Locomotive
Performance on the Narrow Gauge
By
J
W Knowles
It had always seemed to me that the output potential of steam locomotives in relation to their dimensions went down with size. This would mean that the horsepower developed per square foot of grate area was likely to be lower for five square feet then for fifteen and that a small narrow gauge engine was unlikely to develop anything very exciting even "for its size". But this idea has been proved wrong by the calculation of some power outputs for locomotives on the Ffestiniog Railway. The locomotives on that line are normally worked hard on a long climb, especially on heavy peak season trains, and these calculations show the power developed to be of a very high order.
The
Hunslets BLANCHE and LINDA and the Alco MOUNTAINEER can be recorded developing
200 indicated (cylinder) horsepower, 185 rail h.p. (at the driving wheel
rims) and 170 equivalent drawbar h.p. (actual drawbar h.p. corrected for
gradient) for several minutes on the climbs. All three have grates of
5.25 square feet, so these efforts represent 38 i.h.p. per sq. ft. of
grate. |
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LINDA's
front end and new chimney. © Peter Johnson. |
The rebuilding of LINDA with a gas producer firebox (described in Railway Magazine for August 1986) has led to even greater power potential. In August 1985, I was able to record the converted LINDA with eight carriages, 73 tons gross, make a very spirited start from the loop at Rhiw Goch. On the 1 in 80, 21 mph was reached in 5.5 minutes by Tyler's Curve, with full regulator, and cut-offs of 52% on curves and 42% on straights. It was a short effort, but pressure and water level were held, both then and onwards to Tan-y-Bwlch where the gradient is much easier and curves abound, restricting output.
This effort represented 220 i.h.p., 205 r.h.p. and 190 d.h.p., or 42 i.h.p. per sq. ft. of grate. A high standard for a full size, saturated locomotive for such a period is 35 i.h.p. per sq. ft. of grate, for an early superheated machine 40, and for a modern superheated design 50. With conventional narrow fireboxes, all these efforts would have entailed a significant carryover of unburned fuel particles, but on this occasion LINDA had an almost smokeless exhaust. The superheating on all these Ffestiniog engines is very modest, and small in relation to the rest of the steam circuit.
LINDA working a train past Boston Lodge works in August 1985. © Peter Johnson
Recording LINDA'S effort was made possible by Phil Girdlestone, then Workshops Superintendent on the line. He also advised the weights of the carriages (most 7 to 8 tons tare), the cut-offs at various settings, and the results of some 1984 tests of the rolling resistance of the Ffestiniog carriages, for use in the calculations. The gradient details were taken from the FR Guidebook.
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Note:
This article first appeared in issue 117 of "The Narrow Gauge",
magazine of The Narrow Gauge Railway Society. See www.ngrs.org |
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