The ''Monosoupape'' ( French for single-valve), was a

rotary engine The rotary engine is an early type of internal combustion engine, usually designed with an odd number of cylinders per row in a radial configuration. The engine's crankshaft remained stationary in operation, while the entire crankcase and its ...

design first introduced in 1913 by Gnome Engine Company (renamed

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 (81 kW) rotary designs, while another 75,000 were produced by various licensee ...

in 1915). It used a clever arrangement of internal

transfer port Transfer may refer to: Arts and media * ''Transfer'' (2010 film), a German science-fiction movie directed by Damir Lukacevic and starring Zana Marjanović * ''Transfer'' (1966 film), a short film * ''Transfer'' (journal), in management studies * ...

s and a single pushrod-operated exhaust valve to replace the many moving parts found on more conventional rotary engines, and made the ''Monosoupape'' engines some of the most reliable of the era. British aircraft designer

Thomas Sopwith Sir Thomas Octave Murdoch Sopwith, Order of the British Empire, CBE, Hon FRAeS (18 January 1888 – 27 January 1989) was a British aviation pioneer, businessman and yachtsman. Early life Sopwith was born in Kensington, London, on 18 ...

described the ''Monosoupape'' as "one of the greatest single advances in aviation". Monosoupape engines were produced under license in large numbers in Britain, Russia, Italy and the US. Two differing nine-cylinder versions were produced, the 9B-2 and 9N, with differing displacements giving the larger displacement 9N version a nearly-cylindrical shaped crankcase, with the 9N also adopting a

dual ignition Dual Ignition is a system for spark-ignition engines, whereby critical ignition components, such as spark plugs and magnetos, are duplicated. Dual ignition is most commonly employed on aero engines,Crane, Dale: ''Dictionary of Aeronautical Terms, ...

system for increased flight safety. 2,188 units were produced under license in Britain, with an uprated version later built in Russia and the Soviet Union, two of which flew the Soviet

TsAGI The Central Aerohydrodynamic Institute (also (Zhukovsky) Central Institute of Aerodynamics, , TsAGI) is a Russian national research centre for aviation. It was founded in Moscow by Russian aviation pioneer Nikolai Yegorovich Zhukovsky on Decemb ...

-1EA single lift-rotor helicopter in 1931–32.

Background

Unlike other rotaries, the early Gnome engines like the

Gnome Omega The Gnome 7 Omega (commonly called the Gnome 50 hp) is a French seven-cylinder, air-cooled aero engine produced by Gnome et Rhône. It was shown at the Paris Aero Salon held in December 1908 and was first flown in 1909. It was the world's ...

Lambda Lambda (; uppercase , lowercase ; , ''lám(b)da'') is the eleventh letter of the Greek alphabet, representing the voiced alveolar lateral approximant . In the system of Greek numerals, lambda has a value of 30. Lambda is derived from the Phoen ...

and

Delta Delta commonly refers to: * Delta (letter) (Δ or δ), the fourth letter of the Greek alphabet * D (NATO phonetic alphabet: "Delta"), the fourth letter in the Latin alphabet * River delta, at a river mouth * Delta Air Lines, a major US carrier ...

used a unique arrangement of valves in order to eliminate

pushrod A valvetrain is a mechanical system that controls the operation of the intake and exhaust valves in an internal combustion engine. The intake valves control the flow of air/fuel mixture (or air alone for direct-injected engines) into the combu ...

s that operated during the inlet phase of the combustion cycle on more conventional engines. Instead, a single exhaust valve on the

cylinder A cylinder () has traditionally been a three-dimensional solid, one of the most basic of curvilinear geometric shapes. In elementary geometry, it is considered a prism with a circle as its base. A cylinder may also be defined as an infinite ...

head was operated by a pushrod that opened the valve when the pressure dropped at the end of the power stroke. A pressure-operated inlet valve, which was balanced by a counterweight to equalize the centrifugal forces, was placed in the centre of the piston crown, where it opened to allow the fuel–air charge to enter from the engine's central crankcase. Although ingenious, the system had several drawbacks: the cylinder heads had to be removed to perform maintenance of the intake valves, and to adjust the timing correctly. Fuel economy suffered in comparison to other rotaries because the inlet valves could not be opened and closed at the ideal times.

Design

In 1913, Louis Seguin and his brother Laurent (engineers who founded the ''Société Des Moteurs Gnome'' he Gnome motor companyin 1905) introduced the new ''Monosoupape'' series, which eliminated the inlet valve, replacing it with piston-controlled transfer ports similar to those found in a

two-stroke engine A two-stroke (or two-stroke cycle) engine is a type of internal combustion engine that completes a Thermodynamic power cycle, power cycle with two strokes of the piston, one up and one down, in one revolution of the crankshaft in contrast to a f ...

. Beginning with the power stroke, the

four-stroke A four-stroke (also four-cycle) engine is an internal combustion (IC) engine in which the piston completes four separate strokes while turning the crankshaft. A stroke refers to the full travel of the piston along the cylinder, in either directio ...

engine operated normally until the piston was just about to reach the bottom of its stroke (bottom dead center, or BDC), when the exhaust valve was opened "early". This let the still-hot burnt combustion gases "pop" out of the engine while the piston was still moving down, relieving exhaust pressure and preventing exhaust gases from entering the crankcase. After a small additional amount of travel, the piston uncovered 36 small ports around the base of the cylinder, leading to the

crankcase A crankcase is the housing in a reciprocating engine, piston engine that surrounds the crankshaft. In most modern engines, the crankcase is integrated into the engine block. Two-stroke engines typically use a crankcase-compression design, res ...

which held additional fuel–air mixture (the ''charge''). No transfer took place at this point since there was no pressure differential; the cylinder was still open to the air and thus at ambient pressure. The overhead valve exhausted directly into the

slipstream A slipstream is a region behind a moving object in which a wake of fluid (typically air or water) is moving at velocities comparable to that of the moving object, relative to the ambient fluid through which the object is moving. The term slips ...

since no

exhaust manifold In automotive engineering, an exhaust manifold collects the exhaust gases from multiple cylinders into one pipe. The word ''manifold'' comes from the Old English word ''manigfeald'' (from the Anglo-Saxon ''manig'' anyand ''feald'' old and ref ...

could be practically fitted to the spinning crankcase and cylinders. The lack of an exhaust manifold also saved weight and prevented excessive gyroscopic forces in flight. During the exhaust stroke, scavenging occurred as the air moving past the cylinder exterior lowered the pressure inside due to the direct exposure of the exhaust port to the slipstream. The piston continued its exhaust stroke until top dead center (TDC) was reached, but the valve remained open. The piston began to move down on its intake stroke with the valve still open, pulling new air into the cylinder. It remained open until it was two-thirds of the way down, at which point the valve closed and the remainder of the intake stroke greatly reduced the air pressure. When the piston uncovered the transfer ports again, the low pressure in the cylinder drew in the balance of the charge. The charge was an overly rich mixture of air, which was acquired through the hollow

crankshaft A crankshaft is a mechanical component used in a reciprocating engine, piston engine to convert the reciprocating motion into rotational motion. The crankshaft is a rotating Shaft (mechanical engineering), shaft containing one or more crankpins, ...

, and fuel that was continuously injected by a fuel nozzle on the end of a fuel line, entering the crankcase through the hollow crankshaft. The nozzle was in the proximity of, and aimed at, the inside base of the cylinder where the transfer ports were located. The fuel nozzle was stationary with the crankshaft, and the cylinders rotated into position in turn. The compression stroke was conventional. The

spark plug A spark plug (sometimes, in British English, a sparking plug, and, colloquially, a plug) is a device for delivering electric current from an ignition system to the combustion chamber of a spark-ignition engine to ignite the compressed fuel/air ...

was installed horizontally into the rear of the cylinder at the top but had no connecting high-voltage wire. An internal-tooth ring gear mounted on the engine drove a stationary

magneto A magneto is an electrical generator that uses permanent magnets to produce periodic pulses of alternating current. Unlike a dynamo, a magneto does not contain a commutator to produce direct current. It is categorized as a form of alternator, ...

mounted on the firewall, whose high-voltage output terminal was in close proximity to the spark plug terminals as they passed by. This arrangement eliminated the need for

distributor A distributor is an electric and mechanical device used in the ignition system of older spark-ignition engines. The distributor's main function is to route electricity from the ignition coil to each spark plug at the correct time. Design ...

and high-voltage wiring found in conventional mechanically timed ignition systems. This ring gear also drove the oil pump, which supplied oil to all bearings, and through hollow pushrods to the rockers and valves and also drove an air pump which pressurized the fuel tank. The later Gnome 9N engines had

systems for safety, with twin spark plugs per cylinder which were electrically wired, with the wires routed onto the crankcase and a central pair of magnetos driven by the spinning engine crankcase.

Control

Monosoupapes therefore had a single petrol regulating control used for a limited degree of speed regulation. In early examples, engine speed could be controlled by varying the opening time and extent of the exhaust valves using levers acting on the valve tappet rollers, but this was later abandoned due to causing burning of the valves. Instead, a blip switch was used, which cut out the ignition when pressed. This was used sparingly to avoid fouling the spark plugs, since it was only safe to be used when the fuel supply was also cut. The later 160 CV output 9N subtype also featured an unusual method of functioning with its integral dual-ignition setup, that allowed output values of one-half, one-quarter and one-eighth power levels to be achieved through use of the coupe-switch and a special five-position rotary switch that selected which of the trio of alternate power levels would be selected when the coupe-switch was depressed, allowing it to cut out all spark voltage to all nine cylinders, at evenly spaced intervals to achieve the multiple levels of power reduction. The airworthy reproduction Fokker D.VIII parasol monoplane fighter at Old Rhinebeck Aerodrome, uniquely powered with a Gnome 9N, often demonstrates the use of its Gnome 9N's four-level output capability in both ground runs and in flight.

Lubrication

The lubrication system, as with all rotary engines, was a total-loss type in which

castor oil Castor oil is a vegetable oil pressed from castor beans, the seeds of the plant ''Ricinus communis''. The seeds are 40 to 60 percent oil. It is a colourless or pale yellow liquid with a distinct taste and odor. Its boiling point is and its den ...

was pumped into the fuel–air mix. Castor oil was used because it did not readily dissolve into the fuel, and because it offered lubrication qualities superior to other available oils. Over two gallons of castor oil were sprayed into the air during each hour of engine operation. This explains why most rotaries were fitted with cowls, with the lowermost quarter omitted to direct the spray of castor oil away from the pilot. Unburnt castor oil from the engine had a laxative effect on the pilot if ingested. Because the entire engine rotated, it had to be precisely balanced, requiring precision machining of all parts. As a result, ''Monosoupapes'' were extremely expensive to build, the models costing $4,000 in 1916 (approx. $89,000 in 2017 dollars). However, they used less lubricating oil and weighed slightly less than the earlier two-valve engines.

Variants

;Gnome Monosoupape 7 Type A :Seven-cylinder rotary engine, . Bore and

stroke Stroke is a medical condition in which poor cerebral circulation, blood flow to a part of the brain causes cell death. There are two main types of stroke: brain ischemia, ischemic, due to lack of blood flow, and intracranial hemorrhage, hemor ...

: . ;Gnome Monosoupape 9 Type B-2 :Nine-cylinder rotary engine, . Bore and stroke: . ;Gnome Monosoupape 11 Type C :An 11 cylinder version, . ;Gnome Monosoupape 18 Type C :An 18 cylinder version, . ;Gnome Monosoupape 9 Type N :(1917) nine-cylinder rotary engine, larger diameter crankcase than the B-2, 150 or 160 hp (112 or 119 kW), increasing capacity to . Bore and stroke: . ;Gnome Monosoupape 9 Type R :180 hp nine-cylinder rotary engine, development of 9N with same stroke.

Applications

''List from Lumsden.''

Monosoupape 7 Type A

Avro 504 The Avro 504 is a single-engine biplane bomber made by the Avro, Avro aircraft company and under licence by others. Production during World War I totalled 8,970 and continued for almost 20 years, making it the most-produced aircraft of any kind ...

* Avro 511 * Bristol-Coanda G.B.75 *

Sopwith Pup The Sopwith Pup is a British single-seater biplane fighter aircraft built by the Sopwith Aviation Company. It entered service with the Royal Naval Air Service and the Royal Flying Corps in the autumn of 1916. With pleasant flying characteristi ...

* Voisin L

Monosoupape 9 Type B

Airco DH.2 The Airco DH.2 was a single-seat pusher biplane fighter aircraft which operated during the First World War. It was the second pusher design by aeronautical engineer Geoffrey de Havilland for Airco, based on his earlier DH.1 two-seater. The ...

* Airco DH.5 * Blackburn Scout * Blackburn Twin Blackburn * Blackburn Triplane * Bristol-Coanda T.B.8 *

Bristol Scout The Bristol Scout was a single-seat rotary-engined biplane originally designed as a racing aircraft. Like similar fast, light aircraft of the period it was used by the RNAS and the RFC as a "scout", or fast reconnaissance type. It was one o ...

* FBA Type B Flying boat * Nieuport IV * Royal Aircraft Factory B.E.8 * Royal Aircraft Factory F.E.8 * Short S.80 * Short Type C * Sopwith Sociable * Sopwith Type 807 Folder Seaplane * Sopwith Two-Seat Scout * Sopwith Schneider *

* Sopwith F.1 Camel * Vickers Gunbus (FB.2, 3, 5, 6 and 7) * Vickers F.B.12 * Vickers F.B 19 Bullet * helicopter (licence-built as M-2)

Monosoupape 9 Type N

Nieuport 28 The Nieuport 28 C.1, a French biplane fighter aircraft flown during World War I, was built by Nieuport and designed by Gustave Delage. Owing its lineage to the successful line of sesquiplane fighters that included the Nieuport 17, the Nieupor ...

Sopwith Camel The Sopwith Camel is a British First World War single-seat biplane fighter aircraft that was introduced on the Western Front in 1917. It was developed by the Sopwith Aviation Company as a successor to the Sopwith Pup and became one of the b ...

Morane-Saulnier AI The Morane-Saulnier AI (also MoS.27, MoS.29 and MoS.30) is a French Monoplane#Parasol, parasol-wing fighter aircraft that was produced by Morane-Saulnier during World War I.Morane-Saulnier used letters for designations, while official government ...

* Orenco B

Engines on display

* A nine-cylinder Monosoupape engine is on public display at the

Royal Air Force Museum London The Royal Air Force Museum London (also commonly known as the RAF Museum) is located on the former Hendon Aerodrome, in North London's Borough of Barnet. It includes five buildings and hangars showing the history of aviation and the Royal Air ...

. * A nine-cylinder Monosoupape engine is on public display at the Aerospace Museum of California. * A seven-cylinder Monosoupape engine is on display at

Solent Sky Solent Sky (previously known as the Southampton Hall of Aviation) is an aviation museum in Southampton, England. The museum depicts the history of aviation in Southampton, the Solent area and Hampshire. There is a focus on Supermarine, the air ...

. * One Monosoupape built by Peter Hooker - England is on display at the Museo Nacional de Aeronáutica - Morón,

Argentina Argentina, officially the Argentine Republic, is a country in the southern half of South America. It covers an area of , making it the List of South American countries by area, second-largest country in South America after Brazil, the fourt ...

. It is used during exhibitions to explain the rotary engines systems as it shows its operative internal parts. * There is a restored B-2 Monosoupape on display at the

New England Air Museum The New England Air Museum (NEAM) is an American aerospace museum located adjacent to Bradley International Airport in Windsor Locks, Connecticut. The museum consists of three display hangars with additional storage and restoration hangars. Its ...

, Bradley Int'l Airport, Windsor Locks, CT, USA. * TAVAS in Australia have two. http://www.tavas.com.au/rotary-engine.php Both for exhibition in flying aircraft. * A restored Monosoupape 9 Type N is on display in the

Reynolds-Alberta Museum The Reynolds-Alberta Museum is an agricultural museum, agricultural, industrial, and transportation museum in Wetaskiwin, Alberta, Canada. The museum is situated on an property containing the main museum building, an aviation display hangar, and ...

. * An original (unrestored) running nine-cylinder Monosoupape engine is on public display at the South Australian Aviation Museum in South Australia. A video of it running can be found at https://www.saam.org.au/engines.html * A nine-cylinder Monosoupape engine is on public display at the Musée aéronautique et spatial Safran.

Specifications (Monosoupape 9 Type B-2)

References

Citations

Bibliography

* Lumsden, Alec. ''British Piston Engines and their Aircraft''. Marlborough, Wiltshire: Airlife Publishing, 2003. .

External links

Rattling of a Gnome engineGround run of a rare 100 hp ''Monosoupape'' in AustraliaYouTube video of 100 hp Gnome ''Monosoupape'' demonstrationModern reproduction Fokker D VIII powered with 160 hp Gnome MonosoupapeNew Zealand-built (21st century) reproduction Type 9B-2 100 hp Monosoupape runningClassic Aero Machining Service/CAMS Reproduction Gnôme Type 9B-2 ''Monosoupape'' reproduction engine development videoComputer video of how the 100 CV Type 9B-2 Monosooupape Goes Together
{{Aircraft piston engine components 1910s aircraft piston engines Monosoupape Rotary aircraft piston engines