Tuesday, September 25, 2018

Where Goeth The Hobby

This is my first rant on this blog. Sorry but something needs to be said and from the discussions I've heard and been part of I believe there is a lot of agreement on this. So here it is.

Model Railroaders need to get and keep kids interested in the hobby, whatever it takes. They are the future model railroaders that will keep the hobby alive. It's too bad we don't have a way to track the average age of model railroaders. It would tell us how we're doing.

For those of us who get upset when they see a Thomas related train circling a layout (and we know who we are, don't we) before you loudly complain about it, look at the eyes of the kids that also see it. Do they light up? You bet they do! They relate to that engine and everything associated with it. Adults relate more to the trains we normally run. Kids do not. Yes they do like to see them run and the sounds they make but the moment Thomas shows up all eyes are on him! To them he is a train and one they know about and if your wizzbang SD-XX muckity-muck goes by him and blows it's air horn their eyes will follow Thomas. My point here is that:

If you want to keep this hobby alive and thriving in the future, you need to get and keep kids interested in the hobby whatever it takes.

So if you made it this far I thank you for putting up with me. It's an important topic and needed to be mentioned. Please comment on this regardless of whether you agree/disagree or even have a idea on this. Maybe even rant a little.

Another way I thought of was to track subscriber count to Model Railroader Magazine. The last time I checked the current subscriber count to Model Railroader Magazine was about 140,000+. Sorry I do not have the exact count but the Model Railroader web site is currently down. WHAT!?!? (25 SEP 2018 11:20AM)


If you have an idea for a blog post here, let me know. If I can comment on it, I will or I'll see if someone else can and post it.

Explanation Of Atlas Locomotive Lines

Although this information is available from Atlas not everyone knows where to find it.

Master Series: The top model of Atlas' lines. It is broken down into two categories:
  • Gold – includes sound and a dual mode DCC decoder (will run on DC or DCC)
  • Silver – no sound or DCC decoder, most will have an 8 pin DCC plug included
Classic Line: This line consists of older tooling that has been upgraded with features such as separate grab irons and other minor retooled pieces. These are generally only offered without sound and usually have an 8 pin DCC plug, space permitting.

Trainman: This is Atlas' “budget” line. These use the same drive train as the other lines, but the shells have less separate detail added, and are generally only offered in one or two variations or phases for each model.


If you have an idea for a blog post here, let me know. If I can comment on it, I will or I'll see if someone else can and post it.

Friday, August 10, 2018

Soundtraxx Decoder Announcement at National Train Show

On the first day of the National Train Show Soundtraxx announced new Tsunami2 Sound Decoders specific to EMD Diesels and steam locomotives.

Tsunami EMD-2 Decoder

This decoder includes eight new diesel engine sounds:
  • 567 12 cylinder no transition
  • 567C 16 cylinder non-turbo
  • 645E 12 cylinder non-turbo
  • 645E 12 cylinder turbo
  • 645F 16 cylinder turbo
  • 645E 20 cylinder turbo
  • 710G 12 cylinder
  • 710G 16 cylinder
[Author's Note]
A very good reference on these different engines is discussed here including which locomotive models had which engine. Notice that the 567D (turbo) and the dual 567 (E units) are not included with this decoder. For those engine sounds you'll have to get the original Tsunami2 for EMD engines. Isn't this what got Soundtraxx in a bind before? This decoder for this engine, that decoder for that engine. Hope it doesn't get much worse.

The EMD-2 decoder includes more than 50 sound effects, including engine startup, 14 bells, and more than 40 air horns. Also contains Reactive Diesel Dynamic Digital Exhaust. TSU-1100, $129.95; TSU-2200, $124.95; TSU-21PNEM, $109.95; TSU-PNP, $109.95; and TSU-4400, $179.95.

Tsunami Steam-2 Decoder

This new decoder contains an expanded sound library with 28 new whistles, 12 bells, 10 air pumps, 8 dynamos, 10 exhaust chuffs, snifter valve, injectors, Johnson Bar, power reverse, firebox blower, side rod clank, and brake squeal.
This decoder replaces part# 884001 TSU-1100 Steam (Discontinued 08/2018).
TSU-1100, $129.95; TSU-2200, $124.95; TSU-21PNEM, $109.95; and TSU-4400, $179.95.

SoundTraxx - 970-259-0690 - www.soundtraxx.com


If you have an idea for a blog post here, let me know. If I can comment on it, I will or I'll see if someone else can and post it.

Thursday, August 2, 2018

Model Railroad Factory Closing Update

From Model Railroader:

Affa Technology Ltd.'s sudden shutdown has some model train companies looking for other options

In late July Affa Technology Ltd., a Hong Kong-based manufacturer of model trains, radio-controlled toys, scale cars, and other items, announced it had closed. Some of the model railroad manufacturers impacted by this news include American Z Line, Atlas Model Railroad Co., Bowser, ExactRail, Fox Valley Models, InterMountain Railway Co., Trainworx, and Wheels of Time. Several firms shared the news through e-mail, websites, and social media.

“Yes, we have projects at this factory and Trainworx production will be affected,” said Pat Sanders via e-mail. “We are researching our options at this time and hope to get rolling again soon.”

In a blog post, Atlas Model Railroad Co. noted the factory was one of its locomotive and rolling stock suppliers, but the company’s track and accessories were not impacted by the closure. “Atlas is currently working with our network of suppliers to transfer the projects to others for completion,” the blog post continued. “This will cause a delay in some previously ordered products.”

In addition to adjusting production schedules, some firms have finished projects waiting to be shipped. Chris Brimley, vice president of product for ExactRail, wrote in a blog on the firm’s website, “The N scale AutoFlood II hopper is on hold as we move that project to a new factory. We have been told that the HO scale GSI bulkhead flatcar production was actually finished last week but is still sitting at the now-closed factory. We expect these to be on our way to us soon.”

Frank Angstead of InterMountain noted that though there will be a delay in new product releases, the company is already looking for new manufacturing options. “Our expectation is that we will begin shipping a selection of new product within four months,” wrote Angstead in a letter posted online. “Purchase orders with alternate vendors are already being arranged so we anticipate production to resume very soon.”

One theme shared by the manufacturers impacted by Affa’s sudden closing is this will take time to sort out. On the Fox Valley Models Facebook page, company president Matt Gaudynski wrote, “If projects can be moved, it will take a number of months to do so, and then get a new factory up to speed on our projects will take even more time…[We] greatly appreciate your patience and understanding as we move forward through this unexpected interruption.”


If you have an idea for a blog post here, let me know. If I can comment on it, I will or I'll see if someone else can and post it.

Wednesday, August 1, 2018

Shinohara Ceasing Track Production

This has been announced on the Walther's web site.

Dear Walthers customers,

We have some updated information regarding Walthers Code 83 Track to share with you. First, Shinohara is currently working to fulfill a large track order for us, and we expect that shipment of track to arrive later this summer. We will fill as many back orders as possible from that order, and then we will make the remaining track available for purchase. After fulfilling that order, Shinohara will cease track production.

We would like to thank Shinohara for their many years of partnership with Walthers and service to the model train hobby. In addition (and with cooperation from Shinohara), we are already working with a new track supplier and will bring the Walthers code 83 track line back onto the market as soon as possible. We will share more details on this exciting new development in the future. Until then, thank you for your understanding and your support.

Sincerely,

Your friends at Walthers


If you have an idea for a blog post here, let me know. If I can comment on it, I will or I'll see if someone else can and post it.

Tuesday, July 31, 2018

Model RailRoad Manufacturing Plant Closed

Unexpectedly, one of the model railroad plants in China has closed. Apparently, the factory closure was collateral damage from the current environmental rampage China is on to clean up their situation and to meet global agreements. That's the general feeling after this author canvassed several forums concerning the closure.

Bowser posted on their facebook page:
We have been informed that our foreign factory is closed. This will delay HO and N Ready To Run cars, trolleys, Cal Scale and our locomotives. We are looking for a new factory. All delivery dates are now TBA (To Be Announced). Thanks for all support you have given Bowser.
And Atlas, posted on their website on 7/27:
Atlas has received notification from one of our locomotive and rolling stock suppliers that they have closed their factory. (Please note Atlas track and accessories are NOT affected by this delay.) Atlas is currently working with our network of suppliers to transfer the projects to others for completion. This will cause a delay in some previously ordered products. We apologize for this delay, thank you for your continued support, and will update you with more information as it becomes available.
According to Bob The Train Guy the closing also affects other lines.
It is going to be an interesting year for my suppliers. One plant closes unexpectedly and shuts down production of models from some of my favorite producers. The list so far includes Intermountain, Bowser, Atlas, Fox Valley, TrainWorx and Bluford. With the current problems getting track I am not sure of the short term future of the hobby.
According to another forum discussion, those not affected are Athearn, Walthers, Scale Trains, Bachmann and Rapido. Jason from Rapido has already posted that he is willing to help where he can.

I agree with Bob that in the short term it's going to be a bit of a rough ride for the hobby.


If you have an idea for a blog post here, let me know. If I can comment on it, I will or I'll see if someone else can and post it.

Friday, July 27, 2018

Engine Driver Consisting

This post refers to Engine Driver v2.20.59 - JMRI v.12.0

Engine Driver has very much simplified engine consisting. Up until v2.20.57 though it had one missing feature that bothered me and turned off some other model railroaders. That was the application's inability to do what Digitrax calls Universal consisting. That is, before placing an engine in a consist, run it first in the direction you want it to follow in the consist (if it is reversed in the consist it needs to run in reverse first) and then add it to the consist. In older versions of Engine Driver this would not work. In order to get an engine to run in reverse in a consist you had to change its normal direction of travel via CV29 bit 0. Most of the guys I ran with did not want to do that. Why should I have to reprogram an engine to run it backwards in a consist and then have to reprogram it again when I want to run it normally?

Problem solved!! The new version of Engine Driver supports universal consisting and you don't even have to run an engine in the direction it needs to run before consisting it and no CV programming involved! Let's use an example to demonstrate:

We have three locomotives we want to consist - 3120, 3121 and 3123. We want 3123 to run in reverse behind the other two engines.

After opening Engine Driver and connecting to your server, press Loco, punch in 3120 and acquire it. Now Press loco, punch in 3121 and acquire it. Notice the right hand column now has 'Front' listed for each. Now back to the Loco screen, press Loco, punch in 3123 and acquire it. Now press the 'Front' for 3123 and what happens? The 'Front' changes to 'Rear'. Increase the speed of the 3 engine consist now and it works!!!

It doesn't get any easier than that. Thank you Steve Todd.

One thing to watch out for in Preferences is to make sure that under 'Loco Select Preferences' 'Drop Loco Before Acquire' is unchecked. If it's checked you'll never form a consist.


If you have an idea for a blog post here, let me know. If I can comment on it, I will or I'll see if someone else can and post it.

Friday, June 22, 2018

Atlas Acquires Walthers N Scale Locomotive and Rolling Stock Tooling

Below is a press release by Atlas Model Railroad Company Inc.

June 22, 2018

For Immediate Release:

Atlas Model Railroad Company, Inc., and Wm. K. Walthers, Inc. have reached an agreement under which Atlas will purchase all N scale locomotive and rolling stock tooling owned by Walthers, including the Walthers N tooling as well as former Life-Like tooling. Atlas will incorporate this tooling into its Atlas Master, Atlas Classic, and Trainman N scale lines. Walthers will continue to offer N scale items in its Cornerstone, SceneMaster, and Walthers Controls brands, including new items as well as items currently in those lines.

“We feel that this tooling has found a great home with Atlas. They have a strong N scale offering and these tools will help them bring some exceptional products back to the market,” said Phil Walthers, President of Wm. K. Walthers, Inc.

Tom Haedrich, Executive Chairman at Atlas added, “We’re pleased to be bringing these former Walthers N scale models back to the market so that they can be enjoyed by present and future model railroaders alike. These locomotives and rolling stock will fit right in with our existing N scale lines and we are committed to producing them with the latest technology, prototypical accuracy, and high quality you’ve come to expect from Atlas.”

Established in 1932, Wm. K. Walthers, Inc. distributes model trains, accessories, and related items from more than 200 manufacturers, and also manufactures its own exclusive items for its WalthersProto, WalthersMainline, WalthersTrainline, Cornerstone, SceneMaster, Walthers Controls, and WalthersTrack lines.

Founded in 1924 and incorporated in 1949 as Atlas Tool Co. Inc., present day Atlas Model Railroad Co. produces locomotives, rolling stock, track, and accessories in N, HO and O scales for its Atlas Master, Atlas Classic, Trainman, and Atlas O lines.

-30-


If you have an idea for a blog post here, let me know. If I can comment on it, I will or I'll see if someone else can and post it.

Tuesday, June 19, 2018

Clarification on Discontinuing Economi Decoders

On June 6th I published a post concerning SoundTraxx's supposedly discontinuing the 100 and 200 series of Economi decoders (the PnP Economi board #882004 and the 21 pin decoders #881006 & 882006 are continuing to be produced) and the reasons for the confusion surrounding this. After talking with Soundtraxx, they clarified the situation. The two series of decoders are being temporarily discontinued due to the parts shortage until one or both of the following occurs:
  • A different parts supplier is found that can furnish parts in the quantity needed by Soundtraxx
    • Knowing that these parts are used by most of the huge end-product electronics manufacturers (Sony, LG, etc.) in extremely high quantities, if there were other producers then they are most likely also sending their parts to them.
      One thing that worries me here is that if it turns out to become an American supplier, the price will go up.
  • A decoder redesign can be accomplished utilizing parts that are readily available
    • Not the easiest solution. While redesigning you have to insure first, that the new parts will do exactly what the current ones do and second, Soundtraxx can be assured they will be able to get them now and in the future (i.e. supplier stays in business, doesn't discontinue them).
Whatever the solution, I would bet a lot of money that Soundtraxx has been working on this for a while.


If you have an idea for a blog post here, let me know. If I can comment on it, I will or I'll see if someone else can and post it.

Saturday, June 9, 2018

Such a deal Soundtraxx has for you!!!!

If you are interested in Soundtraxx Tsunami 2 decoders you HAVE to go to their website and check out the deal Soundtraxx has on these during the month of June. The gist of it is if you have an old 2nd generation Tsunami (the purple shrink wrapped ones) or certain competitors' sound decoder that you're thinking about replacing, buy a Tsunami 2 decoder in the month of June, send in the receipt plus the older decoder plus their filled out promo form and they will send you a new Tsunami 2 decoder for free!!! Buy-one-get-one-free (BOGO) never had it so good!

There are some restrictions involved but they are completely reasonable and there is a list of acceptable/unacceptable decoders given in the June Promo Form. I've got a couple of 2nd generation decoders I need to replace so I'm off and running on this deal. Get Hot!!!


If you have an idea for a blog post here, let me know. If I can comment on it, I will or I'll see if someone else can and post it.

Wednesday, June 6, 2018

Soundtraxx Discontinuing ECO 100 and 200 Decoders!!

On June 6th Soundtraxx announced that they were discontinuing the Economi ECO 100 and ECO 200 sound decoders. The new products announcement on YouTube for June 6th gives the reasoning behind this and also shows some alternatives. If this proves to be true, the one thing I'm really going to miss is their size. The ECO 100 was really small and would fit in some really tight spaces.

I'm a little taken aback by this as their website page concerning the Economi decoders shows them as NOT discontinued. I will be keeping an eye on their website to see if anything changes. Anyway, they do show one new product that is interesting, the 9 pin to 21 pin decoder adapter.

This allows you to use an 8 to 9 pin adapter if you have a standard NMRA 8 pin plug or hardwire a 9 pin plug to a locomotive, plug the 9 to 21 pin adapter into it and then plug a 21 pin decoder into that. This might seem like a lot of work but if you are stuck with a 21 pin decoder and no locomotive with a 21 pin motherboard (just so happens I am stuck with one of these), then this is the ideal solution. Think about it. It's really not that different from working on plumbing is it (adapter for this, adapter for that)? I have found these adapters on Ebay for $12.95 with free shipping.


If you have an idea for a blog post here, let me know. If I can comment on it, I will or I'll see if someone else can and post it.

Monday, June 4, 2018

Woodland Scenics Just Plug Lighting System Additions

Since I gave the clinic on Woodland Scenics' Just Plug lighting scheme they have added several new sorely needed components to the system.
  • Extension Wire Spool 50 ft. - allows much more distance to put those odd ball lights off by themselves.

  • Extension cable kit - contains 2 cable ends and 2 splicing connectors for implementing the wire mentioned above
  • Port Sharing Device - use this with a Light Hub or Sequencing Light Hub (described below) to add up to four Stick-On or Nano LED Lights per Light Port - essentially another hub
    WARNING:
    Remember that a single power supply can support a maximum current draw of 1000 milliamps (1 amp). You can figure the total current draw of your lights by simply summing the individual draw of each lamp as I explained during the clinic.
  • Sequencing Light Hub - can add up to four lights that individually sequence on and off - includes dimmer and speed controls - can turn sequencing off to use as a Light Hub and add an optional Auxiliary On/Off Switch - see the warning above
There are other new products on their website. Check them out.


If you have an idea for a blog post here for the club, let me know. If I can comment on it, I will or I'll see if someone else can and post it.

Thursday, May 31, 2018

Digitrax LNWI Mystery Solved (Updated 2018-08-08)

After much research plus trial and tribulation. I finally have Digitrax's LNWI WiFi interface figured out and working properly with our club layout. The Digitrax forum on groups.io has been alive with discussion on this hardware. Some of it correct and some not. Some close and some not so close. Here's what the author has figured out.
Key point 1:
    The LNWI channel number must match the duplex channel number 
    (minus 10) that the UR92 is set to.

    WARNING
        The UR92 supports duplex channel numbers 11 through 26 while
        the LNWI only supports channel numbers 11 through 21 
        (1 through 11). If the UR92 is programmed to any of the 
        channels 22 through 26, there is no guarantee the LNWI will
        function properly. Read as - Don't use it!! (or change the 
        UR92 channel number). Hopefully, Digitrax will fix this in 
        a future firmware upgrade

Key point 2:
    The Loconet group name must match between the UR92 and the LNWI.
    Since the LNWI itself has no way to program the group name, how 
    can this be done?

        a. With a throttle plugged into the UR92's front panel and the 
           LNWI plugged into loconet and both turned on, <UPDATE> make 
           a change to the group name and save it in OPT/EDIT mode on 
           the throttle press ENTER on the throttle. This will update 
           the LNWI. No need to make any change.
        <UPDATE>
           b. With power off to the UR92 and the LNWI plugged into it and
           powered on, power on the UR92. The LNWI will be told what 
           the group name and the channel number is.
           Powering up anything in any order makes no difference! It 
           does not force a UR-92 update.
        c. Use the DigiGroupSetup utility provided by Digitrax
           to set up the values. (I cannot get this to work I believe
           because my LocoBuffer-USB interface has a different baud rate
           than the utility supports. Please leave a comment if you 
           figure this out).  

Key Point 3:
         The 'network number' has nothing to do with the UR92. Set this
         via the LNWI's OpSw's as per the instructions. This changes the 
         LNWI's IP network number in case another model railroad club is
         using the same number as your club. It can be 0 through 7. (For 
         the techies it's the third octet in the IP address 192.168.7.1
         the 7 in this case)

Key Point 4
         How can I check what these values are set to on the LNWI to make
         sure they are correct? Simple!! Look at the connections page on 
         your phone (or android device or iPad). You'll see this:

             Dtx1-YYYYYYYY_XXXX-7
         
         Where

             Dtx     -> the Digitrax identifier (can't change this)
             1       -> the duplex channel number (my be different
                        depending on what you set the channel # to)
             YYYYYYY -> the 8 character loconet group name
             XXXX    -> the LNWI ID set by Digitrax (can't change this)
             7       -> the network number
Conclusion
If the channel number and group name displayed on your wifi device do not match what's programmed in the attached UR92 there is no guarantee the LNWI will work properly and it will probably corrupt what duplex throttles can acquire and control. I have seen an improperly configured LNWI hijack a DT402 throttle and not allow it to control ANY locomotive. In this case the throttle will display the group name of the LNWI (which is totally useless to it) not the UR92.

<UPDATE>There may be a concern related to your throttle's firmware version. Throttles with v2.1 (Digitrax's latest) did not seem to have a problem. We were unable to check a throttle that was having a problem with an unsynced LNWI. Updates to follow.

<UPDATE>This author is a regular comitter to both the JMRI and Digitrax forums. Lately on the Digitrax forum it has become apparent that several people have had problems with their LNWI absolutely refusing to sync up to their UR92 regardless of what they have tried and even after following the steps in this post. One of them sent their LNWI back to Digitrax for repair. They received the cryptic message "REPROGRAMMED CPU SHIPPED" whatever that means. This post will be updated after it is received and tested to see if it is fixed.

The Digitrax knowledge base article on the LNWI (KB1053) is located here. As long as you follow the above setup instructions and your LNWI will update you shouldn't have any problems. Have fun.


If you have an idea for a blog post here, let me know. If I can comment on it, I will or I'll see if someone else can and post it.

Sunday, May 6, 2018

Railroad (Yours) Inspired Apparel And More...

I received an advertisement in the mail the other day and thought it may be of interest to some readers of this blog. It's not limited to just railroads either. Here's a tee shirt example:


They also offer Polo shirts, sweatshirts and a whole lot more. So if you're interested they are located here.


If you have an idea for a blog post here for the club, let me know. If I can comment on it, I will or I'll see if someone else can and post it.

Friday, April 20, 2018

This article is copyright A. A. Krug. I did not know how to contact him for permission to reprint this so I'll assume he has no problem as long as I attribute it to him.

Tractive Effort, Horsepower and Speed/Acceleration


Tractive Effort vs. Horsepower

Many people confuse Horsepower (Hp) and Tractive Effort (TE). With this essay I hope to clear that confusion. I use some terms and formulas in this essay that may not be familiar. I suggest that you read the Definitions at the end of this document.
Assume a train that weighs 15,000 tons is stopped on a 1% grade. For every ton of train weight on a 1% grade a force of 20 pounds is acting to roll the train down the hill. A 15,000 ton train produces a force of 300,000 lbs. (15,000 tons x 20 lbs per ton = 300,000 lbs).
To prevent this train from rolling back down the hill we must apply an equal force in the opposite direction to the coupler of the first car. Imagine yourself holding onto the coupler of the first car and trying to hold the train from rolling back down the hill. It should be obvious that try as you might you will not be able to hold the train. No matter how hard you grasp the coupler you cannot hold the train because your shoes will simply slide across the ties and ballast. The adhesion of your shoes to the ties and ballast is not equal to 300,000 lbs. Thus not even if you were Superman could you develop 300,000 lbs of pull (traction) to hold the train.
The level of force required to break the adhesion of your shoes to the ties and thus slide your shoes is dependent upon two things
1.      The coefficient of friction between your shoes and the ties.
2.      The weight on your shoes.
Increase either one of those parameters and your adhesion to the ties increases enabling you to pull harder before sliding.
For the purpose of this article we will say the factor of adhesion of a steel wheel on a steel rail is about 30%. (Actually it is more like 20%-25% but we will get to that later). A factor of adhesion of 30% means that a wheel will stick to the rail so that a pull equal to 30% of the weight on that wheel is required to break that adhesion and slide the wheel. Locomotives have a lot of weight on their wheels. A typical 4 axle GP40 might weigh 280,000 lbs. Four of them weigh 1,120,000 lbs. Thirty percent of 1.12 million pounds equals 336,000 lbs. In other words, it requires a force greater than 336,000 lbs to slide four GP40s. Therefore these locomotives, with their brakes set, will hold the train on the hill since the weight of that train on the grade is only producing 300,000 lbs of pull.

Tractive Effort is the amount of Pull.

You can have pull with no HP. Notice that in the example above we are applying a force, a pull, a Tractive Effort, of 300,000 lbs to that coupler of the first car but we don't need any diesel engines. All we need is at least 1 million pounds of weight on the wheels and a factor of adhesion of 30%. We have Tractive Effort (TE) without any Horsepower (HP).
If I don't need any HP why did I use 4 locomotives? Why not just use one very heavy loco? Because the maximum weight on any single wheel that steel rails can withstand is 35,000 lbs. If we put more weight than that on any wheel it will crush the rail head and create excessive wear or outright failure of the rail. The two wheels on opposite ends of one axle can each carry 35,000 lbs of weight. So the maximum weight on an axle assembly is 70,000 lbs. Since we need a total locomotive weight of at least 1 million pounds that means we need a minimum of 14.3 axles. Three 4 axle locos would only be 12 axles so we must use four which gives us 16 axles.
From this discussion we can see that total locomotive weight determines the maximum amount of tractive effort a locomotive can produce. The number of wheels or the number of traction motors has nothing to do with it. We only add additional wheels to spread the required weight out along the rails to avoid damaging the track. I said that 3 GP40s will not work in this case because they only have 12 axles and each can be weighted no more than 70,000 lbs for total loco weight of 840,000 lbs. At 30% adhesion that only produces 252,000 lbs of TE and we need at least 300,000 lbs. If we take those same 3 GP40s and add two more axles to each unit but DO NOT increase the weight of each unit, then we still only have 840,000 lbs of total weight and 30% of that is still only 252,000 lbs. Adding axles and wheels to locomotives does not increase tractive effort.

HP is the Tractive Effort (pull) times the Speed.

Burn that statement into your brain. It is crucial to understanding this essay.
While our coal train is just sitting on the grade, held there by the locomotives, there is 300,000 lbs of "pull" on the first car's drawbar. Because the train is not moving there is no HP required. But try to move it at 1 mph up that hill and HP is required. The required HP is the TE needed for the grade (300,000 lbs) times the speed (1 mph or 1.47 ft per second) divided by the definition of a HP (550 lb-ft per second).
(300,000 lbs) x (1.47 ft per sec) / (550 lb-ft per sec) = 801 HP
The HP required is 801 HP! Yes just 800 hp will move this coal train up the hill. Amazing isn't it? But will one 800 HP 4 or 6 axle unit do it? No! Because that one 800 hp unit must have at least 1 million pounds on its drivers to prevent it from sliding back down the hill. You must have the weight to get the adhesion required. That means each wheel of an 800 hp 6 axle unit would have to have 84,000 lbs on it. (That is 168,000 lbs. per axle). Oh my, the crushed and broken rails that would leave behind! Not to mention the overloading of bridges and the track structure itself. As I said above, the minimum number of axles we need to spread out the required weight is 14.3 axles. It doesn't matter whether we have four 200 HP 4 axle units, or whether we have one 800 HP 4 axle unit and three 4 axle engineless slugs . It is all the same to the coal train.
One mph is kind of slow. It would take us 24 hours just to get up Parkman hill. We want to go up the hill about 15 mph. 15 mph is a good compromise between taking forever and extreme high power costs. To go up this hill at 15 mph (22 ft per second) requires:
(300,000 lbs) x (22 ft per sec) / (550 lb-ft per sec) = 12,000 HP
Gee now that sounds familiar doesn't it? That is exactly the HP of four 3,000 HP units! So we can use four 3000 HP GP40s. SD70MACs have 6 axles and weigh 420,000 lbs. Again 70,000 lbs per axle. So three of them give us 18 axles and 1.26 million pounds on the wheels, more than enough to produce our required 300,000 lbs of traction. SD70MACs are rated at 4000 HP so three of them are 12,000 HP. Four GP40s or three SD70s, either way you satisfy both the adhesion needed and the HP needed.

Horsepower Alone

Will two 6000 HP units work? No. While you have the required 12,000 hp you can only have 70,000 lbs weight per axle, which times the 12 axles is only 840,000 lbs total. With 30% adhesion and only 840,000 lbs of weight the two 6000 HP units have only 252,000 lbs of adhesion. Not enough to hold or move the coal train. The weight of the train on the grade will slide these two locomotives backwards down the hill. Remember you need at least 300,000 lbs of adhesion (traction).

High HP locomotives on 6 axles create other problems such as traction motor (TM) overheating. Can we pour 1,000 hp into each TM continuously at 10-15 mph without frying them? Low gearing helps. But low gearing lowers the top speed because the TMs will fly apart at high rpms. Here is where AC locos have an advantage over their DC counterparts. AC TM rotors are much more solid than DC TM armatures so they can be geared lower and still have a high top end.

Varying Adhesion

All of the above figures are based on a 30% adhesion factor. IE, the wheels grip the rail with a force equal to 30% of the loco weight. Locomotives of the GP40/SD40 era and their Dash 2 offspring are generally considered to have an adhesion factor of about 25% not 30%. Sand will increase this factor to about 30%. Thus to achieve the 30% adhesion needed for the examples used in this essay so far, these locos may need to be on sanded rail.

Modern locos such as SD70MACs and C44s claim adhesion factors of 36 to 43%! They do this by using sophisticated anti-wheel slip circuits. These circuits allow the wheels to spin slightly faster than the rail speed warrants. It is called creep. Strangely enough, a creeping wheel has a higher factor of adhesion than a stationary or rolling wheel. Thus in theory two 6,000 HP SD90s weighing 420,000 lbs each and achieving an adhesion factor of 36% will produce a TE of 302,400 lbs and should pull the train up the hill at 15 mph.
However, in my experience you cannot count on that 36% adhesion factor in all types of weather and rail conditions. On wet or frosty rail these units slip and you stall. And when you stall you had better set the train air brakes in a hurry or the train will slide these units back down the hill. On the other hand I have had C44s, SD90s and SD70MACs absolutely astound me with what they are pulling. At times they attain greater than 40% adhesion on dry, sanded, rail. It is that "at times" that concerns me. You cannot count on them to do that reliably time after time.

An Actual Experience with High HP Locos and Adhesion

One night I was running a freight up hill at 7 mph with a Dash 9-44CW on the point. I had previously calculated that we should have gone up the hill at 11 mph, so why were we only doing 7 mph? The rail was slightly frosty. I punched up the loco monitor screen on the computer. It showed that this supposedly 4400 HP unit was only putting out 2930 HP!!! It had derated to prevent slipping in spite of the sanders being on. So the adhesion factor of this loco at that time was not the touted 36-43% but instead only 22%. The railroad had paid for a 4400 HP locomotive with 36% adhesion but was only getting a 2930 HP locomotive with 22% adhesion. The common SD40-2 would have done as good as or better in this situation than the hi-tech wonder. This was not a one time occurrence. I have seen similar performances on many occasions,

Horsepower is Speed

Up to now we have assumed that a locomotive has enough power to slip its wheels. That is true only at low speeds. Note that HP is TE times speed. If the speed remains the same and the TE (pull) increases then the HP requirement increases. If the TE remains the same and the speed increases then the HP requirement increases. If you have a fixed maximum Hp, such as a loco has, then as speed increases the TE must come down. The product of the two must remain a constant and is directly related to the HP rating of the loco. On the 12,000 HP coal train above why can't we go faster than 15 mph on the 1% grade? Because 15 mph times the required 300,000 lb of drawbar pull divided by 550 lb-ft per second (the definition of a HP) equals the total locomotive HP. If the train went faster the product of the speed times the pull would be higher and thus the required HP would be higher. But we are limited to 12,000 hp on this consist so it trudges along at 15 mph. Similarly if we throttle down a notch or two, reducing the HP, then the speed is going to drop because there is now less than 12,000 HP available. The drawbar pull account of the grade remains the same at 300,000 lbs and the lower HP means a lower pull x speed figure so the speed must drop until the product is proportional to the new lower HP. This why I like to say HP is speed.

Steeper Grades

We are proceeding at 15 mph up the 1% grade with our 15,000 ton train powered by four 4 axle GP40s. What happens when we encounter a steeper grade with this train? The drawbar pull needed to hold or move a train on a grade is 20 lbs per ton per grade percent. That is where the 300,000 lb figure came from for the 1% grade of the example above. If this train were to roll onto a 1.5% grade what happens? The drawbar pull needed now is 450,000 lbs.
(15,000 tons) x (20 lbs per ton) x (1.5 grade) = 450,000 lbsWe still have only 12,000 hp available. Since HP equals pull times speed, if the pull goes up then the speed must come down. The train speed will drop to 10 mph, the point where the product of the new 450,000 pounds pull and the speed divided by 550 (HP definition) equals the available HP. But we are in real serious trouble here folks. Our four 4 axle locos can only deliver 336,000 lbs of pull because of their 1.12 million lbs of weight on drivers and the 30% adhesion factor. So our locos are going to slip and stall on the hill. Although we have enough HP to pull this train up the 1.5% grade at 10 mph we do not have enough traction to do so. And, again, you had better set the train air brakes as you stall or the train will drag you back down the hill.

Slugs and SDs

So how do we proceed? Well we can't increase the weight on drivers by adding weight to our existing four 4 axle locos because they are already weighted to the max for the rail. The only other way to increase traction, weight on drivers, is to increase the number of drivers. Add more units. We will need to add two more units (8 more axles) to get the weight up to at least 1.5 million lbs so the 30% adhesion factor gives us 450,000 lbs of adhesion. We do not need the added HP of those two units however, they could be just engineless slugs. Without additional HP the train will go up the hill at 10 mph. At this point I would like to point out that if we simply add two 4 axle slugs, which get the power for their traction motors through electrical cables from the original 4 locos that we can do the same thing by switching from GP models to SD models. From 4 axle units to 6 axle units. An SD40 is simply a GP40 with two more axles (with traction motors) and 50% more weight. In other words we've added "half a slug" to each of the 4 units. In this manner we once again have the required weight on drivers by using just four SD40s. These are the same weight and number of drivers as 4 four axle units plus two 4 axle slugs. If we want to go up the hill at 15 mph instead of 10 mph however, we must add the HP. Slugs or converting to SDs will not do. If the additional units added are 3000 hp like the rest then we will again go up the hill at 15 mph. HP is speed.

Helpers

In either case we will not go up the hill very far, probably not at all! Why not? The figures say we will. The one word is Kapow! You are going to break in two. We are now trying to put 450,000 lbs of pull into a coupler rated at 390,000 lbs, it is going to break. So what can we do? Well we could double the hill. Take half the train up to the top and leave it there then come back with the engines and get the second half. When you get both halves to the top, recouple them, make an air test, and proceed. By taking half the train up the hill at a time the required coupler pull is only half that of the entire train or only 225,000 lbs. Well under the 390,000 lb strength of our couplers. This method also requires no more slugs, SDs, or other units. The original 4 GP40s have enough traction to haul half the train up at a time. Unfortunately doubling the hill requires a lot of time. The line is blocked while it is being done and this train and others are delayed for the duration. Alternatively we could put the added two units on the rear of the train to PUSH. We would need another engineer (a helper engineer) or a distributed power set-up (radio controlled slaves). The physics are the same, the coal train and grade could care less where you apply the power just so you have the right amount to move it. But the couplers do care where you put all that power. If you try to put it all thru one coupler, the first one, it is going to say "Screw you, I ain't gonna take this abuse" and it will break to prove its point (you never knew couplers were so animated did you).


Some things left out


Now for you purists, I know I have left out a few things. (If you know enough about this to know that I left things out then you sure don't need to be reading this document).
·        As the grade gets steeper less and less of the loco weight is felt as pressing directly down on the rails so effective weight on drivers decreases slightly. (Do the geometry yourself if you want).
·        I neglected the weight of the locomotives. They don't go up hill for free.
·        I neglected the efficiency of the locomotive's mechanical and electrical transmission.
·        I neglected rolling resistance of the train. At low speeds such as these, on straight rail, rolling resistance for a loaded coal train is only 10-15% relative to the grade resistance. However that will increase the total pull and HP required.
·        I neglected acceleration. The figures given are for steady state running. To accelerate requires more pull than steady speed.


The Weight of the Locomotive

First we'll look at the loco weight. Four 280,000 lB GP-40-2s weigh 1,120,000 lbs. That 1 million pounds of locos does not go up the hill for free. It takes just as much HP to move each of those pounds up the hill as each of the train's pounds. So you should add their weight to the train when calculating traction, speeds, & HP required. In fact this is one reason for 4 axle high HP locos. The more the locos weigh the more of their HP is required to just to move the loco upgrade.

Heavy Haul vs. High Speed.

You may have noticed that most railroads tend to use 6 axle power on heavy trains such as coal and grain while they use 4 axle power on their high speed lighter weight intermodal trains.
  1.  If a particular railroad has a good mix of high speed and heavy haul trains its locomotive roster will be a mixed bag of 4 axle and 6 axle power.
  2. If a railroad, such as BN, has a preponderance of coal and grain trains and/or operates its trains in mountainous territory where grades are steep and speeds are low its roster will be dominated by heavy 6 axle power.
  3. If a railroad, such as ATSF, has a majority of lighter weight high speed intermodal trains and a lot of relatively flat territory its roster will reflect that with lots of high HP 4 axle power and/or lighter weight 6 axle power.
Let’s look at the difference between 6 axle SD40s and 4 axle GP40s. Suppose we want to run a 5200 ton priority manifest train up a 1% grade at 30 mph. This requires 8320 HP. TE is not a consideration because even three 280,000 lb GP40s will have 252,000 lbs of adhesion. Our train only requires 104,000 lbs of adhesion on this grade. Three GP40s weigh a total of 840,000 lbs or 420 tons. These locos require 672 HP just to move themselves up the grade at 30 mph. So our 5200 tons of train requires 8320 HP and the 420 tons of locos require 672 HP to go up this grade at 30 mph, total 8,992 HP. The three GP40s produce 9,000 HP. What happens if we use three SD40s instead of GP40s? Same HP at 3000 each but the SDs weigh much more. Ours are ballasted for lots of TE needed on coal & grain trains. Our SD40s weigh 420,000 lbs each. Three of them weigh 630 tons! To move these SDs up the grade at 30 mph requires 1008 HP. This means we only have 7992 HP left for the train. That means we can only haul 4995 tons at 30 mph instead of the original 5200 that the GP40s hauled. While this may not seem like much difference it is over 4% and a 4% efficiency improvement is a big deal when you are burning 1.6 billion gallons of fuel per year. Trains that run at high speeds don't need heavy locos with lots of Tractive Effort. What they need are light weight high horsepower locos.Here is a table showing the theoretical Tractive Effort a 3000 HP loco produces at various speeds.


Speed
Tractive Effort
60 mph
18,707 lbs
40 mph
28,060 lbs
30 mph
37,415 lbs
25 mph
44,898 lbs
15.0 mph
75,000 lbs
13.4 mph
84,000 lbs
8.9 mph
126,000 lbs

 Using a 30% adhesion factor, a locomotive that weighs 280,000 lbs has 84,000 lbs of adhesion. From the above chart we can see that such a loco can operate as slow as 13.4 mph without slipping. Suppose our railroad has a large proportion of service sensitive intermodal trains and we want to operate those trains no slower than 30 mph on our worst grades. At 30 mph a 3,000 HP loco is only capable of producing 37,415 lbs of Tractive Effort. Therefore as long as we put enough HP on our trains to maintain 30 mph on our worst grades we do not need to make them weigh 280,000 lbs. In fact they only need to weigh about 125,000 lbs because 30% of 125,000 is 37500 lbs of adhesion and we only need 37,415 lbs. We could save a lot of fuel by using these light weight locos instead of the 280,000 lbs heavy weights. If we have four such locos on a train we are saving 310 tons of wasted weight and that translates into saved fuel.A loco that cannot use full throttle below 30 mph without slipping would be rather restricted in its service. So railroads tend to compromise. If instead of 280,000 lb locos or 125,000 lb locos we use a loco weighing 250,000 lbs we still get some of the fuel savings and the loco becomes much more versatile since it can now operate as low as 15 mph in full throttle without slipping.It is in high speed freight service where locos with high HP to weight ratios shine. This is why ATSF had 3800 HP 4 axle GP60s and 4,000 HP 4 axle B40-8s. Since BN had a preponderance of heavy coal & grain trains and even its freights had to contend with steep grades it had 3,800 HP heavy SD60s and 4,000 HP heavy SD70MACs instead of the GP60s and B-40-8s that the ATSF had.Let’s look at this HP to loco weight ratio from another angle. The following chart shows the maximum Tractive Effort of various loco models and the speed at which that maximum TE is achieved. All units are 3,000 HP and we assume a 30 % adhesion factor.


Model
Weight
Max TE
Speed
Total tons on 1% grade
Trailing tons
Light GP40
250,000
75,000
15.0
3750
3625
Heavy GP40
280,000
84,000
13.5
4200
4060
Light SD40
380,000
114,000
9.8
5700
5540
Heavy SD40
420,000
126,000
8.9
6300
6090
 
A first glance at the table looks as if the heavy SD40 is the best loco. It can pull the most trailing tonnage up the 1% grade. But we have to ask ourselves "What is the job?” If the job is to haul as much tonnage up the grade as is possible, then indeed the heavy SD40 is the loco we want. But if the job is to haul as much trailing tonnage up the grade at 15 mph then the SD40 is not the best choice. The following chart shows how much tonnage each of these locos can haul up the 1% grade at 15 mph. Since all the locos are 3,000 HP they all produce the same 75,000 lbs of TE at 15 mph. But the weight of the loco uses up some of that TE. What is left over can pull the freight that is paying the bills.

 
Model
Weight
TE
Speed
Total tons on 1% grade
Trailing tons
Light GP40
250,000
75,000
15
3750
3625
Heavy GP40
280,000
75,000
15
3750
3610
Light SD40
380,000
75,000
15
3750
3590
Heavy SD40
420,000
75,000
15
3750
3540
 
The light weight GP40s can haul 85 more tons of paying freight per unit up the grade at 15 mph than the heavy SD40 can.

Those Superpower units

If you haven't been paying attention you might think that the new 6000 HP single unit locos are destined for heavy haul service. True they are all heavy 6 axle units. But that is because the weight is needed to put that 6,000 HP to the rail without slipping. A 6,000 HP unit that weighs 420,000 lbs and can attain a 43% adhesion factor has an adhesion of 180,600 lbs. The 6,000 HP diesel engine can deliver that 180,600 lbs of Tractive Effort at a speed of 13 mph. Below that speed you cannot use full throttle on these locos because they will slip. That was for an astounding adhesion factor of 43%. What if they cannot maintain that extreme level of adhesion? What if they "only" get 36%? 36% of 420,000 lbs is 151,200 lbs of TE. The 6000 hp diesel can deliver that TE at 15 mph so the loco cannot operate below 15 mph in full throttle without slipping. At an adhesion factor of 30% the lowest full throttle speed is 18 mph. If the rail is wet or frosty can these modern marvels maintain even a 30% adhesion factor? My experience with 4400 HP units is a definite no. The C44s often have trouble maintaining 22% adhesion with bad rail conditions. If a 6,000 HP unit gets down to 22% adhesion it can only operate at full throttle above 24 mph! Thus if you want these behemoths to reliably move your trains over the hills in all kinds of weather you had better dispatch them with trains light enough that they can maintain 24 mph or greater on your steepest hills. That means they are only useful for trains such as intermodals which get a high HP to tonnage ratio. When it is frosty they won't work on heavy freights or coal or grain trains which routinely pull up the hills at 10-12 mph.
The railroad I work for uses 12,000 HP on their coal trains through here and we go up the hills at about 12-13 mph. Note that you can replace the 12,000 HP of 3 SD70MACs, or the 12,000 HP of 4 SD40-2s, with the 12,000 HP of just two SD90s. You have the same HP so you should go up the hills at the same 12-13 mph. But it will be awfully iffy. That is because the minimum speed these 6,000 HP units can operate at full throttle is 13 mph even with an adhesion factor of 43%. If anything causes the train speed to fall below 13 mph even momentarily, you will never regain the lost speed. The train might be temporarily slowed for various reasons. Perhaps the SD90s temporarily lost that 43% adhesion factor and slipped or reduced HP to prevent slipping. Perhaps a wind came up and increased train resistance. At 12 mph the 6,000 HP locos cannot operate in full throttle even if they regain that 43% factor of adhesion. They will slip. Operating at reduced throttle the locos are not producing the 12,000 HP this train needs to travel up the hill at 13 mph. So the train will never accelerate back up to 13 mph where it could again operate at full throttle. Four SD40s or 3 SD70MACs would have no difficulty re-accelerating the train back up to 13 mph. 

That is because they are not operating at the limit of their adhesion as the SD90s are. The 4 SD40s have 12,000 HP just like the two SD90s but the SD40s have a total weight of 1,680,000 lbs and even at a 30% factor of adhesion can operate in full throttle down to 9mph! The 3 SD70MACs weigh 1,260,000 lbs and with only a 30% factor adhesion they can operate at full throttle down to 11.9 mph. If they achieve a 36% factor of adhesion they can operate at full throttle down to 9.9 mph. So either the SD40s or the SD70s have enough reserve adhesion they can operate at full throttle after being temporarily slowed. That allows them to accelerate the train back up to the 13 mph.Thus on an equal total HP basis these high HP units are not equal to their lower HP cousins when used in heavy haul service. And heaven help you (more like helpers help you) if the factor of adhesion on these brutes ever falls below 36% because you won't have enough adhesion to pull that 15,000 ton train up that 1% grade, period. You had better hope that it does not rain, frost, or snow.Keep the high HP units in high speed freight service where they do the most good. You are trading 8 axles of weight on two 3000 HP GP40s or 12 axles of weight on two SD40s for the 6 axles of the new units and you have 25-50% less Hp-wasting weight with the two high HP units. Remember that TE decreases as speed increases, so as long as they keep the HP per ton ratio of the trains high enough to maintain high speeds then the TE will be low enough that these high HP single units won't slip. But try to use them in low speed drag service and they will slip as noted in the coal train discussion above. The slower the train goes up a hill the closer these high powered 6,000 HP wonders perform like the good old 3,000 HP SD40.

The Efficiency of the Locomotive

Next we'll look at the efficiency of the locomotives transmission. Their transmission consists of the generator, traction motors, and gearing. My experience is that the loco's transmission efficiency normally runs in the 80% range. This means that if the physics of the train, grade, and speed dictate X HP then you really need X / .80 HP. If the physics say 12,000 HP then you really need 12,000 /.80 which is 15,000 HP. Another full unit!

Put another way....The 15,000 ton coal train going up a 1% grade at 10 mph requires 9564 HP. That is 8442 HP for the speed up that grade and 1122 HP for the rolling resistance at that speed. (We'll get to rolling resistance in a minute). But that assumes 100% efficiency. At 80% efficiency this train would need 9564 HP / .80 which is 11,995 HP. SURPRISE! That is three 4,000HP SD70MACs or four 3,000HP SD40-2s to get a 15,000 ton coal train up a 1% grade at 10 mph. Sound familiar?

The Rolling Resistance of the Train

Now we'll look at rolling resistance. Assume the same train as above, i.e., 15,000 tons plus 840 tons of locos (4 SD40-2s) rolling at 10 mph on a 1.0% grade. Using the well known Davis formula we get the following values: (note: the Davis formula )is explained at the end of this article)


Resistance
Pull
HP
Grade
316,800 LBs
8447 HP
Rolling
41,880 LBs
1116 HP
Total
358,680 LBs
9563 HP

The calculated HP required is 9563 HP. Since our locos are only about 80% efficient this means we need a HP rating of 12,000 to actually deliver the required 9563 HP.Put the train on a 2000 ft long 3 degree curve and you get:
Resistance
Pull
HP
Grade
316,800 LBs
8447 HP
Rolling
41,880 LBs
1116 HP
Curve
15,840 LBs
422 HP
Total
374,520 LBs
9985 HP

Using a loco efficiency of 80% the required 9985 HP becomes 12,481 HP. The 12,000 HP of four SD40s is not going to be able to pull this train up the hill and around the curve at 10 mph. The speed will drop until the rolling resistance and grade HP drops enough that the actual HP required equals 80% of 12,000 HP (9600 Hp). That speed is 9.6 mph.
At 9.6 mph we get the following values:
Resistance
Pull
HP
Grade
316,800 LBs
8109 HP
Rolling
41,557 LBs
1063 HP
Curve
15,840 LBs
405 HP
Total
374,197 LBs
9577 HP

Acceleration

Let’s look at accelerating trains. The force of acceleration is mass times acceleration. Force = mass x acceleration (F = m * a). A coal train is a very big mass! So even small acceleration s need a lot of force. That force adds to the drawbar pull account of the grade alone and it can break the train in two. If you keep the acceleration low by notching out one notch at a time and allowing speed to increase slowly you can minimize the force of acceleration. If you are reckless and try to accelerate quickly you may end up in two pieces.
Let’s say we want to accelerate a 15,000 ton train at a rate of 1 mph per minute. In other words we want to be going 1 mph faster at the end of one minute than we are going now. To accelerate at that rate requires a steady force of 23,450 lbs. Note that it doesn't matter whether we are going uphill or on the level. We need to supply an additional 23,450 LBs of drawbar pull to accelerate at 1 mph per minute. Horsepower is pull times speed. Since the force to accelerate this train at 1mph/min is a constant, the HP required to accelerate the train varies according to speed. At 10 mph the HP needed is 625 HP, at 40 mph the HP needed is 2500 HP.

An acceleration of 1 mph/minute is slow. It would take a train 60 minutes to go from 0 to 60 mph. But if we want to accelerate at 10 mph per minute it requires 10 times the force and 10 times the HP at each speed. At an acceleration rate of 10 mph per minute the drawbar force needed is 234,520 lbs. At 10 mph that requires 6,250 HP. At 20 mph it requires 12,500 HP. At 40 mph it requires a whopping 25,000 HP. Note that if we have only 12,000 HP then we run out of HP before we reach 20 mph. We can no longer accelerate at 10 mph per minute and will fall back to lower and lower acceleration rate as speed increases.

Keep in mind that these values of drawbar pull and HP are ONLY for acceleration. You still need to supply the normal pull and HP for any grade and rolling resistance. Let’s look at that. A 15,000 ton train on a 1% grade going 8 mph requires 357,104 lbs of pull and 7617 HP. If we have 4 SD40-2s we have 12,000 HP times 80% efficiency = 9600 HP available. 7620 HP is what you get in throttle 7. We have one more throttle notch and 1980 HP (9600-7620) remaining that we can use for acceleration. At the stated 8 mph that equates to 97,345 lbs of additional drawbar pull available. This additional force will accelerate the train at a rate of almost 4 mph per minute. Yeehaw! Put'em in number 8 throttle and we'll be doing 12 mph at the end of the next minute.

Well not quite. A few problems crop up with that assumption. One is that as the train speed increases so does the horsepower required for both the grade and the rolling resistance. So as the speed begins to increase we have less "left over HP" for acceleration. The rate of acceleration will drop; we cannot maintain that 4 mph / minute rate we started with. In fact when we reach 10 mph all of the loco's HP is being used to pull the train and none is left over for acceleration. The speed will level out at 10 mph and stay there. Ain't physics neat?

The second problem is that you just broke the train in two so you are actually stopped. Why? Because the train traveling at 8 mph required 357,104 lbs of drawbar pull to maintain that speed on this grade. When you opened the throttle from notch 7 to notch 8 to accelerate you just put the additional 92,602 lbs of available loco tractive effort into that same drawbar. 357,104 lbs + 92,602 lbs equals a total of 449,706 lbs. Since drawbars are only good for about 390,000 lbs you just pulled one in two. Moral: When you are moving slowly you'd better handle that throttle gently if you want the train to remain in one piece. Acceleration can break trains in two.

Now for the purists, those 4 SD40-2s are not going to develop that 454,449 lbs of TE. That would mean an adhesion factor of 27% and SD40-2s can rarely if ever achieve that. They would most likely slip. But they can develop the 390,000 lb rating of the drawbars either continuously or by slipping and jerking. So either way the train is going to be in two pieces.

Note that the above train theoretically can go up this hill at 10 mph based upon Hp, efficiency, grade, and drawbar strength. Whether it actually can or not is in doubt. If we rolled onto this hill at a speed higher than 10 mph then all would be OK. As the train rolled onto the grade in number 8 throttle it would simply slow down to 10 mph and proceed up the hill. The drawbar force would be that 357,104 lb figure. Well within the rating of the drawbars. But if the train had stopped on this grade or had started from a stop on a lesser grade and was not yet up to 10 mph then we may be in trouble. Under these circumstances we may find ourselves in the situation above where we are only going 8 mph when the entire train is on the hill. We cannot go from notch 7 to notch 8 because the drawbar force will exceed their rating. Thus we cannot get to 10 mph. The only recourse is to slug it out all the way up the hill in the lower throttle position and a lower speed. It is very annoying to know you have the HP to go faster but you can't use it. If you are a real good engineer and really know what you are doing you can get around this obstacle in some cases. How? By applying some independent brakes to the locomotives drivers. Those brakes will absorb some of the extra HP you get when you go from #7 to #8. Therefore that amount of the extra HP and its attendant TE never reaches the train's drawbars. In that manner you can keep the total drawbar force lower than the drawbar rating. As the speed increases you feather off more and more of the independent brake until finally you are at the 10 mph physical limit and the brake is fully released. But make one mistake during that process; fail to coordinate the independent brake just right with the increasing HP as the locos rev up and increase their load....or feather it off too quickly.......and Kapow! You are in two pieces. You have let enough extra TE reach the drawbars that their rating was exceeded. Going 10 mph in #8 vs. 8 mph in #7 saves you 15 minutes on the hour. But if you break it in two attempting to reach 10 mph then you are delayed 2 hours while you chain up a car and set it out and double the hill. If you are not sure of your expertise maybe it is better to just go up the hill at 8 mph in number 7 instead of trying for 10 mph in number 8.

The main point of all this is to hopefully dispel the myth that high HP means lots of pull. It does not. Higher HP means higher pull at higher speeds but the total maximum pull is strictly related to weight on drivers. No HP required. None! Therefore a switch engine which only operates at low speeds does not need, nor can it use, high HP. It needs to be heavy. (but not too heavy that it breaks or turns over light industrial or yard rails). Life is a compromise.


The Davis Formula

Substantial research early in the 20th century led to the development of a general formula for train resistance. Developed by W.J. Davis, it is still sometimes referred to as the “Davis” equation. 



    • Ro = resistance in lbs. per ton 
    • w = weight per axle (= W/n) 
    • W = weight of car 
    • b = an experimental friction coefficient for flanges, shock, etc. 
    • A = cross-sectional area of vehicle 
    • C = drag coefficient based on the shape of the front of the train and other features affecting air turbulence etc.
    • V =  velocity
    • n = number of axles  
The Davis Equation has been substantially updated to reflect modern developments, but its basic form is the same as the original equation.

Definitions 

(as used in this document)

·        Axle - Two wheels and an axle with a traction motor geared to it. All "axles" are powered, there are no idler axles.
·        GP40 - A 4 axle locomotive of 3,000 HP that weighs 280,000 lbs.
·        SD40 - A 6 axle locomotive of 3,000 HP that weighs 420,000 lbs.
·        Slug - A 4 axle unit that has traction motors but no diesel engine. Its traction motors get their electrical power from adjacent units. A concrete weight ballasts the slug to 280,000 lbs.
·        C44- A 6 axle locomotive of 4,400 HP that weighs 420,000 lbs. Actual model designation is Dash 9-44CW.
·        SD70MAC - A 6 axle locomotive of 4,000 HP that weighs 420,000 lbs and has AC traction motors.
·        SD90 - A 6 axle locomotive of 6,000 HP that weighs 420,000 lbs and has AC traction motors.
·        Grade Pull or Grade Resistance - The force required on a grade to prevent a train from rolling back down the hill. It is expressed as 20 lbs per ton per percent of grade.
·        Adhesion - The ability of the steel wheels of a locomotive to "stick" to the steel rails to prevent spinning or sliding of the wheels. The amount of force required to slide the wheels of a locomotive.
·        Adhesion Factor - The ratio of the adhesion to the weight of a locomotive. A good ballpark figure for steel wheels on steel rails is 30%. IE, it requires a force equal to 30% of the loco's weight to slide its wheels.
·        Tractive Effort - The pull developed by a locomotive. The maximum tractive effort value is directly proportional to the weight on drivers and the adhesion.
·        Horsepower - Any combination of pull and speed that equals 550 lb-ft per second. Examples: Pulling with a force of 1 pound for 550 feet and accomplishing that in one second. Pulling with a force of 550 lbs for 1 foot and accomplishing that in 1 second. Pulling with a force of 225 lbs for 2 feet and accomplishing it in 1 second. Etc.


If you have an idea for a blog post here for the club, let me know. If I can comment on it, I will or I'll see if someone else can and post it.