Engines for Long Distance Goods
Although goods trains were usually very much heavier than
passenger, since speed had to be much slower the power needed — the rate of working
— was often less. The four-wheeled British goods wagon with hand brakes ,
loose couplings and grease axle boxes could not safely travel faster than
about 35 mph, and poor brakes limited heavier wagons to 5 mph slower.
High starting effort was important to get a heavy train on the move, although drivers could ‘set back’ until all couplings were slack, then pick up the wagons one by one – a process joyous to the ears!
Heavy loads can be carried efficiently by rail precisely because there is very low friction between steel rail and steel tyres, but for the engine maximum grip for starting and climbing was essential. As many wheels as possible, small in diameter, needed to be driven with ideally, no non-driven (or ‘carrying’) wheels at all.
The 0-6-0 arrangement (no carrying wheels at front; six driving wheels; no trailing carrying wheels) was the first preferred wheel arrangement. When larger engines became feasible in the early 1890’s an extra driving axle was added, to become the 0-8-0. Later, in the ‘E’ class a pair of carrying wheels became necessary to carry the increased cylinder and front-end weight, making them a 2-8-0. The same 2-8-0 configuration was used in the ‘MM’ class, an ex-ROD (Railway Operating Division) and Great Central Railway design, irreverently named “Military Mary’s”. They were not thought to be named after a specific Mary but simply a play on words, unless they could of course be ‘quite contrary’.
The ‘1400 class’ introduced by Mr. F.W. Webb in 1903 were a first attempt at a ‘mixed traffic’ capability. Driving wheels were still small but they were limited to six, and the weight of the front end was guided by a four-wheeled bogie — a much better design for speed. The leading driving axle of the conventional 0-6-0 or 0-8-0 was satisfactory only because speeds were so low.