Axial Steam Engines.

Updated: 5 Mar 2010
Beadle engine added
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An axial or barrel engine has multiple cylinders arranged around and parallel to a central shaft, like the chambers in the cylinder of a revolver. The piston thrust is converted to rotary motion by a swashplate, wobble-plate or Z-crank mechanism. A swashplate looks similiar to a wobble-plate but actually works quite differently, as shown on the Axial IC engines page.


Above: The Shott Axial Engine: 1870.

Model in The Science Museum, London. Author's photo.

This is a demonstration model of a proposed marine steam engine built by George Shott (of Messrs. John Penn and Sons) with the assistance of his two sons George and William Nesbitt Shott. The full-size version was to have two cylinders of 36 in diameter by 18 in stroke, fitted with piston rods and rollers to engage with grooves in two cylindrical cams mounted on the propellor shaft. Two similar but smaller cams on a separate shaft, driven by gears from the main shaft, operated the steam admission and exhaust valves. The propellor shaft passes through the centre of the aft cylinder and piston, and was to be fitted with a four-blade bronze propellor of 7.5 ft diameter. There is no provision for a thrust bearing on the model.

The engine was expected to develop about 520 indicated HP at 120 rpm, with steam at 25 psi. Its claimed advantage was presumably that the fore-and-aft engine format would fit better into a ship hull. No record of full-scale construction has been found.


Left: The Churchward & Messenger Engine: 1877.

The wobble-plate seem to have some sort of stabilising system to the extreme left. A smaller wobble-plate to the right operates slide-valves.

From The Engineer Nov 16th 1877

Here is the original text from The Engineer, 16 November 1877, p359.

"Considering the necessity for reducing the space occupied by marine engines to a minimum, it is perhaps somewhat surprising that the possible advantages attending the application for this purpose of the principle of the Z crank have not been made available, at least for launch or small steamboat propulsion. Except, however, with single-acting engines this has not been done with practical success. We illustrate at page 345 a small launch engine, by Mr.J.Churchward, Dover, in which the principle is applied to single-acting cylinders, but which by the employment of trunk pistons may be made double-acting. The result is a very compact engine of long stroke, the height of the engines being little more than the diameter of the cylinders. In small launches the engine is placed under the smoke-box end of the boiler-locomotive-so that only the space necessary for the latter is required, the engine being in otherwise unused space, and its weight brought to the lowest position possible.

"As will be seen, the two cylinders E are placed horizontally with their axes parallel to the crank shaft, on either side of which they are fixed, the three axes being in the same horizontal plane. The crankshaft runs in bearings, one between the forward end of the cylinders and the other at the stern end of the frame. At the forward end of the cylinders is attached a bracket carrying a vertical pin upon which a horizontally vibrating arm B is pivoted, the ends of the arm being connected to the piston rods O, also by vertical pins. Upon horizontal pins or bearings a short distance from the end joints of the vibrating arm is pivoted a semicircular arm A capable of vertical vibration , the central portion of this arm being provided with a journal into which the crank pin fits. These two vibrating arms thus form bell-crank levers for each cylinder, the motion of the pistons in the direction of the length of the boat being attended by the thrust of the crank pin in a direction at a right angle thereto, the crank pin journal in the semicircular arm being permitted to follow the circular path of the crank pin by the vertical angular play of the arm A on the bearings at its two ends - the two rocking arms, in fact, forming a Hook’s joint, by which the reciprocation of the pistons produces rotation of the crankshaft.

"The slide valves are worked by means of a sheave G mounted upon a pin through the crank shaft, and capable of rocking thereon through an angle sufficient to cause the pins on the sheave strap to travel the distance of the full stroke of the valves. A long feather sliding in a key bed in the crankshaft is connected with this sheave and with the sheave H worked by the reversing lever indicated at J by dotted lines, and by it the sheave G may be placed at any angle necessary for altering the cut-off, and may be placed on either side of an angle of 90 deg. For reversing the engine. By means of this concentric cam and strap for moving the slide valves, any range of expansion may be used, and the lead remains constant, whatever the range, both backward and forward running. When the engine is used for stationary purposes, a governor is attached to the fly-wheel, consisting merely of two weighted levers, the inner ends of which are jointed to a cam on the crank shaft, to which the outer end of the feather above mentioned is attached. An arrangement of automatic expansion gear is thus obtained. Our illustration only shows the design for small single-acting engines, several details of which would necessarily require modification for engines of larger power. One of the 2-horse size has now been at work about eighteen months, and has for a small engine proved very economical in fuel, and shows no particular wear in any of its parts. One new bronze piston ring has been renewed during the time mentioned, but the other ring, being of phosphor bronze, has remained good yet. The engines may be made with any number of cylinders, and the principle of the design has been applied by the inventors to other purposes, as for pumps and water meters."

Text by courtesy of Jonathan Palterman.

Left: The Churchward & Messenger Engine animated.

Another fine animation by Bill Todd.


Left: The West Axial Engine: 1878.

This article claims that West's engine was "now well-known". Here it is driving a Gramme electrical generator at 700 rpm.

The engine has six cylinders and a centrifugal governor, but that is about all we learn here.

No US patent for this engine has been found.

From "The Engineer" 25th January, 1878

Left: The West Axial Engine: 1878.

The West engine makes a cameo appearance in a big two-volume book called "Modern Power Generators", which is famous for its coloured fold-out illustrations. According to Mr French, "A speed of 1000 rpm has been satisfactorily obtained in practice, but the engine is not now manufactured." That was in 1908.

From "Modern Power Generators" by James Weir French, Vol 1, published by The Gresham Publishing Co in 1908


Left: Six-Piston Axial Engine: 1884.

This engine appears in Knight's Dictionary without any attribution, but looking at the unusual piston construction in the drawings above, it is almost certainly West's engine.

This engine has six cylinders pushing on a swashplate or disk. Mr Knight says: "The pistons are single-acting, the pressure of steam in the cylinders tending always to force them against the disk. The shaft makes one revolution for each complete double-stroke of each piston, and as each acts during the same revolution, the six going into operation successively at intervals of 60 degrees, it follows that three pistons are constantly acting on the disk. The strain thus thrown upon the crank and shaft is practically uniform, and there being no dead point, no flywheel is necessary."

Note the horizontal governor to the left of the engine, in front of the output pulley.

From "Knight's Practical Dictionary of Mechanics: Supplement" by Edward H Knight, published by Cassell & Co in 1884, p819

Left: Six-Piston Axial Engine: 1884.

The steam admission and exhaust appears to be controlled by a rotary valve K to the right of the engine. No means for varying the cut-of can be made out.

From "Knight's Practical Dictionary of Mechanics: Supplement" by Edward H Knight, published by Cassell & Co in 1884, p819


Left: Knickerbocker Four-Piston Axial Engine: 1899

"A four-armed yoke is socketed on a centre common to the four pistons. Its spindle is a crank pin, and makes a conical circuit with the crank and shaft. The ends of the yoke are socketed to the pistons by connecting rods. The pistons take steam successively, making a continuous pressure on the circuit of the crank."

The steam admission appears to be controlled by a disc valve to the left.

From "Mechanical Movements, Devices and Appliances" by Gardner D Hiscox, published by Sampson Low, Marston & Co in 1899.

Extensive searching has so far failed to unearth any US patent covering this engine.


Left: The Pioneer Axial Engine: 1903

This four-cylinder axial engine (or rather two of them) powered the Pioneer steam lurry, which is apparently how you spelt "lorry" in 1903. There were two such motors compounded, one high-pressure motor and one low-pressure motor. They were very similar (though presumably the cylinder dimensions were different) and each drove one of the front wheels independently through a vertical shaft and bevel gearing. The rear wheels were the steering wheels, on the Ackermann system. It must have been an interesting vehicle to drive.

This is a wobble-plate rather than a swashplate engine, as the wobble -plate does not rotate- clearly it couldn't without tying the connecting rods into knots. The wobble-plate is at D, and carries gear-teeth D1 that engage with teeth E1 on the casing to stop it rotating. It also carries a smaller ring of teeth at D2, which engage with the teeth F on the output shaft F2. I quote the source: "In this 'seeking-tooth' type of gear the resulting speed of the vertical drive shaft is the difference between the number of teeth in two gear wheels; wheel D2 having 42 teeth and wheel F only 39; the speed reduction is in the ratio of 14 to 1."

Note that the only date I have is that of the book below. It does not give the name of the inventor or the country of origin.

From "The Automobile" ed Paul N Hasluck, published by Cassell & Co 1903, p101. It was based on a book by Lavergne.


Left: The Beadle Axial Engine: 1919. The rotary valves are shown at right.

This two-cylinder axial steam engine was noted as having rotary valve-gear designed by Mr C Hyde Beadle. It is described as being of the "helicrank" type, "of particular value for marine purposes, the cylinders being in axial alignment with the tail shaft."; it is not made clear if Mr Beadle was responsible for the design of the whole engine.

Note that the only date I have is that of the book below. It does not give any dates for the Beadle engine, or its country of origin.

From "Valves and Valve-Gearing" by Charles Hurst, published by Chas Griffin & Co 1903, p180.

This engine had two cylinders, one either side of the "crankshaft" and working in a horizontal plane. At the end of each piston-rod A adjustable rollers B engaging with a groove in the swash-plate C. Hurst describes this as a "helix" which clearly cannot be correct as the piston rods would then make no return stroke. Rotary valves were fitted at each end of the cylinder assembly, and had steam pressure on both sides (ie they were balanced valves) to minimise friction. The valves were driven by a shaft concentric to the main output shaft, driven by a peg in an angular slot in the swashplate. Moving the valve shaft in and out with the handle shown altered the valve phasing and so controlled the cut-off.

These axial steam engines were the forerunners of a number of Axial Internal-Combustion Engines. (Gallery now open)

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