From time-to-time I’ll read something about building a layout, grades, helixes, whatever-- and somewhere in the article it’ll turn out that the scale is HO or N or whatever-- and up until now it sorta just went past me without much thought and I sorta thought about HO and N about the same, one about twice (or half) the size of the other and that’s about it…
And then last night I was reading about somebody’s N-scale helix and it occurred to me that there may be entirely different dynamics at work in one scale versus the other-- and if not in N versus HO, then perhaps a larger scale versus the smaller scales-- G versus N or something…
So does the number of cars a locomotive can pull scale more or less the same comparatively between the scales? Or are, say, O or G scale locos stronger and can pull more cars, or N scale locos stronger and can pull more cars-- and what about grades, where i would imagine that sheer weight of the locos is one of the primary elements of keeping up the tractive effort…?
As a general rule, I think it shakes out about the same between HO and N.
My previous layout was N and my present layout is HO. I haven’t really thought about testing the waters so to speak, but I think it is fairly close.
Yes you can get more weight in an HO loco than you can in N, but N scale cars are lighter in weight as well, plus I believe there is less friction on the truck bearings for N scale.
The maximum number of cars pulled by an engine is constrained by a group of decidedly nonlinear functions. Because of the nonlinearities, coming up with the “optimal” scale that would have the potentially longest train is very difficult. Consider:
the coefficient of friction of the wheels and axles goes up as the scale goes down.
but the weight goes up by the cube as the scale goes up
total friction is usually modeled as the weight times the coefficient
room for weight in the loco is also a cubic function of scale
motors don’t scale up nearly as fast in volume for a given amount of power
strength of materials per thickness has a minimum thickness, but then goes rapidly, but not as rapidly as weight
Having worked in HOn3, which is effectively closer to N than HO I can see the difference. It is much harder to make trucks roll as easily in HOn3 as they do in HO. There is precious little room inside the engines for extra weight. Net result is that it is quite difficult to get an engine to pull a prototype-length train up a prototype grade. The same holds true in N.
Moving up to HO, a die-cast Mikado can usually be made to pull or out-pull the prototype.
In O, motor torque and available current start to creep in as limiting factors - you can stall a motor before the wheels will slip. Remember, for the same scale speed, the engine is going nearly 4x as fast as its N counterpart. Which means less than 1/4 the torque multiplying gear reduction, since larger motors also have less max RPM. Also in O, a 60 car train is close to 60ft long - there just aren’t as many places where you can try to haul 60 cars with your 2-8-2. So it’s really hard to say whether O engines in general out-pull HO or not.
I would suspect the sweet spot is S, where you can get the weight up pretty close to the motor’s torque limit.
It was probably my helix report you’re thinking of. I’ve only ever messed with N scale, and the helix I’ve constructed is the first proper helix I’ve worked with. The particulars are the outside radius is 16", and the grade is 2.9% over 2.5 turns. I can run a 25 to 30 car train up the grade, with three units on the front and two shoving from the rear.
The need for helpers is predicated mostly by the weight of the train, which at 30 cars is more than the couplers can handle. Without the helpers at the back, the train will either separate, or if the knuckles hold, it can end up string-lining. If I had room for a broader radius, that might be less of an issue, but that’s the best I could with what I had to work with.
I’d have to imagine that HO scale would allow for more power on the front, but the radius would naturally have to be wider to get both an operational curve, as well as a reasonable grade given the additional separation between decks. (I only need 2-1/8" to handle my tri-level auto racks). But as noted elsewhere, the HO cars are also going to be heavier. The one saving grace would be the more or less standard application of body mounted couplers.
I guess the bottom line is that physics is physics, and the same equation will determine how much energy is needed to move a certain weight and length while overcoming curvature, friction and gravity. The scales may be different, but proportionally, the factors are the same.
F.Y.I: Must tell you that, when in HO modular club, we had some ratty-running rolling stock. Bought an HO Exxact-Socket journal reamer from REBOXX. Reamed all truck journals on several cars. LOTS of crud came out using the neat little tool! A puff of KD graphite on axle ends, after trucks re-asselbled and those cars ran smooth as silk! THIS type of maintenance can make a WORLD of difference in your loco’s drawbar pull aka number of cars each can handle. My 2 cents…Old Tom aka papsmurf in NH
Yeah, I’d have to go with wm3798 on this one. I once tried to run a little thing up and over a small hill I made under the mainline on my fictitious Conrail Huntley Freight Divison (HFD). I managed to get my locomotives up the side, but as wm said, HO cars are heavier. You would want like a really powerful locomotive with really good traction to attempt it. Plus, the bump was only abot as thick as the wheel gauge on my Dash 8-40c, about 3cm, and, as in real life, made a HUGE difference in speed going up and down.
In general, the larger the scale, the greater the relative effect of a grade. For example, a 2 percent grade compared to level track has a greater proportional effect on a 1:1 (e.g. prototype) train than say an O -scale train which would have a greater effect than an HO-scale train.
Don’t overlook that long curves have a similar effect on train lengths. A 30-inch radius curve creates less resistance than an 18-inch radius curve, for instance. The effects of curves on grades are additive. For instance, a long (train-length) 32-inch radius curve on a 2-percent grade in HO scale is roughly equivalent to a 3-percent grade on the straight.