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The rotary engine is an early type of
internal combustion engine An internal combustion engine (ICE or IC engine) is a heat engine in which the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal co ...
, usually designed with an odd number of cylinders per row in a radial configuration. The engine's
crankshaft A crankshaft is a mechanical component used in a piston engine to convert the reciprocating motion into rotational motion. The crankshaft is a rotating shaft containing one or more crankpins, that are driven by the pistons via the connecti ...
remained stationary in operation, while the entire
crankcase In a piston engine, the crankcase is the housing that surrounds the crankshaft. In most modern engines, the crankcase is integrated into the engine block. Two-stroke engines typically use a crankcase-compression design, resulting in the fuel ...
and its attached cylinders rotated around it as a unit. Its main application was in aviation, although it also saw use in a few early
motorcycle A motorcycle (motorbike, bike, or trike (if three-wheeled)) is a two or three-wheeled motor vehicle Steering, steered by a Motorcycle handlebar, handlebar. Motorcycle design varies greatly to suit a range of different purposes: Long-distance ...
s and
automobile A car or automobile is a motor vehicle with wheels. Most definitions of ''cars'' say that they run primarily on roads, seat one to eight people, have four wheels, and mainly transport people instead of goods. The year 1886 is regarded ...
s. This type of engine was widely used as an alternative to conventional inline engines ( straight or V) during
World War I World War I (28 July 1914 11 November 1918), often abbreviated as WWI, was List of wars and anthropogenic disasters by death toll, one of the deadliest global conflicts in history. Belligerents included much of Europe, the Russian Empire, ...
and the years immediately preceding that conflict. It has been described as "a very efficient solution to the problems of power output, weight, and reliability". By the early 1920s, the inherent limitations of this type of engine had rendered it obsolete.


Description


Distinction between "rotary" and "radial" engines

A rotary engine is essentially a standard Otto cycle engine, with cylinders arranged radially around a central crankshaft just like a conventional
radial engine The radial engine is a reciprocating type internal combustion engine configuration in which the cylinders "radiate" outward from a central crankcase like the spokes of a wheel. It resembles a stylized star when viewed from the front, and is ...
, but instead of having a fixed
cylinder block In an internal combustion engine, the engine block is the structure which contains the cylinders and other components. In an early automotive engine, the engine block consisted of just the cylinder block, to which a separate crankcase was attac ...
with rotating
crankshaft A crankshaft is a mechanical component used in a piston engine to convert the reciprocating motion into rotational motion. The crankshaft is a rotating shaft containing one or more crankpins, that are driven by the pistons via the connecti ...
, the crankshaft remains stationary and the entire cylinder block rotates around it. In the most common form, the crankshaft was fixed solidly to the airframe, and the
propeller A propeller (colloquially often called a screw if on a ship or an airscrew if on an aircraft) is a device with a rotating hub and radiating blades that are set at a pitch to form a helical spiral which, when rotated, exerts linear thrust upon ...
was simply bolted to the front of the
crankcase In a piston engine, the crankcase is the housing that surrounds the crankshaft. In most modern engines, the crankcase is integrated into the engine block. Two-stroke engines typically use a crankcase-compression design, resulting in the fuel ...
. This difference also has much impact on design (lubrication, ignition, fuel admission, cooling, etc.) and functioning (see below). The Musée de l'Air et de l'Espace in Paris has on display a special, "sectioned" working model of an engine with seven radially disposed cylinders. It alternates between rotary and radial modes to demonstrate the difference between the internal motions of the two types of engine.


Arrangement

Like "fixed" radial engines, rotaries were generally built with an odd number of cylinders (usually 5, 7 or 9), so that a consistent every-other-piston firing order could be maintained, to provide smooth running. Rotary engines with an even number of cylinders were mostly of the "two row" type. Most rotary engines were arranged with the cylinders pointing outwards from a single crankshaft, in the same general form as a radial, but there were also rotary
boxer engine A flat engine is a piston engine where the cylinders are located on either side of a central crankshaft. Flat engines are also known as horizontally opposed engines, however this is distinct from the less common opposed-piston engine design, wh ...
s and even one-cylinder rotaries.


Advantages and drawbacks

Three key factors contributed to the rotary engine's success at the time: * Smooth running: Rotaries delivered power very smoothly because (relative to the engine mounting point) there are no reciprocating parts, and the relatively large rotating mass of the crankcase/cylinders (as a unit) acted as a
flywheel A flywheel is a mechanical device which uses the conservation of angular momentum to store rotational energy; a form of kinetic energy proportional to the product of its moment of inertia and the square of its rotational speed. In particular, as ...
. * Improved cooling: when the engine was running, the rotating crankcase/cylinder assembly created its own fast-moving cooling airflow, even with the aircraft at rest. * Weight advantage: rotaries shared with other radial configuration engines the advantage of a small, flat crankcase. The superior air-cooling imparted by the moving engine also meant that cylinders could be made with thinner walls and shallower cooling fins. Their
power-to-weight ratio Power-to-weight ratio (PWR, also called specific power, or power-to-mass ratio) is a calculation commonly applied to engines and mobile power sources to enable the comparison of one unit or design to another. Power-to-weight ratio is a measuremen ...
was further enhanced in comparison with engines that required an added flywheel for smooth running. Engine designers had always been aware of the many limitations of the rotary engine so when the static style engines became more reliable and gave better specific weights and fuel consumption, the days of the rotary engine were numbered. * Rotary engines had a fundamentally inefficient total-loss oiling system. In order to reach the whole engine, the lubricating medium needed to enter the crankcase through the hollow crankshaft; but the centrifugal force of the revolving crankcase was directly opposed to any re-circulation. The only practical solution was for the lubricant to be aspirated with the fuel/air mixture, as in most
two-stroke engines A two-stroke (or two-stroke cycle) engine is a type of internal combustion engine that completes a power cycle with two strokes (up and down movements) of the piston during one power cycle, this power cycle being completed in one revolution of ...
. * Power increase also came with mass and size increases, multiplying gyroscopic precession from the rotating mass of the engine. This produced stability and control problems in aircraft in which these engines were installed, especially for inexperienced pilots. * Power output increasingly went into overcoming the air-resistance of the spinning engine. * Engine controls were tricky (see below), and resulted in fuel waste. The late WWI Bentley BR2, as the largest and most powerful rotary engine, had reached a point beyond which this type of engine could not be further developed, and it was the last of its kind to be adopted into RAF service.


Rotary engine control


Monosoupape rotaries

It is often asserted that rotary engines had no
throttle A throttle is the mechanism by which fluid flow is managed by constriction or obstruction. An engine's power can be increased or decreased by the restriction of inlet gases (by the use of a throttle), but usually decreased. The term ''throttle' ...
and hence power could only be reduced by intermittently cutting the ignition using a "blip" switch. This was only true of the "Monosoupape" (single valve) type, which took most of the air into the cylinder through the exhaust valve, which remained open for a portion of the downstroke of the piston. Thus the mixture of fuel and air in the cylinder could not be controlled via the crankcase intake. The "throttle" (fuel valve) of a monosoupape provided only a limited degree of speed regulation, as opening it made the mixture too rich, while closing it made it too lean (in either case quickly stalling the engine, or damaging the cylinders). Early models featured a pioneering form of
variable valve timing In internal combustion engines, variable valve timing (VVT) is the process of altering the timing of a valve lift event, and is often used to improve performance, fuel economy or emissions. It is increasingly being used in combination with var ...
in an attempt to give greater control, but this caused the valves to burn and therefore it was abandoned. The only way of running a Monosoupape engine smoothly at reduced revs was with a switch that changed the normal firing sequence so that each cylinder fired only once per two or three engine revolutions, but the engine remained more or less in balance. As with excessive use of the "blip" switch: running the engine on such a setting for too long resulted in large quantities of unburned fuel and oil in the exhaust, and gathering in the lower cowling, where it was a notorious fire hazard.


"Normal" rotaries

Most rotaries had normal inlet valves, so that the fuel (and lubricating oil) was taken into the cylinders already mixed with air - as in a normal four-stroke engine. Although a conventional carburetor, with the ability to keep the fuel/air ratio constant over a range of throttle openings, was precluded by the spinning crankcase; it was possible to adjust the air supply through a separate flap valve or "bloctube". The pilot needed to set the throttle to the desired setting (usually full open) and then adjust the fuel/air mixture to suit using a separate "fine adjustment" lever that controlled the air supply valve (in the manner of a manual choke control). Due to the rotary engine's large rotational inertia, it was possible to adjust the appropriate fuel/air mixture by trial and error without stalling it, although this varied between different types of engine, and in any case it required a good deal of practice to acquire the necessary knack. After starting the engine with a known setting that allowed it to idle, the air valve was opened until maximum engine speed was obtained. Throttling a running engine back to reduce revs was possible by closing off the fuel valve to the required position while re-adjusting the fuel/air mixture to suit. This process was also tricky, so that reducing power, especially when landing, was often accomplished instead by intermittently cutting the ignition using the blip switch. Cutting cylinders using ignition switches had the drawback of letting fuel continue to pass through the engine, oiling up the spark plugs and making smooth restarting problematic. Also, the raw oil-fuel mix could collect in the cowling. As this could cause a serious fire when the switch was released, it became common practice for part or all of the bottom of the basically circular cowling on most rotary engines to be cut away, or fitted with drainage slots. By 1918 a
Clerget Clerget-Blin (full name being ''Société Clerget-Blin et Cie'') was a French precision engineering company formed in 1913 by the engineer and inventor Pierre Clerget and industrialist Eugène Blin. In 1939, the company was absorbed into the '' ...
handbook advised maintaining all necessary control by using the fuel and air controls, and starting and stopping the engine by turning the fuel on and off. The recommended landing procedure involved shutting off the fuel using the fuel lever, while leaving the blip switch on. The windmilling propeller made the engine continue to spin without delivering any power as the aircraft descended. It was important to leave the ignition on to allow the spark plugs to continue to spark and keep them from oiling up, so that the engine could (if all went well) be restarted simply by re-opening the fuel valve. Pilots were advised to not use an ignition cut out switch, as it would eventually damage the engine. Pilots of surviving or reproduction aircraft fitted with rotary engines still find that the blip switch is useful while landing, as it provides a more reliable, quicker way to initiate power if needed, rather than risk a sudden engine stall, or the failure of a windmilling engine to restart at the worst possible moment.


History


Millet

Félix Millet showed a 5-cylinder rotary engine built into a bicycle wheel at the Exposition Universelle in Paris in 1889. Millet had patented the engine in 1888, so must be considered the pioneer of the internal combustion rotary engine. A machine powered by his engine took part in the Paris-Bordeaux-Paris race of 1895 and the system was put into production by Darracq and Company London in 1900.


Hargrave

Lawrence Hargrave first developed a rotary engine in 1889 using compressed air, intending to use it in powered flight. Materials weight and lack of quality machining prevented it becoming an effective power unit.


Balzer

Stephen M. Balzer of New York, a former watchmaker, constructed rotary engines in the 1890s. He was interested in the rotary layout for two main reasons: * To generate at the low rpm at which the engines of the day ran, the pulse resulting from each combustion stroke was quite large. To damp out these pulses, engines needed a large
flywheel A flywheel is a mechanical device which uses the conservation of angular momentum to store rotational energy; a form of kinetic energy proportional to the product of its moment of inertia and the square of its rotational speed. In particular, as ...
, which added weight. In the rotary design the engine acted as its own flywheel, thus rotaries could be lighter than similarly sized conventional engines. * The cylinders had good cooling airflow over them, even when the aircraft was at rest—which was important, as the low airspeed of aircraft of the time provided limited cooling airflow, and alloys of the day were less advanced. Balzer's early designs even dispensed with cooling fins, though subsequent rotaries did have this common feature of
air-cooled Air-cooled engines rely on the circulation of air directly over heat dissipation fins or hot areas of the engine to cool them in order to keep the engine within operating temperatures. In all combustion engines, a great percentage of the heat ge ...
engines. Balzer produced a 3-cylinder, rotary engined car in 1894, then later became involved in Langley's ''Aerodrome'' attempts, which bankrupted him while he tried to make much larger versions of his engines. Balzer's rotary engine was later converted to static radial operation by Langley's assistant, Charles M. Manly, creating the notable Manly–Balzer engine.


De Dion-Bouton

The famous De Dion-Bouton company produced an experimental 4-cylinder rotary engine in 1899. Though intended for aviation use, it was not fitted to any aircraft.


Adams-Farwell

The
Adams-Farwell The Adams Company is an American manufacturing concern. It was founded in 1883 and is based in Dubuque, Iowa, United States. Between 1905 and 1912 it produced the Adams-Farwell, a brass era automobile. History The Roberts & Langworthy Iron Work ...
firm's automobiles, with the firm's first rolling prototypes using 3-cylinder rotary engines designed by Fay Oliver Farwell in 1898, led to production Adams-Farwell cars with first the 3-cylinder, then very shortly thereafter 5-cylinder rotary engines later in 1906, as another early American automaker utilizing rotary engines expressly manufactured for automotive use. Emil Berliner sponsored its development of the 5-cylinder Adams-Farwell rotary engine design concept as a lightweight power unit for his unsuccessful helicopter experiments. Adams-Farwell engines later powered fixed-wing aircraft in the US after 1910. It has also been asserted that the Gnôme design was derived from the Adams-Farwell, since an Adams-Farwell car is reported to have been demonstrated to the French Army in 1904. In contrast to the later Gnôme engines, and much like the later
Clerget 9B The Clerget 9B was a nine-cylinder rotary aircraft engine of the World War I era designed by Pierre Clerget. Manufactured in both France and Great Britain (Gwynnes Limited), it was used on such aircraft as the Sopwith Camel. The Clerget 9Bf was ...
and
Bentley BR1 The Bentley BR.1 was a British rotary aircraft engine of the First World War. Designed by the motor car engine designer W. O. Bentley, the BR.1 was built in large numbers, being one of the main powerplants of the Sopwith Camel. Design and develo ...
aviation rotaries, the Adams-Farwell rotaries had conventional exhaust and inlet valves mounted in the cylinder heads.


Gnome

The Gnome engine was the work of the three Seguin brothers, Louis, Laurent and Augustin. They were talented engineers and the grandsons of famous French engineer
Marc Seguin Marc Seguin (20 April 1786 – 24 February 1875) was a French engineer, inventor of the wire- cable suspension bridge and the multi-tubular steam-engine boiler. Early life Seguin was born in Annonay, Ardèche to Marc François Seguin, th ...
. In 1906 the eldest brother, Louis, had formed the Société des Moteurs Gnome to build
stationary engine A stationary engine is an engine whose framework does not move. They are used to drive immobile equipment, such as pumps, generators, mills or factory machinery, or cable cars. The term usually refers to large immobile reciprocating engines, ...
s for industrial use, having licensed production of the Gnom single-cylinder stationary engine from
Motorenfabrik Oberursel Motorenfabrik Oberursel A.G. was a German manufacturer of automobile, locomotive and aircraft engines situated in Oberursel (Taunus), near Frankfurt (Main), Germany. During World War I it supplied a major 100 hp-class rotary engine that was u ...
—who, in turn, built licensed Gnome engines for German aircraft during World War I. Louis was joined by his brother Laurent who designed a rotary engine specifically for aircraft use, using Gnom engine cylinders. The brothers' first experimental engine is said to have been a 5-cylinder model that developed , and was a radial rather than rotary engine, but no photographs survive of the five-cylinder experimental model. The Seguin brothers then turned to rotary engines in the interests of better cooling, and the world's first production rotary engine, the 7-cylinder, air-cooled "
Omega Omega (; capital: Ω, lowercase: ω; Ancient Greek ὦ, later ὦ μέγα, Modern Greek ωμέγα) is the twenty-fourth and final letter in the Greek alphabet. In the Greek numeric system/ isopsephy ( gematria), it has a value of 800. The ...
" was shown at the 1908 Paris automobile show. The first Gnome Omega built still exists, and is now in the collection of the Smithsonian's
National Air and Space Museum The National Air and Space Museum of the Smithsonian Institution, also called the Air and Space Museum, is a museum in Washington, D.C., in the United States. Established in 1946 as the National Air Museum, it opened its main building on the N ...
. The Seguins used the highest strength material available - recently developed nickel steel alloy - and kept the weight down by machining components from solid metal, using the best American and German machine tools to create the engine's components; the cylinder wall of a 50 hp Gnome was only 1.5 mm (0.059 inches) thick, while the connecting rods were milled with deep central channels to reduce weight. While somewhat low powered in terms of units of power per litre, its power-to-weight ratio was an outstanding per kg. The following year, 1909, the inventor
Roger Ravaud Roger is a given name, usually masculine, and a surname. The given name is derived from the Old French personal names ' and '. These names are of Germanic origin, derived from the elements ', ''χrōþi'' ("fame", "renown", "honour") and ', ' ...
fitted one to his ''Aéroscaphe'', a combination
hydrofoil A hydrofoil is a lifting surface, or foil, that operates in water. They are similar in appearance and purpose to aerofoils used by aeroplanes. Boats that use hydrofoil technology are also simply termed hydrofoils. As a hydrofoil craft gains s ...
/aircraft, which he entered in the motor boat and aviation contests at Monaco.
Henry Farman Henri Farman (26 May 1874– 17 July 1958) was a British-French aviator and aircraft designer and manufacturer with his brother Maurice Farman. Before dedicating himself to aviation he gained fame as a sportsman, specifically in cycling and moto ...
's use of the Gnome at the famous Rheims aircraft meet that year brought it to prominence, when he won the Grand Prix for the greatest non-stop distance flown——and also set a world record for endurance flight. The very first successful seaplane flight, of
Henri Fabre Henri Fabre (29 November 1882 – 30 June 1984) was a French aviator and the inventor of the first successful seaplane, the Fabre Hydravion. Henri Fabre was born into a prominent family of shipowners in the city of Marseille. He was educated ...
's '' Le Canard'', was powered by a Gnome Omega on March 28, 1910, near
Marseille Marseille ( , , ; also spelled in English as Marseilles; oc, Marselha ) is the prefecture of the French department of Bouches-du-Rhône and capital of the Provence-Alpes-Côte d'Azur region. Situated in the camargue region of southern Fra ...
. Production of Gnome rotaries increased rapidly, with some 4,000 being produced before World War I, and Gnome also produced a two-row version (the 100 h.p. Double Omega), the larger 80 hp
Gnome Lambda The Gnome 7 Lambda was a French designed, seven-cylinder, air-cooled rotary aero engine that was produced under license in Britain and Germany. Powering several World War I-era aircraft types it was claimed to produce from its capacity of al ...
and the 160 hp two-row Double Lambda. By the standards of other engines of the period, the Gnome was considered not particularly temperamental, and was credited as the first engine able to run for ten hours between overhauls. In 1913 the Seguin brothers introduced the new Monosoupape ("single valve") series, which replaced inlet valves in the pistons by using a single valve in each cylinder head, which doubled as inlet and exhaust valve. The engine speed was controlled by varying the opening time and extent of the exhaust valves using levers acting on the valve tappet rollers, a system later abandoned due to valves burning. The weight of the Monosoupape was slightly less than the earlier two-valve engines, and it used less lubricating oil. The 100 hp Monosoupape was built with 9 cylinders, and developed its rated power at 1,200 rpm. The later 160 hp nine-cylinder Gnome 9N rotary engine used the Monosoupape valve design while adding the safety factor of a dual ignition system, and was the last known rotary engine design to use such a cylinder head valving format. The 9N also featured an unusual ignition setup that allowed output values of one-half, one-quarter and one-eighth power levels to be achieved through use of the coupe-switch and a special five-position rotary switch that selected which of the trio of alternate power levels would be selected when the coupe-switch was depressed, allowing it to cut out all spark voltage to all nine cylinders, at evenly spaced intervals to achieve the multiple levels of power reduction. The airworthy reproduction Fokker D.VIII parasol monoplane fighter at Old Rhinebeck Aerodrome, uniquely powered with a Gnome 9N, often demonstrates the use of its Gnome 9N's four-level output capability in both ground runs and in flight. Rotary engines produced by the
Clerget Clerget-Blin (full name being ''Société Clerget-Blin et Cie'') was a French precision engineering company formed in 1913 by the engineer and inventor Pierre Clerget and industrialist Eugène Blin. In 1939, the company was absorbed into the '' ...
and Le Rhône companies used conventional pushrod-operated valves in the cylinder head, but used the same principle of drawing the fuel mixture through the crankshaft, with the Le Rhônes having prominent copper intake tubes running from the crankcase to the top of each cylinder to admit the intake charge. The 80 hp (60 kW) seven-cylinder Gnome was the standard at the outbreak of World War I, as the Gnome Lambda, and it quickly found itself being used in a large number of aircraft designs. It was so good that it was licensed by a number of companies, including the German
Motorenfabrik Oberursel Motorenfabrik Oberursel A.G. was a German manufacturer of automobile, locomotive and aircraft engines situated in Oberursel (Taunus), near Frankfurt (Main), Germany. During World War I it supplied a major 100 hp-class rotary engine that was u ...
firm who designed the original Gnom engine. Oberursel was later purchased by
Fokker Fokker was a Dutch aircraft manufacturer named after its founder, Anthony Fokker. The company operated under several different names. It was founded in 1912 in Berlin, Germany, and became famous for its fighter aircraft in World War I. In 1919 ...
, whose 80 hp Gnome Lambda copy was known as the Oberursel U.0. It was not at all uncommon for French Gnôme Lambdas, as used in the earliest examples of the
Bristol Scout The Bristol Scout was a single-seat rotary-engined biplane originally designed as a racing aircraft. Like similar fast, light aircraft of the period it was used by the RNAS and the RFC as a " scout", or fast reconnaissance type. It was one o ...
biplane, to meet German versions, powering
Fokker E.I The Fokker E.I was the first fighter aircraft to enter service with the Fliegertruppe of the Deutsches Heer in World War I. Its arrival at the front in mid-1915 marked the start of a period known as the " Fokker Scourge" during which the E.I a ...
Eindeckers in combat, from the latter half of 1915 on. The only attempts to produce twin-row rotary engines in any volume were undertaken by Gnome, with their Double Lambda fourteen-cylinder 160 hp design, and with the German Oberursel firm's early World War I clone of the Double Lambda design, the U.III of the same power rating. While an example of the Double Lambda went on to power one of the Deperdussin Monocoque racing aircraft to a world-record speed of nearly 204 km/h (126 mph) in September 1913, the Oberursel U.III is only known to have been fitted into a few German production military aircraft, the Fokker E.IV fighter monoplane and
Fokker D.III The Fokker D.III (Fokker designation M.19) was a German single-seat fighter aircraft of World War I. It saw limited frontline service before being withdrawn from combat in December 1916. Design and development The M.19 began as an effort to imp ...
fighter biplane, both of whose failures to become successful combat types were partially due to the poor quality of the German powerplant, which was prone to wearing out after only a few hours of combat flight.


World War I

The favourable
power-to-weight ratio Power-to-weight ratio (PWR, also called specific power, or power-to-mass ratio) is a calculation commonly applied to engines and mobile power sources to enable the comparison of one unit or design to another. Power-to-weight ratio is a measuremen ...
of the rotaries was their greatest advantage. While larger, heavier aircraft relied almost exclusively on conventional in-line engines, many fighter aircraft designers preferred rotaries right up to the end of the war. Rotaries had a number of disadvantages, notably very high fuel consumption, partially because the engine was typically run at full throttle, and also because the valve timing was often less than ideal. Oil consumption was also very high. Due to primitive carburetion and absence of a true
sump A sump is a low space that collects often undesirable liquids such as water or chemicals. A sump can also be an infiltration basin used to manage surface runoff water and recharge underground aquifers. Sump can also refer to an area in a cave ...
, the lubricating oil was added to the fuel/air mixture. This made engine fumes heavy with smoke from partially burnt oil. Castor oil was the lubricant of choice, as its lubrication properties were unaffected by the presence of the fuel, and its gum-forming tendency was irrelevant in a total-loss lubrication system. An unfortunate side-effect was that World War I pilots inhaled and swallowed a considerable amount of the oil during flight, leading to persistent
diarrhoea Diarrhea, also spelled diarrhoea, is the condition of having at least three loose, liquid, or watery bowel movements each day. It often lasts for a few days and can result in dehydration due to fluid loss. Signs of dehydration often begin w ...
. Flying clothing worn by rotary engine pilots was routinely soaked with oil. The rotating mass of the engine also made it, in effect, a large
gyroscope A gyroscope (from Ancient Greek γῦρος ''gŷros'', "round" and σκοπέω ''skopéō'', "to look") is a device used for measuring or maintaining orientation and angular velocity. It is a spinning wheel or disc in which the axis of rot ...
. During level flight the effect was not especially apparent, but when turning the gyroscopic precession became noticeable. Due to the direction of the engine's rotation, left turns required effort and happened relatively slowly, combined with a tendency to nose up, while right turns were almost instantaneous, with a tendency for the nose to drop. In some aircraft, this could be advantageous in situations such as dogfights. The
Sopwith Camel The Sopwith Camel is a British First World War single-seat biplane fighter aircraft that was introduced on the Western Front in 1917. It was developed by the Sopwith Aviation Company as a successor to the Sopwith Pup and became one of the ...
suffered to such an extent that it required left rudder for both left and right turns, and could be extremely hazardous if the pilot applied full power at the top of a loop at low airspeeds. Trainee Camel pilots were warned to attempt their first hard right turns only at altitudes above . The Camel's most famous German foe, the
Fokker Dr.I The Fokker Dr.I (''Dreidecker'', "triplane" in German), often known simply as the Fokker Triplane, was a World War I fighter aircraft built by Fokker-Flugzeugwerke. The Dr.I saw widespread service in the spring of 1918. It became famous as th ...
triplane A triplane is a fixed-wing aircraft equipped with three vertically stacked wing planes. Tailplanes and canard foreplanes are not normally included in this count, although they occasionally are. Design principles The triplane arrangement ma ...
, also used a rotary engine, usually the Oberursel Ur.II clone of the French-built Le Rhone 9J 110 hp powerplant. Even before the First World War, attempts were made to overcome the inertia problem of rotary engines. As early as 1906 Charles Benjamin Redrup had demonstrated to the
Royal Flying Corps "Through Adversity to the Stars" , colors = , colours_label = , march = , mascot = , anniversaries = , decorations ...
at
Hendon Hendon is an urban area in the Borough of Barnet, North-West London northwest of Charing Cross. Hendon was an ancient manor and parish in the county of Middlesex and a former borough, the Municipal Borough of Hendon; it has been part of Gre ...
a 'Reactionless' engine in which the
crankshaft A crankshaft is a mechanical component used in a piston engine to convert the reciprocating motion into rotational motion. The crankshaft is a rotating shaft containing one or more crankpins, that are driven by the pistons via the connecti ...
rotated in one direction and the cylinder block in the opposite direction, each one driving a propeller. A later development of this was the 1914 reactionless 'Hart' engine designed by Redrup in which there was only one propeller connected to the crankshaft, but it rotated in the opposite direction to the cylinder block, thereby largely cancelling out negative effects. This proved too complicated for reliable operation and Redrup changed the design to a static radial engine, which was later tried in the experimental Vickers F.B.12b and F.B.16 aircraft, unfortunately without success. As the war progressed, aircraft designers demanded ever-increasing amounts of power. Inline engines were able to meet this demand by improving their upper rev limits, which meant more power. Improvements in valve timing, ignition systems, and lightweight materials made these higher revs possible, and by the end of the war the average engine had increased from 1,200 rpm to 2,000. The rotary was not able to do the same due to the drag of the rotating cylinders through the air. For instance, if an early-war model of 1,200 rpm increased its revs to only 1,400, the drag on the cylinders increased 36%, as air drag increases with the square of velocity. At lower rpm, drag could simply be ignored, but as the rev count rose, the rotary was putting more and more power into spinning the engine, with less remaining to provide useful thrust through the propeller.


Siemens-Halske bi-rotary designs

One clever attempt to rescue the design, in a similar manner to Redrup's British "reactionless" engine concept, was made by Siemens AG. The crankcase (with the propeller still fastened directly to the front of it) and cylinders spun counterclockwise at 900 rpm, as seen externally from a "nose on" viewpoint, while the crankshaft (which unlike other designs, never "emerged" from the crankcase) and other internal parts spun clockwise at the same speed, so the set was effectively running at 1800 rpm. This was achieved by the use of bevel gearing at the rear of the crankcase, resulting in the eleven-cylindered
Siemens-Halske Sh.III Siemens-Halske's Sh.III was an 11-cylinder, air-cooled counter rotary engine developed in Germany during World War I. The engine was a development of the earlier 9-cylinder Siemens-Halske Sh.I. Design The Siemens-Halske Sh.III was an 11-cylind ...
, with less drag and less net torque. Used on several late war types, notably the
Siemens-Schuckert D.IV The Siemens-Schuckert D.IV was a late- World War I fighter aircraft from Siemens-Schuckert (SSW). It reached service too late and was produced in too few numbers to have any effect on the war effort. Earlier designs Siemens-Schuckert's first prod ...
fighter, the new engine's low running speed, coupled with large, coarse pitched propellers that sometimes had four blades (as the SSW D.IV used), gave types powered by it outstanding rates of climb, with some examples of the late production Sh.IIIa powerplant even said to be delivering as much as 240 hp. One new rotary powered aircraft, Fokker's own D.VIII, was designed at least in part to provide some use for the Oberursel factory's backlog of otherwise redundant Ur.II engines, themselves clones of the Le Rhône 9J rotary. Because of the Allied blockade of shipping, the Germans were increasingly unable to obtain the castor oil necessary to properly lubricate their rotary engines. Substitutes were never entirely satisfactory - causing increased running temperatures and reduced engine life.


Postwar

By the time the war ended, the rotary engine had become obsolete, and it disappeared from use quite quickly. The British
Royal Air Force The Royal Air Force (RAF) is the United Kingdom's air and space force. It was formed towards the end of the First World War on 1 April 1918, becoming the first independent air force in the world, by regrouping the Royal Flying Corps (RFC) an ...
probably used rotary engines for longer than most other operators. The RAF's standard post-war fighter, the Sopwith Snipe, used the Bentley BR2 rotary as the most powerful (at some ) rotary engine ever built by the
Allies of World War I The Allies of World War I, Entente Powers, or Allied Powers were a coalition of countries led by France, the United Kingdom, Russia, Italy, Japan, and the United States against the Central Powers of Germany, Austria-Hungary, the Ott ...
. The standard RAF training aircraft of the early post-war years, the 1914-origin Avro 504K, had a universal mounting to allow the use of several different types of low powered rotary, of which there was a large surplus supply. Similarly, the Swedish FVM Ö1 Tummelisa advanced training aircraft, fitted with a Le-Rhone-Thulin rotary engine, served until the mid thirties. Designers had to balance the cheapness of war-surplus engines against their poor
fuel efficiency Fuel efficiency is a form of thermal efficiency, meaning the ratio of effort to result of a process that converts chemical potential energy contained in a carrier (fuel) into kinetic energy or work. Overall fuel efficiency may vary per device ...
and the operating expense of their total-loss lubrication system, and by the mid-1920s, rotaries had been more or less completely displaced even in British service, largely by the new generation of air-cooled "stationary" radials such as the Armstrong Siddeley Jaguar and
Bristol Jupiter The Bristol Jupiter was a British nine-cylinder single-row piston radial engine built by the Bristol Aeroplane Company. Originally designed late in World War I and known as the Cosmos Jupiter, a lengthy series of upgrades and developments turn ...
. Experiments with the concept of the rotary engine continued. The first version of the 1921 Michel engine, an unusual opposed-piston cam engine, used the principle of a rotary engine, in that its "cylinder block" rotated. This was soon replaced by a version with the same cylinders and cam, but with stationary cylinders and the cam track rotating in lieu of a crankshaft. A later version abandoned the cam altogether and used three coupled crankshafts. By 1930 the Soviet helicopter pioneers, Boris N. Yuriev and Alexei M. Cheremukhin, both employed by '' Tsentralniy Aerogidrodinamicheskiy Institut'' (TsAGI, the Central Aerohydrodynamic Institute), constructed one of the first practical single-lift rotor machines with their TsAGI 1-EA single rotor helicopter, powered by two Soviet-designed and built M-2 rotary engines, themselves up-rated copies of the Gnome Monosoupape rotary engine of World War I. The TsAGI 1-EA set an unofficial altitude record of 605 meters (1,985 ft) with Cheremukhin piloting it on 14 August 1932 on the power of its twinned M-2 rotary engines.


Use in cars and motorcycles

Although rotary engines were mostly used in aircraft, a few cars and motorcycles were built with rotary engines. Perhaps the first was the Millet motorcycle of 1892. A famous motorcycle, winning many races, was the Megola, which had a rotary engine inside the front wheel. Another motorcycle with a rotary engine was Charles Redrup's 1912 Redrup Radial, which was a three-cylinder 303 cc rotary engine fitted to a number of motorcycles by Redrup. In 1904 the Barry engine, also designed by Redrup, was built in Wales: a rotating 2-cylinder boxer engine weighing 6.5 kg was mounted inside a motorcycle frame. The early-1920s German Megola motorcycle used a five-cylinder rotary engine within its front wheel design. In the 1940s
Cyril Pullin Cyril Pullin (18 August 1892 – 23 April 1973) was a British inventor, engineer and motorcycle race driver. His inventions contributed to the rotary engine and the helicopter. His son was the pilot for the first successful British helicopte ...
developed the Powerwheel, a wheel with a rotating one-cylinder engine,
clutch A clutch is a mechanical device that engages and disengages power transmission, especially from a drive shaft to a driven shaft. In the simplest application, clutches connect and disconnect two rotating shafts (drive shafts or line shafts). ...
and
drum brake A drum brake is a brake that uses friction caused by a set of shoes or pads that press outward against a rotating cylinder-shaped part called a brake drum. The term ''drum brake'' usually means a brake in which shoes press on the inner surfa ...
inside the hub, but it never entered production.


Other rotary engines

Besides the configuration of cylinders moving around a fixed crankshaft, several different engine designs are also called ''rotary engines''. The most notable
pistonless rotary engine A pistonless rotary engine is an internal combustion engine that does not use pistons in the way a reciprocating engine does. Designs vary widely but typically involve one or more rotors, sometimes called rotary pistons. Although many differ ...
, the Wankel rotary engine has been used by NSU in the Ro80 car, by
Mazda , commonly referred to as simply Mazda, is a Japanese multinational automotive manufacturer headquartered in Fuchū, Hiroshima, Japan. In 2015, Mazda produced 1.5 million vehicles for global sales, the majority of which (nearly one ...
in a variety of cars such as the RX-series, and in some experimental aviation applications. In the late 1970s a concept engine called the Bricklin-Turner Rotary Vee was tested.Popular Science April 1976 The Rotary Vee is similar in configuration to the elbow steam engine. Piston pairs connect as solid V shaped members, with each end floating in a pair of rotating cylinders clusters. The rotating cylinder cluster pairs are set with their axes at a wide V angle. The pistons in each cylinder cluster move parallel to each other instead of a radial direction, This engine design has not gone into production. The Rotary Vee was intended to power the
Bricklin SV-1 The Bricklin SV-1 is a two-seat sports car built from 1974 until late 1975. The car was noteworthy for its gull-wing doors and composite bodywork of color-impregnated acrylic resin bonded to fiberglass. Assembly took place in Saint John, New Bruns ...
.


See also

*
Petrol engine A petrol engine (gasoline engine in American English) is an internal combustion engine designed to run on petrol (gasoline). Petrol engines can often be adapted to also run on fuels such as liquefied petroleum gas and ethanol blends (such as ' ...
*
Monosoupape engine The ''Monosoupape'' ( French for single-valve), was a rotary engine design first introduced in 1913 by Gnome Engine Company (renamed Gnome et Rhône in 1915). It used a clever arrangement of internal transfer ports and a single pushrod-operated ...
* Manly–Balzer engine * Nutating disc engine * Quasiturbine *
Turbine A turbine ( or ) (from the Greek , ''tyrbē'', or Latin ''turbo'', meaning vortex) is a rotary mechanical device that extracts energy from a fluid flow and converts it into useful work. The work produced by a turbine can be used for generating ...
* Wankel rotary engine


Notes


External links


Paris Musee de l'Air combination of "rotary" and "radial" engine-function kinetic display

Smithsonian NASM Gnôme Omega No.1 page

Smithsonian NASM Le Rhône 9J page



Ray Williams' operable miniature rotary engine website

A rotary engine that runs solely on compressed air

Charles Redrup's range of engines

Video of 1909 Gnome Omega Engine - Run April 2009



Bi-rotary engine
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Franky Devaere
{{DEFAULTSORT:Rotary Engine Engine technology Piston engine configurations Motorcycle engines