Minimum radius of curves - standard gauge

Can anybody tell me what minimum radius of standard gauge track would be in a yard situation.
This would need to take eight coupled locos.

Bob.

 

GWR 42XX/5205 20' wheel base 5 chains slow, 28XX/2884 16' 10" wheel base 6 chains slow, 47XX 20' wheel base 7 chains slow.

 

Thanks very much for that, you even got one of the classes correct !

Bob.

 

No simple answer to this. Locos usually had a minimum radius quoted on their spec sheet but would quite often negotiate sharper curves. Gauge widening can help with the rigid wheelbase but you can get to the limit of swing of any pony or other truck which no amount of gauge widening will really help with. Buffer locking could also become a problem if there is no transition or, even worse, reverse curves are involved.

 

The condition of the loco also makes a difference; an engine that has run a few thousand miles will get round a much tighter radius curve than one with newly overhauled wheelsets and axleboxes.

 

So very true.

 

A GWR 47XX 2-8-0 has both side play on the trailing coupled axle and a longer wheel base over the driving wheels than an LNER P2 2-8-2.
Also GWR frames were thicker and a two cylinder locomotive is inherently easier to brace with stretchers than a chassis with an inside
connecting rod to be accommodated - which is supported by what happened when Thompson moved the stretchers rebuilding the P2s.

I would take the two above as good outlying pointers especially with the recent work on new builds of both.
There would be clear military specifications for the various 2-8-0s in both World War I & World II and I think they had flanges on
all wheels.

By the by the S&DR 2-8-0s don't have a long wheel base but it might be a very rigid one: the frames are remarkably braced with a diaphragm plate
right across the frames over the coupled axles forward of firebox throat plate. Apparently designed with some thought to be as near to the plane
of the driving axles as possible - there are rather fetching cutouts to allow the tops of the horn openings around the driving axle boxes through.

 

I love it when a question on this forum starts a thread in which many readers can actually learn something. So much more worth spending never-to-be-regained minutes of our lives visiting NatPres for than pie-in-the-sky WIBN and "The owner of loco X should do this..."

 

I would go at least 2 chain more than whatever the diagram says.
If you are able to, lay the curve out to as large a radius as possible don't limit yourself.

 

Hirn,

The S&D 2-8-0's now on the WSR have a longer coupled wheelbase than the GWR 28xx 2-8-0's, but the S&D engines have (very) generous side play in axleboxes, leading and trailing 11/16", intermediate and driving 5/16". Because of this the two centre axles can move 1" laterally relative to the leading and trailing, this is only possible due to the spherical joints in the coupling rods. Although an advantage on sharply curved track it does allow the locomotives to float from side to side on straight track, a rather soporific ride only partially damped out by the friction pads on the pony truck.

Most GWR tender locomotives are what is termed "easy fit" in axlebox clearances, 1/16" total side play for each axle, this made them less able to negotiate sharp curves. If requested I can post on here the GWR document detailing the axlebox side clearances for each class of loco.

An additional problem is that any axle at the extremity of a rigid wheelbase will not be running radially when negotiating a curve and will always be slipping sideways across the railhead, the effect is worse at the leading wheelset hence the desirability of a leading pony or bogie. The force to do this being provided by the flange of the wheel on the high side rail. The practical way to reduce the resultant wear is to provide regular track mounted rail lubricators at the entry to curves, these are remarkably effective if well maintained and kept filled.

Andy.

 

A locomotive with an equal number of axles (two or four) will traverse curves more easily than one with an odd number of axles (three or five) if the rigid wheel base is the same. That was why the 2-10-0s had flangeless centre driving wheels.