I am coming to you to answer a question presented in one of the Political Forums I frequent…
What are the top and ambient speeds of the major diesel Locomotives currecntly in service? Older types like F-Units? …and of Hudson, Challeneger and Big Boy steam locomotives?
I bring this to this forum for the purpose of debate as well.
The speed of diesel locomotives is governed by the gear ratio, which is specified by the number of teeth on the axle gear (big gear) and on the motor pinion (small gear), like 61:16, for example. The maximum speed of the motor is the limiting factor , since the motor could come apart at too high a speed. In the case of the GP40-2 the speeds are
62:15 max 65mph, min 11.3mph
61:16 max 70mph, min 11.2mph
60:17 max 76mph, min 11.2mph
59:18 max 82mph, min 12.1mph
The minimum speed is the speed at which the motors will not overheat.
By fitting different ratios, 59:18 for example, even higher speeds are possible, but probably requiring higher minimum speeds.
This should start the discussion.
Peter
World’s fastest diesle loco is russian TEP80 which reached 273 km/h/170 mph
How does this work with high-speed electric locomotives like the Acela power units? If they are geared for 150 MPH, do they have a hard problem starting up, or do they have such a large amount of motors for the tonnage that it is not a problem?
Also, in the days of the Hiawatha, they were running steam at 100 MPH plus while today there is a 79 MPH speed limit unless you have special signals (NEC, Empire corridor). What allowed the fast running in times past?
Based on 40" wheels…
E8s have 36" wheels
SD80MACs (and other ACs?) have 45" wheels and totally different gear sets.
Thank you all for your continuing responses.
Hello, my name is Joe Ely Carrales and I am an 8th grade American History teacher in Kingsville, Texas. As a teacher, I am a full combatant in the war on ignorance. When I identify ignorance in myself, I am keen to take action to remedy it.
For years I have been an avid rail fan and student of the Railroad Sciences (as much as time will allow) and have been very active in political and societal internet debate forums (as well as in the Garden Railroad forum). When one sphere of my life intersects another I capitalize on it.
Thank you for the wealth of information that has hence made its way into my mind. I was a bit intimidated by what I had heard about the Trains Magazine forum. I ask that you, at times, excuse and pardon my ignorance in the more specific details of modern railroading as well as nursemaid me through to a fuller better understanding.
Thank you,
Capt Carrales
P.S. I am a Captain in the Civil Air Patrol hence my log on name!
Joe – as several have noted, the maximum speed of a diesel is set by the gearing and wheel diameter; there is a limit (rather high!) on how fast the traction motor can spin, but it usually isn’t a real factor. There is also a limit on minimum rpm at full load current; both of these are set by traction motor design. It is true, however, that for a particular gearing and traction motor, the faster the design speed the less starting torque (pull) there is available. One reason why E8s, for example, made rather dismal freight engines (the other reason was that they had only 2/3 rds of their weight on driven wheels). The same reasoning prevails for straight electric engines (e.g. the Acela or a GG1). Realistic or legal top speeds are set, as Mark noted, by what’s permissible and economically reasonable. There is no engineering reason why, on decent track, diesels can’t go as fast as straight electrics.
Steam engines are a slightly different story. There, driving wheel diameter was a major factor, as very few steam engines were really perfectly balanced. However, steam engines designed for passenger service could, and routinely did, exceed 100 mph (examples include the New York Central’s Hudsons and Niagaras; the Milwaukee Roads Atlantics and Hudsons, Pennsy’s K4s, and others). Other large engines can run at those speeds, too, although they are often best at somewhat lower speeds (the N&W Js, UPs Northerns like the 844, for instance). I believe that the current world speed record (official!) for steam is held by the British LNER railroad’s Mallard, at around 120 – hopefully someone has the correct figure.
Yes, Britans Mallard holds the official record. There are unofficial reports of faster spreeds. PRR 4-4-2 7002 at 127 MPH for example. I read one account of a Pennsy T1 allegedly hitting 130 MPH!
Some additional points that may be of value:
The principal limit on DC speed is, I believe, imposed more by counter EMF than “birdsnesting” considerations with the motor windings. The armature of a DC traction motor works quite nicely as a generator, and induces a higher voltage the faster it’s turning (just as a conventional generator does). Lenz’ law indicates that the polarity of this voltage will counter that of the main-generator supply. One might note that the ‘conventional wisdom’ regarding field weakening in traction motors to gain higher speed will work with diesels, provided adequate armature cooling, brush and commutator integrity, etc. is provided. (Don Oltmann might care to comment on the runaway potential of field-weakened vs. standard traction motors in uncontrolled wheelslip…)
There is a very significant reason, covered here before, why diesels normally can’t produce the high speeds of ‘equivalently-motored’ straight electrics – the absolute hp limit imposed by the diesel motor. Electrics can draw much higher energy from the overhead wire for short periods of time, even at very high developed motor hp – it’s not uncommon to see 7000 to 8000hp on four axles in European power ratings, but it would be most unusual to see internal-combustion power with prime movers of that rating!
So there will be a hard limit on top speed, which is where peak hp output of the engine and traction alternator balances train and aerodynamic resistance (and counter EMF of the traction motors, etc.). If you wonder why the Bombardier high-speed NEL uses a turbogenerator, consider the hp requirements even of something like the Acela when running at high speed (or accelerating at speeds above 120mph or so). For an even more striking figure, look at the power to a TGV when running at its maximum service speed (in case you’re wondering why 25kV isn’t overkill with lightweight trains!). You would not want to have to develop this kind of power with compression-ignition engines (
AFAIK, the Mallard reached 201 km/h, almost 126 mph. Most experts consider it the fastest steam engine in the world, although some Germans claim this title for the 05-class.
The British Railways High Speed Trains (HST) regularly reach 125 mph. The service they provided was called IC 125 in BR-times. The HST are basically two streamlined diesel-locomotives with asymetrical design embracing the passenger cars. AFAIK, the train that hit a potential suicider in the London-area a few days ago was a HST-train.
To cover the earlier (implied) question, Union Pacific’s E units, all of them from the E-2 through to the E-9, had 36" wheels and a 55:22 gear ratio. This allowed the E-9s to run at 98mph at which speed the tractive effort was 7500 lbf. I assume this was the standard gearing, but I don’t know.
The earlier 1936 M10003/4/5/6 units had 36" wheels, 51:22 gearing and were allowed 100mph.
Peter
Overmod – somewhere there exists a video – I know it does; I’ve seen it – of a TGV under a maximum speed maximum power test. A good illustration of the power drawn under those conditions is the intensity of the arcs when the pantographs (both were in use) lifted off the catenary. Truly amazing; looked like lightning bolts.
And on the same train of thought (as it were!) – it is most likely that truly high speed trains not under catenary would use gas turbine prime movers (like the old TurboTrain, but in a much more modern and updated form!) for their alternators, for weight reasons, as you note.
Thanks folks for the correct speed for the Mallard. As you say, their are any number of unverified higher speeds out there (the Milwaukee Road Atlantics must have done close to that, considering their schedules) but Mallard is official and properly timed!
Just remember that there’s a certain amount of ‘flackery’ about the Mallard record run – downhill, over 125 mph for only a bit over 300 yards, and 126 for no more than about 60 yards (IIRC, Sir Nigel Gresley himself didn’t accept the 126 mph as a ‘genuine’ record speed). Remember this is a dynamometer-car speed reading, not an external timing measurement… more accurate, at the time.
And the locomotive had trouble with the inside big-end connecting-rod bearing – an occupational hazard of high-speed runs with the A4’s design of Gresley conjugated valve gear, which caused increased center-cylinder thrust (and hence overloading) at high cyclic speed. If we consider only record speeds that didn’t break the locomotive to achieve, the “official” record, I think, goes to the German 05 class.
I suspect that the Milwaukee F7 Hudsons would reach higher maximum speed than the Atlantics, but would welcome detailed technical argument to the contrary…
… and would still dearly like to know, from an experienced source, what the actual range of top speed achieved by the PRR S1 might have been (I find the purported “141.2 mph” a piece of metric-translated balderdash…)
to sort of follow up… Overmod’s comments on the Mallard speed are quite correct – but at least it was timed. And I’ve never been happy with centre cylinder mechanisms in general; just too complex. The Milwaukee Hudsons may well have been faster than the Atlantics – it would be nice to know, but I don’t suppose we ever will.
Seems to me, though, that a picture of sustained running speeds would be even more interesting than a timed maximum speed. One approach is to look at scheduled timings; the operating department must have had a hand there, and they must have known what the equipment could do – anybody have some information on that?
And there are a number of late designed for passenger service steam engines which must have had the ability of sustained speed over 100 mph – not just the German O5’s. Pity they were never timed – but, I suppose, who knew?
[quote]
QUOTE: Originally posted by Overmod
Some additional points that may be of value:
The principal limit on DC speed is, I believe, imposed more by counter EMF than “birdsnesting” considerations with the motor windings. The armature of a DC traction motor works quite nicely as a generator, and induces a higher voltage the faster it’s turning (just as a conventional generator does). Lenz’ law indicates that the polarity of this voltage will counter that of the main-generator supply. One might note that the ‘conventional wisdom’ regarding field weakening in traction motors to gain higher speed will work with diesels, provided adequate armature cooling, brush and commutator integrity, etc. is provided. (Don Oltmann might care to comment on the runaway potential of field-weakened vs. standard traction motors in uncontrolled wheelslip…)
There is a very significant reason, covered here before, why diesels normally can’t produce the high speeds of ‘equivalently-motored’ straight electrics – the absolute hp limit imposed by the diesel motor. Electrics can draw much higher energy from the overhead wire for short periods of time, even at very high developed motor hp – it’s not uncommon to see 7000 to 8000hp on four axles in European power ratings, but it would be most unusual to see internal-combustion power with prime movers of that rating!
So there will be a hard limit on top speed, which is where peak hp output of the engine and traction alternator balances train and aerodynamic resistance (and counter EMF of the traction motors, etc.). If you wonder why the Bombardier high-speed NEL uses a turbogenerator, consider the hp requirements even of something like the Acela when running at high speed (or accelerating at speeds above 120mph or so). For an even more striking figure, look at the power to a TGV when running at its maximum service speed (in case you’re wondering why 25kV isn’t overkill with lightweight trains!). You would not want to have to
Not to worry - the participants here range from seasoned railroaders to middle schoolers. We even have a thread that surfaces from time to time called “Stupid Question Thread.” We’ve all learned from that one. About the worst that can happen is that someone will point you to a thread where we’ve discussed a topic before.
Welcome, and enjoy!
To speak of flashes from the overhead reminds me of the French speed records of the 1950s where they managed to get BB9004 up to 331km/h or so. CC7107 was also used in the tests, and it was given equal billing, quite unfairly, because it was a production locomotive with export (Spain, Holland, Morocco) potential. It never quite made the same speed.
But the French realised they needed a high voltage to overcome the back EMF, and with a surprising lack of subtlety raised the line voltage from 1500 to 2000 for the duration of the tests.
The trains ran on a long stretch of straight track with three steel cars with full sheathing between cars and a big parabolic “tail” on the rear to reduce drag.
But views from the air (helicopter?) and the ground showed massive flashes from the pantographs as they simultaneously took higher speeds, voltages and currents than they had been designed for!
Peter
Nothing shocking here. In the record run of the TGV voltage was also rised from 25 kV to 30 kV. Besides - 1500V DC is nominal. It may be as high as 1800 near the substation and as low as 1200 far from it or when a train is drawing power.
I find this electrifying. Sorry… I could not resist. I think the PRR steam has the top speeds (unofficial) because there are persistent stories about how these mighty locomotives would hit the stride and run out of safe track and must slow down before hitting the top end.
I feel that Maglev is the key to speed in the future. By removing the wheel and gearing as a limiting factor and using the electricity to actually lift the unit and shove. More juice more shove up to the limits of areodynamics and physical safety.
I have been at 130+ mph in my old 71 Ford with the Boss 351, while this is not a train speed, I want to illustrate that it is very difficult to “Accelerate” a object moving at 130+ to say 150. A friend of mine used a slightly different configuration to be able to break 150+ rather easily.
While Desiels can power large 18 wheelers to about 110 mph with the proper gear ratio vs availible power again there is a limit on physical “power” availible to do the work needed to accelerate or decel the mass at any given weight and speed.
I would have immensly enjoyed the attempts of the French to “Fry up” some of the better performance out of the TGVs and the rather “killjoy” limits on American top speeds even in the NEC.
I feel with any amount of needed force transmitted to the right energy via the right machinery or physical interface (Magnet) you can accelerate any train to any speed you want to.
I want to end with a story about a Milwalkee Road Express passenger train that needed help from a 0-6-0 yard engine to get moving. Once it passed 25 mph on the open main line reaching for the magic 100 mph+ the little 0-6-0 could not release the forces pulling on it’s front coupler and had to be towed at near 100+ for a while until the crew in the big engine was made aware of the problem.