Locomotive (Steam & Diesel) Pulling Capability Tests

[beiland]

This is not meant to be a detailed analysis of this subject,...there are a number of those in other subject threads on various forums

Rather this a few general observations of the subject I experienced recently.

Yesterday I was running some experiments with running a few Rivarossi Allegheny locos around the recently new loop of the bottom deck of my layout. I had advertised 1 or 2 in my inventory for sale. I had some questions from potential buyers about their running qualities. I also wanted to satisfy some of my own questions about their pulling power.

The 'test track' is my newly laid code100 atlas track around the perimeter of my 12x16 foot train shed. Regrettably it is not all level track, but rather rises at a grade of about 4% on a stone arch viaduct on 2 sides of the room (needed to provide clearance for double-stack containers to run under it at its highest part. This makes things a bit more challenging, but its about the minimum grade I could use in my relatively small layout. My trains are going to have to run this grade, both while circling the bottom deck, AND when entering the helix structure for a trip to the top deck.


...before the track was laid

This is just 2 of the Alleghenys I was playing with, one is my most treasured one with heavy weathering, and the other a more lightly weathered one. ( I also discovered an electrical pick-up problem on one of the others, that I documented over on another subject thread).

BTW, none of my Alleghenys have the optional traction tires..


I dragged out some misc freight cars I had, choosing those that had metal wheels. I was real surprised at the wheel slipping I experienced at the top of the grade with only 9-10 cars in tow ! I subsequently added some weight to the locos (1oz,.. then 1.25 oz) and that improved the situation. I'm not so sure I could fit much more than that amount of weight into those boiler shells, so I didn't bother to go further at this time.

Is my track grade really affecting the pulling power of these big locos that much??

 

[beiland]

IHC, Mehano 4-8-2 mountains

I happen to have one of my trusty old cheap Mehano mountains sitting around, and decide to give it a go at the same load. It pulled a little better and slipped its wheels less. Then I added a little weight to her and it got better as well.


I don't think I would have much trouble adding this much weight to her boiler.

 

[beiland]

sacrilege...ha...ha​

Okay I am a committed steam engine fan. But I just might have to modify that some.

I took 3 different diesel 6 axle engines (individually) that I had sitting around and hooked them up to that same freight car group I had been experimenting with. They pulled that group around like with EASE,...no slipping, just plain easy uninterrupted running !.

I guess I can see how these younger folks go for the diesel engine power....wow.

 

[Selector]

It's physics, and it works the same in the real world as it does in the scale world. Traction = adhesion/power. If we have two locomotives with equal weights, driving axles, and power, they should be very close to each other in terms of traction. When you keep the weights the same, but distribute the weight over more driven axles, such as on a steamer, you'll get less friction between the driver tires and the steel rails, and so you'll slip more.

Diesels have all their weight distributed over driven axles, whereas real world steamers have steering trucks that support about 40% of the locomotive's sprung weight. This is why a steamer can haul a train it can't lift, whereas a diesel can lift a train it can't haul.

A steamer, if it doesn't spin, will accelerate over a longer range as its cyclic rate in the pistons rises, whereas the diesel will only accelerate to its geared maximum, at which it's developed tractive effort has dropped. A steamer will be developing its maximum theoretical boiler output, often in excess of 5000 hp in the Berks and larger engines (NYC Niagara 4-8-4 developed 6500 hp at 60 mph), near its maximum permitted track speed. That is why diesels are good for modest loads up to about 60 mph, and less for heavier loads...they just can't move them. Steamers have trouble getting heavy loads underway, and they'll often just spin. But let them get up to 60 plus mph and you'll appreciate all that brutish power churning over the rails below you.

In our models, the diesels often get heavier frames inside them, and even more weight can be added to nooks and crannies such as the tanks if there's no speakers there. The drives are the same, and they often drive only two axles, or maybe four or six, but that extra weight makes a difference.

 

[trailrider]

Selector - "Steamers have trouble getting heavy loads underway, and they'll often just spin. But let them get up to 60 plus mph and you'll appreciate all that brutish power churning over the rails below you."
Having lower starting tractive effort is why steamers would back up slightly, putting slack in the cars, so that they could start one car at a time. Diesels generally won't do that or they would break drawbars!

RMC, when testing a new locomotive (mostly diesels) will weigh the unit and check tractive effort with some type of pull gage, perhaps a fish scale, in ounces. Then they test the unit with "free-rolling boxcars", whatever those might be. I don't have the article in front of me, but when they tested a GP-18, the tractive effort was 3 oz, which corresponded to 47 cars on a straight and level track. When I tested my kitbashed Mantua 2-10-4, it had a pull of 2.8 oz, which I believe calculated to 42 of those cars, theoretically. Of course, I don't have anyplace to test that many cars. Also, this steamer has only the front and rear drivers contacting the railheads (the center drivers are blind and shimmed up off the rails .010" to allow negotiating 18" radius curves. Interesting!

 

[Selector]

One of my top three pulling locomotives is the BLI T1 Duplex with its two middle driver axles blind. BLI faithfully replicated this non-articulated beauty, but they had to compromise for the horribly sharp curves of scale layout tracks. So, the two central axles have no flanges. This locomotive can pull mightily, easily lifting a couple of reefers and six heavyweights up 3% grades. So, with only two driven, weight-bearing axles, all its heft and power have only those four tiny surfaces on which to apply the power.

I'm coming around to the realization, or maybe acceptance is the better term, that one cannot use one's fiddling time more productively on a smaller pike with steeper grades than in finding ways to shoehorn another half an ounce of automotive tire weights into a part of the shell or the frame of an iffy puller. I recall people complaining of the otherwise beautiful P2K steamers of the early 2000's, such as the Berkshires and the 2-10-2. Gorgeous items for the money, really pretty to behold, but they just couldn't pull much more than a few cars on any grade. That may have been something to do with their tire sintering, not sure, but they must have been too light by about three ounces as well.

 

[DakotaLove39]

Tungsten chips. You're welcome.

That's what I used. I am a committed diesel modeler, being 1970's (although I have steamers, too). I ran into the situation of loco weight vs tractive power/effort in 1:87 also.

Proto locomotives, while dated, are absolute beasts for pulling power, and the reason for that is the massive chunk of metal they carry around. Same deal with the Athearn F's, if you guys remember those. Athearn wisened up way back in the day and put a big frame block inside the loco, effectively shrouding the motor in dead weight, to increase pulling power.

Walthers and ScaleTrains locos are much the same, but the ol' Athearn engineers of today aren't as smart, apparently. My Athearn RTR SD40-2's do not compare to ScaleTrains in terms of pulling power, and as I don't always want to drag out 4 locos to get the job done I sought a way to fix this. Fortunately, a friend of mine figured it out before I did and turned me on to tungsten weights for pinewood derby cars. The results are below

North Metro club has a pretty severe helix to get between its main staging and the layout surface. The club also has a nicely performing Piggyback train, which two of my ST's were able to get up that helix without a problem. My two RTR's, however, would not. So, I remedied this by stuffing both of their fuel tanks with tungsten chips I bought off eBay. Each ounce is approximately $4, but well worth it to improve performance. I have since done this upgrade to ALL of my Athearn RTR SD39's, SD40's, SD40-2's and Genesis GP9's with no regrets. So far I haven't found the need to modify my SD45's or SD45T-2, so Athearn must have gotten those right.

I get these chips from one eBay seller named TXalchemist. I have also applied them to other diesels, like my Bowser AS-616 with good results. Anywhere you have open space you can fit these little weights easily. No more trying to fit big wheel weights into a loco hood or boiler. I have also used these chips to improve pilot and pony truck performance on my GS-4's, my Little Joe and my BLI 2-8-2.

 

[beiland]

VERY interesting DakotaLove39,
Could you describe in a little more detail how you prepare and glue in that Tungsten chips / powder.

Or perhaps I should have asked if you have ever used the powdered form?,...since it appears you prefer the chips??

 

[beiland]

Bachmann Mountains​

I have a soft spot for the Mountain locos with the flying pumps and plumbing on their boiler face,..and vandy tenders. So not only do I have a few of those IHC Melano versions, I also have a few of the Bachmann versions. Lets give one of those a try.

It also had some sound. It turns out to be quiet a good puller,...bested the IHC one with the added weight, and the Allegheny.
With some fine tuning and proper lube after its very long storage time it probably will be better.

Lets say I am happy with its performance. Weathered up these are going to look super!!...and I have enough of them to run double-headed often.

 

[beiland]

My 4% Grade​

My grade on this viaduct structure was dictated by my need to be able to run double stack container cars under neath and into my central peninsula,...

So I am stuck with this big grade (BTW the grade in my helix is only 2 -2.5 if I recall properly). I believe my solution is I am going to have to operate double-headed engines very often. I'm OK with that,....besides it looks neat.

Double up these guys and I will really be able to pull some long trains,...at least long in terms of my small, tight radius layout.

 

[dennis461]

sacrilege...ha...ha​

Okay I am a committed steam engine fan. But I just might have to modify that some.

I took 3 different diesel 6 axle engines (individually) that I had sitting around and hooked them up to that same freight car group I had been experimenting with. They pulled that group around like with EASE,...no slipping, just plain easy uninterrupted running !.

I guess I can see how these younger folks go for the diesel engine power....wow.

The biggest advantage diesels (model) have is the ability of the wheels to stay in contact with the track.
Steamer frames and wheel assemblies, without equalization, lose contact vertical and horizontal.