The London, Midland and Scottish Railway (LMS) Princess Royal Class is a class of express passenger 4-6-2 steam locomotive designed by William Stanier. Twelve examples were built at Crewe Works, between 1933 and 1935, for use on the West Coast Main Line. Two are preserved.
Overview
The designer of the class, William Stanier, had previously been Works Manager of the Great Western Railway's depot at Swindon Works, and had been recruited with a brief to replace the LMS's miscellany of locomotives inherited from its constituent companies. He made extensive use of Great Western features in his designs.
To match the power and speed and especially the prestige of the London and North Eastern Railway's express Pacific locomotives, Stanier designed the Princess Royal class almost as soon as he was appointed to the LMS. When originally built, they were used to haul the famous Royal Scot train between London Euston and Glasgow Central.
Design
The class was based on GWR 111 The Great Bear, a design produced in 1907 for the Great Western by George Jackson Churchward. The smokebox and cylinders were closely based on those of the GWR 6000 Class (also known as the King Class). The inside cylinders were abreast the leading bogied wheels and drove cranks on the leading coupled axle, the outside cylinders were abreast the rear bogie wheels (which made substantial cross-bracing necessary between the cylinders and the locomotive frame) and drove crank pins on the centre coupled axle. Each of the four cylinders had its own set of Walschaerts valve gear.Other minor details, such as corks to close oil boxes, closely followed Great Western practice.
Construction
A prototype batch of three locomotives was to be constructed in 1933. Two were constructed as drawn but the third set of frames was retained as the basis for an experimental turbine locomotive.
Turbomotive
The third prototype was constructed with the aid of the Swedish Ljungstrom turbine company and known as the Turbomotive, although not named. It was numbered 6202, in sequence with the Princess Royals. Although 'generally similar' to the rest of the Princess Royals, it used a larger 40 element superheater to give a higher steam temperature, more suitable for turbine use.