Axial Internal-Combustion Engines.
Also known as barrel engines
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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
usually converted to rotary motion by a swashplate or Z-crank
mechanism. The claimed advantages for this engine format were low
frontal area (important for powering aeroplanes) very good balance and
great compactness. On the downside there were major problems with the
swashplate or wobble-plate mechanisms, and access for maintenance was
poor. The axial IC engine was an obvious development of the Axial Steam Engine. No axial IC engines have achieved any sustained success.
AXIAL ENGINE TECHNOLOGY
Wobble-plates and swash-plates are not the same thing:
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| 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
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| 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
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A variation
on the swashplate engine is the cam-plate engine, in which the plate is
not a flat surface, but is given a sinusoidal contour. The pistons can
now be made to move back and forth twice or more during one rotation of
the main shaft, giving more firing strokes and potentially increasing
the power output of an engine of a given size. See The Dynacam Engine below.
There is a whole gallery of non-axial cam engines just around the corner from here.
An engine expert speaks:
"Such cylinder arrangements
have serious disadvantages with regard to accessibility and mounting
structure, which would make them undesirable for most services even if
a reliable mechanism could be developed. There is no likelihood of such
engines becoming important competitors to the conventional types."
(Quote from The Internal-Combustion Engine in Theory and Practice by Charles Fayette Taylor, 2nd edition, pub MIT press 1985. This book is a standard work on the subject of IC engines)
While I hesitate to argue
with Charles Taylor, I don't see his point about accessibility and
mounting structures. Accessibility for adjustments with the engine
running would of course be a challenge with one of the rotating-barrel
types; doing a compression test would be a most interesting procedure.
The doubt about the reliability of wobble & swash mechanisms is
more telling. However, I don't doubt that if we really needed axial
engines with long-term reliability for some reason, the problem could
be solved.
There have been some
unconventional engines which have used wobble-plates but are in
different galleries of the Museum because they have even more unusual
features. One example is: The Selwood-Hughes Engine which had toroidal cylinders.
THE SMALLBONE AXIAL ENGINE: 1906
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Above: 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.
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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 is the seven-cylinder
Macomber, a rotating-barrel wobble-plate type. The ball joints between
the connecting rods and the plate make it clear that it is of the
wobble-plate persuasion.
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| 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 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.
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| Left: The Macomber Axial Engine: 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 there was no possibility of
adding 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.
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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.
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| 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 1042018, 1912
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It is a bit of a mystery why axial rotary engines should have been so popular in the early days of flying; The Trebert engine of 1912 and The Nedoma-Najder of 1924
are two more examples on this page. The snags include the difficulty of
getting the fuel/air mixture to the whirling cylinders, the
impossibility of using anything but stub exhausts, and all sorts of
potential problems with centrifugal force affecting the valvegear, the
lubrication, and so on.
On the upside you got a very heavy flywheel for free (ie with no added
weight) but then there was already a big propellor attached to the
output shaft, and I would have thought that gave quite a bit of
flywheel action.
More conventional rotaries
such as the well-known Gnome engine were, for a short time, successful
at powering early aircraft. Having cylinders arranged radially, they
had the advantage of air-cooling of the whirling cylinders; this was an
advantage an axial rotary did not enjoy. But... the heavy rotating mass
gave rise to interesting gyroscopic effects. It gave the Sopwith Camel
remarkable turning power- in one direction. This, in the hands of an
expert, could be very useful in combat. To an inexperienced pilot it
could all too easily be lethal. The gyroscopic problems, coupled with
breathing restrictions due to the convoluted air-fuel delivery path,
meant that rotaries fell out of use after the First World War.
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.
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| 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
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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.
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| 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
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| 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 1215434, 1917
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| 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.
Another brilliant animation by Bill Todd
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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.
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| 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.
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THE MICHELL AXIAL SWASHPLATE ENGINE: 1920
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.
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| 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.
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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.
Above: Longitudinal section of an 8-cylinder 4-piston Michell engine meant for road vehicles: 1927. Source: NACA
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.
Above: Section through piston and valves of 8-cylinder 4-piston Michell engine for road vehicles: 1927. Source: NACA
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.
Above:
Longitudinal section in front of swashplate, and end view, of
8-cylinder 4-piston Michell engine for road vehicles: 1927. Source: NACA
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.
Above: Longitudinal section of a 300HP 8-cylinder 4-piston Michell engine for driving gas compressors: 1927. Source: ME
This illustration comes from a 1927 sales brochure, and in this case it shows two horizontal
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 irrelevant.
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| 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.
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| Left: Michell engine in the Powerhouse Museum, Sydney, Australia engine: 1927
The same engine from the other side.
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| 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.
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| 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.
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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.
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| 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.
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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
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| 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.
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Above: 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
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Above: 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.
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| Bore | 4.25 in
| | Stroke | 5.5 in
| | Displacement | 1404 in3 (23,007 cc)
| | Output | 425 HP at 2000rpm
| | Weight | 749 lb
| | Diameter | 20in
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| The vital statistics of the Almen engine
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Above: 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.
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THE OUTBOARD ENGINE: 1922
The 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 1932.
Lars
Eimar owns anAlengine bearing the number 308, so presumably at least
this number were built, making it one of the more sucessful axial
engines.
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| Left: The Engine: 1922
Four-cylinder static barrel wobble-plate type.
The 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 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
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| Left: The 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
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| Left: The 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 Ai instruction book; kindly provided by Lars Eimar.
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| Left: 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 sideways while the engine was fixed in some way. 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: 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.
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THE LAAGE AXIAL CAM ENGINE: 1923
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| 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
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THE NEDOMA-NAJDER ENGINE: 1924
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)
THE BRISTOL AXIAL ENGINE: 1934
This
engine was originally conceived as a power unit for buses and coaches,
presumably because its compact format would allow it to be installed
below the floor. Note the wobble-plate on the Z-shaped crankshaft, and
one of the axial pistons and cylinders at the top. The engine had a
single rotary valve to control induction and exhaust, which can be seen
between the piston/cylinder and the cooling fan at the right. Some
complication were required to make the wobble-plate move correctly, and
the resulting vertical stabiliser arm can be seen just below the
Z-crank.
Charles Benjamin Redrup was hired by the Bristol Tramways and Carriage
Company in 1931 to design this engine, and several variants were used
in Bristol buses during the late 1930s. The engine went through several
versions from RR1 to RR4. RR4/2 (ie engine number 2) gave 145 HP at
2900 rpm on the test bench.
A change of management at the Bristol Tramways company caused development to be stopped in October 1936.
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| 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.
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THE SPAROST CAM ENGINE: 193?
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| 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
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THE ALFARO AXIAL SWASHPLATE ENGINE: 1938
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| 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.
The history of this engine is
currently rather obscure. It appears to have been 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.
The engine had no valve system
when operated as a two-stroke. (4-stroke operation was also envisaged)
The exhaust ports were uncovered by the piston moving down, while the
inlet ports, fed with compressed air from a geared blower, were
likewise piston-controlled.
Image from Charles Fayette Taylor
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Alfaro took out US patent no 2,080,846. No photographs of the engine have so far been discovered.
References:
Cullom,
"The Alfaro Engine," Civil Aeronautical Authority Technical Development
Report No. 4, Jan 1939. See also Auto. Ind., Dec. 1, 1939.
THE WOOLER AXIAL ENGINE: 1947
This
six-cylinder static-barrel wobble-plate engine was designed by John
Wooler (?-1955) who was better known as a motorcycle engine designer,
for aircraft use. See here for more on John Wooler. (Wikipedia link)
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| 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
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| 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.
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THE DYNA-CAM ENGINE: 1941
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| 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
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| 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
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| 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
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TORPEDO ENGINES
The
cylindrical format of the axial engine is ideally suited to fitting in
torpedos, and any lack of durability in the swashing/wobbling mechanism
is not a problem if the operational life is measured in minutes.
The
US Navy Mark 46 torpedo, designed to attack high-performance
submarines, is powered by an axial IC engine. Variations of this
torpedo are expected to remain in service until the year 2015, so axial
engines are very much with us.
The engine runs on a monopropellant called Otto fuel II. (nothing to do
with the Otto cycle) This fearful stuff is a mixture of three synthetic
substances: propylene glycol dinitrate (the main component),
2-nitrodiphenylamine, and dibutyl sebacate. It is a red-orange oily
liquid and a stable substance until vapourised and heated, when its
three components react. The fuel itself is toxic and one of the
products of combustion is highly toxic hydrogen cyanide gas. This
monopropellant system is unlike earlier torpedos which carried a tank
of highly compressed air for the combustion of paraffin.
There are some details of the Mark 46 torpedo, though not much about the engine, in: Wikipedia (external link)
Details
of the Mark 46 engine have, perhaps not surprisingly, so far proved
impossible to find, and it is not unlikely that even looking for them
will land the Museum staff in Guantamo Bay. However, this video claims
to show the Mark 46 Torpedo axial engine mechanism in action: Youtube video (external link)
The video is of poor quality but it looks as though the engine uses a wobbleplate rather than a swashplate format.
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| 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
that is 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.
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This
is an unlabelled cut-away drawing of a torpedo produced by the "Sea
Thermal Engineering Research and Design Institute" of St. Petersburg
(Russia) that features a wobbleplate engine in the 300-1350 kW (heavy
multi-purpose torpedo) or 60-200 kW (small torpedo) power output range.
The original drawing is titled "Multipurpose depth homing torpedo", but
unfortunately it is not currently clear which model it is or what fuel
it uses, though it is probably of the kerosene-oxygen wet-heater type.
It's nothing to do with axial engines, but here is a torpedo engine with rotary valves.
CURRENT AXIAL ENGINE DEVELOPMENTS: 2008
Work continues on axial IC engines. Here is one company: The Axial Vector Engine Corporation (external link)
There is an animation of their engine on Youtube (external link)
Axial
have apparently acquired the assets of the Dyna-Cam Engine Corp; this
news item appeared in the Portland Business Journal on Thursday, July
6, 2006:
"Dyna-Cam lawsuit settled.
Axial
Vector Engine Corp. said Thursday that is has signed a settlement
agreement and mutual release with Dennis Palmer and Patricia Wilks
resolving the lawsuit filed by Axial over the purchase of the Dyna-Cam
assets.
The agreement was signed May 16, effective June 30. The settlement
involved confirmation by Palmer and Wilks of the agreements wherein
Axial acquired all rights, titles, assets and interest to Dyna-Cam
Engine Corp., including related Web sites and domain names."
This video shows a 4 Cylinder "Gas Powered" wobbleplate engine, apparently uploaded by a company called Gyroscope.com: Youtube video (external link)
BIBLIOGRAPHY
- Some Unusual Engines by L J K Setright, pub Mechanical Engineering Publications Ltd, 1975
- The Knife and Fork Man (Biography of Charles Redrup) by Bill Fairney, pub Diesel Publishing, 2007
