The 5AT Locomotive
A modern high performance steam locomotive

The above diagram shows the locomotive in its final post-FDC outline.
The diagram below shows it in its near-original outline with small tender

General Characteristics

The present proposal aims to deliver a brand new high-performance steam locomotive for the haulage of high speed main line charter trains at the lowest cost, yet incorporating features designed to maximise the return on the capital investment It will be designed to 'state of the art' steam locomotive technology which guarantees a level of performance far exceeding that of former steam, yet without sacrificing any of the steam locomotive's rugged simplicity, nor its aesthetic appeal. It is to feature the following general characteristics, so as to have the highest level of acceptability to all sectors of the railway industry involved in charter train operation.

  • High power : weight ratio, the key to high-speed capability.
  • High thermal efficiency.
  • High maximum operating speed, as required for slotting in with other traffic.
  • Low fuel and water consumptions.
  • Long operating range between supplies replenishment.
  • Extreme reliability, giving high availability for service.
  • Low maintenance requirements.
  • Low overall operating cost.
  • High route availability.
  • High level of in-built operational safety.
  • High level of convenience for operating crews.
  • Aesthetically attractive for creating the true steam 'ambience' and a striking 'image'.
  • Environmentally-friendly operation, e.g. minimal pollution.
  • The locomotive, excluding the tender, is to be based on the size and format of the British Railways Standard Class 5MT 4-6-0 design of 1951 (as described on the "73082 Camelot Locomotive Society" website at The reasons for this are as follows.

    Given the level of power : weight ratio now possible in steam traction, it is an appropriate size of locomotive for the intended duty of main line charter train service.

    The deep firebox of a 4-6-0 has, size for size, a higher evaporative capacity than a shallow firebox boiler, and is ideally suited to burning oil or coal (using the Gas Producer Combustion System). Basing the design on an existing one will significantly reduce the design complexity, time and cost. All overall dimensions constrained by the moving structure gauge being kept within those of the BR Class 5MT will facilitate route acceptance.

    A modest size locomotive allows a large tender without exceeding the permissible length for turning facilities, this in turn maximising the very important parameter of operating range between supplies replenishment. The route availability is high - it is a 'go-anywhere' type.

    The relatively small taper boiler gives good forward visibility from the cab, a factor of paramount importance to safe operation at high speed.

    The 4-6-0 is the quintessential British locomotive type, for it was in Britain that the 4-6-0 was developed more than anywhere else, and the Class 5 may be considered to be the quintessential 4-6-0. It is considered most appropriate to build on this, and the present proposal will define the limit of performance for this type of locomotive.

    Specification Summary:

  • Maximum axle load: 20 metric tons (same as BR Class 5MT).
  • Engine weight in working order: 80 ~ 90 metric tons (the load on the leading bogie will be determined at the detail design stage, hence precise weight cannot now be given).
  • Adhesive weight: 60 metric tons.
  • Tender weight, full supplies: 80 metric tons.
  • Overall engine and tender weight, full supplies: 160 - 170 metric tons.
  • Overall length over buffers of engine and tender: 22,1 metres (72 feet 6 inches).
  • Tender capacity (assuming oil fuel): fuel 7 metric tons, water 46,3 m3 (10 200 gallons).
  • Coupled wheel diameter: 1 880 mm (6 feet 2 inches, same as BR Class 5MT).
  • Boiler pressure: 2 100 kPa (305 psi).
  • Performance Summary:

  • Nominal starting wheel rim tractive effort = 146 kN (32 830 lb), requiring a starting coefficient of adhesion of 0,248.
  • Maximum rated drawbar power on level tangent track = 1 890 kW (2 535 hp) at 113km/hr (71 mph).
  • Maximum indicated cylinder power = 2 580 kW (3 460 hp) at 170 km/h (106 mph). This = 32,3 kW/ton of engine weight (43,3 hp/ton) assuming the engine weight = 80 tons.
  • Power : weight ratio data for complete trains comparable with diesel and electric traction - see comparison diagram on Home page.
  • Overall thermal efficiency of the locomotive, when oil fired, referred to the cylinder output corresponding to the maximum rated drawbar power = 14,1% (this will not be the locomotive's maximum figure).
  • The corresponding indicated specific steam consumption, based on steam to the cylinders only = 1,90 kg/MJ (11,2 lb/hp-h).
  • Maximum continuous operating speed = 180 km/h (112,5 mph). The locomotive will be designed for 10% over-speed, i.e. 200 km/h (125 mph). Note that this is the speed the locomotive will be designed to be capable of, and does not imply that it will be permitted to operate at such a speed. This is discussed in Section 4 of the Business Plan (not included in these web pages).
  • Rated maximum steam supply from the boiler = 17 000 kg/h (37 500 lb/h).
  • Maximum steam temperature = 450°C.
  • Operating range at constant maximum drawbar power (1 890 kW at 113 km/h)*:
    Based on fuel supply = 560 km (350 miles)
    Based on water supply = 370 km (230 miles)
  • Operating range under representative average main line service conditions (113 km/h overall average train speed assumed):
    Based on fuel supply = 930 km (580 miles)
    Based on water supply = 620 km (385 miles)
  • * Note: 1 890 e.d.b. kW at a constant 113km/h implies the haulage of a 1075 ton 29 coach train. The ranges at both maximum power and under representative average service conditions will therefore be greater than given with the trailing loads more likely to be found in actual service (say 300 to 500 tons).

    Other Criteria

  • Reliability. In its truest sense this means that locomotives will achieve the necessary reliability "on the road" with very little maintenance effort. Good reliability is of major importance because (i) in-service failures which disrupt other services will be increasingly less tolerated, (ii) the intensive servicing and maintenance which steam received in the past (and which is still required on today's heritage locomotives) will become too costly, and (iii) spare parts will be expensive as they will tend to be special items manufacture in small quantities. Even at the present state of the art reliability and simplicity do go together, and the format of the Class 5AT - a 2-cylinder single expansion 4-6-0 - is about as simple as a main line locomotive can be. Reliability is also very much a question of good detail design, and every attention will be given to this point at the detail design stage. Naturally features of proven high reliability, such as roller bearings, will be incorporated wherever possible. The level of reliability will be such that it is expected that major overhauls will only be required at approximately 400 000 km (250 000 mile) intervals, with intermediate overhauls (dictated only by tyre wear) at some 200 000 km (125 000 mile) intervals, and major servicing (e.g. boiler washout) at a minimum of 20 000 km (12 500 miles).
  • Low operating cost will be a consequence of the locomotive's high thermal efficiency, giving low fuel and water consumption, high reliability, giving low maintenance expense, and low lubricating oil consumption due to the extensive use of sealed roller bearings.
  • The high route availability of a locomotive conforming to the size of the BR Class 5MT will not be confined to Britain alone. Due to the tight British moving structure gauge such a locomotive could run virtually anywhere in the world on standard gauge tracks taking 20-ton axle load, having thus a truly 'universal' route availability. This gives the potential advantage that the same design is suitable for service in many countries where steam charters are run.
  • Adhesion. The relationship between maximum wheel rim tractive effort and adhesive weight is generally well-balanced throughout the Class 5AT's speed range, and especially at the high speeds at which most miles will be run. Although it will be a modest-size locomotive, it is worth noting that the 4-6-0 type has the same level of adhesive weight as much larger 4-6-2's and 4-6-4's (the only European locomotives of these two wheel arrangements which exceeded the adhesive weight of the GWR 'King' Class 4-6-0's were the Belgian Class 1 4-6-2's and the LMS Turbomotive). An analysis of the principal latter-day standard gauge express passenger steam locomotives in fifteen European countries (including the UK), covering 27 classes, gave wheel arrangements of 4-6-0, 4-6-2, 4-6-4, 4-8-0, 4-8-2, and 2-8-4. 74% of the classes concerned were 6-coupled types, and the 8-coupled locomotives were often where axle load was restricted or gradients severe. The average adhesive weight of these 27 classes was 63,4 tons, only 5,7% more than that of the Class 5AT. Therefore the proposed 4-6-0 has the same order of adhesive weight as that generally found on the last of the steam-era express passenger locomotives running on standard gauge European railways, an era when train weights were generally heavier than they are now.

  • Last updated 15 Feb 2005 - Feb05 version of post-FDC drawing substituted