Axial Internal-Combustion Engines

AXIAL ENGINE TECHNOLOGY

Wobble-plates and swash-plates are not the same thing:

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

THE SMALLBONE AXIAL ENGINE: 1906

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.

THE LAMPLOUGH AXIAL ENGINE: 1910

This engine is rather obscure. The image below appears on the Net as "Lamplough's rotary engine" without any mention of the word "axial". It is only a rotary engine in that the engine and propellor rotate while the crankshaft is fixed; it has no relation to Wankel-type rotary engines. The trail is confused by a conventional radial 6-cylinder rotary aero engine that was built and exhibited by Lamplough; that suggests that this was also intended to be an aero engine.

Left: The Lamplough Axial Engine: 1910 From Modern Engines by Rankin Kennedy, Vol V (1912 edition)

This image is clearly a drawing. I have seen a very similiar image entitled "Positive explosion turbine" (!) but that too looked very much like a pen-and-wash drawing. Currently, it is not clear if the engine was actually built or not.

Lamplough & Son Ltd were based at the Albany Works, at Willesden Junction in North-West London; the company was founded in 1899.

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)

These sections show a four-cylinder two-stroke engine with eight opposed pistons, but it seems that two of the four cylinders (those without fins) are pumping cylinders that compress the charge for the power cylinders. This does not sound as if it would give a good power/weight ratio. A gear-driven magneto is fitted at the left end of the engine; since this does not appear to rotate with the main body of the engine, it is not clear how the electricity was routed to the spark plugs whizzing round.

Having only the drawing above to go on, I consulted the redoubtable Bill Todd, and he said:

"It's not a wobbler, it's a swashplate/cam engine. At each end of the cylinders, two pairs of con-rods push on a rocker pivoting about the axis F. Each rocker has tapered rollers (C) running in a flattened V groove cam/swashplate (D) at its end of a fixed hollow shaft. The whole cylinder assembly rotates, breathing through the hollow shaft."

Note the eccentric visible in the top left drawing. I though this might be someting to do with ensuring accurate swashing, (see the Redrup engines for more on this) but Bill says:

"The eccentric controls the pumping cylinders input valve timing (but may also control scavenge timing - hard to see from the drawing)"

Left: The Lamplough Axial Engine animated A superb animation by Bill Todd.

Bill has decoded the valve operation as follows:

The fuel/air mix enters throught the central shaft from the left. (magneto end) where it escapes into the central distribution chamber.

As the power pistons close together on a compression stroke, the pumping pistons are retracting, drawing the mix into the pump cylinder via the ports in the lower right input chamber. The pumping cylinder (at the bottom) is divided in two parts connected only by ports in the pump-cylinder sleeve

On the power stroke, the pump compresses the mix, via left side ports, into the lower left transfer chamber and up to the cylinders transfer ring, ready for the left piston to open the transfer ports.

At the bottom of the power stroke the main transfer ports (upper left) and exhaust ports open and allow the fresh mix to scavenge the cylinder through the exhaust holes (upper right).

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?

THE MACOMBER AXIAL ENGINE: 1911

The first IC axial engine the indefatigable staff of the Museum have tracked down that was definitely constructed and put into use are the five and seven-cylinder rotating-barrel wobble-plate engines designed by Walter G Macomber. The ball joints between the connecting rods and the plate make it clear that it is of the wobble-plate persuasion.

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.

• MODEL "A"
• HORSE POWER-- 50-60 Brake
• SPEED-- 800 to 1400 Revolutions per minute
• CYLINDERS-- Seven
• BORE-- 4 1-4 inch.
• STROKE-- Variable, 4 1-4 inch Maximum
• AIR COOLED-- Guaranteed not to overheat.
• VALVES-- Very large. Set in head, operated from single cam sleeve on main shaft. Four cycle movement.
• IGNITION-- High tension Bosch Magneto. No wiring.
• CARBURETOR-- Special. Injection system to order only.
• OILING SYSTEM-- Absolutely positive. Self contained, automatic without a moving part.
• BEARINGS-- D. W. F. and New Departure Ball Bearings throughout.
• GREATEST EXTERNAL DIAMETER-- 19 inches.
• LENGTH OF SHAFT-- 34 inches. Six inches allowed for attachment of propeller.
• WEIGHT-- 250 lbs. complete with above equipment.
• PRICE-- $2000.00 F. O. B. Los Angeles.
• TERMS-- 25% cash with order; Balance C. O. D., or sight draft with bill of lading.

This list raises one or two questions. "Positive lubrication" implies pumped pressure lubrication, and it is not easy to see how that could be done without a pump having some moving parts. It is also difficult to see how fuel injection would have worked, if this means an injector on the cylinder head or in the inlet port.

How many engines were built and sold is currently unknown. It is recorded that it made at least one successful flight in May 1911, in a plane piloted by Charles F Walsh.

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.

THE TREBERT AXIAL ENGINE: 1912

This remarkable rotary axial aeroplane engine was produced by Henry L.F. Trebert, who had an engine works in Rochester, NY.

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

The air-cooled engine had six axial cast-iron cylinders and a central rotary valve, which communicated with the small finned cylinders at the end of the main cylinders, from which the spark plugs protrude. The stationary valve had a one inlet and one outlet port on its periphery, connecting to the radial cylinders as they passed. Since the ports have to open every two revs of the crank the cylinders have to revolve at half engine speed.
Cylinder bore was 3.75in, stroke 4.25in, and the total displacement 4521cc (282 in3) It was rated at 60 HP. It used a Panhard carburetor and Mea magnetos. The weight (fully equipped) was 230lb, giving 3.83 lb/HP. Overall length was 22in, and outside diameter 15.5in.

The Trebert company also produced a barrel-type marine engine.

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.

THE GNOME AXIAL ENGINE: 1911

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

THE STATAX AXIAL ENGINE: 1913

The first IC axial engine in Europe (sometimes erroneously stated to be the first ever) was a on-off prototype built by Statax-Motor of Zurich, Switzerland in 1913; it was designed by Dr. F.J.M. Hansen who apparently had links with the German air force in WW1. The engine was confiscated after the war by the British authorities and ended up in the Science Museum in London, though it is not, I believe, currently on display.

In 1914 Statax moved to London and planned a series of rotary engines, but apparently only a 5 cylinder version giving 40 HP was ever made. It was put into a Caudron G.II aeroplane to compete in the British 1914 Aerial Derby but was withdrawn. Dr Hansen produced an all-aluminum version of the engine in 1922, but it is not clear if it was produced in any quantity. Much improved versions were introduced by Statax's German division in 1929, giving 42 HP in a sleeve valve version called the 29B.

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.

THE SALMSON AXIAL ENGINE: 1913

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

The propellor shaft is at the right, and at the left end of the engine there appears to be some sort of cooling fan for a radiator. Just to the right of the fan is a series of levers of uncertain function- they look to be too far away from the cylinders to be valves. Below this is an auxiliary that is probably a dynamo, driven from the periphery of the fan.

Flight gave the following specs:

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

The casing at right with the offset shaft emerging presumably contained reduction gearing so the engine could turn faster than the propellor. This seems rather advanced for the time.

The Salmson company survived until 1951.

THE RILEY ENGINES: 1914

THE MICHELL AXIAL SWASHPLATE ENGINE: 1920

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.

Michell used his bearing and his knowledge of lubrication to design several swashplate engines. Between the piston and the swashplate is a hemispherical thrust block with a raised and rounded leading edge which helps the oil film get between the thrust block and the swashplate. Michell took out US patent No 1,409,057 for his engine in 1922. This has been mis-referenced as 1,404,057 in other patents referring to it, and as a result it took some tracking down.

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.

The stalk-type piston P is cast integral with the cylindrical yoke which slides in segmental guides concentric with the cylinder bore, the swashplate rim running through the annular gap between the inner and outer guides, as shown in the small drawing below. The swashplate S and the clutch member C (the presence of which seems to indicate that this engine was intended for road use) are attached to a flange on the main shaft. This shaft turns in two self-aligning ball-bearings; there is also a thrust bearing T to take the force of the power strokes on the swashplate. The valves are of the conventional overhead poppet type, actuated by rockers and ball-ended push-rods driven by the face cam F, which is driven at one quarter engine speed through idler pinion and an internal gear ring. The cylinder head at left contains concentric induction and exhaust manifolds at I and E. The auxiliaries were driven by means of spiral bevel gear, with a shaft passing radially between two of the cylinders.

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.

As with several other engines in this gallery, an odd number of cylinders are used because this gives a uniform firing interval; five cylinders gives an interval of 144 degrees. (720/5)

THE ALMEN A-4 WOBBLE-PLATE ENGINE: 1921

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.

Bore 4.25 in Stroke 5.5 in Displacement 1404 in3 (23,007 cc) Output 425 HP at 2000rpm Weight 749 lb Diameter 20in

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."

THE ALI OUTBOARD ENGINE: 1922

The ALI axial outboard engine was designed by Arvid Lind in Sweden, and reached the market in 1922. It was a popular choice for racing competition, but its general use was limited as it was expensive to produce, costing twice as much as an ordinary engine. The factory in Stockholm was closed when the inventor died in 1932.

Lars Eimar owns an Ali engine bearing the number 308, so presumably at least this number were built, making it one of the more sucessful axial engines.

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: Ali Engine No 308, owned by Lars Eimar The tiller functioned as a "kickstart" similar to that on a motor cycle; presumably it was pulled sharply upwards. The power output with the standard carburettor was 4 HP at 1400 rpm. The metal dome on the top covered the spark-plugs and kept them dry. This engine, and engine No 306, in the Tekniska Museet, (The Swedish National Museum of Science and Technology) are believed to be the only remaining examples of this engine. Below: Ali Engine No 308, with the top cover removed This exposes the sparkplugs and the central distributor. The yellow HT lead that runs up from the magneto can be seen. There appear to be two fuel tanks, each with a silver filler plug. Photographs and information kindly provided by Lars Eimar.

THE ROLLS-ROYCE AXIAL ENGINE: 1923

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

THE WISHON ROTARY-VALVE AXIAL ENGINE: 1923

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

THE LAAGE AXIAL CAM ENGINE: 1923

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

THE NEDOMA-NAJDER ENGINE: 1924

Above: The American Nedoma-Najder engine: 1924. Five-cylinder rotating barrel wobble-plate type

From NACA technical memorandum No 462, translation of Motorwagen Nov 20, 1927:

The stationary hollow shaft W rests on bearings A at each end. Around it revolve five cylinders Z, and the housing G carrying flange N for the propellor hub. The housing revolves on hollow shaft W on long bushings and in ball-bearing A at the propeller end. Gear Z1 is screwed to the front end of the revolving housing, and meshes with front planetary gear Z2, which transfers its motion to geared bushing Z3, which revolves at the same speed as housing G but in the opposite direction. The bushing B is keyed to Z3, on which the wobble plate T revolves on two ball bearings, being carried along by arm C which is fixed to housing G.

Due to the opposite motions of the bushing B and wobble plate T, a complete working cycle occurs in each cylinder for each revolution of the housing. The five aluminium cylinders were of 70mm diameter and 68mm stroke, with a single cast iron sleeve valve. The pistons were also of aluminium.

The sleeve valves were actuated by five shafts each carrying a helical groove and a gear meshing with a gear ring on the stationary hollow shaft. Two of these gears also operated two separate oil pumps. The inventor claimed an engine giving 40HP at 1400rpm would weigh 74kg, giving 1.83kg/HP.

The engine was intended for use in light aircraft, where its low frontal area would have reduced drag. It was the subject of United States Patent US1492215 (29 Apr 1924)