Planet Class
Design and development
By mid-1830 Robert Stephenson had concluded that the Rocket pattern, with its inclined external cylinders, was inherently limited for fast running — the rocking motion of the cylinders caused unsteady running at speed. His response was a fundamental redesign: the new locomotive would have its cylinders mounted horizontally between the frames at the smokebox end, driving a cranked rear axle. This put the cylinders close to the centre of the locomotive, eliminated almost all rocking, and produced a vastly smoother-running engine. The boiler was carried on a strong wooden sub-frame reinforced with iron, providing a much more rigid platform than Rocket's exposed-firebox arrangement.
Planet was delivered to the Liverpool & Manchester Railway in October 1830 and immediately demonstrated its superiority: it hauled trains at higher speeds, with greater fuel efficiency, and with much less mechanical wear than the Rocket-pattern engines. Over the following three years Stephenson and other builders produced over thirty Planet-type locomotives for British and overseas customers, and the basic layout — inside cylinders, cranked driving axle, multitubular boiler, smokebox at the front — became the universal pattern for British locomotive practice for the next 130 years.
Service and withdrawals
The original Planet worked the Liverpool & Manchester Railway from October 1830, hauling both passenger and goods traffic. The class proved highly successful and remained the L&MR's standard motive power until superseded by the larger Patentee-type engines from 1834. Most were withdrawn during the late 1830s and 1840s.
The original locomotives were not preserved, but a working full-size replica of Planet was built for the Manchester Museum of Science and Industry and operates regularly on the museum's demonstration line at the original Liverpool Road station — itself the oldest surviving railway station in the world.
Identification features
2-2-0 layout with a single pair of large driving wheels behind the firebox, inside cylinders mounted between the frames at the smokebox end, and a cranked rear driving axle. The boiler is carried on a sandwich-frame structure of timber and iron. No leading bogie; the front carrying wheels are mounted directly to the frame.
Notable locomotives
- Planet (1830, not preserved)
- Planet replica (Science and Industry Museum, Manchester)