• SCOA-P Locomotive Drive wheels

  • Discussion of steam locomotives from all manufacturers and railroads
Discussion of steam locomotives from all manufacturers and railroads

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  by Cactus Jack
Anyone have any information on how successful these were in actual service and why more locomotives did not have them ?

Would they have been a practical boxpok substitute for large American steam ?
  by Allen Hazen
Cactus Jack-- I hope you are still following this forum! I just (27.xii.2015) noticed this old question of yours as I scrolled up to a more recent 'disc' driver string, about Baldwin Disc versus Boxpok drivers.

The SCOA-P driver was used on a fair number of Australian locomotives, particularly Victorian Railways R-class (Hudsons: if you really want to gt an American rail fan to think he's slipped into an alternative reality, show him a picture of a Hudson… with a Belpaire boiler!) and late 2-8-2 (I think). As far as I know, it was fully satisfactory. Tests and calculations suggested it was lighter in weight, as well as cheaper, than a comparable Boxpok design would have been. The cheaper bit I can well believe: it looks like a much simpler structure, so I would guess it was easier to make.

The locomotives it was sussed on, however, were much lighter than late North American steam: perhaps two-thirds the axle loading. I'm not an engineer, so have no "intuitions" about whether the SCOA-P was "scalable" for use on much heavier power. But that's the technical question that would have to be answered.

My guess, though, is that the technical question was historically irrelevant: a design originating from the 'Steel Company of Australia' would have been N.I.H. (Not Invented Here), and so wouldn't even have been considered in North America! (Also, of course, it came to late: the Victorian R-class was built in the 1950s, after U.S. railroads had stopped buying new steam.)
  by Pneudyne
There is a good article on the SCOA-P wheels available here: http://www.enuii.org/vulcan_foundry/mis ... entres.pdf" onclick="window.open(this.href);return false;.

This is part of a larger site: http://www.enuii.org/vulcan_foundry/index.htm" onclick="window.open(this.href);return false;.

The article itself is undated, but I’d guess mid-1950s. Possibly it was originally published in the Vulcan house magazine: http://www.enuii.org/vulcan_foundry/magazine.htm" onclick="window.open(this.href);return false;.

As well as on steam locomotives, the SCOA-P wheel was much used on small diesel switchers of the rigid-framed, rod-drive type that were favoured in the British-influenced world in the early days of dieselization. It should not surprise me if the diesel locomotive applications accounted for the majority of installations. Those small switchers were not at all good riders, with much yawing motion that would have imposed high lateral wheel (and railhead) loadings. (A short cab ride in a Vulcan-Drewry six-wheel model in Tasmania back in 2011 demonstrated that in spades.)

Whether the SCOA-P wheel would have been scalable to match American requirements is unknown, but I’d say that the Boxpok was anyway a fundamentally better approach. Still, that the web-spoke wheel had a place in American practice indicates that there was room for different and perhaps not-quite-as-good approaches, at least if home-grown.

  by Pneudyne
The SCOA-P wheel was covered by US patent 2609229, filed 1948 January 07 with priority date 1947 February 17. So it was essentially too late for use by the US steam locomotive builders, at least for domestic production, even had there been any interest.

That patent may be found simply by searching Google Patents using its number.