REF: Rail wheel profile and "to do" list update

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Proto87Stores

Re: REF: Rail wheel profile and "to do" list update

Postby Proto87Stores » Wed Jun 19, 2019 7:26 pm

Will,

What I demonstrated was only that a pair of freely rolling “wagons” did not derail on a tight radius oval at speed, under several special conditions which would be unlikely to exist on a typical P4 layout and would likely affect the Nadal formula for that case.

1. The entire oval was double check railed due it being simulated girder rail.
2. The inner rail head was an untypical very sharp edge due the flange way slot being etched.
3. The lateral force friction was via nickel-silver wheels on nickel silver rail. No steel involved.
4. The bogie wheels were 9.5 mm dia. on a very short 19 mm wheel base, which separately and together considerably reduced the wheel angle of attack for that radius.
5. The wheel suspension was freely moving equalization, which meant that all wheels under lateral forces all had optimum and equal weighting. No springing.
6. There was no locomotive pushing or pulling a heavy train of multiple high friction wagons, which would significantly increase the lateral forces on wagons near to the locomotive.

As a contrary example, I use the same rail and radii for testing self powered RTR streetcar and similar vehicles with RP25 wheels and no suspension. E.g. https://www.youtube.com/watch?v=viWH5qybDbA.

That makes the wheel/rail interface quite different with a much lower Nadal formula value. While the video shows successful operation at moderate speed with a heavier small locomotive, far lighter cars reliably derail on curves if travelling faster than a few scale mph. But if they are additionally weighted, they generally hang on safely at up to prototypically safe scale streetcar operating speeds. A true example of realism in modelling practice.

Therefore, It would be beyond a stretch to project my results to predict a similar likely wheel climbing weight threshold of a long P4 train on a more reasonable radius. You’d have to calculate that threshold for more normal P4 worse case running conditions, such as a 4-6-2 with 6 ft drivers, a 6 wheel tender, on a 48” radius curve, pulling a full length passenger train of say 12 coaches. And I suspect that threshold would be considerably different.

This performance difference does however raise the concern that the current Suspension Digest does not even mention Nadal and that there are requirements that all wheels exceed the minimum necessary weight carrying level. So it offers no help in calculating or even ball park estimating the necessary wheel weighting required to prevent wheel climbing derailments. Unfortunately, instead the emphasis is on ignoring the past successful weight equalizing systems with designs intentionally place differing weights on driving and carrying wheels., without any understanding or regard for what the wheel weights actually need to be.

Andy

Resubmitted in revised form June 19, 2019


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