From the very beginning the Trust regarded Tornado not as a replica or copy of any one of its 49 predecessors, but as the fiftieth A1. This simple decision gave the Trust licence to make small changes to the design to better suit modern manufacturing techniques and to fit in with the modern high speed railway, while remaining demonstrably faithful to the greater part of the original design.
The original A1 class numbered 49, which, with many components shared with other classes, favoured manufacturing techniques, suited to batch production. In particular, extensive use was made of steel castings. In most cases the cost of approval of other manufacturing techniques caused the Trust to choose steel castings as per the originals. However for some item such as the star stay which supports the brake cylinder, a fabrication was produced. Extensive use has been made of patterns made from expanded polystyrene which are ideal for one off items and cost between one third and a half of a comparable wood pattern.
The principal change from the original design is the boiler. Tornado's boiler was designed as a fully welded vessel with a steel firebox as opposed to the original that was riveted and had a copper firebox. The reason is that, with the exception of a small cottage industry which supports the existing preservation movement, there is no capacity to produce a large riveted boiler in the modern pressure vessel industry.
This method of construction did not significantly increase the technical risk as extensive use was made of welded boilers and steel fireboxes in the USA and other overseas countries. Also the successful Bulleid Merchant Navy and West Country classes had fully welded inner and outer fireboxes made from steel.
Requirements for modern operating conditions
Brakes: the A1 class was equipped with a steam brake for the locomotive and vacuum brake for the train. As it is expected that the locomotive will spend most of its operating time on the main line, the Trust has decided to make air brakes the primary braking system for the locomotive. To enable the locomotive to haul vacuum braked stock on heritage railways, a vacuum ejector will be fitted with the vacuum train pipe being controlled through an air/vacuum proportional valve.
In addition to the automatic fail-safe air brake system, the locomotive will be equipped with a straight air brake to assist with shunting and coupling.
AWS/TPWS: the original locomotives were fitted with the BR vacuum brake AWS (Automatic Warning System). By the time Tornado is in service, the new TPWS (Train Protection and Warning System) will be required. This is designed to be a direct replacement for the AWS as fitted to air braked diesel and electric stock, however it is not so readily swapped with the vacuum AWS equipment. There will also be a need to fit a data recorder to all motive power running on Network Rail. Radio will also have to be fitted.
Electrical system: arising from the above plus the possible fitment of video cameras to relay locomotive action to the train, there will be a significantly increased requirement for electrical power on the locomotive. As built, the A1s had a 350 watt 24v AC turbo alternator fitted which powered light bulbs for marker lights, cab gauge lighting and certain lights for maintenance purposes. When the AWS was fitted, a separate 24v battery set was provided.
Tornado therefore has a dual battery system: a vital service battery to power the AWS/TPWS and cab radio and a general services battery for the other demands. The alternators continuously charge these, backed up if necessary by an auxiliary generator in the support coach or a mains shore supply when stabled. The charging circuitry has been designed to ensure preferential charging of the vital services battery.
Range and capacity
Tornado's tender has been redesigned internally eliminating the water scoop and increasing the water capacity from 5000 gallons (22,700 litres) to around 6,200 gallons (28,150 litres) and reducing coal capacity from 9 tons to 7.5 tons.
The range of a steam locomotive is governed by water capacity, lubricant consumption and fuel capacity. Water is the most significant limitation with most locomotives hauling loaded trains at express speeds being limited to about 100 miles (160 km) between fillings of the tender. For the A1 class an average of 40-45 gallons (113-137 litres) per mile is to be expected. Thus the standard 5000 gallons (22,700 litres) capacity of the tender will give about 100 miles (160 km) allowing 500 gallons (2,270 litres) in reserve.
With the capacity of the tender augmented to 6,200 gallons (27,240 litres) plus a possible 8,000 gallons (36,320 litres) in a future second vehicle, a range of around 300 miles (480 km) non-stop would be practicable. This would allow operation from Euston to Carlisle or Kings Cross to Newcastle.
Full oil pots and lubricators would ensure a comfortable 300 miles (480 km) range – the Elizabethan non-stop runs totalled about 400 miles (640 km) with the shed runs at either end. The original locomotives had a coal capacity of 9 tons of coal which gave about 350 miles (560 km) of range. Tornado's reduced coal capacity of 7.5 tons will give a range of about 290 miles (470km).
The A1 class was designed to cope with the heaviest regular East Coast trains of the post-war period. These were regularly loaded to 15 coaches or 550 tons. The locomotives were capable of maintaining 60-70 miles per hour (95-110 km/hr) on level track. However, the asset of Tornado will be the ability to haul lighter (10-11 coach trains) at higher speeds to fit in with modern traffic patterns.