Rotary engine
Overview
 
The rotary engine was an early type of internal-combustion engine, usually designed with an odd number of cylinders per row in a radial configuration
Radial engine
The radial engine is a reciprocating type internal combustion engine configuration in which the cylinders point outward from a central crankshaft like the spokes on a wheel...

, in which the crankshaft
Crankshaft
The crankshaft, sometimes casually abbreviated to crank, is the part of an engine which translates reciprocating linear piston motion into rotation...

 remained stationary and the entire cylinder block
Cylinder block
A cylinder block is an integrated structure comprising the cylinder of a reciprocating engine and often some or all of their associated surrounding structures...

 rotated around it. Its main application was in aviation, although it also saw use in a few early motorcycle
Motorcycle
A motorcycle is a single-track, two-wheeled motor vehicle. Motorcycles vary considerably depending on the task for which they are designed, such as long distance travel, navigating congested urban traffic, cruising, sport and racing, or off-road conditions.Motorcycles are one of the most...

s and cars
Automobile
An automobile, autocar, motor car or car is a wheeled motor vehicle used for transporting passengers, which also carries its own engine or motor...

.

This type of engine was widely used as an alternative to conventional in-line
Straight engine
Usually found in four- and six-cylinder configurations, the straight engine, or inline engine is an internal-combustion engine with all cylinders aligned in one row, with no offset...

 or V engine
V engine
A V engine, or Vee engine is a common configuration for an internal combustion engine. The cylinders and pistons are aligned, in two separate planes or 'banks', so that they appear to be in a "V" when viewed along the axis of the crankshaft...

s during World War I
World War I
World War I , which was predominantly called the World War or the Great War from its occurrence until 1939, and the First World War or World War I thereafter, was a major war centred in Europe that began on 28 July 1914 and lasted until 11 November 1918...

 and the years immediately preceding that conflict, and has been described as "a very efficient solution to the problems of power output, weight, and reliability".

By the early 1920s, however, the inherent limitations of this type of engine had rendered it obsolete, with the power output increasingly going into overcoming the air-resistance of the spinning engine itself.
Encyclopedia
The rotary engine was an early type of internal-combustion engine, usually designed with an odd number of cylinders per row in a radial configuration
Radial engine
The radial engine is a reciprocating type internal combustion engine configuration in which the cylinders point outward from a central crankshaft like the spokes on a wheel...

, in which the crankshaft
Crankshaft
The crankshaft, sometimes casually abbreviated to crank, is the part of an engine which translates reciprocating linear piston motion into rotation...

 remained stationary and the entire cylinder block
Cylinder block
A cylinder block is an integrated structure comprising the cylinder of a reciprocating engine and often some or all of their associated surrounding structures...

 rotated around it. Its main application was in aviation, although it also saw use in a few early motorcycle
Motorcycle
A motorcycle is a single-track, two-wheeled motor vehicle. Motorcycles vary considerably depending on the task for which they are designed, such as long distance travel, navigating congested urban traffic, cruising, sport and racing, or off-road conditions.Motorcycles are one of the most...

s and cars
Automobile
An automobile, autocar, motor car or car is a wheeled motor vehicle used for transporting passengers, which also carries its own engine or motor...

.

This type of engine was widely used as an alternative to conventional in-line
Straight engine
Usually found in four- and six-cylinder configurations, the straight engine, or inline engine is an internal-combustion engine with all cylinders aligned in one row, with no offset...

 or V engine
V engine
A V engine, or Vee engine is a common configuration for an internal combustion engine. The cylinders and pistons are aligned, in two separate planes or 'banks', so that they appear to be in a "V" when viewed along the axis of the crankshaft...

s during World War I
World War I
World War I , which was predominantly called the World War or the Great War from its occurrence until 1939, and the First World War or World War I thereafter, was a major war centred in Europe that began on 28 July 1914 and lasted until 11 November 1918...

 and the years immediately preceding that conflict, and has been described as "a very efficient solution to the problems of power output, weight, and reliability".

By the early 1920s, however, the inherent limitations of this type of engine had rendered it obsolete, with the power output increasingly going into overcoming the air-resistance of the spinning engine itself. The rotating mass of the engine also had a significant gyroscopic precession: depending on the type of aircraft, this produced stability and control problems, especially for inexperienced pilots. Another factor in the demise of the rotary was the fundamentally inefficient use of fuel and lubricating oil caused in part by the need for the fuel/air mixture to be aspirated through the hollow crankshaft and crankcase.

Description

A rotary engine is essentially a standard Otto cycle
Otto cycle
An Otto cycle is an idealized thermodynamic cycle which describes the functioning of a typical reciprocating piston engine, the thermodynamic cycle most commonly found in automobile engines....

 engine, but instead of having a fixed cylinder block
Cylinder block
A cylinder block is an integrated structure comprising the cylinder of a reciprocating engine and often some or all of their associated surrounding structures...

 with rotating crankshaft
Crankshaft
The crankshaft, sometimes casually abbreviated to crank, is the part of an engine which translates reciprocating linear piston motion into rotation...

 as with a conventional radial engine
Radial engine
The radial engine is a reciprocating type internal combustion engine configuration in which the cylinders point outward from a central crankshaft like the spokes on a wheel...

, the crankshaft remains stationary and the entire cylinder block rotates around it. In the most common form, the crankshaft was fixed solidly to an aircraft frame, and the propeller
Propeller
A propeller is a type of fan that transmits power by converting rotational motion into thrust. A pressure difference is produced between the forward and rear surfaces of the airfoil-shaped blade, and a fluid is accelerated behind the blade. Propeller dynamics can be modeled by both Bernoulli's...

 simply bolted onto the front of the crankcase
Crankcase
In an internal combustion engine of the reciprocating type, the crankcase is the housing for the crankshaft. The enclosure forms the largest cavity in the engine and is located below the cylinder, which in a multicylinder engine are usually integrated into one or several cylinder blocks...

.

Three key factors contributed to the rotary engines 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 cylinders acted as a flywheel
    Flywheel
    A flywheel is a rotating mechanical device that is used to store rotational energy. Flywheels have a significant moment of inertia, and thus resist changes in rotational speed. The amount of energy stored in a flywheel is proportional to the square of its rotational speed...

    .
  • Weight advantage: many conventional engines had to have heavy flywheels added to smooth out power impulses and reduce vibration. Rotary engines gained a substantial power-to-weight ratio
    Power-to-weight ratio
    Power-to-weight 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 measurement of actual performance of any engine or power sources...

     advantage by having no need for an added flywheel.
  • Improved cooling: when the engine was running the rotating cylinder block created its own fast-moving cooling airflow
    Aerodynamics
    Aerodynamics is a branch of dynamics concerned with studying the motion of air, particularly when it interacts with a moving object. Aerodynamics is a subfield of fluid dynamics and gas dynamics, with much theory shared between them. Aerodynamics is often used synonymously with gas dynamics, with...

    , even with the aircraft at rest.


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 engines and even one-cylinder rotaries.

Like radial engines, rotaries were generally built with an odd number of cylinders (usually either 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.

Distinction between "Rotary" and "Radial" engines

Rotary and radial engine
Radial engine
The radial engine is a reciprocating type internal combustion engine configuration in which the cylinders point outward from a central crankshaft like the spokes on a wheel...

s look strikingly similar when they are not running and can easily be confused, since both have cylinders arranged radially around a central crankshaft. Unlike the rotary engine, however, radial engines use a conventional rotating crankshaft in a fixed engine block.

Rotary engine control

It is often asserted that rotary engines had no carburetor
Carburetor
A carburetor , carburettor, or carburetter is a device that blends air and fuel for an internal combustion engine. It is sometimes shortened to carb in North America and the United Kingdom....

 and hence power could only be reduced by intermittently cutting the ignition using a "blip" or coupe momentary push-button switch, operating in a manner directly opposite that of a kill switch
Kill switch
Kill switch, also called an e-stop, is a security measure used to shut off a device in an emergency situation in which it cannot be shut down in the usual manner...

 for other types of internal combustion engines, which grounded the magneto when pressed, shutting off power to the spark plugs and stopping ignition. However, rotaries did have a simple carburetor which combined a gasoline jet and a flap valve, or "bloctube" style throttling device, for throttling the air supply. Unlike modern carburetors, it could not keep the fuel/air ratio constant over a range of throttle openings; in use, a pilot would set the throttle to the desired setting (usually full open) then adjust the fuel/air mixture to suit using a separate "fine adjustment" lever that controlled the fuel valve.

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. After starting the engine with a known setting that allowed it to idle, the air valve was opened until maximum engine speed was obtained. Since the reverse process was more difficult, "throttling", especially when landing, was often accomplished by temporarily cutting the ignition using the blip switch.

By the middle stages of World War I, some throttling capability was found necessary to allow pilots to fly in formation, and the improved carburetors which entered use allowed a power reduction of up to 25%. The pilot would close off the air valve to the required position, then re-adjust the fuel/air mixture to suit. Experienced pilots would gently back off the fuel lever at frequent intervals to make sure that the mixture was not too rich: a too-lean mixture was preferable, since power recovery would be instant when the fuel supply was increased, whereas a too-rich mixture could take up to seven seconds to recover and could also cause fouling of spark plugs and the cylinders to cut out.

The Gnôme Monosoupape was an exception to this, since most of its air supply was taken in through the exhaust valve, and so could not be controlled via the crankcase intake. Monosoupapes therefore had a single petrol regulating control used for a limited degree of speed regulation. Early models also featured a pioneering form of variable valve timing
Variable valve timing
In internal combustion engines, variable valve timing , also known as Variable valve actuation , is a generalized term used to describe any mechanism or method that can alter the shape or timing of a valve lift event within an internal combustion engine...

 to give greater control, but this caused the valves to burn and therefore it was abandoned.

Later rotaries still used blipping the ignition for landing, and some engines were equipped with a switch that cut out only some rather than all of the cylinders to ensure that the engine kept running and did not oil up. A few 9-cylinder rotaries had this capability, typically allowing 1, 3, or 5 cylinders to be kept running. Some 9-cylinder Monosoupapes had a selector switch which allowed the pilot to cut out six cylinders so that each cylinder fired only once per three engine revolutions but the engine remained in perfect balance. Some documentation regarding the Fokker Eindecker
Fokker Eindecker
The Fokker Eindecker was a German World War I monoplane single-seat fighter aircraft designed by Dutch engineer Anthony Fokker. Developed in April 1915, the Eindecker was the first purpose-built German fighter aircraft and the first aircraft to be fitted with synchronizer gear, enabling the pilot...

 shows a rotary selector switch to cut out a selected number of cylinders suggesting that German rotaries did as well.

By 1918 a Clerget
Clerget
Clerget was the name given to a series of early rotary aircraft engine types of the World War I era that were designed by Pierre Clerget. Manufactured in both France by Clerget-Blin and Great Britain by Gwynne Limited, they were used on such aircraft as the Sopwith Camel and Vickers Gunbus.In the...

 handbook advised that all necessary control was to be effected using the throttle, and the engine was to be stopped and started by turning the fuel on and off. Pilots were advised to avoid use of the cut out switch as it would eventually damage the engine.

The blip switch is, however, still recommended for use during landing rotary-engined aircraft in modern times as it allows pilots a more reliable, quick source of power that lends itself to modern airfields. The landing procedure using a blip switch involved shutting off the fuel using the fuel lever, while leaving the blip switch on. The windmilling propeller allowed the engine to continue to spin without delivering any power as the aircraft descended. It was important to leave the blip switch on while the fuel was shut off to allow the spark plugs to continue to spark and keep them from oiling up, while the engine could easily be restarted simply by re-opening the fuel valve. If a pilot shut the engine off by holding the blip switch down without cutting off the fuel, fuel would continue to pass through the engine without combusting and raw fuel/air mix would collect in the cowling. This could cause a serious fire when the switch was released, or alternatively could cause the spark plugs to oil up and prevent the engine from restarting.

Millet

Félix Millet showed a 5-cylinder rotary engine built into a bicycle wheel at the Exposition Universelle
Exposition Universelle (1889)
The Exposition Universelle of 1889 was a World's Fair held in Paris, France from 6 May to 31 October 1889.It was held during the year of the 100th anniversary of the storming of the Bastille, an event traditionally considered as the symbol for the beginning of the French Revolution...

 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
Darracq
Automobiles Darracq S.A. was a French motor vehicle manufacturing company founded in 1896 by Alexandre Darracq.Using part of the substantial profit he had made from selling his Gladiator bicycle factory, Alexandre Darracq began operating from a plant in the Parisian suburb of Suresnes...

 in 1900.

Hargrave

Lawrence Hargrave
Lawrence Hargrave
Lawrence Hargrave was an engineer, explorer, astronomer, inventor and aeronautical pioneer.- Early life :Hargrave was born in Greenwich, England, the second son of John Fletcher Hargrave and was educated at Queen Elizabeth's Grammar School, Kirkby Lonsdale, Westmorland...

 first developed a rotary engine in 1889 using compressed air, intending it to be used in powered flight. Weight of materials and lack of quality machining prevented it becoming an effective power unit.

Balzer

Stephen Balzer of New York, a former watchmaker, constructed rotary engines in the 1890s. He was interested in the rotary layout for two main reasons:
  • In order to generate 100 hp at the low rpm
    Revolutions per minute
    Revolutions per minute is a measure of the frequency of a rotation. It annotates the number of full rotations completed in one minute around a fixed axis...

     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
    Flywheel
    A flywheel is a rotating mechanical device that is used to store rotational energy. Flywheels have a significant moment of inertia, and thus resist changes in rotational speed. The amount of energy stored in a flywheel is proportional to the square of its rotational speed...

    , 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 in which they were mounted were at rest, which was important, as the low airspeed attainable by aircraft of the time provided limited cooling airflow, and alloys of the day were less advanced than they are now. Balzer's early designs even dispensed with cooling fins, although subsequent rotaries did have this common feature of air-cooled engines.


Balzer produced a 3-cylinder, rotary engined car in 1894, then later became involved in Langley
Samuel Pierpont Langley
Samuel Pierpont Langley was an American astronomer, physicist, inventor of the bolometer and pioneer of aviation...

'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
Charles M. Manly
Charles M. Manly was an American engineer who helped Smithsonian Institution Secretary Samuel Langley build The Great Aerodrome, which was intended to be a manned, powered, winged flying machine....

, creating the notable Manly-Balzer engine.

De Dion-Bouton

The famous De Dion-Bouton
De Dion-Bouton
De Dion-Bouton was a French automobile manufacturer and railcar manufacturer operating from 1883 to 1932. The company was founded by the Marquis Jules-Albert de Dion, Georges Bouton and his brother-in-law Charles Trépardoux....

 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
Adams-Farwell
Adams-Farwell was a brass era American automobile manufacturer from Dubuque, Iowa, founded by Herbert and Eugene Adams and Fay Oliver Farwell at the end of the 19th century....

 was another early US rotary engine which was being manufactured for use in automobiles by 1901. Emil Berliner sponsored its development 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
Clerget 9B
-See also:-Bibliography:* Gunston, Bill. World Encyclopaedia of Aero Engines. Cambridge, England. Patrick Stephens Limited, 1989. ISBN 1-85260-163-9...

 and Bentley BR1
Bentley BR1
-See also:...

 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 gifted engineers and the grandsons of famous French engineer Marc Seguin
Marc Seguin
Marc Seguin was a French engineer, inventor of the wire-cable suspension bridge and the multi-tubular steam-engine boiler.- Biography :...

. In 1906 the eldest brother, Louis, had formed the Société des Moteurs Gnome
Gnome et Rhône
Gnome et Rhône was a major French aircraft engine manufacturer. Between 1914 and 1918 they produced 25,000 of their 9-cylinder Delta and Le Rhône 110 hp rotary designs, while another 75,000 were produced by various licensees, powering the majority of aircraft in the first half of the war on...

 to build stationary engine
Stationary engine
A stationary engine is an engine whose framework does not move. It is normally used not to propel a vehicle but to drive a piece of immobile equipment such as a pump or power tool. They may be powered by steam; or oil-burning or internal combustion engines....

s for industrial use, having licensed production of the Gnom single-cylinder stationary engine from Motorenfabrik Oberursel
Motorenfabrik Oberursel
Motorenfabrik Oberursel A.G. was a German manufacturer of automobile, locomotive and aircraft engines situated in Oberursel , near Frankfurt , Germany. During World War I it supplied a major 100 hp-class rotary engine that was used in a number of early-war fighter aircraft designs...

, who would themselves build similar rotary aviation engines for the German aircraft of the Luftstreitkräfte
Luftstreitkräfte
The Deutsche Luftstreitkräfte , known before October 1916 as Die Fliegertruppen des deutschen Kaiserreiches , or simply Die Fliegertruppen, was the air arm of the Imperial German Army during World War I...

 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 was a 5-cylinder model which developed 34 hp, and which was a radial rather than a rotary. They then turned to rotary engines in the interests of better cooling, and the world's first production rotary engine, the 7-cylinder, 50 hp "Omega
Gnome Omega
|-See also:-Bibliography:* Lumsden, Alec. British Piston Engines and their Aircraft. Marlborough, Wiltshire: Airlife Publishing, 2003. ISBN 1-85310-294-6....

" was shown at the 1908 Paris automobile show. The Gnome Omega No. 1 still exists, having been preserved by Lauren S. McCready
Lauren S. McCready
Rear Admiral Lauren S. McCready was one of the builders and founders of the United States Merchant Marine Academy, "Kings Point."...

, and is now in the collection of the Smithsonian's National Air and Space Museum
National Air and Space Museum
The National Air and Space Museum of the Smithsonian Institution holds the largest collection of historic aircraft and spacecraft in the world. It was established in 1976. Located in Washington, D.C., United States, it is a center for research into the history and science of aviation and...

. 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 thick, while the connecting rods were milled with deep central channels to reduce weight. While somewhat low powered in terms of horsepower per litre, its power-to-weight ratio was an outstanding 1 hp per kg.

The following year, 1909, the inventor Roger Ravaud fitted one to his Aéroscaphe, a combination hydrofoil
Hydrofoil
A hydrofoil is a foil which operates in water. They are similar in appearance and purpose to airfoils.Hydrofoils can be artificial, such as the rudder or keel on a boat, the diving planes on a submarine, a surfboard fin, or occur naturally, as with fish fins, the flippers of aquatic mammals, the...

/aircraft, which he entered in the motor boat and aviation contests at Monaco. However, it was Henry Farman
Henry Farman
Henri Farman Henri Farman Henri Farman (26 May 1874 – 17 July 1958 was a French pilot, aviator and aircraft designer and manufacturer with his brother Maurice Farman. His family was British and he took French nationality in 1937.-Biography:...

's use of the Gnome at the famous Rheims aircraft meet that year which brought it to prominence, when he won the Grand Prix for the greatest non-stop distance flown - 180 kilometres (111.8 mi) - and also created a world record for endurance flight.

The very first successful seaplane flight, of Henri Fabre
Henri Fabre
Henri Fabre was a French aviator and the inventor of Le Canard, the first seaplane in history.Henri Fabre was born into a prominent family of shipowners in the city of Marseilles. He was educated in the Jesuit College of Marseilles, where he undertook advanced studies in sciences. He then studied...

's Le Canard, was powered by a Gnome Omega on March 28, 1910 near Marseille
Marseille
Marseille , known in antiquity as Massalia , is the second largest city in France, after Paris, with a population of 852,395 within its administrative limits on a land area of . The urban area of Marseille extends beyond the city limits with a population of over 1,420,000 on an area of...

.

Production of Gnome rotaries increased rapidly, with some 4,000 being produced before World War I, and the Omega's power output was increased to 80 hp, and eventually to 110 hp. By the standards of other engines of the period, the Gnome was considered not particularly temperamental, and was considered reliable, being 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 eliminated the cylinder inlet valves, and had a single exhaust valve in each cylinder head which doubled as an air intake. Each cylinder had transfer ports of the type used on two-stroke engines at its bottom which connected with the crankcase. 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 which was later abandoned due to causing burning of the valves. 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, and was the last known rotary engine design to use such a cylinder head valving format.

Rotary engines produced by the Clerget
Clerget
Clerget was the name given to a series of early rotary aircraft engine types of the World War I era that were designed by Pierre Clerget. Manufactured in both France by Clerget-Blin and Great Britain by Gwynne Limited, they were used on such aircraft as the Sopwith Camel and Vickers Gunbus.In the...

 and Le Rhône
Le Rhône
Le Rhône was the name given to a series of popular rotary aircraft engines produced in France by Société des Moteurs Le Rhône and the successor company of Gnome et Rhône. They powered a number of military aircraft types of the First World War...

 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
Motorenfabrik Oberursel A.G. was a German manufacturer of automobile, locomotive and aircraft engines situated in Oberursel , near Frankfurt , Germany. During World War I it supplied a major 100 hp-class rotary engine that was used in a number of early-war fighter aircraft designs...

 firm who designed the original Gnom engine. Oberursel was later purchased by Fokker
Fokker
Fokker was a Dutch aircraft manufacturer named after its founder, Anthony Fokker. The company operated under several different names, starting out in 1912 in Schwerin, Germany, moving to the Netherlands in 1919....

, whose 80 hp Gnome Lambda copy was known as the Oberursel U.0. It was not at all uncommon for French Gnomes, as used in the earliest examples of the Bristol Scout
Bristol Scout
The Bristol Scout was a simple, single seat, rotary-engined biplane originally intended as a civilian racing aircraft. Like other similar fast, light aircraft of the period - it was acquired by the RNAS and the RFC as a "scout", or fast reconnaissance type...

 biplane, to meet German versions, powering Fokker E.I
Fokker E.I
|-See also:-References:NotesBibliography* Boyne, Walter J. The Smithsonian Book of Flight for Young People. Washington, DC: Smithsonian Institution, 1988. ISBN 0-689-31422-1....

 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
Fokker E.IV
|-See also:...

 fighter monoplane and Fokker D.III
Fokker D.III
-Bibliography:* Gray, Peter and Owen Thetford. German Aircraft of the First World War. London: Putnam, 1962. ISBN 0-93385-271-1*Green, William and Gordon Swanborough. The Complete Book of Fighters. New York: Smithmark, 1994. ISBN 0-8317-3939-8....

 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
Power-to-weight 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 measurement of actual performance of any engine or power sources...

 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. The rotating mass of the engine also made it, in effect, a large gyroscope
Gyroscope
A gyroscope is a device for measuring or maintaining orientation, based on the principles of angular momentum. In essence, a mechanical gyroscope is a spinning wheel or disk whose axle is free to take any orientation...

. During level flight the effect was not especially apparent, however when turning the gyroscopic precession became noticeable. Due to the direction of the engine's rotation the left-turns required some degree of 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, while the Sopwith Camel
Sopwith Camel
The Sopwith Camel was a British First World War single-seat biplane fighter introduced on the Western Front in 1917. Manufactured by Sopwith Aviation Company, it had a short-coupled fuselage, heavy, powerful rotary engine, and concentrated fire from twin synchronized machine guns. Though difficult...

 suffered to such an extent that it required left rudder for both left and right turns and could be extremely hazardous if full power was used over the top of a loop at low airspeeds. Trainee Camel pilots were warned to attempt their first hard right turns only at altitudes above 1000 ft (304.8 m). Predictably, the Camel's most famous German foe, the Fokker Dr.I
Fokker Dr.I
The Fokker Dr.I Dreidecker was a World War I fighter aircraft built by Fokker-Flugzeugwerke. The Dr.I saw widespread service in the spring of 1918...

 triplane
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 may occasionally be.-Design principles:...

, also used a rotary engine, usually the Oberursel Ur.II clone of the French-built Le Rhone 9J
Le Rhône 9J
|-See also:-Bibliography:* Lumsden, Alec. British Piston Engines and their Aircraft. Marlborough, Wiltshire: Airlife Publishing, 2003. ISBN 1-85310-294-6....

 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
Charles Benjamin Redrup
Charles Benjamin Redrup was a British aeronautical engineer and inventor, who designed several innovative axial engines.-Early life:Redrup was born in Newport, Wales in 1878, his father moving to Barry, Vale of Glamorgan shortly afterwards...

 had demonstrated to the Royal Flying Corps
Royal Flying Corps
The Royal Flying Corps was the over-land air arm of the British military during most of the First World War. During the early part of the war, the RFC's responsibilities were centred on support of the British Army, via artillery co-operation and photographic reconnaissance...

 at Hendon
Hendon
Hendon is a London suburb situated northwest of Charing Cross.-History:Hendon was historically a civil parish in the county of Middlesex. The manor is described in Domesday , but the name, 'Hendun' meaning 'at the highest hill', is earlier...

 a 'Reactionless' engine in which the crankshaft
Crankshaft
The crankshaft, sometimes casually abbreviated to crank, is the part of an engine which translates reciprocating linear piston motion into rotation...

 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 the Air Ministry and Redrup changed the design to a static radial engine which later flew in Vickers F.B.12
Vickers F.B.12
|-See also:...

b and F.B.16
Vickers F.B.16
|-See also:-References:* Andrews, C.F. and E.B. Morgan. Vickers Aircraft since 1908. London:Putnam, 1988. ISBN 0 85177 815 1.*Bruce, J.M. British Aeroplanes 1914–18. London:Putnam, 1957....

 aircraft.

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.

One clever attempt to rescue the design, in a similar manner to Redrup's British "reactionless" engine concept, was made by Siemens AG
Siemens AG
Siemens AG is a German multinational conglomerate company headquartered in Munich, Germany. It is the largest Europe-based electronics and electrical engineering company....

. 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 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 Sh.III
Siemens-Halske's Sh.III was an 11-cylinder, air-cooled rotary engine developed in Germany during World War I, similar to the Sh.I.-Design:It shared with its predecessor the unusual design feature of having its internal workings rotating in a clockwise direction as seen from "nose-on", within the...

, with less drag and less net torque. It was also apparently the only rotary engine to use a normal carburetor, which could be controlled by a conventional throttle, just as in an in-line engine. Used on the Siemens-Schuckert D.IV
Siemens-Schuckert D.IV
The Siemens-Schuckert D.IV was a late-World War I fighter aircraft from Siemens-Schuckert . Considered by many to be the best fighter to see action during the war, it reached service too late and was produced in too few numbers to have any effect on the war effort.-Earlier designs:Siemens-Schuckert...

 fighter, the new engine created what is considered by many to be the best fighter aircraft
Fighter aircraft
A fighter aircraft is a military aircraft designed primarily for air-to-air combat with other aircraft, as opposed to a bomber, which is designed primarily to attack ground targets...

 design of the war.

One new rotary powered aircraft, Fokker's own D.VIII
Fokker D.VIII
-See also:-References:* Weyl, A.R. Fokker: The Creative Years. 1988. ISBN 0-851778-17-8....

, was designed at least in part to provide some use for the Oberursel factory's backlog of otherwise redundant 110 hp Ur.II engines, themselves clones of the Le Rhône 9J
Le Rhône 9J
|-See also:-Bibliography:* Lumsden, Alec. British Piston Engines and their Aircraft. Marlborough, Wiltshire: Airlife Publishing, 2003. ISBN 1-85310-294-6....

 rotary.

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
Royal Air Force
The Royal Air Force is the aerial warfare service branch of the British Armed Forces. Formed on 1 April 1918, it is the oldest independent air force in the world...

 probably used rotary engines for longer than most other operators - the RAF's standard post-war fighter, the Sopwith Snipe
Sopwith Snipe
The Sopwith 7F.1 Snipe was a British single-seat biplane fighter of the Royal Air Force . It was designed and built by the Sopwith Aviation Company during the First World War, and came into squadron service a few weeks before the end of that conflict, in late 1918.The Snipe was not a fast aircraft...

, used the Bentley BR2
Bentley BR2
-See also:-Bibliography:* Gunston, Bill. World Encyclopedia of Aero Engines. Cambridge, England. Patrick Stephens Limited, 1989. ISBN 1-85260-163-9*Jane's Fighting Aircraft of World War I. London. Studio Editions Ltd, 1993. ISBN 1-85170-347-0...

 rotary, and the standard trainer, the Avro 504
Avro 504
The Avro 504 was a World War I biplane aircraft made by the Avro aircraft company and under licence by others. Production during the War totalled 8,970 and continued for almost 20 years, making it the most-produced aircraft of any kind that served in World War I, in any military capacity, during...

K, had a universal mounting to allow the use of several different types of low powered rotary, of which there was a large surplus supply. However, the cheapness of war-surplus engines had to be balanced against their poor fuel efficiency
Fuel efficiency
Fuel efficiency is a form of thermal efficiency, meaning the efficiency 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, which in turn may vary per application, and this spectrum of variance is...

 and the operating expense of their total loss lubrication system.

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.

Use in cars and motorcycles

Although rotary engines were mostly used in aircraft, a few cars and motorcycles were built with rotary engines. A famous motorcycle, winning many races, was the Megola
Megola
The Megola was a German motorcycle produced between 1921 and 1925 in Munich. Like Bimota, the name is a portmanteau derived loosely from the names of its designers Meixner, Cockerell, and Landgraf.-An Unusual Design:...

, which had a rotary engine inside the front wheel. Another motorcycle with a rotary engine was Charles Redrup
Charles Benjamin Redrup
Charles Benjamin Redrup was a British aeronautical engineer and inventor, who designed several innovative axial engines.-Early life:Redrup was born in Newport, Wales in 1878, his father moving to Barry, Vale of Glamorgan shortly afterwards...

'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
Barry Engine
The Barry Engine first appeared in 1904 when it was exhibited at the Stanley Exhibition in London's Burners Hall. Designed by Charles Benjamin Redrup and manufactured in partnership with Alban Williams by the Barry Motor Company, the engine was a two-cylinder supercharged rotary 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.

In the 1940s Cyril Pullin
Cyril Pullin
Cyril Pullin 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 helicopter flight in 1938. Cyril Pullin died in 1965 aged 72....

 developed the Powerwheel, a wheel with a rotating one-cylinder engine, clutch
Clutch
A clutch is a mechanical device which provides for the transmission of power from one component to another...

 and drum brake
Drum brake
A drum brake is a brake in which the friction is caused by a set of shoes or pads that press against a rotating drum-shaped part called a brake drum....

 inside the hub, but it never entered production.

Cars with rotary engines were built by American companies Adams-Farwell
Adams-Farwell
Adams-Farwell was a brass era American automobile manufacturer from Dubuque, Iowa, founded by Herbert and Eugene Adams and Fay Oliver Farwell at the end of the 19th century....

, Bailey, Balzer and Intrepid, amongst others.

Other rotary engines

Besides the configuration described in this article with cylinders moving around a fixed crankshaft, several other very different engine designs are also called rotary engines. The most notable pistonless rotary engine
Pistonless rotary engine
A pistonless rotary engine is an internal combustion engine that does not use pistons in the way a reciprocating engine does, but instead uses one or more rotors, sometimes called rotary pistons...

, the Wankel rotary engine
Wankel engine
The Wankel engine is a type of internal combustion engine using an eccentric rotary design to convert pressure into a rotating motion instead of using reciprocating pistons. Its four-stroke cycle takes place in a space between the inside of an oval-like epitrochoid-shaped housing and a rotor that...

 has also been used in cars (notably by NSU
NSU Motorenwerke AG
NSU Motorenwerke AG, normally just NSU, was a German manufacturer of automobiles, motorcycles and pedal cycles, founded in 1873. It was acquired by Volkswagen Group in 1969...

 in the Ro80
NSU Ro 80
The NSU Ro 80 was a technologically advanced large sedan-type automobile produced by the German firm of NSU from 1967 until 1977. Most notable was the powertrain; a , 995 cc twin-rotor Wankel engine driving the front wheels through a semi-automatic transmission employing an innovative vacuum system...

 and by Mazda
Mazda
is a Japanese automotive manufacturer based in Fuchū, Aki District, Hiroshima Prefecture, Japan.In 2007, Mazda produced almost 1.3 million vehicles for global sales...

 in a variety of cars such as the RX-series which includes the popular RX-7 and RX-8), as well as in some experimental aviation applications.

In the late 1970s a concept engine called the Bricklin-Turner Rotary Vee was being tested. The Rotary Vee is similar in configuration to the elbow steam engine
Elbow engine
An elbow engine is a piston-based engine typically fed by steam or compressed air to drive a flywheel and/or mechanical load. Although not commonly used today for practical purposes, it is still built by hobbyists for its uniqueness.- Principle of operation :...

. The Rotary Vee uses piston pairs connected as solid V shaped members with each end floating in a pair of rotating cylinders clusters. The rotating cylinder cluster pair 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 yet gone into production. The Rotary Vee was intended to power the Bricklin SV-1
Bricklin SV-1
The Bricklin SV-1 was a gull-wing door sports car assembled in Saint John, New Brunswick, Canada. The body panels were manufactured in a separate plant in Minto, New Brunswick. Manufactured from 1974 until early 1976 for the U.S. market, the car was the creation of Malcolm Bricklin, an American...

.

See also

  • Petrol engine
    Petrol engine
    A petrol engine is an internal combustion engine with spark-ignition, designed to run on petrol and similar volatile fuels....

  • Monosoupape engine
    Gnome Monosoupape
    The Monosoupape , was a rotary engine design first introduced in 1913 by Gnome Engine Company...

  • Manly-Balzer engine
  • Nutating disc engine
    Nutating disc engine
    A nutating disc engine is an internal combustion engine comprising fundamentally of one moving part and a direct drive onto the crankshaft...

  • Quasiturbine
    Quasiturbine
    The Quasiturbine or Qurbine engine is a proposed pistonless rotary engine using a rhomboidal rotor whose sides are hinged at the vertices. The volume enclosed between the sides of the rotor and the rotor casing provide compression and expansion in a fashion similar to the more familiar Wankel...

  • Turbine
    Turbine
    A turbine is a rotary engine that extracts energy from a fluid flow and converts it into useful work.The simplest turbines have one moving part, a rotor assembly, which is a shaft or drum with blades attached. Moving fluid acts on the blades, or the blades react to the flow, so that they move and...

  • Wankel rotary engine
    Wankel engine
    The Wankel engine is a type of internal combustion engine using an eccentric rotary design to convert pressure into a rotating motion instead of using reciprocating pistons. Its four-stroke cycle takes place in a space between the inside of an oval-like epitrochoid-shaped housing and a rotor that...


External links

The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
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