Radial Steam Engines

Gallery opened: Nov 2007

Last update: 30 March 2013

Updated: 21 Jan 2020 Radial steam engine in a propellor
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Radial steam engines have three or more cylinders arranged at an equal spacing on a circle around the crankshaft. The cylinders stay still while the crankshaft revolves; this may seem a crashingly obvious statement but there were such things as rotary engines, in which the crankshaft stayed still and the cylinder assembly revolved around it. These should not be confused with the other sort of rotary engine, in which some kind of a piston rotated in a fixed housing.


The Brotherhood engine was a popular and successful three-cylinder radial design that was adapted for various operating fluids. A large number were used as water engines, for driving hydraulic capstans in docks and so on, but they were also widely used as steam engines. Versions for steam use are shown here; it is notable that the steam versions show considerable design differences from the water-driven version.

Left: The Brotherhood Radial Engine: axial section

A intriguing feature of this engine is the use of large spherical pivots instead of a conventional "little end" bearing inside the pistons. The main exhaust valve is a port uncovered by the sphere as the angle of the connecting rod changes. There are also uniflow-like supplementary exhaust ports that are uncovered as the piston reaches the bottom of its stroke. The crankcase is used as an exhaust manifold.

From Modern Power Generators

Left: The Brotherhood Radial Engine: longitudinal section

This shows the steam inlet arrangements. Steam enters at left and passes through some rather convoluted passages to a piston-type inlet valve, driven from an eccentric on the crankshaft. There appears to be no means of varying the cut-off.

Power is taken off from the flexible coupling on the right.

From Modern Power Generators

Above: The Brotherhood Radial Engine: alternative valvegear

This image is believed to show an earlier version of the Brotherhood engine. There are no spherical ends to the connecting rods, and the piston valves are driven from extensions on the next piston going anti-clockwise. There appears to be no means of varying the cut-off.

Left: The Brotherhood Radial Engine: account of a test

From Model Engineer & Electrician for 23 June 1904, p593


Left: Captain Richardson's radial steam engine in a propellor: 1932

This not-too-sound idea appeared in 1932. The accompanying article says: "Airplane designers are far ahead of engine designers in aircraft developments and many of the leading minds of the engineering world are striving to develop engines of suitable design for tomorrow’s airplane needs. Among them is Captain Richardson, of the Great Lakes Aircraft Corporation, for whom the aeronautical world has profound respect." But probably not after he went public with this idea.

If you want to power an aeroplane by steam, which has been done, sort of, it is surely simplest to have the engine attached to the fuselage, rather than going round with the propellor. (early rotary-engined aeroplanes notwithstandng) Apart from anything else, you have to pass the steam into and out of the engine through a rotating bearing. The artist who drew this appears to have had no notion that the steam would expand on passing through the engine, as the inlet and exhaust pipes are of the same diameter.

Captain Richardson may have thought it was clever and weight-saving to combine the steam cylinders with the propellor blade roots, suggesting that the heat from the cylinders would prevent icing, but it looks to the Museum Staff to be an engineering nightmare. At this point the advantages of Variable-pitch propellers were well-known , and it would be interesting to try adding that feature to the integral steam cylinders...

From Modern Mechanix Aug 1932, p112


Left: Radial steam engine in a car wheel: Dec 1932

This article appeared in 1932, when steam cars were no longer considered remotely competitive with the internal combustion engine.

Since there does not seem to be room for connecting rods and a crankshaft, this may have been a cam-type engine. But I suppose it still counts as radial because of the layout of the cylinders.

There is of course no reason why the use of steam would enable the wonderfully increased power output and reduced fuel consumption stated in the article. So far no other trace of this idea has been found.

From Modern Mechanix Dec 1932

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