tgbcvr Wrote:
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> The double Fairlies are loved by and well suited
> to the Ffestinog Rly in Wales. One crew
> essentially runs two locomotives, their bogies
> swivel so they handle tight curves, and the line
> is short meaning the limited range/fuel supply
> isn’t an issue. A disadvantage is that if one of
> the locomotive halves goes down, then of course
> both are in the shop.

To make your point, the minimum curve on that line as built was something like 50 degrees. I think the tightest curves have been widened a bit since, but not by much. I assume this kind of tight curvature was a relic of the line's origin in the1830's as horse- and gravity-powered with no thought given to steam locomotion. Horses and 4-wheel minecarts don't care overmuch about curve radius. Also, this is 19th-century Britain, so these locomotives probably did not have enclosed cabs as built, lessening the problem of firing clearance with the cab walls due to said cab walls quite likely not existing at first.

I don't know that the fairlie is necessarily a bad design, but I think it can safely be called a design that's best suited only to some very specific conditions. The Kitson-Meyer comes to mind as another double articulated design that worked fine in some very specific conditions but never saw widespread usage.