BMMECNYC NWP SWP I don't think you'll get over 40, 30 or so will be about the highest I'd guess, also remember to make your max allowable length a bit lower than what it takes to stringline, that way you can take into account increased car weights ect. 100% dependant on the railroad. My club runs trains of 60 plus cars with head end power only (level track and 35/37 in curves).
My minimum mainline radius is 30", but that occurs in only one place, and not on the track described below.
I've run a train of 71 cars up the 45' long 2.9% grade between the main level of the layout and the upper level. The run includes two horseshoe-type curves of 34" radii, and a series of much wider S-bends. The train was pulled by four re-motored Athearn switchers, then by four modified Bachmann Consolidations, and then by four modified Athearn Mikados, with all versions sucessfully reaching the top. The experiments continued with the same loco sets in various configurations: two on the head-end and two pushing, three on the front and one pushing, one on the front and one on the rear, with the other two spaced roughly evenly within the train, and these tests were repeated, mixing the various loco types in the same manner. All combinations were able to move the train up that hill, without slipping, stringlining or derailments, and all on DC power.
If you're running DCC, consisting your locos would seem to me to be the best way to simulate DPU railroading, while helper service would be better represented by separate locos (not mu'd power) not consisted and each with its own operator, just as real helpers are operated.For my DC-powered trains, if the train needs more than one locomotive to move up a hill, or even to move on level track, then almost any locomotive could be a suitable helper, unless its performance was grossly mismatched with that of the other locomotive. The need for exactly matched locomotives is, in my experience, a fallacy.
Wayne
NWP SWP I don't think you'll get over 40, 30 or so will be about the highest I'd guess, also remember to make your max allowable length a bit lower than what it takes to stringline, that way you can take into account increased car weights ect.
100% dependant on the railroad. My club runs trains of 60 plus cars with head end power only (level track and 35/37 in curves).
Ive run as many as 58 cars behind a single, ballasted P2k 2-8-4. More behind a pair of SD60s.
As Steven mentioned earlier, the key is similar units. Getting the speed tables close is key. That way you dont have suprises (this applies to unmanned DPU). Manned helpers can work as long as you watch the slack carefully (need not be speed matched exactly, but you have to communicate with the other operators so you dont have epic derailments (or do if you want these).
Ran a 128 car train once (prior to switching to different couplers). It ended with an epic accordion looking derailment due to the head end loosing power in a different power district.
If you feel comfortable with a few derailments take say 20 or so cars with two 6 axle units on the lead and run them arund a few times, go on the main and passing sidings, or both/all mains if there's multiple mains, if you don't derail that means your good, bump the number to 30, then 40, 50, and 60 add more units to the lead and go again, do this till there's a stringline, that's your max continuous car length, I don't think you'll get over 40, 30 or so will be about the highest I'd guess, also remember to make your max allowable length a bit lower than what it takes to stringline, that way you can take into account increased car weights ect.
Experiment till you have a number that works, go from there, DPU or Mid-train Helpers are for extra pulling power and to act as "anchor" points to prevent string lining.
Steve
If everything seems under control, you're not going fast enough!
Figure average car length, note lighter cars like flats, centerbeams, etc. Should be farther back in the consist as possible, my club does 1970s so the cars of the era are what I've based my figures on.
What's the sharpest radius on you railroad?
My club has minimum radius of about 36 inches, and max grade of 3 percent in the helixes, 30 cars is longest continuous string of cars before you string line, so 20 is what I do as max between helpers, if you a want to run say 60 cars put four six axle units on the lead, two more 20 cars back, do three four axle units 20 more cars back, don't put units on the tail because that will reek havoc on the train physics unless you have a friend to man the throttle on just that set, that way they can keep the units at a slightly lower speed to keep tension on the consist.
Wound that include length of cars? A 65 or 70 foot reefer then a 30 or 50 foot boxcar then a long center beam flat car, etc figue into the equation? A merchandise train can have various length cars with various weights next to each other which can lead to string lining.
Depending on curvature is how often you need a loco, if you can get 40 cars around with locos on the lead without string lining then use that as a standard, if it's 30 do 30, 20 and so on.
I am now trying to decide what weight and/or length of a train would be appropraite for mid train DPU units and/or rear helpers. Any suggestions or ideas will be appreciated.
No apology necessary. I know that BNSF used manned helpers over Cajon pass, but I have not been in that area for some years. Do they still use them or are the trains all DPU now?
I will be using mid-train DPU on some of my longest and heaviest trains such as my coal train which will be 46 cars and weigh 1342 grams and the iron ore train which will be 36 cars and weigh 1132 grams. There will be others later on, but most will not need mid train DPU, just front and rear.
Well Ira, being the stickler you are for prototypical details, I should have left the Rockies out of the picture. You are right that DPUs are taking over where manned helpers once were the norm.
BNSF used manned helpers, behind a DPU on coal trains moving through Colorado, going to Texas. The helpers are equiped with a device known as Helper Link, that allows them to drop off on the fly.
The NS on HSC, uses manned helpers in both direction, West bound for the push, East bound for the braking.
The CN in my part of country, used a helper to get over the ruling grade of their Waukesha sub. named Byron Hill.
My main point was that manned helpers are still used, but as you point out, not as often as they once where, with the use of DPUs.
I do not have a comprehensive list of railroads who still use them and where. Sorry if I was too vague in my previous statement.
Mike.
My You Tube
Which other railroads use manned helpers over the Rockiies on a regular basis? Please clearify your statement.
caldreamerHelpers are pretty much a thing of the past, but since this is "MODEL RAILROADING", the use of helpers is up the owner of the railroad.
Far from it. Just watch some videos on the NS as they deal with Horse Shoe Curve. They are a part of everyday operations, along with other roads that deal with getting across the Rockies.
You are exactly right. We got off on a tangent, but an interesting one. I think that running DPU, either on the rear or midtrain (not often used) from all of the videos that I have seen. Helpers are pretty much a thing of the past, but since this is "MODEL RAILROADING", the use of helpers is up the owner of the railroad. As I stated in an earlier post, helpers add additional interest and complexity to running a railroad. It was stated by I believe Volkver that when a train is under powered or an engine breaks down and helpers have to be sent, it can SCREW UP the best laid plans of running a railroad smoothly in a hurry, even when you only run DPU.
The original question was 'Helpers vs DPU'. Helpers basically run with a manned crew to get a train over the ruling grade, and then are cut off and return. DPU usually runs over the entire crew district and is un-manned. One of the reasons to run DPU mid-train is to reduce the trailing tonnage limit by breaking up the train so that the trailing tonnage behind each set of locomotives does not exceed the rating for the grade.
Modeling BNSF and Milwaukee Road in SW Wisconsin
One of these days I am going to put one of my U50B's on the layout and load it up until it stalls. I weigh each car as I put it on the layout so I will know exactly what the maximum weight that engine can pull. It will be an intersting experiment.
caldreamer My favorite engine for pure pulling power are the old Con Cor U50B's. I have tested them up my 2.93 percent grade and they will pulll 450 grams (14) ounces at half power without even working hard. They are the heavist engines that I know and maybe that increases there adhesion factor. I wish I had the equipment to actualy measure that.
My favorite engine for pure pulling power are the old Con Cor U50B's. I have tested them up my 2.93 percent grade and they will pulll 450 grams (14) ounces at half power without even working hard. They are the heavist engines that I know and maybe that increases there adhesion factor. I wish I had the equipment to actualy measure that.
mbinsewiIt was designed so that everyone that wanted a big locomotive could have one, and still work on a tighter radius.
Just to complement your post I link to a photo on the TCS website that shows the construction of the underframe: https://www.tcsdcc.com/Customer_Content/Installation_Pictures/HO_Scale/Athearn/Gas%20Turbine/Gas%20Turbine%20(4).JPG
It shows an Athearn gas turbine, but the U50 got the same kind of bolster connecting the two trucks on each side. The swivel point is the center of the inner truck making weigh balancing very difficult.
The OMI U50 has all axles driven. The truck connecting bolster swivels around the mid point between the two truck centers as on the prototype: https://www.picclickimg.com/00/s/ODUzWDEyODA=/z/z78AAOSwgv5ZeOV8/$/OVERLAND-MODELS-OMI-67111-HO-UNION-PACIFIC-UP-VERANDA-_57.jpg
It is a photo of a veranda turbine. It was the only one I was able to link directly.
Brasstrains.com OMI U50D photos require some browsing through the thumbnails: https://www.brasstrains.com/classic/Product/Detail/041552/HO-Overland-Models-OMI-6421-1-UP-Union-Pacific-U50D-Diesel-37
Regards, Volker
My mainline minimum radius is 16 inches which is considered a wide radius in N scale. I had a Bachmann DDA40X and designed my curves so that they could handle the four axle trucks of this locomotive.
Plus, if you have power to all of the trucks, you'll probably limit the radius it will handle effectively without some "wheel climb" constantly causing derailments, as it pulls a loaded train.
It was designed so that everyone that wanted a big locomotive could have one, and still work on a tighter radius.
NWP SWPI wish Athearn had given their U50s and Veranda Turbines dual motors and had all trucks powered but seems that only the inner trucks are powered the outer ones are just dummies.
The question is, is a second motor needed? If the wheels slip and the motor doesn't get hot when the locomotive is hold back the one motor is strong enough.
Powering the outer truck too is a design challenge. You need to design the locomotive in a way that all 4 trucks carry the same load. Otherweise the higher loaded trucks move the train while the lesser loaded already slip.
On the other hand you might then need a second motor adding to the complexity like matched motors and decoders for two motors.
So there were good reasons to construct the model as is, I think. That the U50 model doesn't pull more than a SD40-2 model isn't ideal.Regards, Volker
I wish Athearn had given their U50s and Veranda Turbines dual motors and had all trucks powered but seems that only the inner trucks are powered the outer ones are just dummies.
NWP SWP've run four SD40-2s in DPU (two leading, two more 20 cars in) on a 40 car train, it had trouble getting up the 3% grade of the helix, had I put say a pair of GP20s on the lead as helpers it probably would've handled it,
Question: Usually there is the nominal grade of the helix plus the resistance caused by the curve. John Allen found an equation to calculate the fictional grade cause by the curves. g(curve) = 32/r; r in inch, g(curve) in %
For a 3% helix with 24'' radius. Grade = 3 + 32/24 = 4.33%
On model railroads helpers or DPUs work best when they are really needed to get a train up the hill. Otherwise the inner train dynamics might lead to problems. These will not occur with head end helpers.Regards, Volker
P.S.: For those interested in train physics like tractive effort and train resistance here is a slide show: http://slideplayer.com/slide/4696076/
All is based on the Davis equation which considered parts that are speed independent, dependend on speed, and dependend on speed². The coefficients were empirical developed. Over time the equation was adjusted to developments in the railroad industry, e.g. roller bearings.
I've run four SD40-2s in DPU (two leading, two more 20 cars in) on a 40 car train, it had trouble getting up the 3% grade of the helix, had I put say a pair of GP20s on the lead as helpers it probably would've handled it, why did I run two units mid train? Because at the club the limit of cars you can pull around the curves is 30 otherwise you'll stringline, so I put the units mid train to act as "anchor points" to prevent the phenomenon.
Someday when I get the chance I'll do a 60 car train and break the record of longest train on the layout which is currently 48, one ghing that's important, SPEED MATCHING, otherwise not good.
Many ways lead to Rome.
Some experiment, others are trying a way more based on prototype practice. The results seem to be the same, somehow the train gets over the hill. SometimeRegards, Volker
I guess I've been doing it all wrong. If one loco doesn't pull the train, I add another, and if needed, I'll add a third. Usually don't have to.
But if I do, I'll usually add more cars, just to see what I can get away with.
caldreamerPhysics is physics no matter the size from 1:1 down to 1:110 z scale. These laws DO NOT change.
You are right, physics are he same and I said before, if it works for you it is OK for me.
But that doesn't mean it is physically correct. First of all the tractive effort (TE) doesn't represent the weight of the train it can pull but it is a train's resistance it can overcome.
Second, TE is dependend on weight on driver (W) and adhesion factor (Fa): TE = W * Fa; As scale weight is W/160³ for N-scale, physically TE scales down the same way to Scale TE = TE/160³. In reality it is even less than that as adhesion of our locomotives is less than of the prototype. Cause: Different materials, no wheel slip control.
Power assignement doesn't have to be science, only believable and representing prototype practice. In our model world 4-axle and 6-axle locomotive weigh the same and pull the same compared to the real thing.Regards, Volker
All of my rolling stockhas, or will have metal wheel sets and are tested to be ABSOLUTLY free rolling. By that I mean the that they will roll on the SLIGHTEST grade of there free will. Physics is physics no matter the size from 1:1 down to 1:110 z scale. These laws DO NOT change. My AC engones are over rated n my tonnage chart, but since I will be pulling long trains up the grade and will be using from three to four units that really does not matter. As long I have enough power to get over he mountain.
NWP SWP Has anyone tested to see if their locomotive pulls the scale tonnage of the real deal?
Has anyone tested to see if their locomotive pulls the scale tonnage of the real deal?
It is nearly impossible to do this as the rolling characteristics are not the same for a model as the prototype.
On the prototype at least here in Australia, the ratio for dead level track to move a freight car was considered to be 8lbs of tractive effort per ton. Where I lived in Adelaide, the ruling grade to Melbourne was 2.5% (we call it 1 in 40) and the required traction was considered to be close to 100lbs TE per ton to get over the hills.
This is with very free rolling prototype freight cars but the smaller scales do not roll proportionately as well as prototype cars.
I believe that an SD40 (based on the Western Australian L class diesel) puts out around 80,000 lbs starting TE which translates to nearly 10,000 tons on dead level track. A 1% (1 in 100) grade would reduce this by a factor of about 3 so that would make a load of 3300 tons and that does not take into account the friction of curves, which would reduce it even more!
HO freight cars do not roll any where as well as the prototype but think of their weight multiplied by 87 cubed and each one would weigh about 90 tons, accompanied by Delrin trucks which are OK for our purposes but have a higher coefficient of friction compared to wheel bearings.
Regardless of whether you go DPU or helper, I have found (from a DC operator point of view) that taking a leaf out of the KCS operating procedure that I know of (and no doubt there are others), putting more load behind the mid train helper will make the operation smoother.
Cheers from Australia
Trevor
Instead of using ounces, I use grams. Where an SD40-2 is rated at 175 grams on a 2.93 percent grade.