A motorcycle engine is an engine that powers a motorcycle.

Motorcycle engines may be two-stroke or four-stroke internal combustion engines, but other types have been used in small numbers. The engine typically drives the rear wheel. Most engines have a gearbox with two to six ratios, reverse gear is rare but does exist for sidecar use. Power is sent to the driven wheel by belt, chain or shaft. In Europe, before the 1969 Honda CB750, engine capacities typically ranged from about 50 cc to 750 cc; but since then machines with capacities up to 2,300 cubic centimetres (140 cu in) Triumph Rocket 3 have become common. In the USA, motorcycles with large capacities have been common for much longer.


History[edit]

Earliest motorcycle engine concept. This 1818 caricature was thought for many years to be entirely fanciful, until the Michaux-Perreaux, Roper and other steam cycles were rescued from obscurity, and the stories of the early steam cycle experiments were rediscovered. There were no steam motorcycles in 1818, but there soon would be.




The first motorcycles were powered by steam engines. The earliest example is the French Michaux-Perreaux steam velocipede of 1868. This was followed by the American Roper steam velocipede of 1869, and a number of other steam powered two and three wheelers, manufactured and sold to the public on through the early 20th century.[1]

Using frames based both on the earlier boneshaker and the later—and in many ways completely modern—safety bicycle design, these early steam motorcycles experimented with a variety of engine placement strategies, as well as transmission and options. While today nearly every motorcycle has its engine in the center of the frame; this became standard only around 1900-1910[verification needed] after nearly every possible engine location was tried. The origins of the scooter engine arrangement (including the shaft drive) can be traced back to the 19th century but the current layout became generally adopted after the Great War. The modern equivalent became universally popular in the 1950s[verification needed] and remains much the same today.[1]

The Otto cycle gasoline internal combustion engine was first used on an experimental two-wheeler created by Gottlieb Daimler to test the practicality of such an engine in a vehicle. This motorcycle, the Daimler Reitwagen, is credited as the world's first motorcycle by many authorities, partially on the assumption that a motorcycle is defined not as any two-wheel motor vehicle, but a two-wheel internal combustion engine motor vehicle.[1] The Oxford English Dictionary, for example, defines the word motorcycle this way.[2][3] The steam cycles were also simply neglected and forgotten by many historians, even as the Michaux-Perreaux waited forty years[verification needed] on display in the National Motor Museum, Beaulieu.[verification needed][4]

In recent years, a surge in interest in clean energy has put many new electric powered two wheelers on the market, and they are registered as motorcycles or scooters, without the type of powerplant being an issue. Diesel motorcycles were also been experimented with briefly throughout the 20th century, and are again the subject of interest due to fuel economy and the needs of military logistics. The USMC has ordered a new diesel motorcycle, the M1030 M1, that can use the same fuel, JP-8, as the rest of their armored vehicles, aircraft, cars and trucks.[5]

The overwhelming majority of the motorcycles produced and used in the world today have small displacement air-cooled single-cylinder engines, both two- and four-strokes.[citation needed] In the wealthier parts of the world, Europe and Japan, larger displacements and multiple cylinders are common alongside small-displacement bikes required by various licensing and rider experience requirements, and so a very diverse range of sizes, cylinder numbers, configurations, and cooling systems are seen on the road. Many developed countries have graduated licensing, where a rider is licensed for a period of time to ride only smaller-displacement motorcycles before being allowed to ride larger ones. In the United States, there are no such mandates, and so the mix is skewed even further to the largest displacements, consumer demand drives manufacturers to offer their largest motorcycles to that country, and to export far fewer sub-600 cc (37 cu in) models to the American market.[citation needed]

Types[edit]
Almost all production motorcycles have gasoline (UK petrol) internal combustion engines. Both four-stroke and two-stroke engines are used, but strict emission laws have led to far fewer two-strokes. A few have used Wankel rotary engines, but no Wankel bikes are currently in production. Motorcycle engines can be air cooled or liquid cooled, and optionally include oil cooling as well. Some scooters use batteries and an electric motor. (The 2009 TT races introduced a new category 'TTX' for electric bikes using fuel-cells or batteries).

Motorcycle engines can be mounted transversely; with the crankshaft aligned perpendicular to the frame or longitudinally, with the crankshaft parallel to the frame. Motorcycles with transversely mounted engines are more suited to have chain or belt final-drive. Motorcycles with longitudinally mounted engines are more suited for shaft final-drive.

Motor scooters often have the engine as part of the rear suspension, so the engine is not fixed rigidly to the main frame. Instead, the combined engine-transmission-swingarm assembly is pivoted to follow the road surface and is part of the "unsprung weight". The chain final-drive of scooters runs in an oil-bath within the engine casings. "Step-throughs" motorcycles may have a rigidly fixed engine, or may have a scooter-type arrangement.

Two-stroke and four-stroke[edit]
Two-stroke engines have fewer moving parts than four-stroke engines, and produce twice the number of power strokes per revolution; consequently, two-stroke engines are more powerful for their mass. Two-strokes offer stronger acceleration, but similar top speed compared to a four-stroke engine.[citation needed] They are also easier to start.[citation needed] Two-stroke engines have shorter life due to poorer piston lubrication, since lubrication comes from the fuel-oil mix.

Four-stroke engines are generally associated with a wider power band making for somewhat gentler power delivery, but technology such as reed valves and exhaust power-valve systems has improved ride-ability on two-strokes.[citation needed] Fuel economy is also better in four-strokes due to more complete combustion of the intake charge in four-stroke engines.

Nevertheless, two-strokes have been largely replaced on motorcycles in developed nations due to their environmental disadvantages. Cylinder lubrication is necessarily total-loss and this inevitably leads to a smokey exhaust, particularly on wide throttle openings. Two-stroke-engined motorcycles continue to be made in large numbers, but mostly low-power mopeds, small scooters and step-through underbones where they still compete strongly with four-strokes (including the highest-selling motorcycle of all time, the 50 cc Honda Super Cub). The major markets of two-stroke motorcycles are in developing nations.

Cylinder heads (four-stroke)[edit]
Main article: Cylinder head
Cylinder head design has a significant effect on the efficiency of combustion, and hence the power output of the engine. The head may be flat, in which case the combustion chamber resides within the cylinder and/or a depression in the piston crown, but usually a "dome" within the cylinder head provides most of the combustion volume. In motorcycles, valve gear tends to be side valve, overhead valve (ohv) with pushrod operation, (single)overhead cam, (s)ohc, and double overhead cam, dohc. A cylinder with desmodromic valves may have three or even four camshafts. An ohc (or dohc) cylinder head will have at least two valves per cylinder (1 inlet and 1 exhaust), but multi-valve engines may have three (2 inlet and 1 exhaust), or four (2 inlet and 2 exhaust), or even five (3 inlet and 2 exhaust). Cylinder heads are the hottest part of the engine and require adequate cooling, typically air cooling, oil cooling or liquid cooling.

Some motorcycles such as Harley-Davidsons, Moto Guzzis and BMWs become identifiable by their cylinder-head types, namely airhead, panhead, oilhead, and even knucklehead.[4][6] The Ducati desmos head enables higher rpm to be achieved without detrimental valve float.

Valve control (four-stroke)[edit]
See also: Variable valve timing
In a side-valve engine, the valves are operated from the "underhead" cam without special valve gear. Overhead valve (OHV) engines have valves operated by pushrods. Single- and double-overhead camshaft (SOHC and DOHC, respectively) engines have overhead camshafts typically operated by chain, belt, gear train or bevel gear drive.

The earliest motorcycle engines had exhaust valves operated in the same way as a side-valve engine, but they had overhead intake valves held closed by a weak spring. The intake valve was opened by the suction caused by the intake stroke. As the need for mechanical control of the intake valve arose, the design was modified by adding another cam to the camshaft and using a pushrod and rocker arm to operate the intake valve.[7]

Honda equipped the CBR400F with REV (described as "revolution responding type valve pausing mechanism") in 1983,[8] This system enabled to switch over the number of valve operations per cylinder between low and medium speed revolution range and high speed revolution range. In 2002, Honda introduced HYPER VTEC in the VFR800 Interceptor. In 2006, Kawasaki introduced VVT in the Concours 14.[9]

Unit construction[edit]
Main article: Unit construction
Engines and gearboxes were originally separate items, the gearbox being driven by a "primary chain". Later designs combined the two elements into a single "unit construction". Some manufacturers, such as Norton and Enfield continued with "pre-unit" construction until recently, and Harley-Davidson still makes pre-unit engines today.

In the early 1960s, BSA introduced new short-stroke unit construction 500 and 650 cc parallel twins to replace their existing pre-unit long-stroke engines. Triumph modified their large pre-unit 500 and 650 cc parallel twins into unit-construction engines. The smaller Triumph 350 and 500 cc twins had been unit construction from their introduction in 1957. The decision by Lucas to discontinue making dynamos and magnetos, and to produce only alternators and coil ignition systems, was a significant factor in forcing the redesign.

Traditionally, engines and gearboxes had separate lubrication systems with different grades of oil; but modern practice is to use the same oil for both.

Cylinders and configuration[edit]
The majority of motorcycle engines are configured as singles, parallel twins, triples, fours and sixes; and all these may be inline or transverse. Vee engines include V-twins and V-fours, and horizontally opposed engines include flat-twins, flat-fours and flat-sixes. Wankel engines are either single-rotor or twin-rotor. Bigger bikes tend to have more cylinders for smoothness and increased power. Modern singles range in capacity from 50 cc to 660 cc, twins from 175 cc to 1,800 cc, triples from 380 cc to 2,300 cc, and so on.

Single[edit]

1960 BSA Gold Star
Main article: Single-cylinder engine
Single-cylinder engines (aka "singles" or "thumpers") have the cylinder vertical, inclined or horizontal, the last type most common in step-through motorcycles. Single-cylinder engines require both a larger flywheel and a heavier-duty gearbox than multicylinder engines. Small singles are cheap to build and maintain and are suitable as cheap utility motorcycles.

Until the mid-1960s, road-racing machines (such as Matchless, AJS and Norton) tended to be large singles, but since then multicylinder racers have become the norm. Off-road bikes still use single-cylinder engines; but the new category of dual-sport bikes tend to use twins or triples.

Twin[edit]
Straight

1962 Honda CB77 Superhawk 305 cc (18.6 cu in) twin engine.
Main article: Straight-two engine
Starting with Edward Turner's 1937 Triumph Speed Twin design, and until the mid-1970s, the parallel-twin was the most common British motorcycle type. Parallel-twins are usually mounted transversely, with the cylinders side by side above the crankshaft, and with exhaust pipes at the front, in the cool airstream. Longitudinal twins (aka "inline twins") include the 500 cc Sunbeam S7 and S8. There are three crankshaft configurations for this engine: 360°, 180°, and the newer 270°. Parallel twins usually have only two main bearings.

V-twin

Harley-Davidson Sportster V-twin
Main article: V-twin engine
In a V-twin engine the cylinders form a "V" around the crankshaft. A Vee-angle of 90°, as used by Ducati and Moto Guzzi, can give perfect primary and secondary balance, with a pleasingly irregular firing order. A lesser angle gives a more compact motor, but one which is prone to vibration, such as 42° (Indian), 45° (Harley-Davidson), 52° Honda, and 60° (Aprilia). Most V-twins have a single crankpin shared by side-by-side connecting rods (so that the cylinders are slightly offset), but a variation is to have a single crankpin with "fork & blade" con-rods, to keep the cylinders in line. Non-90° V-twins may have offset crankpins to try to reduce vibration.

V-twins may be mounted either longitudinally with the cylinders protruding either side (e.g. Honda CX500 and Moto Guzzi ), or transversely,[10](e.g. Harley Davidson, Ducati, Hesketh, Vincent, Moto Morini and Aprilia). Transverse V-twins can raise difficulties in cooling the aft cylinder, and in siting the airbox, battery, aft carburetter, and aft exhaust pipe.

Flat twin

BMW's opposed twin on a 1954 R68
Main article: Flat-twin engine
In a flat-twin (boxer) engine, the cylinders are horizontally opposed. The boxer has perfect primary balance, balance only a small rocking couple, and (unlike a V-twin), regular firing intervals, producing very low vibration levels (without the use of counterbalance shafts). Such engines are usually mounted with a longitudinal-crankshaft, with the cylinders protrude into the airstream, so that a flat twin can satisfactorily be air-cooled. Flats twins are made by BMW, Ural, Harley-Davidson's WW2 "XA" model, Marusho, and historically by Douglas. The longitudinal mounting makes the flat twin highly suitable for shaft final drive.

Some early motorcycles used transverse-crank flat twin engines.

Tandem twin
Main article: U engine
The Tandem Twin where the cylinders are longitudinal, and have two cranks geared together such as Kawasaki's KR250 road bike and KR250 and KR350 GP Bikes. A tandem twin is effectively a pair of geared singles, and is to be distinguished from an inline twin such as the Sunbeam S7. Tandem twins are suitable primarily for two-stroke racers.

Triple[edit]
Inline triple

Triumph Rocket III inline-3
Main article: Straight-three engine
Three-cylinder engines, aka triples, are normally mounted transversely. The British Hinckley Triumph factory has specialised in transverse triples, although their 2,300 cc Rocket III has its engine mounted longitudinally. Other examples are the Benelli' "Tre"and the Yamaha XS750. The Italian firm Laverda made a few 1,000 cc and 1,200 cc triples. Curiously, some Laverda Triples had 120° cranks, while some had 180° cranks (essentially three-quarters of a four). BMW made the K75 longitudinally mounted 750 cc triple with the cylinders parallel to the ground. Meriden Triumph developed the 750 cc Trident, from which BSA "badge-engineered" the Rocket-3.

Some triples were two-strokes. The Kawasaki triples were produced with capacities of 250, 350, 400, 500, and 750 cc in the 1970s, while Suzuki produced 380, 550, and 750 triples (the last being water-cooled). Motobecane made 350 cc and fuel-injected 500 cc triples with 3 into 4 pipes in the early seventies. Honda produced the water-cooled V-3 two-strokes MVX250 and NS400. There have been various race bike triples such as Kawasaki KR750, Suzuki TR750 transverse 3's, and Proton/Modenas KR3, Honda NS500 V-3s.

Four[edit]
Four-cylinder engines are most commonly found in a transverse-mounted inline four layout, although some are longitudinal (as in the earlier BMW K100). V-4 and boxer designs (as in the earlier Honda Gold Wing) have been produced. One of the more unusual designs was the Ariel Square Four, effectively two parallel-twin engines one in front of the other in a common crankcase – it had remarkably little vibration due to the contra-rotating crankshafts.

Inline four

Honda CB750 transverse inline-4
Main article: Inline-four engine
[icon] This section requires expansion. (April 2010)
Production of four cylinder motorcycles began with the FN Four in 1905. The FN had its engine in line with the frame; this layout would be copied by manufacturers in Europe and the United States before World War II.[11] In the United States, inline fours made by Henderson and Indian were bought by enthusiasts and by police departments, the latter using them as pursuit motorcycles.[12][13][14]

Since the advent of the Honda CB750 straight-four engine, straight-fours have dominated the non-cruiser street motorcycle segments. The German manufacturer Münch based their motorcycles on four-cylinder car engines (e.g. Mammut 2000 has a 2.0l with a turbo and cylinder heads by Cosworth).

Flat four


A flat-4 or horizontally opposed-4 is a flat engine with four cylinders arranged horizontally in two banks of two cylinders on each side of a central crankcase. The pistons are usually mounted on the crankshaft such that opposing pistons move back and forth in opposite directions at the same time, somewhat like a boxing competitor punching their gloves together before a fight, which has led to it being referred to as a boxer engine. The configuration results in inherently good balance of the reciprocating parts, a low centre of gravity, and a very short engine length.


Main article: V4 engine
Honda uses V4 engines in the ST series and VFR series. As for two-stroke engines, there were four cylinders in the smaller classes such as Kawasaki's 125 cc KR3 square 4 and Yamaha's 250 cc RD500 V4 (RZ 500 in the US). Yamaha later raced transverse four TZ500/700/750's and virtually all the bikes in the last decade of the two-stroke GP500 era were fours (first squares then Vees) i.e. Honda, Kawasaki, Cagiva, Suzuki, Yamaha - Kawasaki also experimented with a trapezoidal four the 602S. Yamaha made the V4 RD500LC, and Suzuki the RG400 and RG500 square four road bikes.

Square four
Main article: U engine § Square four engine
A square four is a U engine with two cylinders on each side. This configuration was used on the Ariel Square Four motorcycle from 1931 to 1959. This design was revived as a two-stroke version on some racing Suzuki models, and their subsequent road-going version the RG500. Although some racing success was achieved, the road bikes didn't sell in great numbers, and the design was phased out in favour of in-line, four-stroke designs, as at the time two-stroke engines were quickly being superseded by more economical, reliable, and emissions-friendly four-strokes.




Main article: V5 engine
Honda has produced five-cylinder engines for racing, the RC211V 990 cc V5. No V5 engines are currently available in commercial production motorcycles.

Just prior to their collapse, BSA planned a modular family of bike engines based around a 200 cc single. The range was to include the single, a 400 cc twin, a 600 cc triple and a 1000 cc V5. None of these motorcycles reached production.[15]






Main article: Straight-six engine
The 1,047 cc Honda CBX was produced from 1978 to 1982. The 1,300 cc Kawasaki KZ1300 was produced from 1979 to 1989. Benelli made the 750 cc and 900 cc the Sei from 1972 to 1978. Honda made a 250 cc straight-six GP bike. The BMW K1600GT and K1600GTL, which were launched in 2011, have a transverse-mounted 1,649 cc engine.

Flat 6
Main article: Flat-six engine
The six-cylinder engine is currently used by Honda in the Gold Wing, and had previously been used in the Valkyrie and the Rune, both of which were cruiser developments of the Gold Wing.



Main article: V-8 engine
Galbusera built a V8 in 1938, and Moto Guzzi experimented over a period of two years with its dual-overhead-cam 500 cc V8 (the Otto Cylindri) in the 1950s. Some custom and one-off motorcycles use more than six cylinders. For example, the Boss Hoss motorcycle uses (5,700 cc, 6,000 cc and 8,200 cc) Chevy V-8 crate motors. In the 1990s Daimler-Chrysler manufactured a limited number of Tomahawk concept bikes featuring a Dodge Viper's V-10 engine. Australian company Drysdale have built short runs of 750 cc V8 superbikes and 1L V8 roadgoing motorcycles, both with engines specifically developed for the purpose. No major motorcycle manufacturer has used eight or more cylinders, although Honda made the 'almost' V8 oval-piston NR750 road bike and NR500 GP bike (having eight connecting rods, for example) and Morbidelli has shown two V8 prototype road bikes, but has yet to get off the ground.

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, in which the crankshaft remained stationary, with the entire crankcase and its attached cylinders rotating around it as a unit in operation. Its main application was in aviation, although it also saw use before its primary aviation role, in a few early motorcycles and automobiles.

This type of engine was widely used as an alternative to conventional inline engines (straight or V) during World War I and the years immediately preceding that conflict. They have been described as "a very efficient solution to the problems of power output, weight, and reliability".[1]

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 caused 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 to aspirate the fuel/air mixture through the hollow crankshaft and crankcase along with the lubricating medium, as in a two-stroke engine.
A rotary engine is essentially a standard Otto cycle engine, but instead of having a fixed cylinder block with rotating crankshaft as with a conventional radial engine, 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 was simply bolted to the front of the crankcase.

Three key factors contributed to the rotary engine's success at the time:[2]

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.
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 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, 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[3] 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[edit]
Rotary and radial engines 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[edit]
Monosoupape rotaries[edit]
It is often asserted that rotary engines had no carburetor and hence power could only be reduced by intermittently cutting the ignition using a "blip" switch. This was literally true only of the "Monosoupape" (single valve) type, which took the air supply in through the exhaust valve, and so could not be controlled via the crankcase intake. The "throttle" (fuel valve) of a monosoupape therefore provided only a very 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 an attempt to give greater control, but this caused the valves to burn and therefore it was abandoned.[1]

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 in perfect balance.[4] 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[edit]
Most rotaries however, 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 cylinder block, 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. 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 "throttling back", especially when landing, was often accomplished 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 preventing the engine from restarting. 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 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.[1]

Pilots of surviving or reproduction aircraft fitted with rotary engines still find, however, 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 failure of a windmilling engine to restart at the worst possible moment.

History[edit]
Millet[edit]

An 1897 Félix Millet motorcycle.
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 in 1900.[1]

Hargrave[edit]
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.[5]

Balzer[edit]
Stephen Balzer of New York, a former watchmaker, constructed rotary engines in the 1890s.[6] He was interested in the rotary layout for two main reasons:

To generate 100 hp (75 kW) 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, 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 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[edit]
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.[1]

Adams-Farwell[edit]
Main article: Adams-Farwell

An Adams-Farwell five cylinder rotary adapted for helicopter experimentation
The Adams-Farwell 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 and Bentley BR1 aviation rotaries, the Adams-Farwell rotaries had conventional exhaust and inlet valves mounted in the cylinder heads.[1]



Gnome[edit]

Sectional views of Gnome engine
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. In 1906 the eldest brother, Louis, had formed the Société des Moteurs Gnome[7] to build stationary engines for industrial use, having licensed production of the Gnom single-cylinder stationary engine from Motorenfabrik Oberursel—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 34 hp (25 kW), 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 50 hp (37 kW) "Omega" 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.[8] 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 (0.75 kW) per kg.

The following year, 1909, the inventor Roger Ravaud fitted one to his Aéroscaphe, a combination hydrofoil/aircraft, which he entered in the motor boat and aviation contests at Monaco. However, Henry Farman'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—180 kilometres (110 mi)—and also set a world record for endurance flight. The very first successful seaplane flight, of Henri Fabre's Le Canard, was powered by a Gnome Omega on March 28, 1910 near Marseille.

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 70 hp Gnome Lambda 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.[citation needed]

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.[9] 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 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 firm who designed the original Gnom engine. Oberursel was later purchased by Fokker, 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 biplane, to meet German versions, powering Fokker E.I Eindeckers, in combat, from the latter half of 1915 on.


A German Oberursel U.III engine on museum display
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 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[edit]
The favourable power-to-weight ratio 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, 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.[10] 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. 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, 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.[11] In some aircraft, this could be advantageous in situations such as dogfights. The Sopwith Camel 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 1,000 ft (300 m).[12] The Camel's most famous German foe, the Fokker Dr.I triplane, 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 at Hendon a 'Reactionless' engine in which the crankshaft 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,[13] 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.


A preserved Siemens-Halske Sh.III in a Vienna museum.
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 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, with less drag and less net torque.[14] Used on several late war types, notably the Siemens-Schuckert D.IV 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.[15]

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 110 hp (82 kW) 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 from India the castor oil necessary to properly lubricate their rotary engines. Substitutes were never entirely satisfactory - causing increased running temperatures and reduced engine life.[16][17][18]

Postwar[edit]
By the time the war ended, the rotary engine had become obsolete, and it disappeared from use quite quickly. The British Royal Air Force 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 230 hp) rotary engine ever built by the Allies of World War I. 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. However, designers had to balance the cheapness of war-surplus engines against their poor fuel efficiency and the operating expense of their total-loss lubrication system.

The first version of the 1921 Michel engine, an unusual opposed-piston cam engine, was a rotary engine.This was soon replaced by a very similar version, with the same cylinders and cam, but with the cylinders stationary and the cam track rotating in lieu of a crankshaft. A later version abandoned the cam altogether and used three coupled crankshafts.

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 Swedish FVM Ö1 Tummelisa advanced training aircraft served until 1935 and was fitted with a Le-Rhone-Thulin 90hp rotary engine.

Use in cars and motorcycles[edit]
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[3] was mounted inside a motorcycle frame.

In the 1940s Cyril Pullin developed the Powerwheel, a wheel with a rotating one-cylinder engine, clutch and drum brake inside the hub, but it never entered production.

Cars with rotary engines were built by American companies Adams-Farwell, Bailey, Balzer and Intrepid, amongst others.

Other rotary engines[edit]
Besides the configuration described in this article with cylinders moving around a fixed crankshaft, several different engine designs are also called rotary engines. The most notable pistonless rotary engine, the Wankel rotary engine has been used by NSU in the Ro80 car, by Mazda 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.[19][20] 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.