Notches and Speed

[tree68]

First of all, we all know there are many variables that govern train speed, independent of the throttle setting. We'll have to set all of them aside for just a moment...

Assuming a billiard table flat section of track, and a reasonable HP/T ratio, are there some expected "equilibrium" speeds for the eight notches on the classic throttle? Are there situations (including on track with a "normal" profile) where the track speed and the equilibrium speed don't match? Does that involve constant throttle adjustments?

Seems like I've seen that newer locomotives have throttles that are nearly infinitely variable, which would obviously address the issue. Even half notches would ease the problem, I would think.

So, from the operating/mechanical crowd - what's the story?

[CopCarSS]

Good question Larry. I've always wondered how 8 notches were enough for the throttle. Especially considering how much control a steam locomotive had in this aspect (not only was there plentyt of travel on the throttle, the engineers could play with the valve timing, too). It would seem that teaching a bunch of steam era engineers to run the new diesels with only 8 nothces of throttle would be a little difficult. I'm curious on the answers to this one...

Chris

[jchnhtfd]

I'll be interested in the road guys response, too -- but one thing to remember here, and why 8 notches works: power or drag to weight ratio. Various cars and trucks have power to weight ratios on the order of 20 to 200 hp per ton. A typical train may be a tenth of that, if that. Thus to get a train going, you 'floor' it (well, not really, not all at once, but fairly quickly) and wait. And wait some more. Until it gets up to track speed. Eventually. Once you are there, if all things are equal, you come back to 3 or 4, and the speed changes very slowly (no grade) because the dang thing is so heavy in relation to the drag. Cars and trucks don't do that; you back off, you slow down -- so you always have to feather the throttle.

[mvlandsw]

Track speed and the equilibrium speed almost never match. In the territory that I work constant throttle adjustment is the normal procedure.The only exception is when the train is too heavy or the grade too steep to reach the allowed speed. The only locomotive that I know of that has infinitely variable throttle positions is the Amtrak F40PH when the head end power is being used. This is done because the diesel engine has to run at a constant speed to produce the proper frequency AC power for the cars. A throttle like that would be nice on some of the newer freight units. Using only eight notches produces too much of a power change per notch for smooth train handling in some situations. I sometimes use the power reduction feature available on some locomotives to manually control the power increase between notches. This works well on the older locomotives that have a switch and rheostat but on the units with the computer screen control it is too clumsy and slow to bother.

[mvlandsw]

QUOTE: Originally posted by jchnhtfd

I'll be interested in the road guys response, too -- but one thing to remember here, and why 8 notches works: power or drag to weight ratio. Various cars and trucks have power to weight ratios on the order of 20 to 200 hp per ton. A typical train may be a tenth of that, if that. Thus to get a train going, you 'floor' it (well, not really, not all at once, but fairly quickly) and wait. And wait some more. Until it gets up to track speed. Eventually. Once you are there, if all things are equal, you come back to 3 or 4, and the speed changes very slowly (no grade) because the dang thing is so heavy in relation to the drag. Cars and trucks don't do that; you back off, you slow down -- so you always have to feather the throttle.

Light engines respond much like cars and trucks.

[Sterling1]

QUOTE: Originally posted by CopCarSS

Good question Larry. I've always wondered how 8 notches were enough for the throttle. Especially considering how much control a steam locomotive had in this aspect (not only was there plentyt of travel on the throttle, the engineers could play with the valve timing, too). It would seem that teaching a bunch of steam era engineers to run the new diesels with only 8 nothces of throttle would be a little difficult. I'm curious on the answers to this one...

Chris

I know on some early GE units may have had more than 8 notches, but then again maybe not.

[jchnhtfd]

QUOTE: Originally posted by mvlandsw

QUOTE: Originally posted by jchnhtfd

I'll be interested in the road guys response, too -- but one thing to remember here, and why 8 notches works: power or drag to weight ratio. Various cars and trucks have power to weight ratios on the order of 20 to 200 hp per ton. A typical train may be a tenth of that, if that. Thus to get a train going, you 'floor' it (well, not really, not all at once, but fairly quickly) and wait. And wait some more. Until it gets up to track speed. Eventually. Once you are there, if all things are equal, you come back to 3 or 4, and the speed changes very slowly (no grade) because the dang thing is so heavy in relation to the drag. Cars and trucks don't do that; you back off, you slow down -- so you always have to feather the throttle.

Light engines respond much like cars and trucks.

True, very true. Sorry. I was thinking whole trains...[:I]

[Randy Stahl]

Remember that the traction motors fly apart at too high of speeds. Depends on the gear ratio. counter EMF limits top tractive speed .
GE U-30 C had 1/2 notches.
Randy

[Anonymous]

mvlandsw pretty well sums it up. Trains accelerate very slowly because of their obvious weight or type of grade their on. You cannot compare their acceleration capabilties to that of a car or truck. Any type of throttle modulation may take a long time to notice a increase or decrease of speed. I am talking in the order of at least 15 seconds and even minutes. Basically I am saying is the train speed response time is very slow. There is no real need to have a throttle that you could fine tune. Any depriciable difference in grade you are ajusting the throttle a long time before your actually on it to start compensating for the decrease or increase in speed. Most trains are not over powered so on an average run the speed may seldom reach the subdivision max except on descending grades even in throttle 8. Longer trains are easier to maintain a constant speed in hillier grades because it has a tendancy to average out. While one part of the train is going up hill the other part is going down. In my experience real short trains require more throttle regulation because either your whole train is going up the grade or down.

Brent

Brent

[arbfbe]

The physics is horsepower equals speed. On your perfectly flat pool table railroad on any given train, the more horsepower you have on it the faster it will go. Each throttle setting has a horsepower out put for that unit or consist. On a Dash8-44C these equate to about 600hp in throttle 1 to 4400hp in throttle 8. The train of between one and 300 cars will reach a peak speed for each throttle position for the unit. At some point for each throttle position there will be a speed where the friction of the trailing tonnage will not allow the train to move any faster. Adding horsepower by increasing the throttle position or adding another unit will increase the speed of the trailing tonnage.

Eight throttle positions gives enough control to the engineer, there is no need for any more. It is a factor of three solenoids in the governor and 2 to the 3rd power means there are eight permutations and combinations available for control. Adding another solenoid would mean 2 to the 4th power or 16 combinations. When you are talking of masses involved in train tonnages the difference between 8 and 16 is insignificant.

alan

[Anonymous]

can't you use the brake to help with the speed to?

[M636C]

I posted a comment on this in another thread some time ago, but here it is again: The 8 notch throttle was designed by EMD to allow the 567 engine to run at fixed speeds at which torsional (twisting) vibration in the crankshaft was minimised. The eight notches, allowed fixed speeds at which minimal torsional vibration was experienced, and this has been continued with more modern EMD locomotives. GE introduced a 16 notch control which had alternate notches equivalent to the EMD system. This meant that a GE under MU control with an EMD only ran in the eight notches selected by the EMD controller, missing out the half notches. A GE controlling an EMD could use the half notches, but the EMD just went through the eight notches as the GE selected the alternate notches. I understand that GE have given up on this sytem, because there was no real advantage.

English Electric had a different system entirely, where the notch throttle was replaced by a "Power Lever" which had infinite settings and controlled the engine through a load regulator, a big electro-mechanical device, later replaced by an electronic equivalent without much success at first. This meant that you started the locomotive and moved the power lever to the maximum power you wanted. The loco would start off and the engine would progressively come up to the power level you selected automatically. A good example of this was running a locomotive on a load box, a dummy load controlled by moving steel plates in and out of salt water. The locomotive would be started and the power lever was moved around to the stop at maximum. With the plates fully submerged, the loco was still at idle, but as they were removed, the resistive load increased and the diesel increased in power until it was at full power. At the end of the test, the load was reduced by lowering the plates back and the diesel automatically returned to idle. I thought this was just great, but in actual traffic, the power lever would be moved in much the same way as an eight notch throttle.

In fact, EMD units have an accelerating relay which prevents the locomotive being "notched up" too quickly and putting too much strain on the power equipment. In the Queensland Railways model GL8C this had an isolating switch which allowed the locomotive to be notched up very quickly while hauling suburban passenger trains which not only stopped frequently but were light enough not to overload these small (60 tons, 1000HP) locomotives, but required the fastest acceleration available to meet their schedules.

I hope this makes things clearer

Peter

[PNWRMNM]

There is another aspect no one else has mentioned which is that the situation you laid out is seldom if ever obtained in the real world. Even if you have a bit of dead level track it may have curves which increases drag. In reality over "flat" ground you will have all sorts of dips and humps, particularly on an old line and/or a line built cheaply so your speed will vary at constant throttle.

Mac

[tree68]

QUOTE: Originally posted by PNWRMNM

There is another aspect no one else has mentioned which is that the situation you laid out is seldom if ever obtained in the real world. Even if you have a bit of dead level track it may have curves which increases drag. In reality over "flat" ground you will have all sorts of dips and humps, particularly on an old line and/or a line built cheaply so your speed will vary at constant throttle.

Mac

Actually, that was my opening disclaimer:

QUOTE: Originally posted by Tree
First of all, we all know there are many variables that govern train speed, independent of the throttle setting. We'll have to set all of them aside for just a moment...

I'm just wondering how close to "set and forget" the throttle might come. Even with the variables, is it possible for an engineer to pick a notch and essentially sit back and "enjoy the ride?" Up grades in notch 8 doesn't count.

[daveklepper]

Some modern electric locomotives and multiple unit cars allow the operator/engineer to simply set the speed he/she wishes and automatic speed control does the rest. I don't know of any diesels that do this.

[zardoz]

QUOTE: Originally posted by tree68

QUOTE: Originally posted by PNWRMNM

There is another aspect no one else has mentioned which is that the situation you laid out is seldom if ever obtained in the real world. Even if you have a bit of dead level track it may have curves which increases drag. In reality over "flat" ground you will have all sorts of dips and humps, particularly on an old line and/or a line built cheaply so your speed will vary at constant throttle.

Mac

Actually, that was my opening disclaimer:

QUOTE: Originally posted by Tree
First of all, we all know there are many variables that govern train speed, independent of the throttle setting. We'll have to set all of them aside for just a moment...

I'm just wondering how close to "set and forget" the throttle might come. Even with the variables, is it possible for an engineer to pick a notch and essentially sit back and "enjoy the ride?" Up grades in notch 8 doesn't count.

My experience was that if your train had the 'correct' amount of power for the tonnage, "cruising speed" would be in about the 5th notch.

Regarding "light engines", the good-old SD40-2 would accelerate rather quickly. I had two SD40-2's accelerate from 0 to 60 in 30 seconds!! Not too bad, considering it was 400 tons of metal. Had a GE go from 0-60 in 30 minutes (just kidding; they wern't quite that slow...almost, but not quite).

What was also fun was when you ran light engines and were going real fast, to switch over to full dynamic brakes (on a SD40-2) at speed; the resulting rapid deceleration was a marvel to behold (it would almost lift you out of the seat!).

[Anonymous]

tree68

On the railroad I work for each train has a horsepower to ton ratio that they would ideally have. On our bulk trains or most non manifest trains it is based on the minimum horsepower to get over the ascending grade that train will go over.The fast freights or differrent symbol trains carry a hp to ton ratio that the company deems fit to maintain a reasonable time schedule. More often than not this is seldom met because of power shortages. Where I work once you get up the hill you can haul 9200 tons with 1 GE AC4400 for a total of 135 miles and the next subdivision they could even put on more tonnage. If the wind is blowing I have gone the whole trip without leaving throttle 8 except for train meets. The average time for a non stop train of this kind would be close to six hours. Likewise on coal empties you can put it in throttle 8 the whole trip because of the wind drag. Pretty slow at times and you wonder will the trip ever end:)
The railroad tries to distribute power to be used in the most efficient way or to get the maximun use from it. You get good fuel econnomy at the expense of speed.

Brent

Brent

[mvlandsw]

QUOTE: Originally posted by daveklepper

Some modern electric locomotives and multiple unit cars allow the operator/engineer to simply set the speed he/she wishes and automatic speed control does the rest. I don't know of any diesels that do this.

EMD and GE AC units have automatic speed control built into their computers. Most of them work only up to 10 mph but I have seen a few that work up to 15 mph.

[daveklepper]

I have yet to be in the cab of an AC diesel. How does the speed control work? Are there presents for say 4 mph, 8, 12, 15? Or is it continually variable with a digital readout?

On the electrics (mu's) I've seen both arrangements: On one mu subway train operating over the Manhattan Bridge, the motorman set the speed at 18 mph, and the speed held up the grade, on the level, and on the descent, precisely matching the changes in aspect (yellow to green) of the speed control wayside signals. If I remember correctly, the orginal Metroliner mu's, perhaps only some and not all (or maybe it only worked on some!), the engineer could dial the speed he wished to maintain and it was continuiously available all the way up 160 mph (which I never saw, I think the maximum was 128 mph on one occasion). This may have been an experimental installation, some 36 years ago. Anyone with more precise information is welcome to comment and correct.

All the diesels I ever rode had the 8-position throttle, including the GP-7 B&M 1567 that had been modified with the test load regulator control intended for the GP-9. The one time I got to run that locomotive it did take th eight position to pull up a grade on the Portsmouth, NH, - Somerville freight (about 50 cars), but most of the time notch 4 or 5 was enough to keep up to track speed. I think this line only goes as far as Newburyport, MA, and is owned by the MBTA and used for commuter service. I wonder if there continues to be freight service on the line, including its branch to Gloucester and Rockport. At one time it extended beyond Portsmouth, NH, rejoining the main line via and providing a second Boston - Portland, ME route. Through trains used both lines up through WWII, and both were double-track, except for the single-track portion on the Newburyport-Portsmouth line in the tunnel in Salem, which still exists.

[mvlandsw]

The speed control on the AC diesels is variable by tenths of a mile per hour. It is available in power or dynamic braking. The early GE's are a real pain to set because when turned on the set speed is zero and you have to pu***he button 100 times to get to 10 mph. Later ones have a button that lets you set the current speed as the target speed. EMD uses a button that will scroll up or down through the speed range and can set finer increments. (.01 increments iirc). Both control only the engine output, not the air brakes.

[Anonymous]

QUOTE: Originally posted by zardoz

QUOTE: Originally posted by tree68

QUOTE: Originally posted by PNWRMNM

There is another aspect no one else has mentioned which is that the situation you laid out is seldom if ever obtained in the real world. Even if you have a bit of dead level track it may have curves which increases drag. In reality over "flat" ground you will have all sorts of dips and humps, particularly on an old line and/or a line built cheaply so your speed will vary at constant throttle.

Mac

Actually, that was my opening disclaimer:

QUOTE: Originally posted by Tree
First of all, we all know there are many variables that govern train speed, independent of the throttle setting. We'll have to set all of them aside for just a moment...

I'm just wondering how close to "set and forget" the throttle might come. Even with the variables, is it possible for an engineer to pick a notch and essentially sit back and "enjoy the ride?" Up grades in notch 8 doesn't count.

Had a GE go from 0-60 in 30 minutes (just kidding; they wern't quite that slow...almost, but not quite).

Now that is funny. [:D]


Good question Larry. I will have to read this thread when I have more time. [:)]