Also known as barrel engines

Gallery opened June 2008
Updated: 7 Dec 2019

New Lamplough engine animation
More on Duke engine (contemporary)

Left: A wobble plate motor wobbling.

A wobble plate does not go round; it is mounted on the Z-shaped crankshaft by a bearing. It is articulated to the connecting rods by ball-joints, and clearly if it did go round would tie these rods in knots. As you can see here, it does not need to be a plate as such, but can be more of a spider.

One problem with this configuration is that friction between wobble-spider and crankshaft tends to cause rotation of the spider which upsets its alignment with the pistons. Here an arm is shown moving in a channel to constrain the movement of the wobbler, but there are more sophisticated methods of stabilisation, such as those used by Charles Redrup in The Bristol axial engine, which is a good example of the type.

Another fine animation by Bill Todd

Left: A swash plate motor swashing.

A swashplate is rigidly fixed to the crankshaft, and goes round with it as a unit. Therefore the connecting rods are not fixed to the plate in any way, but push on it with rollers or slipper pads that can glide over the surface of the plate as it turns. Note that two rollers are needed, one each side of the swashplate, so it can both pull and push on the pistons.

The only examples of pure swashplate engines on this page are The Michell engine and The Alfaro Engine.

Another fine animation by Bill Todd

Left: The Smallbone axial engine patent: US 821,546 of 22nd May 1906.

Four cylinder wobble-plate gas engine; static barrel type. Water cooled.

This design by Harry Eales Smallbone is the first example of an axial IC engine found so far. It was intended to run on town gas, not gasoline/petrol. It is not currently known if it was ever built or if it was successful.

Smallbone took out Canadian patent CA 82570 rather earlier in July 1903. The patent is not viewable on the Canadian Patents Database.

Left: The Lamplough Axial Engine: 1910

From Modern Engines by Rankin Kennedy, Vol V (1912 edition)

Left: The Lamplough Axial Engine: 1910

These are the only known drawings of the engine.

From Modern Engines by Rankin Kennedy, Vol V (1912 edition)

Left: The Lamplough Axial Engine animated

A superb animation by Bill Todd.

Left: The Lamplough Axial Engine animated

In this animation the cylinders are stationary, and the central mounting shaft is shown rotating, for clarity of viewing.

The eccentric (coloured bronze) oscillates the cylindrical valves that cover and uncover the ports in the pumping cylinders.

A superb animation by Bill Todd. Is it not wonderful?

Left: The Lamplough Axial Engine: 1910

Despite the dramatic name of Positive Explosion Turbine, this is obviously the Lamplough engine as described above. It looks as though the illustration was derived from a photograph; this is currently the only evidence that the engine was built.

This picture is from the journal Flight for 27 August 1910.

Left: The Macomber Axial Engine: 1911.

In 1911 the Macomber Rotary Engine Company of Los Angeles, USA placed one of the first axial internal-combustion engines on the market. It had five or seven cylinders and a variable compression ratio, altered by changing the wobble-plate angle and hence the length of piston stroke.

It was a rotary engine in the sense that the whole engine rotated apart from the casings at each end.

According to the manufacturer's literature, it was 'Guaranteed not to overheat', which given the small amount of finning on the cylinders, and the fact that each cylinder would be moving in the slipstream of its neighbour, seems to me a little optimistic.

Left: The Macomber Axial Engine: (7-cylinder version) publicity material.

The text on the right-hand page is none too clear, so I have reproduced it below. Rather surprisingly, it does not give the engine capacity.

The cylinders were individual iron castings, with inclined valves in the cylinder heads, working in a plane through the axis of the central shaft. The inlet valve was on the inside, and drew the fuel-air mixture through the hollow shaft, from a carburetor mounted on the end of the engine. The exhaust valve was on the outside, and the exhaust goes straight out into the air through the D-shaped apertures visible in the photograph, which suggests that the engine when running would have been surrounded by a ring of exhaust flame. Because of the rotating barrel it was hard to add a silencing system.

Each pair of valves operated from a single rocker pivoted between them, which much have placed some remarkable restrictions on valve timing. One end of each rocker engaged with a groove in a four-lobe cam mounted on the central shaft. This cam was rotated by gearing.

Ignition was by a Bosch magneto operated by the cam gears. The spark was led through six inch cables to a stationary electrode on the top of the front bearing case, from which sparks jumped to the tops of the spark plugs as they passed within one-sixteenth of an inch of it.

Left: Patent drawing of the Macomber Axial Engine: 1912.

This shows a big lever 37 that alters the piston stroke and so the compression ratio, while engine is running. The patent makes it clear that this was a way controlling the power output; this sounds like a pretty poor idea as it would waste a lot of fuel running inefficiently at low compression, compared with simple throttling which reduces the amount of fuel/air drawn in.

The fuel/air reached the cylinders from the right (carburettor not shown) via the hollow central shaft and the annular distributor 57. The breathing arrangements look very inefficient.

The 4-lobed cam 46 operating the valve rockers 44 can be seen; it was driven by gearing so that for each rotation of the engine it went round 7/8 of a rotation; acording to the patent this gave the correct valve timing.

From US patent 1,042,018 granted 1912

Left: Macomber Axial Engine (7-cylinder) for the Macomber-Eagle car: 1915

The Macomber engine was applied to cars; the Eagle Macomber Company began in Los Angeles consructing a cycle car with an axial engine in 1914. The firm moved to Chicago, then in late 1915 to Sandusky, Ohio. There they produced a full-sized car with a corresponding increase in engine size.

This is the seven-cylinder engine fitted to the larger car. There is an updraft carburettor at the right, the fuel/air mixture reaching the cylinders through the hollow shaft. There is a Bosch magneto to the left.

Left: The Eagle-Macomber car: 1915

The Eagle-Macomber company had difficulty in raising finance, and there were intractable problems with the engine design. They tried building a yet larger engine, but the company disappeared in 1918.

There was also a Macomber-powered racing car, but it was not a success.

Left: Macomber 5-cylinder engine in the Eagle-Macomber cycle-car: 1912

This is the smaller 5-cylinder 12 hp engine; the cycle-car was small and so is the engine. It appears to have stub exhausts so was presumably horribly noisy. The 7-cylinder version above has exhaust pipes leading to the wobble-plate end of the engine, where they were presumably gathered into some sort of cylindrical header.

Source: The Gas Engine for January 1912. (This seems to mean 'Gasoline Engine' rather than propane etc)

Left: Macomber 5-cylinder engine in the Eagle-Macomber cycle-car: 1912

Here is Walter Macomber holding the smaller 5-cylinder 12 hp engine. It is a small engine but still weighs 115 pounds, so Mr Macomber is clearly no weakling.

Regrettably towards the end the text becomes very doubtful:

'One of the most important features of the Macomber engine is the entire absence of reciprocating parts.'

So what are the pistons doing if not reciprocating???

The author of this article, Charlton Lawrence Edholm, (1879-1945) could not expect to escape The Museum staff. He was a writer and illustrator for magazines. There are some biographical details here. In fact he is already on this website as the author of an article on a two-wheeled car.

Source: The Gas Engine for January 1912.

Left: The Trebert Axial Engine: 1912

The Trebert engine was a rotary; the cylinders and crank case revolved, while the central shaft remaine stationary. This is the only axial engine in this gallery that does not use either a wobble-plate or a swashplate. Instead each axial cylinder drove a small crankshaft, with bevel gears at the inner end of each shaft engaging with a large gear on the central output shaft; power output was taken from the crankcase end. The propeller speed was thus reduced to one-half of crankshaft speed.

The engine was covered by US patent 1215434, 1917.

From: The Airplane Engine Encyclopedia by Glen D Engle, pub 1921, Otterbein Press. Original source

Left: The Trebert Axial Engine animated

In this animation the engine has been held stationary and the central shaft allowed to revolve, so the action of the multiple crankshafts is clear. In reality the engine went round but the shaft was fixed.

Another brilliant animation by Bill Todd

Left: The Trebert Axial Engine patent

The carburettor L is at extreme left and the magneto M at extreme right; W is the ignition cable, running to a fixed terminal at left, from which the spark jumped to the top of each plug as it went past.

From US patent 1,215,434 granted 1917

Left: The Trebert Axial Engine animated

Here the engine is rotating, as it did in real life. Note carburettor & stub exhaust at extreme left.

The rotary valve is just to the right of this.

Left: Rumours of a Gnome Axial Engine: 1911

This cutting, from 'Air Eddies' the gossip column of Flight, describes what is clearly an axial engine. The design is described as a 'stationary motor' which I assume means that unlike the Gnome rotary engines, the cylinders stayed still while the crankshaft revolved.

From Flight 23 Dec 1911

Left: The Statax Axial Engine.

The joints between the connecting rods and the plate show that it is a wobble-plate engine rather than a swash-plate type.

The carburettor and magneto can be seen at the left of the drawing. Unlike the Macomber, in the Statax the carburettor was at the 'wrong end' so the fuel-air mixture had to be drawn thrugh a hollow shaft that ran most of the length of the engine.

Image kindly provided by Richard T Jones.
Original source: The Airplane Engine Encyclopedia by Glen D Angle, published in 1921 by Otterbein Press.

Left: Salmson Axial Engine: 1911

The Salmson engine was shown at the Paris air salon, which opened in the Grand Palais on 15th December 1911. Despite the visible fins, it was water-cooled.

From Flight 23 Dec 1911

Nominal HP

60

Bore (mm)

75

Stroke (mm)

260

RPM

1300

Weight (kg)

100

Price (Francs)

10,000

Left: Salmson Axial Engine: 1913

This axial engine was shown at the Paris air show on 1913; it is obviously different from the 1911 version above.

Salmson had started making aero-engines in 1908, but became famous for making nine-cylinder radials, like the Salmson 9. The recently updated Wikipedia page on Salmson now describes a series of seven axial engines, running from 1908 (Model A) to 1912. (Model K) Model A was only bench-tested, and it is not clear if any of the others were flown. All were water-cooled.

From Popular Mechanics Jan 1913

Left: Riley Axial Engine patent, 1914

This drawing comes from British patent 18,204 granted on the First of August, 1914. This patent covered both 2-stroke and 4-stroke designs. Both engines had eight cylinders, unlike other aero engines both radial and rotary, that almost always had an odd number of cylinders to get a good firing order.

Above: Cutaway drawing of the Riley 4-stroke axial engine, 1914

This drawing shows the air-cooled, 4-stroke version of the Riley axial engine. This time all eight cylinders were power cylinders, and there appear to have been eight separate camshafts, driven by helical gears from the central shaft. The valves were operated by pushrods and rocking levers.

Left: Percy Riley: date unknown

It is believed that none of the axial engines planned by Percy Riley ever left the drawing board, allegedly due to lack of enthusiasm on the part of the Ministry of Munitions.

An exhibition of David Styles' drawings, some eighty-odd in number, is planned at the California Automotive Museum in Sacramento for late summer 2012. Examples of a Brooklands Riley Nine and an ERA are planned for exhibit with the drawings.

Left: The Australian Michell swashplate engine: 1927. Eight-cylinder static barrel swashplate-plate type

The swashplate (a seriously thick piece of metal) and part of one of the cylinders can be seen through the open hatch on top.

Anthony Michell (pronounced, but not spelt, Mitchell) is famous for inventing the Michell thrust-bearing in 1905; the unique feature of the bearing is the ring of sector-shaped pads making contact with a fixed shaft collar through a pivot or ball-joint. As the shaft rotates oil is pumped between collar and pads. The load is taken by the wedge-shaped oil film, without metal-to-metal contact, and this allows bearing pressures more than ten times greater than the previous sytem of multiple massive plane-faced collars contacting with fixed shoes. The Michell bearing made possible increases in ship size.

Learn more about it at: Powerhouse Museum.

Left: Michell slipper pad

The piston C has a socket that which mates with the spherical back of the slipper pad B, which is rigidly fixed to the actual slipper pad A. The line of thrust passing through C and B is set slightly behind the centre of area of A, (much exaggerated in diagram) which causes the pad to tilt very slightly (about one minute of arc, according to Newton & Steeds) and forces a wedge-shaped film of oil W between the pad A and swashplate S.

From The Motor Vehicle by Newton & Steeds, pub Iliffe, date unknown but post 1921, p104.

Left: A 5-cylinder 5-piston Michell engine meant for road vehicles: 1921

This is believed to be an early engine, possibly the one Michell installed in his own Buick. (see below)

To the left is the gearbox. There is an odd casing projecting up from the engine, with what appears to be a small control lever at the top; the purpose of this is currently unknown.

Left: A 5-cylinder 5-piston Michell engine meant for road vehicles: 1921

So far little has been discovered about how this engine relates to the eight-cylinder design below in terms of priority.

Here the gearbox is on the right.

Left: Longitudinal section of an 8-cylinder 4-piston Michell engine meant for road vehicles: 1927

The hemispherical thrust-block and the sliding surface consisted of one piece of steel with a white-metal lining. Despite the ingenious thrust-block mechanism, the swashplate still required copious lubrication. A gear-type scavenge pump at the bottom of the sump pumped the oil up into a tank, from which it flowed by gravity to a pressure oil pump that delivered it at 5 psi to several nozzles that sprayed it against the swashplate and the camshaft drive.

Source: NACA

Left: Section through piston and valves of 8-cylinder 4-piston Michell engine for road vehicles: 1927

Michell established The Crankless Engine Company in 1920 to develop designs, manufacture prototypes and to try to sell licences from overseas manufacturers for large-scale production. From a Fitzroy (Australia) workshop he produced pumps, compressors, automobile engines and aero and gas engines. Serial numbers were assigned to fifty-four machines and of these at least forty-five were built, making the Michell one of the more successful axial engines. The company ceased active operations in Australia in 1928 but design and manufacture carried on in England and the USA. The principal overseas manufacturer, George Waller & Sons of Stroud, Hampshire, England, had by 1971 built 116 engines, mainly gas fuelled, for driving compressors which ranged in capacity up to 500,000 cubic feet (14,160 m³) per hour.

It was this design that was taken to the USA in 1921 by Casey, accompanied by a mechanic went to the US. Much bench testing of the engine was completed by General Motors at Dayton, Ohio and by Ford at Detroit. Casey reported the engine was found to be about 10% more efficient than a conventional engine, but the cost of the extensive retooling required was not justified by the improvement. The large US auto firms declined to adopt it. Another crankless engine was fitted to Michell's own Buick car and used regularly including a long trip from Melbourne to Sydney and back in 1924.

Image source: NACA

Left: Longitudinal section in front of swashplate, and end view, of 8-cylinder 4-piston Michell engine for road vehicles: 1927

The left drawing shows the two vertical camshafts at each end of the engine, which also drove the oil and water pumps, connected by a large horizontal gear wheel at bottom centre. Quite how these were driven from the main shaft is not currently clear.

Source: NACA

Left: Longitudinal section of a 300HP 8-cylinder 4-piston Michell engine for driving gas compressors: 1927

This illustration comes from a 1927 sales brochure, and in this case it shows two horizontal overhead camshafts at each end. Michell engines of this type are believed to have been used by the Australian Gas Light Company for pipeline pressure boosting. According to one source they were built by the National Gas Engine Company of England, which presumably implies they were fuelled by the gas they were pumping. It does however raise the question of why these unconventional engines were used in an application where their main advantage- low frontal area for aeroplane use- was wholly irrelevant.

Left: Michell engine in the Powerhouse Museum, Sydney, Australia: 1927

This engine (No 37) gave 70 HP at 750 rpm. Length 5', Width 30', Height 33'. Weight 10-12 cwt.

By modern standards, not a lot of power from half a ton of engine.

Left: Michell engine in the Powerhouse Museum, Sydney, Australia engine: 1927

The same engine from the other side.

Left: Michell engine in the Powerhouse Museum, Sydney, Australia engine: 1927

A plate on the side of the engine; the function of the lever is unknown. This confirms that some Michell engines were built by the National Gas Engine Company, Ashton-under-Lyme, England.

Left: A single-ended Michell engine: 192?

This single-ended (ie not horizontally opposed) five-cylinder Michell engine is probably an early version.

It demonstrates a problem with swashplates. On the power stroke, the piston pushes the swashplate. On exhaust & compression strokes, the swashplate pushes the piston. But on the induction stroke, the swashplate has to pull the piston, and so there have to be slipper pads on both sides of the plate. and the piston has to be constructed so it hooks round the edge to hold the pad on the rear side. This no doubt why so many of these engines are horizontally opposed; doubling the number of cylinders in this way requires no more slipper pads.

The Dynacam and Michell solve the problem by having the swashplate in the center of the engine, with opposed pistons that are joined up round the edge of the swashplate, so to speak.

From The Motor Vehicle by Newton & Steeds, pub Iliffe, date unknown but post 1921, p105.

Left: Single-ended Michell engine piston guides: 192?

Note the pegs attached to the slipper pads to prevent them rotating around the cylinder axis. These can be seen in their arc-shaped cavities in the main drawing above.

Left: The Almen aero engine: 1921

Eighteen horizontally-opposed cylinders in two sets of nine with a central wobble-plate; static barrel type. Water cooled. Rotary valve disc at each end of the engine.

The A-4 was the fourth experimental barrel engine built by John O Almen of Seattle, Washington State, for testing at McCook Field, Ohio. The engine project began in 1921 and by the mid-1920s, the A-4 had passed its acceptance tests. Despite this success the Almen engine never went into production, because of a growing emphasis by the US Army Air Corps on air-cooled radial engines with large frontal area. European air forces generally preferred water cooled engines.

Like other barrel engines, the Almen had a much smaller frontal area than other water-cooled engines of similar horsepower, promising reduced air resistance when installed in an aeroplane. It was rated at 425 hp but weighed only 749 pounds (a power/weight ratio of 1.76 lb/hp), a significant achievement for the time.

This example is in The National Museum of the USAF at Dayton, Ohio.

Left: The Almen aero engine

This shows the other side of the engine. The propellor mounting flanges are on the left, and the dual distributors to the right. Dual ignition was fitted, calling for 36 spark plugs.

Photograph by kind permission of Phil Callihan. See his remarkable website at http://airpower.callihan.cc/default.htm

Left: The internals of the Almen engine

Below the crankshaft is a sectioned cylinder containing one of the double-ended pistons. The cooling water pump is at bottom right.

The vital statistics of the Almen engine

Left: The Almen engine patent: US1255973 of Feb 12, 1918

The patent described an eleven-cylinder engine with a single wobble-plate at one end.

Fuel/air was fed from the carburetor 30 through the hollow shaft at the left, and entered the cylinder through ports in the rotary valve 31. The wobble plate was fitted with a gear ring 45 that engaged with a fixed gear ring 46 on the casing 11 to prevent the wobble plate from twisting round. Another gear ring 47 drove gear ring 48 on the end of the valve extension piece 49, so that the rotary valve rotated at one tenth of the speed of the main shaft but in the opposite direction. The lower cylinder is shown with a valve port 33 lined up to release the exhaust gases.
The patent was assigned to the Almen-Crosby Motors Company.

Left: The wobbling of the Almen engine animated by Bill Todd

Bill says:

'The two outer gears have the same number of teeth and 'stabilize' (transmit the crankshaft torque to the casing) the inner pair have a differential number of teeth and rotate the inlet/exhaust valve.'

Left: The Ali Engine: 1922

Four-cylinder static barrel wobble-plate type.

The Ali is a two-stroke water-cooled petrol engine with four working cylinders above the wobble-plate and four scavenging pump cylinders below it, intended for use as an outboard engine for boating. The Ali has magneto ignition.

The leftmost drawing is a section through the cylinders. That to the right is a section between the cylinders.

The magneto can be seen at the right of the rightmost drawing, driven from the central shaft by spur gearing and a layshaft. An HT cable can be seen running from here to the top of the engine, where the distributor is mounted at the extreme top of the central shaft, between the spark plugs.

From NACA technical memorandum No 462, translation of Motorwagen Nov 20, 1927
Original source: Zeitschrift Des Vereines Deutscher Ingenieure (The magazine of the Association of German Engineers) p1405, 1925

Left: The Ali Engine in plan view : 1922

The U-shaped thing to the right is the ignition magneto. The rest of the grey area is believed to be the fuel tank(s).

From NACA technical memorandum No 462, translation of Motorwagen Nov 20, 1927
Original source: Zeitschrift Des Vereines Deutscher Ingenieure (The magazine of the Association of German Engineers) p1405, 1925

Left: The Ali Engine: 1922

The engine partly disassembled, showing the working pistons with sculpted tops; the nearest one has been removed to reveal the wobble plate. The scavenge pistons can be seen below the wobble plate. The carburettor is at lower right, at lower left is the tiller arm, with the kickstart mechanism below the arm pivot.

The upper part of the central shaft drives the distributor.

From the Ali instruction book; kindly provided by Lars Eimar.

Left: The Rolls-Royce engine: 1923

In 1921 Rolls-Royce had expressed an interest in an axial engine and the following year an Air Ministry contract allowed the design and build of one experimental engine. This was a seven-cylinder arrangement with a cast-iron cylinder block and cast-iron detachable cylinder heads. The bore was 3 inches, but the capacity is currently unknown. Push-rod operated overhead valves were used and a car-type carburettor fitted. Some development work was done, but by 1925 interest had waned and the project passed to Napier's. Nothing appears to be known of its development, if any, after this point.

The engine is mentioned in a well-known book 'I Kept No Diary' by F.R. Banks; he says it was probably intended for motorcar use, since it was of only 3 litres cylinder capacity, which is small for an aero engine. This capacity would make the stroke 3.7' which seems a reasonable figure for the era.

Photo: Rolls-Royce Ltd

Left: The Wishon engine patent: 1923

The Wishon engine was a wobble-plate design patented by Ralph Wishon in 1923. (US patent no 1,476,275) It is unusual as it sought to combine the axial engine principle, using opposed-pistons, with rotary valves. There were nine cylinders, and hence 18 pistons. The rotary valves valves were double-walled sleeves in the central section of the engine, surrounding the combustion spaces, and were driven by a complex train of epicyclic gearing.

Induction is through the left section of the hollow centre shaft.

Drawing from US patent 1,476,275

Left: The Wishon engine rotary-valve gear train

This drawing has a certain beauty to it. Gear 21 on the central shaft drives the wheels 20, which carry pinions 18 that mesh with the inner teeth 16 of wheel 14. The outer teeth 15 on this wheel drive the rotary valves 13. While the teeth on these valves are close together, they do not mesh.

On the downside, all of this complex coggery was mounted in the very centre of the engine, making it somewhat less than accessible.

But was this engine ever built? Certainly the text of the patent appears to show that Mr Wishon knew what he was talking about, but Googling 'Wishon engine' yields nothing. The extra difficulties of rotary valves would probably have prevented any prototype from being successful.

Drawing from US patent 1,476,275

Left: The Laage axial cam aero engine: 1923

The propellor hub is at the left. The engine had 8 double-ended pistons working in 16 air-cooled cylinders, pushing on the cam with rollers. The cam (with apertures in it to reduce weight) can be seen in the top centre of the engine, with a drive roller in place. The Laage engine worked on a six stroke cycle, the details of which are currently obscure; the lower drawing shows that the curve of the cam was not a simple sinusoid, and that no doubt has something to do with it.

The engine was designed in France by E Laage. Although cam drive patents go back farther than the 1920s, the Laage engine was probably the first cam-drive axial engine. According to the source, 'the engine has ... disappeared' which does not exactly sound like a commercial triumph.

From NACA technical memorandum No 462, translation of Motorwagen Nov 20, 1927
Original source: Zeitschrift Des Vereines Deutscher Ingenieure (The magazine of the Association of German Engineers) p1405, 1925

Left: The Redrup cam engine

At some point Redrup also designed a cam-based axial engine. This demonstration model is in the Manchester Museum of Science and Industry. Regrettably it is in a glass case so you can't turn the handle.

Author's photograph

Left: The Bristol Axial Engine on a testbed.

I have not been able to determine which version of the engine this is.

From Some Unusual Engines by LJK Setright, pub Mechanical Engineering Publications Ltd, 1975.

Left: The Bristol Axial Engine animated

Showing the crank-driven vertical stabiliser arm designed to give the correct kinematics.

Animation by Bill Todd

Left: The Russian Sparost Cam Engine: 193?

This axial engine was developed in the 1930's. It had six enormous cylinders, driving a cam roller that fitted in between two sinusoidal ridges. In the photograph the cam roller can be seen at top centre,with its piston rod to the left of it. The Soviet Sparost was rated at 600 HP (how honestly is anyone's guess) and it was expected to reach 1200 HP by the late 1930's. As usual, the goal was a powerful engine with low frontal area.

The cutaway example shown here is in
The Soviet Air Force Museum at Monino.

Image from The Development of Aero Piston engines by Bill Gunston

Left: The Russian Sparost Cam Engine

Another view.

The cutaway example shown here is in
The Soviet Air Force Museum at Monino.

Image from The Soviet Air Force Museum

Left: The Hulsebos-Hesselman axial oil engine

Because it is a five-cylinder engine, only one cylinder at the top is visible in section. I indicates the injector and S the spark-plug.

The wobble plate was stabilised with an attached bevel gear that meshed with another fixed to the main body of the engine, preventing the plate from rotating around the crankshaft. The bevel gear teeth are coloured blue in the drawing.

The valves were of the usual poppet type with horizontal stems, operated by rockers and pushrods, from a cam ring running at ¼ crankshaft speed. A valve can be seen just below the injector.

There is a Wikipedia page for the engine, but little information is given.

Pic from The Modern Diesel Engine, 5th edition, Iliffe & Sons Ltd

Left: The Sterling Axial Diesel Engine

It appears that the air entrance is on the left, and the output shaft on the right, as in the diagram below.

This engine is unknown to Google, though you do get lots of hits for Stirling hot-air engines.

Source: Diesel Engines by von Bongart. Pub Van Nostrand, 1938

Left: The Sterling Axial Diesel Engine

This swashplate engine was intended to run as a two-stroke Diesel. The scavenge air to blow the exhaust gases from the opposed power cylinders in the centre was compressed by the pistons on the left.

Notice the use of a rotary valve at the air intake.

Left: The Alfaro swashplate engine: 1938

This is the only engine so far uncovered that has horizontally-opposed cylinders and a swash-plate at each end. This configuration doubles the number of rollers or bearing pads required compared with engines that have a single central swash-plate. Note that rollers rather than slipper-pads are used to contact the swashplates.

It was designed by the Spanish pilot Heraclio Alfaro. (who was knighted at the age of 18 by King Alfonso III for designing, building, and flying the first aeroplane in Spain) The engine was on test at MIT in 1934, where Alfaro was teaching. It had been built in Springfield, Mass, by the Indian Motorcycle Company.

According to Aerofiles, the engine had 4 cylinders and developed 155 HP from 167 cu in. (2737 cc)

Image from Charles Fayette Taylor

Left: The Alfaro swashplate engine: 1938

The trumpet air-intake at the right suggests that induction took place down the central shaft. The black thing pointing up at an angle is the distributor, while the other auxiliaries are not identified. Note the belt drive at top right.

The photo is from the book 'A 1911 Spanish Pilot and MIT AeroEngineer and his 1938 AeroEngine – Upgraded for today by Stephen DuPont' ISBN 0-9777134-0-7. Stephen Dupont was the son of the president of the Indian Motorcycle Company, and worked as a student with Alfaro at MIT on this engine. Stephen is now 93 but still able to recount stories and discuss engines – he only recently quit flying his Pitts Specials at the age of 88 due to failing eyesight.

Image kindly provided by Darren Powell.

Left: The Dyna-Cam Engine

This engine has six double-ended pistons working in six cylinders, making it equivalent to a twelve-piston engine. All 12 combustion chambers are fired in a single revolution of the drive shaft. The sinusoidal cam can be seen, together with four of the six pistons and two empty cylinders.

The history of this engine is proving hard to track down, not least because access to the old dynacam.com website in internet archives is blocked; clearly this is part of The General Conspiracy.

However, the story so far: the engine appears to originate from a design by the Blazer brothers, who worked for Studebaker in 1916. They sold the rights to Karl Herrmann, Studebaker's head of engineering. He developed it over many years, taking out a patent in 1941; see US patent 2237989.

Image from The Knife and Fork Man (Biography of Charles Redrup) by Bill Fairney

Left: The Dyna-Cam Engine internals

Note that the thickness of the cam (and it is everywhere very substantial) varies, appearing thinner where it is at a more oblique angle; this is because it runs between two rollers, in each piston, that are at a fixed spacing.

The engne received FAA Type Certificate E-293 on Dec 31, 1981.

By 1961 Herrmann was eighty years old, and sold everything to Dennis Palmer, one of his employees. At this point the Dyna-Cam name was attached to it. Eventually the engine was flown for seven hours in a Piper Arrow in 1987, but Dyna-Cam fell out with Piper in 1988, and things appear to have rested there until recently.

The assets of the Dyna-Cam Engine Corp were acquired by the Axial Vector Engine Corporation in 2006. The engine now has a 92-year history, which I should think must be unique.

Image from Piston Aero Engines

Left: The Dyna-Cam Engine on test

Or is it? The mounting brackets look a bit flimsy, and it doesn't appear to be in a test cell.

Note the exhaust connections running upwards from each end of the engine.

Image from

Left: The Wooler Axial Engine: 1947.

This engine is similar to the Bristol axial engine, but has two wobble-plates, the angled discs that can be seen at each end. They were driven by 12 opposed pistons working in six cylinders. Some confusion about this engine has arisen because LJK Setright, in his book Some Unusual Engines, in a moment of uncharacteristic imprecision describes it as a swashplate engine; however it is a wobble-plate engine, not a swashplate engine.

Note SU carburettor at the extreme right. The tall dark thing top right is probably the distributor.

Engine in The Science Museum, London

Left: The Wooler Axial Engine: 1947.

A view of the wobble-plate at the the carburettor end.

The engine is on display in the Aeroplane Gallery of The Science Museum, London. Author's photograph.

Left: The Searle Rotocom Engine: 1981

The central rotary valve is rotated at one and one-half engine speed by two belts (left of drawing) that also drive the ignition contact-breaker H.

Note the ignition electrode K that contacts each spark plug at the appropriate time. Remarkably, the spark plugs are mounted in the top of the piston rather than in the cylinder head; they don't look too accessible.

Popular Science October 1981

Left: The Searle Rotocom Engine

The cycle of operations.

Popular Science October 1981

Left: The propulsion sytem of a converted Mark 37 torpedo

The output power is delivered to the propellers by counter-rotating shafts; one driven by the cam and pistons and the other from the reacting housing of the engine which is free to rotate. These two shafts drive counter-rotating propellers. The engine exhaust gases, and perhaps the engine cooling water, exit via the hollow inner shaft. The rotating engine housing also drives the fuel pump and seawater pump by gearing, and apparently also powers the control-surface actuators.

From Mark 37C Torpedo System Technical Description, NVR 73-50, 1973, a Northrop document describing updating the Mk 37 torpedo to the C version.

Left: The back end of a Russian torpedo

The wobbleplate engine can be seen to the left; to the left of that is a thing like a cotton-reel, presumably the heater/combustion chamber.

Image from a special issue of 'National Defense' (a Russian arms & military technologies magazine) for EURONAVAL 2008, the leading international trade fair for naval defense that took place in Paris-Le-Bourget exhibition center from 27 to 31 October 2008. This was kindly brought to my attention by Pr. Théodose Lamartre.

Left: Duke axial engine: 2011

The Duke Engine is said to be already in an advanced state of development; it is claimed that multicylinder engines are operational and have been tested in Australasia and Europe, and are soon to be tested at Mahle Powertrain in the USA.

Update Dec 2019: The Duke website does not appear to have been updated since 2013...