of a tender would vary significantly. Mark Vinski
Yep 30 tons of coal and 30K gallons of water weigh a gram to two.
Never too old to have a happy childhood!
mvlandswIf leaf springs work best on equipment with a fairly constant weight why would they be used on steam locomotive tenders
Because ride quality does not matter to the extent it would with paying passengers or freight.
Overmod Euclid I would not assume that leaf springs were not used in reefer trucks. There was a genre of trucks known as "swing motion" trucks... Note that 'swing motion' and 'swing hanger' trucks are two potentially different things, and they control the lateral component of ride more than vertical secondary suspension. A major issue with any truck involving a separate bolster is that if the springs break or dislocate there is an immediate and catastrophic effect usually leading to derailment. This type of truck was intended for a smoother ride and was widely used on cattle cars... You should probably link a couple of images to show these, as I think you have a particular interest in many of these largely-forgotten late-1800s evolved truck designs. Some of the things that were tried to improve 'ride' as speed and load increased are ingenious but strange to modern eyes. ... with sets of elliptical leaf spring sets mounted with their length parallel with the swinging spring plank. The leaf spring sets were naturally stable in accommodating the oscillating spring plank... For the record, the technical term for this is full-elliptic. These were extensively used on carriages where extreme light weight and substantial suspension excursion were expected. We are much more familiar with semi-elliptics using shackles to accommodate length changes where needed. I can go into the reasons why full elliptical are and aren't used if there in any interest. The action of the leaf springs caused the individual leaves to slide in relation to each other as the spring flexed. So in effect, leaf springs have moving parts. The leaves sliding against each other as the spring flexes causes friction, which dampens the spring rebounding action. So they act as shock absorbers used on motor vehicles in addition to just flexing to absorb shock loading from rough track. Note that in road conditions these springs might corrode and wear severely, and develop cracks difficult to detect 'in place'. When a leaf fails in a full-elliptic spring it has about twice the effect on safety that it would in a semi elliptic -- this before we get into pin lubrication or how the spring is attached at the perches. And then we can think about the squeaking and other noise... As an amusing aside, the most expensive Nova ever built took pride in the fact that Teflon sheets were provided between the leaves of its primitive rear suspension. This kept noise down and ride pretty good... but required as you'd expect good sudpension damping, more than the stock 'shock absorbers' would happily provide. Meanwhile on the PRR T1s the limits of good modern leaf-spring self-damping were encountered pretty early, and not too happily. PRR and/or Baldwin tinkered with this later than 1947, finally using resonance-breaking snubber spring rate at the tied ends of the equalization. There are many design variables in car trucks and several of them are related to dampening out the bounce of pure coil springs. One method is to use more than one diameter of coil springs. The different coils have differing spring rates... Bear in mind that the spring rate has no necessary connection with spring diameter; 'nesting' snubbers has to do far more with getting long-travel springs coaxial than with providing resonance breaking detuning in the spring nest as a whole. There is another consideration here, which was comparatively less seen in olden days: springs wound for variable spring rate on compression. You used to see this often in heavy American automobiles, where part of the spring that compressed in initial short excursion from ride height would be comparatively soft, but once these were compressed the effective rate of the spring would rise, possibly becoming very stiff indeed just as the suspension travel got to the bumpstops. In a typical three-piece truck there isn't really enough spring travel to accommodate more than a little variable-rate winding unless the springs are carefully designed and consistently made. Hence you see trucks on some coal trains that involve elastomer pads (which can have even more indefinite spring rate and inherent damping than even high-friction leaf springs do) to support some of the loaded weight resiliently while retaining decent travel and riding for what is often low-tare equipment.
Euclid I would not assume that leaf springs were not used in reefer trucks. There was a genre of trucks known as "swing motion" trucks...
You should probably link a couple of images to show these, as I think you have a particular interest in many of these largely-forgotten late-1800s evolved truck designs. Some of the things that were tried to improve 'ride' as speed and load increased are ingenious but strange to modern eyes.
For the record, the technical term for this is full-elliptic. These were extensively used on carriages where extreme light weight and substantial suspension excursion were expected. We are much more familiar with semi-elliptics using shackles to accommodate length changes where needed. I can go into the reasons why full elliptical are and aren't used if there in any interest.
Note that in road conditions these springs might corrode and wear severely, and develop cracks difficult to detect 'in place'. When a leaf fails in a full-elliptic spring it has about twice the effect on safety that it would in a semi elliptic -- this before we get into pin lubrication or how the spring is attached at the perches. And then we can think about the squeaking and other noise...
Bear in mind that the spring rate has no necessary connection with spring diameter; 'nesting' snubbers has to do far more with getting long-travel springs coaxial than with providing resonance breaking detuning in the spring nest as a whole.
What is the difference between swing motion trucks and swing hanger trucks? I have always understood that swing hangers were a component part of swing motion trucks.
The swing motion trucks I refer to have swing hangers that allows side-to-side oscillation of the spring plank, which is suspended like a pendulum from by the two swing hangers, which each hang from fixed pivot points on the truck transom, which is rigidly connected to both truck side frames.
I find substantial reference in books by John White. He describes swing motion trucks as kind of fad movement school of thought within the industry, and its point was to produce a smoother ride. One component of that advocacy was the widespread advocacy of humane treatment of livestock riding in railcars. Swing motion essentially mitigated the harsh side-to-side jolting resulting from trucks lurching from side to side due to low rail joints.
Why would a breakage of an elliptical spring necessarily cause a derailment? Wouldn’t the floating bolster and broken spring simply drop down somewhat, but continue to be carried on the swinging spring plank?
I can see how a broken swing hanger would cause a derailment. With that failure, the floating bolster, the spring, and the swinging spring plank would all drop together, allowing the swing spring plank to come down and rest on the track structure. I assume that at least some swing motion trucks were equipped with safety straps that would catch and hold suspended, a fallen spring plank caused by a broken spring hanger.
What caused swing motion trucks to lose favor and all but disappear in a relatively short time was their cost of complexity and maintenance.
Interestingly, Mr. White also comments that of all railroad rolling stock, it is the steam locomotive tender that is the most difficult to design with adequate suspension. He says this is due to it having the greatest difference between its loaded and empty weight.
Incidentally, when I speak of coil spring diameters of different spring rates, I am not referring to the diameter of the spring coil as changing the rate. What I am saying is that coil diameter was reduced in order to fit the spring into the truck by placing it inside of the primary coil spring of a larger diameter. That was a good use of otherwise wasted space. In addition, it is my understanding that the larger and smaller diameter springs were of differing spring rates, but this was due to other rate changing factors such as the number of turns and the wire diameter of the coil.
The reason for using springs of different rates was that it would tend to dampen rebound just as snubbers or shock absorbers to.
EuclidWhat is the difference between swing motion trucks and swing hanger trucks?
Swing-hanger trucks (whether inside or outside, a significant distinction when classifying passenger trucks) are intended to do one particular thing: put the point where actual lateral compensation is provided as low in the truck structure as practical. While the practical advantage of OSH in practice was not always 'compelling' over ISH (much as for outside-bearing over inside-bearing lead trucks) it isn't difficult to appreciate the advantages for lateral control as well as minimized roll concerns from a good late OSH design (see the Nee Haven example in White's The American Passenger Car (vol.2 if you have the separated version).
In a way this can be said to model the action in bolster support of drop-equalizer pedestal trucks (as seen on reefers and express cars in some head-end M&E-type service when good riding was expected).
The issue here is that the 'spring plank' carries the imposed weight of the car, while almost at the same time you say the pin is carried in the transom of a presumably-rigid H structure of transom and sideframes (like a bent version of the Ohio-truck frame). A moment's reflection will show this won't work with a plank-equipped design; follow how the weight load gets imposed on the track back up through the wheels and suspension to better appreciate this, particularly in a rigid-transom-to-sideframe structure.
This brings us back to whether you actually need pinned swing hangers to allow 'truck swing' relative to the carbody. I would argue that the lead spring arrangement in earlier trucks provides both the compliance and effective damping for this, much of the time.
The problem is that the elliptic spring is dynamically unstable on breakage at all four connection points -- the lever arm at the points of the perches being enormous, and the tendency for the pinned ends of the paired semielliptics to separate wildly when unpinned being similarly great. If there were positive location of the spring plank relative to the truck frame by positive means, say some pedestal arrangement or even radius rods, the effect would be as you note. Any breakage in an elliptic carrying railroad-car load would tend to allow not just dropping in vertical ride height but twisting of what might be considerable magnitude between the plank and side frame. No less a consideration is the ensuing tilt of the carbody, quite possibly exceeding gage clearance or coming into interference contact with a passing train, or inducing load shift.
I assume that at least some swing motion trucks were equipped with safety straps that would catch and hold suspended, a fallen spring plank caused by a broken spring hanger.
Incidentally, when I speak of coil spring diameters of different spring rates, I am not referring to the diameter of the spring coil as changing the rate. What I am saying is that coil diameter was reduced in order to fit the spring into the truck by placing it inside of the primary coil spring of a larger diameter. That was a good use of otherwise wasted space.
[wuote] In addition, it is my understanding that the larger and smaller diameter springs were of differing spring rates, but this was due to other rate changing factors such as the number of turns and the wire diameter of the coil.[/quote]The important thing is that they did not 'have' to be; there is no implicit requirement that resonance-breaking 'snubbing' has to be applied coaxially. It turned out to be advantageous to tinker with spring rates to give the 'combination' of nested springs fitting in one position of, say, the spring nest in a three-piece truck the same load-bearing vs. empty change in effective riding compliance while providing resolve-breaking action.
The reason for using springs of different rates was that it would tend to dampen rebound just as snubbers or shock absorbers do.
Keep in mind that the original sense of 'snubber' was precisely the use of resonance-breaking, not the use of elastomer for suspension and damping (cf. washing-machine tub suspension over the years). When I was looking at how to rebuild GG1s for high speed in the '70s I learned that the early engines were designed with "snubbers" which were subsequently found not only to be unnecessary, but were actively removed as the engines were shipped. I of course thought this meant either composite elastomer or some kind of hydraulic damper as on modern road power ... it did not; the reference was to differently-tuned springing.
cowcatcherrider Overmod, Wow, you provided a lot of info... much appreciated. Now I'll take a chance and put my surplus (leaf spring) arch bar caboose trucks on an HO wooden reefer kit that's nearing completion; and see if any rivit counters notice.
Overmod has pretty well laid it out; the whys and wherefores of the advantages of coil springs vs. leaf springs.
"... A major issue with any truck involving a separate bolster is that if the springs break or dislocate there is an immediate and catastrophic effect usually leading to derailment..."
Derailment in any of its many phases is costly to the railroad it happens to. Coil springing while it might not be the perfect solution; is seeming more cost effective in the long run.
#1 The 'Bottom Line' is what the management constantly has its eyes on. #2 is the addage: "...If it ain't broke, don't fix it..."
With #1 and#2 there are no linitations on experimenting with, or testing a potentially 'new' way that might be a true improvement.
Coil springs in most trucks are complimented by some sort of snubber or shock-abosorber to elinate the oscilation discussed earlier. This kind of damping is inherent in leaf-springs, as also discussed earlier.
By far the most popular streetcar trucks were the Brill 77, 177, and their derivatives, including the duplicate made by Third Avenue in their own E65th Street shops, but using some parts from Brill. Except for Cincinnati Car Co., even Brill's competitors used these trucks on some of their production. On this brilliantly-designed truck, the half-eliptacle leaf sprint acts as equalizer bar as well as the main spring.
Keep in mind also that the action of a three-piece truck represents almost an ideal of what is required for effective running. One of the great demonstrations of this was the existence of trains like the Super C, which could routinely reach 90mph without requiring particularly special truck tuning or retrofit. Another was the short-lived expectation that lozenging was so serious a prospective threat to stack-train operation that X-shaped pinned reinforcement between the bottoms of the side frames would be necessary -- from time to time I see trucks with the brackets, but no equipment in them.
One point about coils that may not be evident to casual 'lookers' is that there may be nine separate spring positions in the sideframe, any of which might have nested coils inside. Note that this facilitates the longitudinal rocking action that makes these trucks so flexible in cross-level following, allows much more metal in support (so each spring can have variable rate wound in for better load vs. unload riding) and, not least, failure or outright breakage of one spring poses almost no danger. The alignment of the side frames with the bolster is a critical part of the design, both to prevent lozenging/skewing resonance oscillations and to help damp side frame motion relative to the bolster -- note that some lateral compliance can be included if desired.
I think the critical thing that makes long-travel swing motion on freight cars less 'essential' is improvements in line, surface, and LWR low-joint elimination in the ROW. Remember that no little part of the English disdain for equalized locomotives is predicated on 'permanent way' standards far higher than North American practice in the heyday of the swing-motion craze. (Things like the 'Blomberg' trucks are a bit different as they are leading under power, which is a different discussion).
BTW it is my opinion that you'll see multiple thin leaf springs in many of the Blomberg trucks, in part so breakage or derangement of one 'set' will not damage others or destabilize the suspension action. If you are putting leaf springs on a reefer, do NOT use the kind of caboose trucks with just one wide leaf to carry the constant load of the cab 'lovingly'...
Mr. Klepper -- use of a center-pinned or perched spring as an equalizer is not an unusual thing-- you find it in some diesel trucks including (surprisingly perhaps) the 'AAR type A' switcher truck and, I believe, the Batz truck. A different form of spring giving this action without pinned hangers is visible in the Ohio tender trucks (of which the original and early-modified trucks on NYC 999 are the most recognizable example) and it might be noted that these trucks acquire three-piece-like flexibility if the side frames are pinned to rotate at the bolster and the axle bearings allowed a little play, rather than the pieces made into a rigid H frame loaded at its outer corners.
I assume the “Ohio Truck” was a design was used only on tenders, and I have seen it in many photos of 4-4-0 engines in the Pioneering Era; with the most recent example being on CStPM&0 4-6-0s built around 1900. I sent a letter and a drawing to John White to inquire about it, and he was not sure of its origin, but thought it may have been called the “Ohio Truck.” So that is not much evidence for the name, but at least, it is one identifier.
I assume that truck design was specifically intended to produce an optimum ride for tenders, which White had described as being the most difficult rolling stock from which to attain a good ride.
The truck has no spring plank. It has a solid wooden transom connecting the two rigid truck side frames. Together, they would constitute the rigid “H” structure when seen in a top view. Then the loading of the tender is carried from the tender side sills, directly down to the tops of the four journal boxes through a large leaf spring on each side of the tender.
The truck does not transfer any weight down onto the transom through a center bearing as is typical of a truck with a bolster. Instead the Ohio truck has a form of center bearing that only keeps the truck in the proper position in the horizontal plane through a mechanical center bearing, but the bearing bears no downward axial loading. Its loading is only radial for the purpose of maintaining the truck location under the tender.
The tender does move up and down in relation to the truck by virtue of its suspension on the four end points of the two elliptical springs. To accommodate this up and down movement of the tender in relation to the truck, the center bearing is able to telescope while maintaining its radial positioning of the truck under the tender.
As the truck loading compresses the two leaf springs, the two ends of each spring move further apart as the arc of the springs are flattened. Apparently one end of each leaf spring is pinned to the journal box top on which it sits, and the other end is free to slide on top of the journal box. Both ends of each leaf spring are retained in the horizontal plane by being boxed into position by an open-top cast iron tub feature.
There is just one issue that poses a problem that seems practically unsolvable. That is the need for the truck to pivot as it departs from straight track and enters curved track. The truck would pivot relative to the tender frame. It is the tender frame that establishes the position of the two leaf springs. Thus if the leaf springs are fixed to the tender frame, how can the spring ends accommodate the arced course of travel of the journal boxes as the truck transitions from straight track to curved track and vice versa?
The only possibility I can see is that the tips of the two leaf springs simply slide on the tops of the journal boxes. They would have to slide this way when the tender frame bounced up and down, causing the spring tips to spread and retract in that bouncing action. Also, the truck does not rotate much in curves due to the relatively short spacing between the two trucks, so maybe the small distance of spring sliding was not an issue. Nevertheless, it does seem like such an approach to accommodating some truck pivot is a compromise that might have consequences in premature wear or excess stress of the leaf spring assembly. In any case, for a truck design that is almost lost history, it was in widespread use over a long span of time. So it must have been viable.
Althogh the Brill trucks saw wide streetcar use, they were very rare on interurbans and any rail cars thar ran regularly over 45 mph or carried any heavy loads. But they did cope better than some other designs with some imperfect track. In North America, before the PCC era, a majority of double truck and three-truck articulated cars had them.
Since Ron did so much of the legwork researching these trucks (a few years ago, in a very carefully-detailed thread on RyPN that has many pictures) I'll let him continue a bit -- he can, for example, talk about some very interesting changes that were made over the years to these trucks, many to provide stiffer lateral control of the high arched springs either at the toes or the perches, and to box in the toes where they bear on the H-frame. The 'history in pictures' of the high-speed years of NYC999 afford just such an evolution...
We put out a call for people to visit some of these tenders to make specific observations about the curve-following and cross-level 'articulation' (in the 4x4 sense) issues. That opportunity remains open today.
An unusual application of the Brill truck was the GE electrification of the narrow-gauge Boston Revere Beach and Lynn Railroad. Wood, open-platform coaches, very similar to typical Chicago, Brooklyn, and Manhattan elevated cars, were made into MU mutor cars with one of the two tracks replaced by a two-motor narrow-gauge Brill 77E truck. This left the car with a coil-spring MCB truck at one end and a leaf-spring 2-motor Brill at the other. Never head any complaint about this. Trailers did not have any trucks replaced.
Have not found a side-view photo showing this adequately. Hope another reader can and will.
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