"HORSES FOR COURSES" EVEN APART FROM RACING !

BERNBOROUGH

When I was a child the great horse BERNBOROUGH was the darling of the Newspapers and the Newsreel Cameras. Out of 37 Starts the great horse had 26 Wins 2 Seconds and one Third. At one stage he had 15 consecutive wins carrying heavy weights and finished that streak carrying 10Stone 5 Pounds in the long Doomben 10,000. 

Not many horses have that sort of stamina. So we have the phrase "Horses for Courses" - some horses can perform better on certain racecourses than others.

"Hello!" You are thinking to yourself is Tony a secret racehorse fanatic? NO! This is just a diversionary way of introducing some information about......steam locomotives!

Most people looking at a steam locomotive will not think twice about any of its features. But to the initiated a great deal can be told about it's designer's and owner's intentions for it by even a brief glance. The main giveaway is the size of the larger wheels - the DRIVING WHEELS as they are called. If they are small, the main purpose of the locomotive is strength - it will usually be a Goods / Freight locomotive. If the wheels are very large , it's main purpose is speed - it will always be a passenger train locomotive.

NSWGR 36 Class Passenger Locomotive 4-6-0 5 Feet 9 Inches Driving Wheels

NSWGR 57 CLASS 4-8-2 Goods Locomotive of 1927 5 Feet Driving Wheels

But the "Horses for Courses" principle has still more far-reaching influence on the design of a steam locomotive.At  the most basic level, the "loading gauge" must be considered. This is the maximum height and width that the locomotive must conform to so that it will fit into tunnels, under signal frames and bridges and be able to pass trains on adjoining tracks without contact and also pass through Station platforms without contact. These last two requirements are not simple  because curves of varying intensity will cause the locomotive to protrude at a tangent to the curve as it goes around it. In fact when first brought into service (in the days before computers) the 57 Class was found to be unable to pass through some stations until the platforms were shaved back. Even beyond these basic measurements, comes the matter of weight, both absolute and distributed along the length of the locomotive. Absolute : the bridges and viaducts to be traversed must be able to support the dense weight of the locomotive.; distributed : the weight will be heaviest on the axles of the Driving Wheels - this is important to ensure the maximum adhesion of the wheels to the track, but still it must not be too great for those same bridges and viaducts.

Having got that basic requirement right, there is the question of  turning the locomotive at the end of its planned runs. In Australia especially most lines end in rural areas, in a dead-end. The locomotive needs to be turned on a turntable for its return trip. The size of that turntable will govern the size of the locomotive that can be employed. That is the size of the locomotive complete with its coal and water carrying tender.  Turntables in NSW were fairly commonly 50 Feet in diameter in major facilities they were even larger, but if the locomotive was to serve widely it must conform to the lowest diameter. Sometimes when there were problems, smaller 6 Wheel tenders were used to shorten overall length.

So that covers the basic concerns that must be addressed. But more is demanded: the routes the locomotive is expected to cover and the gradients which will be encountered must be carefully studied in order to determine the steam generation that will be required. Regular heavy climbing up stiff gradients will require large amounts of steam to be generated. This in turn will govern the size of the boiler and the firebox , and it will also determine the amount of water and coal that the tender must carry having regard to the water replenishment opportunities along those route. The size of the boiler will also need to take into account the desired size of the Driving Wheels and the loading gauge once again. 

                                          "FLYING SCOTSMAN"  4-6-2 in Australia

                                                        NSWGR 38 Class 4-6-2

Here we see the "horses for courses" factor fully at work. The famous locomotive "Flying Scotsman" was designed by Sir Nigel Gresley specifically to haul the "Flying Scotsman" express between Kings Cross Station London 392 miles to Edinburgh Scotland   . It did this at sustained high speed and was able to draw water from pans set between the tracks without stopping.It was the most famous train in the pre-War Empire. YET  when the "Flying Scotsman" locomotive made a prolonged visit to Australia some years back and double-headed with 3801 over the Blue Mountains, it quickly became apparent that it did not have the steaming capacity for the prolonged strenuous climbing required . The result has been described as 3801 pulling "Flying Scotsman" and their train over the tough route.  

So when one looks at a steam locomotive one is seeing the complex solution to a wide variety of problems and challenges. Designing a steam locomotive is an  art  underpinned by much science.