FAQ1 - Aren't the performance claims for the 5AT a bit exaggerated?:


The following answer is taken from Wardale's response to Leonard Staghurst whose letter was published in Steam Railway #277 (see 'Articles and Letters' page of this website):

"Unfortunately Mr. Staghurst's comments betray his lack of knowledge, not only of what is possible with steam traction but also of what has already been achieved. Consider the following.

Item

SAR 26 Class 4-8-4

5AT 4-6-0

Type of locomotive

Rebuild of 1950's design

New design

Quality of thermodynamic design

Restricted by structural limitations of existing design

State of the art

Number of cylinders

2

2

Simple or compound

Simple

Simple

Valves/valve gear

Piston/Walschaerts

Piston/Walschaerts

Boiler pressure, lb. per sq. in.

225

305

Fuel

Coal

Gas oil or diesel fuel

Ash content of fuel

15%

0

Fuel calorific value Btu/lb.

12,000

18,400

Engine weight (excluding tender), metric tons

123

80

Maximum indicated h.p.

5060 (peak of measured i.h.p. curve)

3460 (calculated)

i.h.p. per ton of engine weight

41.1

43.3


The above figures, which are amply supported by other data, show eloquently enough that the calculated power capacity of the 5AT is perfectly realistic, and I regard achieving it as a formality (and surpassing it a probability) - even on this planet! Likewise all factors concerning thermal efficiency, except the target combustion efficiency at maximum evaporation, which I have acknowledged will be a difficult problem. But that does not mean impossible, simply that very good engineering will be required to achieve it."

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Page created 19 Jan 2003