What are some maximum values for S scale drawbar pull? I want to be able to test the locomotive I’m building when I finish it, but I only want to buy 1 scale.
Obviously the answer will depend upon a bunch of variables, and I don’t have any S scale myself. However, to give you one point on a curve, there was a review of an S scale American Models GP35 in the April 1993 MR. There was not a description of the model’s construction, but it appears that the body was plastic with a metal underframe.
The engine weight was given as 22 ounces, and the pull was 4 ounces. The text stated that there was room to add weight for more traction.
Regards
I found two more points for your S scale drawbar curve.
There was a review in the April 2000 MR for an S-Helper Service EMD SW1. This model was described as metal and plastic and weighed 16.5 ounces. The drawbar pull was 2 ounces.
There was also a review in the June 1998 for another S-Helper service model, this one an EMD SW9. The model weighed 19.5 ounces and had a drawbar pull of 5.9 ounces.
I suspect that there are other S scale reviews in MR, but I’m finding that the resource magazine index is not complete.
Again, I hope that this information might be useful.
There’s a good chance that that SW9 had traction tires, as a nominal value for the best drawbar pull from a locomotive (with all wheels powered) is about 25% of the loco’s weight. Before wheel slip control, this applied to both models and the real thing.
Another method of determining drawbar pull is through the use of an incline plane. You’ll need a length of straight track affixed to a board which is hinged at one end, with the other end capable of being raised in known increments of grade percentage.
Multiply the weight (in ounces) of the locomotive by the percent of grade (expressed as a decimal figure) that the loco will climb. For example, the loco below, weighing 32 oz., will climb a 26% grade.
.26X32oz.=8.3oz.of drawbar pull
Wayne
I don’t know if S scale engines come with traction tires. Anyway, the review did not mention them and went on to say that “all axles are powered and all wheels pick up electricity”.
I too have heard the 25% rule, so I can’t explain the apparent discrepancy. Since the OP was only looking for reference numbers, the reported values are probably close enough.
This is actually a very helpful number, and it means I can put off buying the measuring gauge until after I finish my locomotive. That is, as long as it also applies to steam locomotives.
I think that as a maximum value, it would apply to steam as well as diesel. However, leading or trailing wheels, if they support some of the weight, will limit the figure as will the friction and play in the side rods, etc. Many steam locos don’t offer a lot of space in which to add extra weight, either, so most don’t even approach that 25% figure.
Wayne
None of my Showcase Line diesels from S Helper have traction tires. I have the SW1, SW9, and NW2. I don’t believe the others have them either. I haven’t measured drawbar pull on any of them so I can’t comment.
You can find additional information on their web site http://www.showcaseline.com/
Enjoy
Paul