my understanding is the the MAX tractive effort (TE) is ~25% of the adhesive weight equally distributed over the drivers of a steam locomotive. Anytime the TE exceeds this value, slipping occurs.
what is the MAX TE while slipping?
slipping will cease when the TE generated by the cylinders drops below the the MAX TE while slipping. of course there are ways (e.g. sanding) to increase the value and stop slipping besides simply allowing cylinder force to drop.
does it matter how fast (rpm) the drivers are turning?
is it related to the cylinder force at the rails?
expecting a quantitative answer (e.g. 10%)
greg - Philadelphia & Reading / Reading
gregcMy understanding is the the MAX tractive effort (TE) is ~25% of the adhesive weight equally distributed over the drivers of a steam locomotive.
This is an empirical rule. Of course, the actual point of slipping is affected by a great many things, both 'on' and 'off' the locomotive, so the functional point at which adhesion would be lost could vary from the nominal 25%, and often did.
Anytime the TE exceeds this value, slipping occurs.
It's important to remember that this was far from true in practice, unless you define it as a tautology like the joke interpretation of 'never exceed stress limits'. Of course the engine will have the propensity to slip when the effective static friction between wheel tread and railhead (as enhanced by sand, reduced by compressed leaf matter or water, etc.) is broken, but that's not a hard and immutable percentage even for a given locomotive or type.
What is the MAX TE while slipping?
This is affected by a great many things, and more so if some kind of traction control is being used (as was seldom present explicitly on reciprocating locomotives, but it could be mimicked by (for example) careful modulation of the independent. In most cases the practical onset of destructive amounts of slip can be delayed by using 'more throttle and less reverser cutoff' as you get lower torque peaks and less pressure 'peakiness' at points in the stroke that way.
The practical TE you develop is not, of course, that which prevails at the onset of observed slipping; it comes at the point where the drivers are slipping so much of the time they can't re-establish sufficient traction, or they start to accelerate under heavier steam to the point where traction never gets re-established at all. The situation can be thought of as analogous to driving in mud, where there may be some benefit to spinning the wheels to establish some forward motion to 'get off a bad spot' but little benefit once the wheels have 'broken away'.
[quote] ... slipping will cease when the TE generated by the cylinders drops below the MAX TE while slipping.[quote]
There are better ways to express this; something important is that the actual 'slipping' comes initially only during a comparatively small part of each quarter revolution (in a two-cylinder DA simple) and will likely self-arrest after a relatively small further rotation unless there is so much 'surplus power' represented in the steam expansion available at that time that the wheel can stay in lower sliding-friction adhesion conditions all the way to the 'next' excess torque point. You can readily understand why having the throttle partially closed helps arrest such a slip; as the cyclic rpm increases in a propagating slip, effective mass flow per stroke falls, and with that go increased wiredrawing effects, the tendency being to reduce effective pressure rather quickly to the point adhesion of some kind gets re-established "more easily".
of course there are ways (e.g. sanding) to increase the value and stop slipping besides simply allowing cylinder force to drop.
Not all the ways are always good. In particular, sanding can be troublesome because once the engine slips, the sand makes the re-establishment of static friction more immediate, too, and this causes greater shock to the rods, pins, etc. When this happens with lightweight rods, like thin Timken rods, and the speed of the slip has propagated to a relatively high rate, the momentum effects alone of the prompt stoppage can be dramatic. This concern is usually overlooked by lay people, but it should be remembered when developing 'adhesion enhancement' designs.
Other methods of increasing adhesion go right back to the beginning of road locomotives in this country - look at the Miller traction enhancer. Active methods of adding effective weight to driving axles, or relieving it from other axles, are similarly old (as in steam cylinder lifting on driver axles) or very new (as with the generations of 4-motor six-wheel-truck AC locomotives and conversions we've seen in the past decade or so).
In most modern cases, the weight on drivers is sufficiently high that 'traction increasers' would have more weight and complexity than deserved by the problem they purport to address ... remember, in almost all cases, that the load of a train has been calculated under complex conditions to be 'as near the economic capability of the engine to get over the road' and therefore simply carrying a few fewer tons or providing better bearings or car-tread dressing is a much more sensible approach than loading 'er down and then just barely restraining the slips. A careful understanding of the effect of even near-slip operation on driver wheeltread wear produces much the same reordering of effective priority.
In general, slipping is less observed at higher cyclic rpm, BUT this leads into the phenomenon of high-speed slipping as applied to the PRR duplexes. If there is an increased propensity to unload one of a small group of drivers transmitting a high horsepower, the effective adhesion drops by what may be a substantial number, in effect taking the adhesion in a jump from somewhere around your nominal 4.00 to something that may even be below 3 (if, say, one wheel of a 4-coupled duplex engine were to lose all adhesion going over a low joint, open frog, or cross-level defect). If the engine had been running very close to its physical adhesion limit at the time, this momentary added propensity to slip may induce enough acceleration under running mass flow conditions to keep the engine slipping for some time, or even continue destructively at some higher balancing speed where some additional traction is being generated but at heavy cost in wheel and railhead wear and heating. This phenomenon was observed often enough to become used as an argument against unconjugated duplexes in general, even in the presence of workable low-speed-slipping devices like a properly-proportional version of the analog computer device used on the PRR Q2s.
Yes, but not directly. The issue is far less the developed 'cylinder force' than it is the instantaneous friction conditions in the zone of 'interaction' between the rolling wheel and the contact patch on the railhead. The existence of sanding is a recognition that 'friction modification' is a better approach than fast cylinder modulation (which of course is difficult if not impossible with normal piston valves and radial valve gear).
As a general rule of thumb, you'll see the effective FA for a given locomotive used in the calculations to assign a correct train resistance in a given service. If the FA as built results in problems, expect the engine to be rebuilt or modified -- to increase it, if you continue having problems (as with the progressive effective 'porkification' of the PRR T1s) or reduce, if the weight that imposes a given FA results in excessive rail load or the effect of augment. On the other hand, at least part of the fairly common changing of locomotive pressure in various contexts might involve changing both MEP and peak pressure at the cylinders, and not just better boiler life (lower) or better nominal thermodynamics (upper).
Wardale was trying to instruct locomotive drivers (British usage, locomotive engineers in US) to arrest a slip by retarding the reverser to shorten the cutoff.
To me, the most obvious action is backing off on the throttle. In my car, I lift my foot off the accelerator pedal; I don't shift the transmission into a higher gear. On the other hand, maybe working the reverser makes the dips in the cyclic steam-locomotive torque curve even lower and halts a slip that way?
The idea of letting the wheel slip to get traction in mud or deep snow is one of those vain hopes -- my wheels are spinning, but I still have some forward momentum so if I keep going, maybe I can make it? I have experienced such in both automobiles as well as with a farm tractor.
With respect to the variability of adhesion, which applies to the varying conditions for roads, for hayfields and for rails, John Kneiling wrote in Integral Train Systems that 15% adhesion was what you could count on, regardless of "what the vendor is telling you." This would be for diesel electrics, which don't connect the powered axles to rotate at the same speed. You are essentially going by a worst-case low value because once one axle slips, the remaining axles need to pick up the train load and eventually all axles will slip.
One of the selling points of the Krauss-Maffei diesel hydraulic locomotive was a 30% adhesion factor. The three axles in each truck were interconnected by drive shafts to the single torque converter transmission link to a diesel prime mover -- there were two diesel engines in that locomotive, one for each truck. The knock on this arrangement, at least according to Railway Age reporting on this, was that the wheels needed to be turned on the shop lathe to within 1 mm of the same diameter -- a rod-drive steam locomotive along with the one-inverter-per-truck EMD design for their early AC-drive locomotives have a similar requirement.
The figure of 25% for a two-cylinder steam locomotive probably takes into account cyclic torque, and for three-cylinder steam with smoother torque, I heard 30% adhesion claimed as with the shaft-drive diesels. I regard the need to keep the drivers on a steam locomotive nearly the same diameter was the least of the concerns of why the railroads switched to the diesel-electric locomotive, and the maintenance requirement for wheels was probably the least of the troubles Rio Grande and Southern Pacific experienced with their KM's.
Of course with AC drive and computers to catch a slip much faster than any human locomotive driver, 40% adhesion is claimed. I kind of wonder how that work out out on the road -- there are YouTube videos of crews with their 40% adhesion stopping and having to double the hill.
Oh, on the subject of transfering weight to get more traction, Wardale writes that the Chinese QJs had a "traction booster" that was an air cylinder that transfered weight through the equalizer beams from the carrying axles to the drivers. Someone on this Forum once mentioned that the 6-axle AC locomotives having only 4 traction motors -- apparently BNSF uses them in intermodal service -- have a similar thing. The idea is that you overload the drivers only at low speeds to help with starting or help with not getting stuck, but the drivers have their normal loading at higher speeds where impact damage to the tracks and bridges is the limiting factor?
If GM "killed the electric car", what am I doing standing next to an EV-1, a half a block from the WSOR tracks?
Some comments inline, instead of differently-ordered or prioritized:
Paul MilenkovicWardale was trying to instruct locomotive drivers (British usage, locomotive engineers in US) to arrest a slip by retarding the reverser to shorten the cutoff.
The primary issue here is the difficulty of doing that effectively under working conditions. First, the implication is that you're dealing with high required TE under uncertain conditions (in other words, close to the expected point of slip propagation) which means you want to return to previous throttle and cutoff as promptly as you departed them. This is difficult -- tedious, at best -- to accomplish merely with a screw reverse of adequate precision. whether or not the reverser has 'power assist' or even power implementation. If you have something like a lever-operated Hadfield, or one of the Franklin Precision installations with a quadranted lever (as, I believe, on NKP 765) vs. a wheel (as on most of the early NYC Hudsons) the advice is reasonably correct, as there can be as little reflected force or misapplied 'force feedback' as there is in the controls for a Hulett, and even if practice is required there are reasonable haptics for returning the reverser to steady-state high power even a beat before the physical slip has come to a stop (eliminating some of the effective control latency effects).
To me, the most obvious action is backing off on the throttle. In my car, I lift my foot off the accelerator pedal; I don't shift the transmission into a higher gear.
If steam-locomotive throttles worked as easily as accelerators, and on the same kind of compensated spring-return linkage, modulating the throttle would indeed be a preferred way to handle slips, although perhaps with slightly longer latency as steam mass flow 'downstream' of wherever the throttle is will continue to have some effect. This can in some examples of design (I consider them 'misdesign') produce pronounced continued slipping even with the throttle closed, the 'Blue Peter' accident being one particularly poignant thing. There, by the time the driver recovered the presence of mind to close the regulator, there had been sufficient carryover into the elements to keep the slip propagated to the point of severe inertial damage. A modern American engine with front-end throttle doesn't have that problem, but there may still be issues with the mass flow downstream of the throttle poppets.
And there is considerable inertia in the linkage even to a proportional air-throttle arrangement like the one on PRR T1s -- and issue with effective response from the physical throttle, due to the sequential poppet actuation and some concerns with back pressure on required opening force. Most of the time it is relatively difficult to get a smooth, proportional 'feel' to a steam-locomotive throttle, and it can be especially difficult to modulate the thing effectively between 'closed enough to stop the slip' and 'open exactly as wide as I had it before'. (There are some ways around both this and the problem of quick reverse changes followed by positive return to previous vernier setting, but they're probably too technical for interest here)
On the other hand, maybe working the reverser makes the dips in the cyclic steam-locomotive torque curve even lower and halts a slip that way?
It's the peaks, not the dips, that matter. Controlling the excursion of effective pressure is more important than the concomitant shortening of the torque peaks (and the implied larger throttle opening/mass flow needed to maintain torque with the gear in such position). Shorter peaks give lower average power, which gives lower average torque, which implies shorter and less-sustainable slip duration.
The idea of letting the wheel slip to get traction in mud or deep snow is one of those vain hopes -- my wheels are spinning, but I still have some forward momentum so if I keep going, maybe I can make it?
The point is that you're maintaining some forward tractive effort -- it may be at a lower percentage than with a 'static coefficient of engaging friction' but still at a percentage of the greater 'available horsepower' represented by the higher rotational speed. It's only justifiable -- to the extent it's justifiable at all -- if done in the expectation that slips are being caused by short or transient conditions and once the section in question has been passed, or the train accelerated out of a speed range where the slip recovery manifestly involves ability to start, the problem will stop.
It's a dumb practice anywhere and any time, and you can expect an actual owner of a given steam locomotive to react strongly to avoid or prevent it if they can.
However, this is very different from the idea of 'microslipping' or creep, which became a staple of diesel-electric operation as early as the 1970s. There the idea is to permit torque well above that corresponding to a given conservative adhesion limit, but arrest any detected slip within a tiny fraction of a rotation to re-establish physical adhesion. The sum of the torque communicated through the railhead adds up to be 'greater' than the average continuous torque that could be supported shy of any slip -- or so goes the explanation. It evidently works, and doesn't produce too much wheeltread or railhead damage or lateral corrugation or more railroads would eschew it...
Doing this level of precise slip arrest on a steam locomotive of conventional design is difficult. About the only type I've seen that could do this via the throttle or reverse would be the Besler motor locomotive. What's needed is something that can implement a quick clamping of the driver(s) involved, and equally fast release of the applied additional friction; I've proposed several ways to implement this including the likely method for T1 replica 5550. The best use of this would NOT be in conjunction with either the reverser control or the throttle per se; you'd either associate it with the same detection that triggers the wheelslip light on a given engine, or use a pushbutton 'shot' like a Franklin air-actuated booster control.
[quote]With respect to the variability of adhesion, which applies to the varying conditions for roads, for hayfields and for rails, John Kneiling wrote in Integral Train Systems that 15% adhesion was what you could count on, regardless of "what the vendor is telling you."[quote]
Traditionally, of course, any effective 'variability of adhesion' would have to be factored into the assigned train resistance for any particular run, with an implied tolerance for a certain amount of transient slipping -- or an understanding and acceptance of potential slowing or delays regarding from an enforced doubling, need for assisted 'shove', etc. In the old days before 'lazy' PSR this would have been fairly well known 'empirically' when assigning power to trains knowing the likely prevailing conditions. "15%" translates into a FA of 8, and if you tried to sell a locomotive so designed to any business-oriented railroad they would laugh you out of the office.
Which is not to say I haven't had my arguments with prospective manufacturers who think grossly-derated traction motors and the like are 'attractive propositions to preclude slipping'. Those that didn't listen got woodshedded by the buyer community in fairly short order!
This would be for diesel electrics, which don't connect the powered axles to rotate at the same speed. You are essentially going by a worst-case low value because once one axle slips, the remaining axles need to pick up the train load and eventually all axles will slip.
What normally happens if one axle slips is that the reduced TE quickly produces a fall in speed. That by itself precludes additional slipping until the torque 'rebalances' at the lower speed -- at which point the slipping axle is likely to have recovered merely because of the decrease in speed. So the more likely scenario is that you continue to see various axles 'blink' into slip and then appear to recover, as the speed falls, rather than massive and progressive slip until the train stops cold. Of course if the train is so overloaded that the axles slip even at lowest speed, even instantaneous speed, you'll get a stall. I'm tempted to add that only the stupid allow protracted slip, of axles or whole locomotives, of the type you sometimes see graphically illustrated in videos or 'after' pix.
One of the selling points of the Krauss-Maffei diesel hydraulic locomotive was a 30% adhesion factor. The three axles in each truck were interconnected by drive shafts to the single torque converter transmission link to a diesel prime mover -- there were two diesel engines in that locomotive, one for each truck.
There are more problems with this operationally than may first appear -- you have to consider the shock of torque coming on and off the bearings in the Cardan-shaft universals, and on the effective contact patch at the crowns of the gear teeth. Since there is usually low shock absorption, even to 'quill drive' spring standards without damping, in the whole drivetrain of a diesel-hydraulic downstream of the converter array, you should not be surprised to see bad effects, particularly as there will be a tendency for a particular axle 'at the point of slipping' to repeatedly bang its bearings and teeth, perhaps several times per second, at the full torque differential between slip and adhesion. Issues as you'd expect get dramatically worse as loose motion begins to open up at the universals, teeth begin to spall or fret, and foreign matter begins to affect the tribology.
You may have noted the rousing success of conjugated truck axles in North American railway practice since the early 1960s. This despite its relative success in a number of other fields, including HSR with low unsprung mass (which almost demands some kind of shaft final drive even with small PM-AC traction motors).
... the wheels needed to be turned on the shop lathe to within 1 mm of the same diameter -- a rod-drive steam locomotive along with the one-inverter-per-truck EMD design for their early AC-drive locomotives have a similar requirement.
All this is correct -- note that you could happily operate with even substantially-mismatched wheel diameters, just without having excessive microslipping and interaxle drive-means shock and wear. Note that the ACE 3000 in particular called for regular 'underfloor' dressing of the driving-wheel profile even though the effective 'higher wear' (presumably up to an equivalent of a 'magic wear rate' for freight-car wheels) would result in more frequent changeouts of the 'one wear' cast drivers...
The figure of 25% for a two-cylinder steam locomotive probably takes into account cyclic torque, and for three-cylinder steam with smoother torque, I heard 30% adhesion claimed as with the shaft-drive diesels.
There are some arguments about the adjustment to a "FA of 4.00 criterion" when using something giving better cylinder operation, like good RC poppet-valve gear or Willoteaux valves. Most of these have at least the tacit effect of increasing the effective pressure peak, or shortening its effective duration, during much of the anticipated 'higher economy' operation. Usually the response from the design community mirrored Wardale's installation of that ridiculous Herdner valve: throw away 'economy' when starting integrity, or lower slipping in poor conditions, became an emergent priority.
Keep in mind that many three-cylinder designs don't have the geometric elegance of a pure Swiss drive. Much of the effect on 'average wheelrim torque' can, and turns out to be, practically achievable with a two-cylinder DA if you control the rise and peak of cylinder thrust more carefully. A method to accomplish this was inherent in the operation of the Franklin type D 'automatic cutoff' setup as implemented in the Army 2-8-0 project ... admittedly, not very sophisticated from an armchair-thermodynamicist's point of view!
... the maintenance requirement for wheels was probably the least of the troubles Rio Grande and Southern Pacific experienced with their KM's.
It wasn't really mentioned as a prime concern in any of the early discussions I had on these in the early '70s, when perhaps there was still some future for large conjugated-truck power. (We might remember that in this context the Ingalls Shipbuilding 2000hp passenger-unit proposal also used conjugated trucks like this, and a modern locomotive using a Bowes drive instead of torque converters would have been practical at early-Seventies horsepower levels)
The initial thing that would have killed them was Germanic service requirements. Under the guarantee, all the lubricant in the multiple final drives had to be changed every thirty days ... almost certainly using some German-spec lubricant with relatively colossal delivered cost. There was a comparable requirement for the fluid used in the converters. All the shaft balances and universal-bearing lubrication had to be checked and (probably expensively) kept patent on some regular basis. (This was against the requirement for a typical nose-suspended alternative: run some Crater into the gearcase and let it go until you have to service the wheelset for excessive wear...)
Then there was the fun if you had to do any kind of switching, or even reversing, with one of these things. If you think a GE is slow to load, imagine having to wait while all four transmissions mechanically reversed (a Trains article on them referred to "thump ... thump ... thump ...thump"). Of course we all, of a certain age, remember the grave consequences for the torque converter if we reversed while still rolling forward ... so be sure the engine is completely stopped and won't be bumped by, say, slack rollout with the converter engaged to the driveline. The omnipresent threat of driveline or converter damage if you were so imprudent to rush this stately process ... which you will notice involves repeated stops of the consist using full service-brake application ... which of course wouldn't be covered by the guarantee is again a whole world of consideration you don't have on a practical diesel-electric.
Of course with AC drive and computers to catch a slip much faster than any human locomotive driver, 40% adhesion is claimed.
Again, the practical import of this begins, and ends, with the people determining load factors for practical trains. It is much likelier that the practical effects of higher adhesion are manifested in very-slow-speed operation than in allowing 'heavier' trains on grades ... but any railroad thinking it could, in fact, operate heavier consists taking advantage of 'better' adhesion would pretty quickly have to test that assumption against reality -- or train its crews to know when to reject a given job with a given power consist...
... on the subject of transfering weight to get more traction, Wardale writes that the Chinese QJs had a "traction booster" that was an air cylinder that transfered weight through the equalizer beams from the carrying axles to the drivers.
If it's deemed cost-effective, someone can always try it -- as noted, the concept dates back almost to the very first use of practical locomotives for long-distance service. As with boosters, there are 'vogues' for traction increasing that die out as the cost and relative worth change (in North America, with better technologies and increasing engine size -- see precise riding cutoffs as another unfortunate casualty with periodic attempts at functional renaissance.
Someone on this Forum once mentioned that the 6-axle AC locomotives having only 4 traction motors -- apparently BNSF uses them in intermodal service -- have a similar thing. The idea is that you overload the drivers only at low speeds to help with starting or help with not getting stuck, but the drivers have their normal loading at higher speeds where impact damage to the tracks and bridges is the limiting factor?
Well, aside from semantics, that's a logical interpretation of what that system is intended to do; we had a pretty good explanation a couple of months ago that what the system does is move the spring seats for the idler axle up in the truck frame, not 'jack' the axle itself, thereby allowing more of the weight to come on the other axles naturally without linkage concerns. This is in my opinion a much better way than throwing additional load on powered axles as most of the active 'traction increasing' methods in legacy steam practice appear to have done.
I don't remember the full mechanical details, but it's easy to check: one of the earlier implementations of 'articulated power' in Germany around the beginning of the 20th Century involved a jackable axle, I think a powered one, in one of the engine's trucks. You can probably get to a copy of Wiener for the bloody details quicker than I can. There too, apparently (at least as I recall) there were ride-quality issues that nipped the idea in the bud fairly quickly.
what is the TE (by adhessive weight) while slipping?
gregcwhat is the TE (by adhesive weight) while slipping?
I had thought the adhesive weight can be taken as relatively unchanging under the 'usual' sorts of slip condition (there is little load-transfer difference, and little effective lifting by, say, vaporization of water under the load patch). Thinking about it, a repeated 'catch and release' sequence could result in some wheel lift against the suspension, which would result in a little unloading. That in turn might be critical in very-close-to-adhesion-limit situations.
The real difference is in the effective force expressed in the plane of 'interest' here, which is related to the longitudinal friction at the point of contact. This is compromised, in a slip, by some percentage corresponding to the difference, under adhesion loading, between static and sliding friction of the tread and railhead material (including any contaminants).
Several things then come to affect the effective 'sliding friction' of the contact area. One of these is the relative speed with which asperities on the rotating wheelrim engage with their 'counterparts' on the railhead -- you will not be surprised by the development of those 'sparks' when you consider the difference between whetting a knife or chisel on a stationary stone at various hand speeds vs. engaging the same edge on the same type of stone on a honing or grinding wheel. (This is part of the reason why it is so important to stop a slip as soon as possible, within a few degrees of rotation, even if you can't friction-modify the contact with sand or supersonic dry air or whatever).
I see a couple of theoretical possibilities with the spark-throwing, though. There is enormous quench between the mass of the wheelrim and the mass of the railhead, so even though there is obvious heat and patent melting involved in the picture you provided -- with the relatively low shear viscosity of the 'melt zone' providing decidedly lower tractive friction, in just the way the liquid film provides the 'skating' action between a runner and an ice surface -- so almost the moment sufficient energy is not going into the 'interface' it will freeze as a weld, which has enormous effective shear strength. However, the longer a spin like this is propagated, the greater the prospective 'melt zone' and the likelihood you'll start to cut a little chordal divot into the railhead, out of which the driver now would have to climb. The physics then become dramatically skewed toward allowing rotation rather than forward motion; as I noted, I became effectively stuck in the middle of my level driveway when one wheel with an open diff melted itself an almost imperceptible divot in the ice coating it. What I didn't mention then was that I tried increasing the adhesive weight by several hundred pounds (which only cut the divot a little deeper) and substantially jacking up the back of the car (which only decreased the factor of adhesion) -- only lifting the entire tread clear of the divot and interposing something with better friction would have gotten me out...and this would be somewhat difficult to do 'in the field' with equalized suspension on a wheel so affected than with an English locomotive with individually suspended driver axles.
OvermodI had thought the adhesive weight can be taken as relatively unchanging
TE is expressed in lbf. so TE by ashesive weight (lbs) is a %
not interested in why there are sparks. might assume TE during slip is even less than w/o sparks.
if the TE is zero, then train should have slowed, which i don't observe. So i conclude that TE during slip > 0 (i.e 0%).
if speed is maintained, then TE is ~equal to train resistance plus grade, if any grade (~ tonnage * grade).
but looking for references to what is an estimate for TE during slip.
friction and friction coefficiecnt for various materials lists the static coef for steel-on-steel as 0.8. don't understand why max TE for locomotives is nominally 0.25. Is this because the surface area are is so small (i.e. wheel on plate)?
the page also says
Typically steel on steel dry static friction coefficient 0.8 drops to 0.4 when sliding
does this imply that if MAX TE is 25%, then it is 12.5% while slipping?
gregc Overmod I had thought the adhesive weight can be taken as relatively unchanging
Overmod I had thought the adhesive weight can be taken as relatively unchanging
not interested in why there are sparks.
You should be, if only for the reason that you don't see sparks in a considerable number of slip events. That specifically includes most of the published videos of low-speed slipping of PRR T1s, a far heavier locomotive probably on far greater train resistance than a Black 5. Not only is the slip producing a dramatic amount of frictional heating, it is liberating a higher mass of 'thrown metal'.
As with where the 'surplus energy' moving gas in a locomotive front end is concerned, we need to be concerned with where these things come from in order to appreciate the magnitude of the forces concerned, which may not be evident but still affect the situation dramatically.
might assume TE during slip is even less than w/o sparks.[]quote] As you point out, if you're wilfully ignorant of what produces the sparks, you could 'assume' anything. And still not care... but then, why mention it? If the TE is zero, then train should have slowed, which i don't observe. So I conclude that TE during slip > 0 (i.e 0%).
As you point out, if you're wilfully ignorant of what produces the sparks, you could 'assume' anything. And still not care... but then, why mention it?
If the TE is zero, then train should have slowed, which i don't observe. So I conclude that TE during slip > 0 (i.e 0%).
This is considerably less that a Eureka! moment, as I just spent considerable time explaining why TE in slip may be a major percentage of 'full adhesion'. Perhaps you don't care to read for comprehension, in which case I may have to explain in better English. Or provide better examples.
If TE in slip went to zero, or near zero, any slip would immediately propagate into a spin and the train not recover until the wheels completely came to a standstill (and the asperities re-interlocked, or surface bonding/welding in the patch reestablished itself). This is NOT the behavior we observe in real life, and any theory has to be adapted to explain what we do observe.
Unfortunately there has been relatively little experimentation with TE available in slip, as most if not all operating policy on steam locomotives provided by owning railroads has been to stop a slip when observed, and take means to arrest one and then preclude any repeat once the situation is observed. It would have been possible, for example, when conducting the high-speed rotational testing Kiefer did on 'greased rails' to experiment with measuring the developed pull at a drawbar 'tether' during the process (which spun a J3a up to the rotational equivalent of 161mph by Kiefer's own observation) and this would have given a range of pull vs. mismatch speed that might have been instructive. Likewise a similar test with different types of 'lubricant' present -- including water and compacted-leaf 'composite' -- would have given information with minimal amounts of rail burn or wheeltread damage that would translate directly into, among other things, preparing effective consists in inclement conditions. I have not seen results of any such testing if in fact it were done.
If speed is maintained, then TE is ~equal to train resistance plus grade, if any grade (~ tonnage * grade).
You need to go back and look at the definition of train resistance and compensated grade, as much of the important meaning inherent in that tilde has been incorporated 'for reference' in no small part precisely to prevent incipient slipping whenever possible in operations.
In practice, I believe a certain amount of slipping was included when calculating the minimum speed to be reached on a given grade, together with the loss of TE inherent in a 'reasonably experienced' slip recovery by a knowledgeable engineer. It is my opinion, based on comparatively little, that most of the accommodation here was intended to be met by a lower achieved speed -- or accommodation like doubling or dropping cars from the consist -- rather than by fancy continuation under frequent slipping and recovery. Having said that, though, I got the impression from some reports, including one account by E.T.Harley, that typical SOP on PRR with duplexes was to tolerate a certain amount of repeating high-speed slip when operating 'near the limit' on bad track or in bad weather. That was inherently self-limiting but I don't think it can be denied that it would produce additional track and locomotive damage.
... looking for references to what is an estimate for TE during slip.
If you have access to continuous dynamometer-car records that contain notation of slip incidence (perhaps as annotations for beginning and end) and you know the appropriate climate conditions, etc. prevailing during the test, you might be able to get a reasonable approximation by looking at the shape of the drawbar-pull trace during the 'incident'. If you then compared this deceleration to comparable acceleration of the same consist at known measured TE, you could winkle out a 'difference' corresponding to the lost TE during the duration of the slip.
Of course, you could also 'gin up a fairly simple strain gauge arrangement to measure instantaneous drawbar pull (obtaining the desired variable directly, rather than through some indicated horsepower conversion calculation) and observe what this does during various types of observed slip, including any sustained ones. It would not involve substantial expense to produce such an installation (it could fit rather neatly between any two coupler faces) or to 'remote' its data transmission to something like a cell phone for collection, and the only additional component (likewise 'remotable' would be some means of detecting the occurrence and relative rotational-speed differential of drivers during a slip. I see no reason why the data derived from this comparatively simple approach wouldn't give you precisely the information you want, under a wide range of the potential conditions affecting it, to of course nearly an arbitrarily small percentage of non-methodological observational error.
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OvermodOf course, you could also 'gin up a fairly simple strain gauge arrangement to measure instantaneous drawbar pull
i've measured the pull on an HO brass 0-6-0 at 2.3 oz, loco weight 10.5 oz. while slipping.
is ~22% of weight on drivers roughly what i'm looking for?
gregcI've measured the pull on an HO brass 0-6-0 at 2.3 oz, loco weight 10.5 oz. while slipping. is ~22% of weight on drivers roughly what i'm looking for?
I think that's a reasonable range. I've complained backward and forward that you can't always extrapolate rules of thumb from 1:1 scale to models; but many of the sources of error tend to cancel each other out (the adhesion patch may be much larger and somewhat stickier, but the effect of even small track irregularities cause slipping in an unsuspended wheelbase). But models would share the fundamental similarities that gravity is the major component inducing adhesion, and (absent frog snot) you have reasonably metal-to-metal friction producing adhesion. So I wouldn't be surprised that ~25% is reasonable.
In the bad old days, I think motors 'cogged' badly enough that they would induce and then sustain slipping shy of what 'adhesion' in a world of more perfect smooth torque would involve. What I'd like to see tests done with is the 'project' locomotive that was described in MR in the early '70s, the one with the low-slack Delrin chain driven by a coreless motor. Dress the wheeltreads to a prototypical polish finish, and perhaps profile them to finescale 1:87 (whatever the formal name of that standard is not) and then use something like a metallurgical microscope to determine the precise moment of 'breakaway' into slip with increasing load. Then repeat the test for different rail and track constructions, different methods of 'gleaming', the presence or absence of the various kinds of anti-crud dressing (or the effect of various kinds of rail cleaning) when you have a 'standard' locomotive that eliminates the usual sources of nonproportional slip.
Does the scale method that you're using to determine drawbar pull allow you to determine the point at which traction is re-established (i.e. can it move relative to the locomotive as a dynamometer car would?) It might be interesting for someone to build a 'test car' comparable to the full-scale English version in the 1930s that used dynamic braking for fine resistance control...
As an alternative, I could mention Magne-Traction ... all kidding aside, some of the approaches mentioned in a thread on a British system not too long ago on the MR forum could be used to fine-tune effective 'weight on drivers' (as measured via strain gages between driver axle and body, or similar direct method) and make up a comparative table of how fine weight differences affect adhesion when everything else is held reasonably common. A similar approach might be worked up to adjust the relative running resistance of a trailing consist over a fairly substantial distance or range of physical features.
https://photos.app.goo.gl/huQBZ3XQHLVQrgKF7
Adhesion rating vs trip reliability. Circa 1990
-Don (Random stuff, mostly about trains - what else? http://blerfblog.blogspot.com/)
Don,
That's a really nice chart!
FWIW, I've read stories where the Milwaukee Little Joe's could deliver 30 to 35% adhesion on occasion, but certainly not 80% of the time.
- Erik
Erik_MagThat's a really nice chart!
I have a request in to Progress Rail Locomotive to see if they'll furnish an updated edition. Be interesting to see the effect of improvements since the SD70MAC days...
The inverter per axle should be capable of better adhesion than the SD70MAC inverter per truck design, though it may not be as great as the difference between the SD70 and SD70MAC. I would also suspect that synchronous traction motors would have a small advantage over induction motors.
oltmannd https://photos.app.goo.gl/huQBZ3XQHLVQrgKF7 Adhesion rating vs trip reliability. Circa 1990
What a difference between the SD60 and SD70. I bet the radial trucks had a lot to do with this.
When I worked some of our mountain grade territory I made a point of paying attention to how different locomotive consists would do on a couple unit trains that almost always ran with the same tonnage. I found that EMD power with radial trucks (mainly SD75I and SD70M-2 units, all DC) would climb grades 1 or 2 mph faster than DC GE units of equivalent horsepower, and the EMD-powered trains would stall less frequently. Having a EMD leading a GE was noticeably superior to the other way around.
ES44AC's would slip and lose more speed in curves, but the AC creep control really seemed to shine as the speed dropped. I don't think I ever stalled on those hills with AC power.
A major problem with all the DC GE units is that they will drop their load entirely upon slipping. Nothing like watching the loadmeter needle flick back and forth between 0 and 1000 amps, while the thing is trying to jerk your train apart.
In addition, some genius at GE programmed the Dash-8's to not sand above 7 mph. By the time you have lost that much speed it is often too late.
I only had SD60's a few times, but they seemed to be even worse than a Dash-8 for traction.
Greetings from Alberta
-an Articulate Malcontent
gregc what is the TE (by adhessive weight) while slipping?
Not as dramatic, but still a good show..
https://www.youtube.com/watch?v=dSmtV8hrlAY
2010ChallengerNot as dramatic, but still a good show.. https://www.youtube.com/watch?v=dSmtV8hrlAY
More dramatic (and infamous), but not at all a good show:
https://www.youtube.com/watch?v=YjsNbzg1UaI
For those who are 'balanced' three-cylinder adherents, this is a sobering incident to consider. Note that the supposed "140mph" rotational speed is considerably lower than that reached in actual test on the New York Central, with a 2-cylinder engine, in the late 1940s, but the inertial damage was catastrophic.
The video states that the problem began with priming that 'made the regulator difficult to close', but my understanding was that the actual problem of significance was that after the initial slip the driver let go of the screw regulator, which whipped around and hit him; this ran the gear 'down in the corner' and by allowing heavy mass flow caused the priming to blow a considerable mass of water into the superheaters, which were ahead of the throttle valve. Getting the throttle closed then did little to arrest the slip propagation, but it is notable that at no time before the damage to cylinders and motion was anywhere near enough adhesion re-established to brake the rotation. Whether effectively-smoother torque peaking contributed to this is an open, and perhaps interesting, question for discussion.
SD70Dude oltmannd https://photos.app.goo.gl/huQBZ3XQHLVQrgKF7 Adhesion rating vs trip reliability. Circa 1990 What a difference between the SD60 and SD70. I bet the radial trucks had a lot to do with this. When I worked some of our mountain grade territory I made a point of paying attention to how different locomotive consists would do on a couple unit trains that almost always ran with the same tonnage. I found that EMD power with radial trucks (mainly SD75I and SD70M-2 units, all DC) would climb grades 1 or 2 mph faster than DC GE units of equivalent horsepower, and the EMD-powered trains would stall less frequently. Having a EMD leading a GE was noticeably superior to the other way around. ES44AC's would slip and lose more speed in curves, but the AC creep control really seemed to shine as the speed dropped. I don't think I ever stalled on those hills with AC power. A major problem with all the DC GE units is that they will drop their load entirely upon slipping. Nothing like watching the loadmeter needle flick back and forth between 0 and 1000 amps, while the thing is trying to jerk your train apart. In addition, some genius at GE programmed the Dash-8's to not sand above 7 mph. By the time you have lost that much speed it is often too late. I only had SD60's a few times, but they seemed to be even worse than a Dash-8 for traction.
Interesting observations, especially about the radial trucks. That could easily be the difference. While the SD70 and SD60 have different controls systems, they are still basically trying to do the same thing - trying to maximize TE within the constraints of a DC propulsion system. So, it's not surprising they perform about the same.
The taking the sand away thing... I remember them explaining why, but I'm not sure I remember the details. The main reason is that when you are in "wheel creep" mode, the sand actually makes things worse under most conditions. Sounds like that is a "not always".
oltmannd The taking the sand away thing... I remember them explaining why, but I'm not sure I remember the details. The main reason is that when you are in "wheel creep" mode, the sand actually makes things worse under most conditions. Sounds like that is a "not always".
I would suggest that those technicians did not ride very many trains.
I cannot think of any time that holding the sander on did not improve the locomotive's performance. Even the ES44AC's did noticeably better with the sander held on.
When starting a train you do have to be careful not to make a pile of sand on the rail, that the wheels will then have to climb over. But as long as the train is moving this is not an issue.
Both EMD and GE units seemed to perform best at very low speeds (less than 5 mph) with the sander held on, the throttle in notch 5 or 6 (to prevent excessive slipping, at low speeds you can't use the extra amperage anyway) and about 15-20 PSI on the independent brake. But you have to play around with the controls to find what happens to be the optimum setting, each day and locomotive consist are a little bit different.
I can recall several instances where we climbed the last portion of a grade at less than 1 mph in heavy rain, but did not stall. Sand is what kept us going.
Going back to Balt's point on another thread about skilled operators getting the most out of their equipment, which Engineer was running could also be a big difference. Some guys would just pull the throttle out to 8 and not care, while others would try everything to avoid stalling, and keep playing with the controls as I described.
oltmanndThe taking the sand away thing... I remember them explaining why, but I'm not sure I remember the details. The main reason is that when you are in "wheel creep" mode, the sand actually makes things worse under most conditions.
The reason ... and what the creep makes 'worse' ... is associated with wheel and rail wear, contamination by grit and dust, and signal contact issues. If I recall correctly, worn wheeltreads cause problems with the radial tracking that can lead to track geometry concerns. It's almost impossible to think of a better grinding compound than sand embedded in flange grease ... or 'used' sand in TOR "lubricant" on the railhead, if you're using it.
Sand will cause a bit more immediate 'bite' during creep modulation, and I think the effectively high-frequency motion leads to additional fine grinding of the sand to where it may more easily get through seals into grease lubrication, and potentially at least some fretting-type wear patterns.
I also get the impression that sanders fail open or dribble more than laymen probably think they do. Over time all that sand in all those wrong places starts to add up, and of course if your operations model depended in part on there still being some 'later' you might have expensive stalls or doubling on your plate.
Did anyone here have any experience with the GE supersonic rail blower as an alternative to sanding? It seemed so promising and then disappeared so quickly without a trace...
Overmod Did anyone here have any experience with the GE supersonic rail blower as an alternative to sanding? It seemed so promising and then disappeared so quickly without a trace...
You mean the Automatic Rail Cleaner (ARC) system? When working properly it does a great job of producing clean, dry rail in front of the locomotive, but in my opinion it has two major flaws.
1. It is entirely automatic, the Engineer has no control over when it activates, other than to disable it entirely in the computer. It does not activate in many instances where it would help, while also activating when it is not needed.
2. It uses a very large amount of air, and there have been cases where it has drawn the main reservoir down below brake pipe pressure, which of course starts setting the brakes on the train.
RE: wheels being damaged from spinning, if a railroad insists dispatching such underpowered trains, then they have to accept that extra wear and tear on the equipment is a cost of doing business in that manner.
SD70Dude oltmannd https://photos.app.goo.gl/huQBZ3XQHLVQrgKF7 Adhesion rating vs trip reliability. Circa 1990 What a difference between the SD60 and SD70. I bet the radial trucks had a lot to do with this. In addition, some genius at GE programmed the Dash-8's to not sand above 7 mph. By the time you have lost that much speed it is often too late. I only had SD60's a few times, but they seemed to be even worse than a Dash-8 for traction.
I wouldn't blame GE for that sanding speed, thats typically a factor in the software and each railroad has set specifications on sanding characteristics, sanding in emergency, trainline sanding, manual/auto sanding speeds, inboard/outboard Sanding Etc.
Entropy SD70Dude oltmannd https://photos.app.goo.gl/huQBZ3XQHLVQrgKF7 Adhesion rating vs trip reliability. Circa 1990 What a difference between the SD60 and SD70. I bet the radial trucks had a lot to do with this. In addition, some genius at GE programmed the Dash-8's to not sand above 7 mph. By the time you have lost that much speed it is often too late. I only had SD60's a few times, but they seemed to be even worse than a Dash-8 for traction. I wouldn't blame GE for that sanding speed, thats typically a factor in the software and each railroad has set specifications on sanding characteristics, sanding in emergency, trainline sanding, manual/auto sanding speeds, inboard/outboard Sanding Etc.
You are of course correct that the different railroads can specify and modify different features on their locomotives. I initially thought that the Sanders were one of these, but found it interesting that the CN, C&NW, UP and ATSF/BNSF spec units (CN bought a lot of secondhand Dash-8's) all behave the same with regard to sanding.
Then I looked it up in my copy of "The 1st and 2nd Generation Locomotive Handbook", published by the International Association of Railway Operating Officers. On page 129 it states that Dash-8 models have the manual trainline sand nullified at speeds above 7 mph.
EntropyI wouldn't blame GE for that sanding speed, thats typically a factor in the software and each railroad has set specifications on sanding characteristics, sanding in emergency, trainline sanding, manual/auto sanding speeds, inboard/outboard Sanding Etc.
Sand is expensive. And an engine without emergency stopping sand is FRA defective (in the US).
It's been fun. But it isn't much fun anymore. Signing off for now.
The opinions expressed here represent my own and not those of my employer, any other railroad, company, or person.t fun any
zugmann Entropy I wouldn't blame GE for that sanding speed, thats typically a factor in the software and each railroad has set specifications on sanding characteristics, sanding in emergency, trainline sanding, manual/auto sanding speeds, inboard/outboard Sanding Etc. Sand is expensive. And an engine without emergency stopping sand is FRA defective (in the US).
Entropy I wouldn't blame GE for that sanding speed, thats typically a factor in the software and each railroad has set specifications on sanding characteristics, sanding in emergency, trainline sanding, manual/auto sanding speeds, inboard/outboard Sanding Etc.
Is that only for lead units, or for trailing units as well?
There are a number of places where we change direction that do not have a wye or loop. What was the trailing unit now becomes the leader. I've lost count of the number of times I have found the new lead unit to be out of sand.
SD70DudeIs that only for lead units, or for trailing units as well?
§ 229.131 Sanders.Except for MU locomotives, each locomotive shall be equipped with operable sanders thatdeposit sand on each rail in front of the first power operated wheel set in the direction ofmovement.GuidanceThe section has two qualifiers, in that MU locomotives are exempt and that each locomotive ina consist shall have operable sanders that deposit sand in front of the first power-operatedwheel set in the direction of movement. At a servicing facility where the direction of alocomotive or locomotive consist is unknown, the inspector should require the railroad to haveall out-board sanders operational prior to departure. However, if a locomotive is inspected at thehead end of the train, only the sanders in the direction of the train movement must beoperational. Locomotives used in yard switching service, which normally move in bothdirections, should have the outboard sanders operational. A hole in the sand delivery pipe is notan inoperative sander. The mere presence of a hole in the sander hose or pipe is not sufficient toestablish a violation under section 229.131, without detailed discussion of the hole’s impact onthe sander’s ability to operate. FRA is required to establish that the sander is not depositing sandin front of the wheel. However, if sand is being discharged at eye level and constitutes apersonal injury hazard, it should be reported under section 229.45.
SD70Dude Entropy SD70Dude oltmannd https://photos.app.goo.gl/huQBZ3XQHLVQrgKF7 Adhesion rating vs trip reliability. Circa 1990 What a difference between the SD60 and SD70. I bet the radial trucks had a lot to do with this. In addition, some genius at GE programmed the Dash-8's to not sand above 7 mph. By the time you have lost that much speed it is often too late. I only had SD60's a few times, but they seemed to be even worse than a Dash-8 for traction. I wouldn't blame GE for that sanding speed, thats typically a factor in the software and each railroad has set specifications on sanding characteristics, sanding in emergency, trainline sanding, manual/auto sanding speeds, inboard/outboard Sanding Etc. You are of course correct that the different railroads can specify and modify different features on their locomotives. I initially thought that the Sanders were one of these, but found it interesting that the CN, C&NW, UP and ATSF/BNSF spec units (CN bought a lot of secondhand Dash-8's) all behave the same with regard to sanding. Then I looked it up in my copy of "The 1st and 2nd Generation Locomotive Handbook", published by the International Association of Railway Operating Officers. On page 129 it states that Dash-8 models have the manual trainline sand nullified at speeds above 7 mph.
The modern GE AC units, at least until the latest batch, have been able to give manual/train line sand in power at any speed. Our modern EMD units won't in power except at very low speed. (Both will allow manual sanding in dynamics at any speed.) I just love listening to the wheels 'singing' on wet rail going up Blair hill waiting for the darn computer to decide to put down sand. Which it waits too long to do, that is, if it puts down any sand at all.
Jeff
jeffhergertI just love listening to the wheels 'singing' on wet rail going up Blair hill waiting for the darn computer to decide to put down sand. Which it waits too long to do, that is, if it puts down any sand at all.
zardoz jeffhergert I just love listening to the wheels 'singing' on wet rail going up Blair hill waiting for the darn computer to decide to put down sand. Which it waits too long to do, that is, if it puts down any sand at all. Jeff, have there been any instances of the locomotive's 'decision' to drop sand result in a sudden traction 'grab' that resulted in scrap metal creation?
jeffhergert I just love listening to the wheels 'singing' on wet rail going up Blair hill waiting for the darn computer to decide to put down sand. Which it waits too long to do, that is, if it puts down any sand at all.
Jeff, have there been any instances of the locomotive's 'decision' to drop sand result in a sudden traction 'grab' that resulted in scrap metal creation?
No, that hasn't happened. Yet. Most don't seem to put much sand down once they finally deem it needed.
jeffhergert zardoz jeffhergert I just love listening to the wheels 'singing' on wet rail going up Blair hill waiting for the darn computer to decide to put down sand. Which it waits too long to do, that is, if it puts down any sand at all. Jeff, have there been any instances of the locomotive's 'decision' to drop sand result in a sudden traction 'grab' that resulted in scrap metal creation? No, that hasn't happened. Yet. Most don't seem to put much sand down once they finally deem it needed. Jeff
It's more the lack of sand and associated surging, slipping, and load dropping that does that.
The GE Dash-8's and Dash-9's are especially bad for dropping their load completely, just long enough for the power to roll back into the train and bunch the slack on the first couple cars. Then they throw the full load back on and yank the slack out hard....
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