Simulated 3% slope for testing

[rbryce1]

The railroad I am designing (Alaska), no matter how I look at things, will work best if one section of track is on a 3% grade for 12 feet of incline (12 ft up, straight over a 4' long bridge, then back down 12').  The train on this rail will be 9 McKinnley Explorer passenger cars with 4 Bachmann GP40 diesels.

The Model Railroad Club I belong to has an incredibly long 2% grade to test this with, but nothing on 3%.

Is there a method of creating the drag this train will have on a 3% slope using weights in hopper cars to simulate the extra 1% slope?  If so, how would you determing how much weight to add to the 7 passenger cars to do this?

For example, if the car weighs 3 oz on a 2% slope would it be the same as a car weighing 4.5 oz on a 2% slope to simulate a car weighing 3 oz on a 3% slope?

[rogertra]

The railroad I am designing (Alaska), no matter how I look at things, will work best if one section of track is on a 3% grade for 12 feet of incline (12 ft up, straight over a 4' long bridge, then back down 12').

To help ease that grade, could the bridge also be built with the bridge deck a grade?  There's nothing in any engineering book that says bridge decks have to be level, thousands of them, on railroads throughout the world, are built on a grade.

Many modellers seem to think all bridge decks should be level but this isn't so in the real world.

Cheers

Roger T.

[rbryce1]

Not really, the bridge is the actual high point connecting two mountains over a very steep valley and mountain lake.  The bridge is 44" long and 8" high in itself, so I need to climb 8" just to get to the bridge.  Right now it is laid out to use a 2% grade, but needs 16' of run to do it, and that is starting 4" above the base grade.  Using 3% will cut the run down to 12' of run, but at a steeper grade.

[jward]

if 4 units can't pull 9 cars up a 3% grade then you need to find better motive power.

seriously, run your test with the full consist on the 2% grade, then reduce to number of locomotives to the bare minimum needed to get up the grade. double that number and you should have more than enough power on the 3%.

having several gp40s on my roster, and a 4% grade on 18r curves, i will run a test for you. but my recollection is that they should be good for at least 5 cars each. i do know my gp7 will pull 12 up the 4%. 

[rbryce1]

Thank you Jeff.  I would really like to now before building the grade and finding I can't negotiate it.  I haven't had the best of luck with these locomotive's pulling power.  Of course, my alternate option is replacing the locomotives, but they are really hard to find in the Alaska line.

[Jerrys HO]

rbryce,

I can not recall if you are DC or DCC (I believe you are DCC if I remember correctly).
One thing I have done which may  have been an illusion is to replace the standard Bachmann decoder with a decoder with BEMF. I have used both Digitrax and NCE which both are nice. It seemed to make a huge difference on my grade which was close to a 4% till I restructured the grade.
I have many Geeps and the ones I upgraded are much better pullers than the others.

Jerry

[jbrock27]

Bob, I think what you are finding with the GP40s is they lack the weight that other brands have, that would increase their pulling ability.

I like Roger's point about bridges.

Currently, I need to determine for myself, if adding cork roadbed to track running underneath a trestle held up by the tallest Atlas bridge piers, will result in the track being raised up too much for traffic moving underneath the trestle to clear the underside of the trestle

[West Bound]

You could  setup 3 or 4 feet of temporary track on a 3% grade with one of your passenger cars and pull it with a pulling meter such as this one at Micromart?   

http://www.micromark.com/digital-pull-meter,9577.html

John

[K487]

rbryce1:

Don't know if this would apply to you, but......

All of my B'mann diesels have 2 to 4.5 ounces of weight added - helps a lot.  But I have to "pay" for the room inside the shell.  How?  By discarding the DCC board - I'm strictly a DC guy anyway.  Also, particularly on GPs and SDs, when I add the weight I bias it toward the front so that the whole weight of the loco is equalized over both trucks; again better pulling power. 

Note that even though just one of my weight-added (4.5 oz) B'mann SD40-2s can start and pull 65 cars (85% with plastic wheels) on level track around my layout, I always use two engines to ease the stress and the train runs a little smoother, and sometimes I use three locos just for my viewing pleasure.

You know, I just had a peculiar thought and I'll share it with you.  I believe that 6-axle diesel locos have by default 50% more pulling power/traction than 4-axle diesels, at least on an ounce-for-ounce basis.  Maybe you could have one or more "leased" 6-axle locos helping your GP40s in consist or as pushers.  At the least it would add some interest even if the 6-axle loco(s) were not needed.

K487

[jbrock27]

I was thinking of you and your practice when I made my previous post Doug

[Doneldon]

You know, I just had a peculiar thought and I'll share it with you.  I believe that 6-axle diesel locos have by default 50% more pulling power/traction than 4-axle diesels, at least on an ounce-for-ounce basisK487

K487-

I think maybe this isn't so. While it's true that a loco with six-wheel trucks has 50% more contact with the rails than does a loco with four-wheel trucks, the weight on each axle is only two-thirds as much as what the four-axle trucks have. That's going to make a significant difference in the larger loco's adhesion and will just about negate all of the difference afforded by having more metal on metal.

Realistically, how much of a load a loco can haul is a function of its weight and the strength of its motor. The number of axles doesn't make much of a difference. The reason that six-axle locos have more power than four-axles ones is that they are just naturally bigger and heavier. If a larger motor gets stuck into the larger inside space, that will give an additional advantage to the larger loco.

When the twelve-inches-to-the-foot railroads go shopping for new locomotives, many factors drive their decision but one of them is not the number of axles on the candidate locos because more axles automatically means more power. The number of axles is important only in how well the rails and structures (bridges, trestles and such like) can handle the locomotive's weight. Lighter track construction might mean six-wheel axles to reduce the PSI of each wheel on the rails. If you can spread out a loco's weight by making it longer or giving it more axles, you might be able to use more powerful locos on lighter rails. This has been true since the earliest days of steam. The railroads didn't progressively build or order larger locomotives because the looked nice; they did it because they needed to spread out the weight. If anything, the railroads would have preferred that every locomotive be an 0-4-0. That would be mechanically simple, inexpensive to maintain, able to use smaller turntables and engine facilities and able to negotiate tighter curves than their longer brothers with all of the extra wheels. They would also use less fuel because they wouldn't be dragging around the huge weight of a large locomotive versus a small one.
                                                                                                                                                                     -- D

[jward]

it should be noted that on the real railroads, the 6 axle locomotives were usually significantly heavier than their 4 axle counterparts. this is especially true on units built after about 1960. the weight difference is usually enough to give similar weight per axle on each type. for example an sd40 and a gp40 will have a similar weight per axle. the 6 axle units will also have significantly more pulling power due to the horsepower spread over more motors. each motor gets less of a share of that horespower. 4 axle locomotives tend to be slippery due to their higher horsepower per axle.

the exceptions for light rail doneldon referred to were for locomotives built in the first generation of diesels, often by minority builders, which often featured an unpowered center axle. they may have been 6 axle locomotives, but only 4 were powered. locomotives in this configuration were built by alco baldwin fm and gmd (canada)......those locomotives were also built to be as light as possible. they were never intended to be heavy duty mainline locomotives.

most of the early adopters of true 6 axle locomotives embraced them because they needed to move heavy trains over steep grades. pennsy, sp, and n&w are good examples. railroads with a flatter profile, such as new york central or rock island tended to stick with 4 axle units.

[ebtnut]

Weight per axle was a very important factor in locomotive acquistion.  It was probably most important when it came to bridges.  Railroad bridges were normally rated with the Cooper system, with the rating number (i.e., Cooper 30) being the maximum weight per axle the bridge could safely support.  As noted above, early diesels such as the SD-9 or RSD-5, were essentially the same loco with six-wheel trucks, and sometimes that center axle wasn't powered.  By the same token, in the waning days of steam you might find that the roads' biggest power had already gone to the scrap line, but some light branches used small locos right to the end becuase the line couldn't support even a GP-9 (see, Wabash Mogul, among others).  As a side note, the B&O's Dockside 0-4-0T's weighed in at about 120 tons, meaning their axle loading was about 60 tons, just about the same as a main line 2-8-4. 

[Desertdweller]

The Milwaukee Road in the 1960's determined it was more cost-efficient to have special light axle locomotives built than to upgrade the track on certain branch lines.  They had a series of lightweight SD7's built with special trucks and even extra-small fuel tanks.  These were 6-motor locos.

They later had  special model SDL-39's built with the same principle.

In the first generation, they had RSC2's for branch line work.  These were used into the 1970's.  These were A-1-A trucked units ( center axle was an idler).

The last loco I ran was a BNSF ES44C4.  This GE unit had A-1-A trucks with a twist:  the center (non-powered) axle could be raised or lowered to put additional weight on the drive axles when needed to prevent wheel slip.  Running one of these felt just like running a loco with 6 powered axles.

Les

[K487]

jbrock27:

I've been busy, just got back to this thread.  Thank you for your reference.

All:

Wow, getting into the mechanics, math, axle spacing, unpowered center axles on some engines, etc. of the 1to1 engines was very eye-opening, educational, and a little confusing.  But I can understand all the experimentation by the railroads - every little improvement helps the bottom line (and often employee safety).

However, thank you all for sharing the info (and jward I liked your first paragraph).  And believe it or not I've had some real-world experience with this when, for 16 years, I made my living as an independent contractor bidding on and moving high/wide/overweight items in the US, Canada and Mexico (moved about 155 loads in that time period).  What I'm getting at here is what you all have addressed - total weight per axle (railcar + load + tiedown materials), axle spacing, track condition, bridge restrictions, etc.   However, in this work traction for movement was assumed and not directly addressed.

Donaldon:

You said, "I think maybe this isn't so. While it's true that a loco with six-wheel trucks has 50% more contact with the rails than does a loco with four-wheel trucks, the weight on each axle is only two-thirds as much as what the four-axle trucks have. That's going to make a significant difference in the larger loco's adhesion and will just about negate all of the difference afforded by having more metal on metal."

You're probably right - I've not weighted a 4-axle diesel engine to equal the same amount I do to my SD40-2s (total of 22 to 22.5 oz each).  The reason is - generally not enough room, or I'm too lazy to stuff small cut-off pieces of lead weights into cracks and crevices. However, (and I know you all know this) on a straight weight-added-on basis (to a 4-axle and 6-axle engine) to their "nominal" capacity, our 6-axle engines (all 6 driving) almost always out-pull the 4-axle ones.   

Or - do you have some 4-axle diesel engines that out pull your six axle ones?  You might have - I'll bet some of those powered B units (filled with metal weight from the factory) can out pull some run-of-the-mill 6-axle units.  Interesting - sort of like the real world.

So, what I'm learning is to be careful of what I say about railroad wheel-traction physics (and probably some other technical items.)     The railroads have spent over a century doing this in the real world, and you folks are sharing some of that learning.

Thank you again.

K487 (aka Doug)