View source for Gnome Monosoupape

<!-- This article is a part of [[Wikipedia:WikiProject Aircraft]]. Please see [[Wikipedia:WikiProject Aircraft/page content]] for recommended layout. -->
{{short description|Type of aircraft rotary engine}}
{{infobox aero engine
 |name= Monosoupape 
 |image = Gnome 9N 1917 160 hp.jpg 
 |caption = A 1917 Gnome 9N 160 hp ''Monosoupape'' rotary engine, with [[dual ignition]] provision. Diameter is 95cm (37.4 in)
 |engine_type= [[Rotary engine|Rotary]] [[Aircraft engine|aero engine]]
 |national_origin = France
 |manufacturer= [[Gnome et Rhône]] 
 |first_run= 1913
 |major_applications={{ubl | [[Airco DH.2 ]] | [[Nieuport 28]] }}
 |number_built = 
 |developed_from = 
 |developed_into = 
 |variants_with_their_own_articles = 
}}

The '''''Monosoupape''''' ([[French language|French]] for '''single-valve'''), is a [[rotary engine]] design first introduced in 1913 by [[Gnome Engine Company]] (renamed [[Gnome et Rhône]] in 1915). It uses an arrangement of internal [[transfer port]]s to replace the automatic centre-piston inlet valve found on earlier Gnome engines. The elimination of the inlet valve removed a common source of engine failure but also resulted in increased fuel consumption.<ref name="Laux">{{cite magazine |last=Laux| first=James M|title=Gnome et Rhône - An Aviation Engine Firm in the First World War: Le Rhône|magazine=Aerospace Historian|publisher=Air Force Historical Foundation |date=March 1980|volume=27|issue=1|pages=19–26}}</ref> 

French aircraft manufacturers ordered relatively few Monosoupape engines preferring other types including Gnome et Rhône's own [[Le Rhône]] series.<ref name="Laux" /> 2,188 Monosoupape engines were manufactured in Britain,<ref name="Lumsden">{{Cite book |last=Lumsden |first=Alec |title=British Piston Engines and their Aircraft |date=2002 |publisher=Airlife Publishing |isbn=1853102946 |pages=153 |language=en}}</ref> with additional licensed production taking place in Italy and the United States.<ref name="Laux" /> 

British aircraft designer [[Thomas Sopwith]] described the ''Monosoupape'' as "one of the greatest single advances in aviation".<ref name="nahum">{{cite book |last=Nahum |first=Andrew |title=The Rotary Aero Engine |publisher=NMSI Trading Ltd |year=1999 |isbn=1-900747-12-X}}</ref> However the type was also criticised for its poor reliability with [[Royal Flying Corps]] commander [[Hugh Trenchard, 1st Viscount Trenchard|Hugh Trenchard]] describing it as a "beast of an engine".<ref>{{Cite book |last=Morrow Jr |first=John H |title=The Great War In The Air: Military Aviation from 1909 to 1921 |date=1993 |publisher=Smithsonian Institution Press |isbn=978-1560982388 |location=United States |pages=261}}</ref>  

==Background==
Unlike other rotaries, the early Gnome engines like the [[Gnome Omega]], [[Gnome Lambda|Lambda]] and [[Gnome Delta|Delta]] used a unique arrangement of valves in order to eliminate [[Overhead valve|pushrod]]s that operated during the inlet phase of the combustion cycle on more conventional engines. Instead, a single exhaust valve on the [[Cylinder (engine)|cylinder]] 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'' [the Gnome motor company] in 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]].<ref name="Laux" /> Beginning with the power stroke, the [[four-stroke cycle|four-stroke]] engine operated normally until the piston had traveled half way to 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]] 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]] since no [[exhaust manifold]] could be practically fitted to the spinning crankcase and cylinders.<ref name="Manual" />{{rp|pp=7–12}}

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 centre|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 three quarters 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.<ref name="Manual">{{Cite book |title=The Care of the 100 h.p Monosoupape Engine |date=1917 |publisher=The Gnome and Le Rhone Engine Company |location=London |asin=B0DHV3RDQC}}</ref>{{rp|pp=7–12}}

The charge was an overly rich mixture of air, which was acquired through the hollow [[crankshaft]], 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.<ref name="Manual" />{{rp|pp=7–12}}

The [[spark plug]] 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 [[ignition magneto|magneto]] 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]] and high-voltage wiring found in conventional [[Ignition system#Mechanically timed ignition|mechanically timed ignition systems]].<ref name="Manual" />{{rp|pp=17-22}}  This ring gear also drove the oil pump, which supplied oil to all [[Bearing (mechanical)|bearing]]s, and through hollow pushrods to the rockers and valves. The ring gear could also be used to drive a petrol pump or and air compressor to pressurize the fuel tank.<ref name="Manual"/>{{rp|pp=27–33}} The later {{cvt|160|hp}} Gnome 9N engines had [[dual ignition]] 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'' had a single petrol regulating control used for a limited degree of speed regulation.<ref name="Manual" />{{rp|pp=44–49}} 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 {{cvt|160|hp}} 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.<ref name="kozaero">{{cite web |url=http://www.kozaero.com/look-at-the-gnocircme-9n-rotary-engine.html |title=(A) Look at the Gnôme 9N Rotary Engine |last1=Murrin |first1=Fred |last2=Phillips |first2=Terry |date= |website=kozaero.com |publisher=KozAero |access-date=August 13, 2021}}</ref>{{efn|In order to keep the engine running smoothly on reduced power settings, it was necessary for the selector switch to cut out all cylinders at evenly spaced intervals. It was also beneficial to have all cylinders firing periodically to keep them warm and to prevent the spark plugs from fouling with oil.  The selector switch has five positions, zero (0) for off and four running positions, one through four (1-4) (see Photo 5). The Gnôme 9N had two magnetos (and two spark plugs per cylinder) and the selector switch was wired to the right magneto only, so it was necessary for the pilot to turn off the left magneto if he wanted to change the speed of the engine.<ref name="kozaero" />}} 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<ref>{{cite AV media |people= |date=August 4, 2019 |title=Old Rhinebeck Fokker D.VIII Startup and Takeoff |medium=YouTube |language=English |url=https://www.youtube.com/watch?v=EzdjWP0-mnM |access-date=August 13, 2021 |archive-url=https://web.archive.org/web/20210813130952/https://www.youtube.com/watch?v=EzdjWP0-mnM |archive-date=August 13, 2021 |format=YouTube |time=0:12 to 2:00 |location=Old Rhinebeck Aerodrome |publisher=Sholom |id= |isbn= |oclc= |quote= |url-status=live }}</ref> and in flight.

===Lubrication===
[[File:Sopwith Tabloid RAFM.jpg|thumb|The [[Sopwith Tabloid]] reproduction shows the sheet-metal cowling used to redirect the oil sprayed by the rotating engine.]]

The lubrication system, as with all rotary engines, was a total-loss type in which [[castor oil]] 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.<ref>[http://www.pilotfriend.com/aero_engines/aero_soupape.htm#r Gnome Monosoupape Type N Rotary] Retrieved on 18 February 2009.
</ref> Unburnt castor oil from the engine had a laxative effect on the pilot if ingested.<ref>{{Cite book |last=Setright|first =IJK|title=The Power to Fly : The Development of the Piston Engine in Aviation |publisher=Allen and Unwin|year=1971 |page=27|isbn=978-0043380413}}</ref> However, ''Monosoupape'' engines used less lubricating oil, and weighed slightly less, than earlier Gnome series engines with intake valves in the piston crown.<ref name="vivian">{{cite book|last=Vivian|first=E. Charles|title=A History of Aeronautics|publisher=Kessinger Publishing|year=2004|page=255|isbn=1419101560}}</ref>

==Variants==
;Gnome Monosoupape 7 Type A
:Seven-cylinder rotary engine, {{cvt|80|hp}}. [[Bore (engine)|Bore]] and [[Stroke (engine)|stroke]]: {{cvt|110 x 150|mm|in}} .
;Gnome Monosoupape 9 Type B-2
:Nine-cylinder rotary engine, {{cvt|100|hp}}. Bore and stroke: {{cvt|110 x 150|mm|in}}. 
;Gnome Monosoupape 11 Type C
:An 11 cylinder version,  {{cvt|200|hp}}.
;Gnome Monosoupape 18 Type C
:An 18 cylinder version,  {{cvt|240|hp}}.
;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 {{convert|15.8|L|cuin|abbr=on}}. Bore and stroke: {{cvt|115 x 170|mm|in}}.
;Gnome Monosoupape 9 Type R
:180 hp nine-cylinder rotary engine, development of 9N with same {{cvt|170|mm|in}} stroke.

==Applications==
===Monosoupape 7 Type A===
*[[Avro 504]]
*[[Avro 511]]
*[[Bristol TB.8#Variants|Bristol-Coanda G.B.75]]
*[[Sopwith Pup]]
*[[Voisin L]]

===Monosoupape 9 Type B===
{{colbegin}}
*[[Avro 504]]
*[[Airco DH.2]]
*[[Airco DH.5]]
*[[Blackburn Scout]]
*[[Blackburn Twin Blackburn]]
*[[Blackburn Triplane]]
*[[Bristol-Coanda T.B.8]]
*[[Bristol Scout]]
*[[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]]<!-- Improved S.74 -->
*[[Sopwith Sociable]]<!-- 'Tweenie' -->
*[[Sopwith Type 807 Folder Seaplane]]
*[[Sopwith Two-Seat Scout]]<!-- 'Spinning Jenny' -->
*[[Sopwith Schneider]]
*[[Sopwith Pup]]
*[[Sopwith F.1 Camel]]
*[[Vickers Gunbus]] (FB.2, 3, 5, 6 and 7)
*[[Vickers F.B.12]]
*[[Vickers F.B 19 Bullet]]
{{colend}}

===Monosoupape 9 Type N===
*[[Nieuport 28]]
*[[Sopwith Camel]]
*[[Morane-Saulnier AI]]
*[[Orenco B]]

==Engines on display==
* A nine-cylinder Monosoupape engine is on public display at the [[Royal Air Force Museum London]].
* 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]].
*  One Monosoupape built by [[Peter Hooker]] - England is on display at the [[Museo Nacional de Aeronáutica de Argentina|Museo Nacional de Aeronáutica]] - [[Morón, Buenos Aires|Morón]], [[Argentina]]. 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]], Bradley Int'l Airport, Windsor Locks, CT, USA.<ref>{{cite web |url=http://neam.org/index.php?option=com_content&view=article&layout=edit&id=1103 |title = New England Air Museum}}</ref>
* TAVAS in Australia have two. http://www.tavas.com.au/rotary-engine.php {{Webarchive|url=https://web.archive.org/web/20141022165354/http://www.tavas.com.au/rotary-engine.php |date=2014-10-22 }} Both for exhibition in flying aircraft.
* A restored Monosoupape 9 Type N is on display in the [[Reynolds-Alberta Museum]].
* 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)==
{{pistonspecs|
<!-- If you do not understand how to use this template, please ask at [[Wikipedia talk:WikiProject Aircraft]] -->
<!-- Please include units where appropriate (main comes first, alt in parentheses). If data are missing, leave the parameter blank (do not delete it). For additional lines, end your alt units with )</li> and start a new, fully-formatted line with <li> -->
|ref=''Lumsden''<ref name="Lumsden" />
|type=9-cylinder, single-row, [[rotary engine]]
|bore={{cvt|110|mm}}
|stroke={{cvt|150|mm}}
|displacement={{cvt|12.8|L|cuin}}
|length={{cvt|107.4|cm|in}}
|diameter={{cvt|95|cm|in}}
|width=
|height=
|weight= {{cvt|137.4|kg}}
|valvetrain=Single overhead valve with cylinder ports 
|supercharger=
|turbocharger=
|fuelsystem=
|fueltype=40-50 [[Octane rating|Octane]] petrol
|oilsystem=Total loss, [[castor oil]]
|coolingsystem=Air-cooled
|power={{cvt|86|kW|hp}} at 1,300 rpm (Maximum power)
|specpower=
|compression=4.85:1
|fuelcon=
|specfuelcon=
|oilcon=
|power/weight=
|reduction_gear=Direct drive, right-hand tractor, left-hand pusher
}}

==See also==
{{aircontent
<!-- other related articles that have not already linked: -->
|see also=
*[[Gnome Omega]], [[Gnome Delta|Delta]] and [[Gnome Lambda|Lambda]] (earlier seven-cylinder Gnome designs with inlet valve in piston crown)

<!-- designs which were developed into or from this aircraft: -->
|related=

<!-- relevant lists that this aircraft appears in: -->
|lists=
*[[List of aircraft engines]]

<!-- For aircraft engine articles.  Engines that are of similar to this design: -->
|similar engines=
*[[Bentley BR1]]
*[[Clerget 7Z]]
*[[Clerget 9B]]
*[[Le Rhône 9J]]
*[[Oberursel U.I]]
<!-- See [[WP:Air/PC]] for more explanation of these fields. -->
}}

== Notes ==

{{notelist}}

==References==
{{reflist}}

==External links==
{{Commonscat}}
*[http://www.lincolnbeachey.com/gno.html Rattling of a Gnome engine] {{Webarchive|url=https://web.archive.org/web/20051024093219/http://www.lincolnbeachey.com/gno.html |date=2005-10-24 }}
*[https://www.youtube.com/watch?v=jd-eDJGdQOY Ground run of a rare 100 hp ''Monosoupape'' in Australia]
*[https://www.youtube.com/watch?v=CYc-H8Wg-MQ YouTube video of 100 hp Gnome ''Monosoupape'' demonstration]
*[https://www.youtube.com/watch?v=L0-LXM8acEQ Modern reproduction Fokker D VIII powered with 160 hp Gnome Monosoupape]
*[https://www.youtube.com/watch?v=FB80M6oAi5o New Zealand-built (21st century) reproduction Type 9B-2 100 hp Monosoupape running]
*[https://www.youtube.com/watch?v=TtMu8mrwM2k Classic Aero Machining Service/CAMS Reproduction Gnôme Type 9B-2 ''Monosoupape'' reproduction engine development video]
*[https://www.youtube.com/watch?v=Gh3W-9gZXFw Computer video of how the 100 CV Type 9B-2 Monosooupape Goes Together]
*[http://www.kozaero.com/look-at-the-gnocircme-9n-rotary-engine.html Koz-Aero's "Look at the Gnome 9N Monosoupape" Article]

{{Gnome-Rhône aeroengines}}
{{Aircraft piston engine components}}

[[Category:1910s aircraft piston engines]]
[[Category:Gnome-Rhône aircraft engines|Monosoupape]]
[[Category:Rotary aircraft piston engines]]