Editing Rotary engine (section)

===Gnome===
[[File:Gnome-GA section.png|thumb|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 [[Gnome et Rhône|Société des Moteurs Gnome]]<ref>{{cite web |title=SAFRAN |url=http://www.safran-group.com/site-safran/groupe/histoire/ |language=fr |quote=Le 6 juin 1905, Louis et Laurent Seguin fondent la société des moteurs Gnome à Gennevilliers |access-date=2009-09-14 |archive-date=2011-02-28 |archive-url=https://web.archive.org/web/20110228085617/http://www.safran-group.com/site-safran/groupe/histoire/ |url-status=live }}</ref><!-- for Gnome spelling see also: http://www.lincolnbeachey.com/gno2.jpg, http://en.wikipedia.org/wiki/File:Salon_de_locomotion_aerienne_1909_Grand_Palais_Paris.jpg, http://img.allposters.com/images/pic/VAS/0000-6164-4_b~Gnome-Rohne-Motorcycle-Posters.jpg--> to build [[stationary engine]]s 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 {{convert|34|hp|abbr=on}}, 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 {{convert|50|hp|abbr=on}} "[[Gnome Omega|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]].<ref>{{cite web|url=http://www.nasm.si.edu/collections/artifact.cfm?id=A19990069000|publisher=Smithsonian Institution|title=Gnome Omega No. 1 Rotary Engine|access-date=14 April 2012|archive-date=19 April 2012|archive-url=https://web.archive.org/web/20120419071116/http://www.nasm.si.edu/collections/artifact.cfm?id=A19990069000|url-status=live}}</ref> 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&nbsp;hp Gnome was only 1.5&nbsp;mm (0.059 inches) thick, while the connecting rods were milled with deep central channels to reduce weight. While somewhat low powered in terms of units of power per litre, its power-to-weight ratio was an outstanding {{convert|1|hp|abbr=on}} 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. [[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—{{convert|180|km|mi}}—and also set a world record for endurance flight.  The very first successful seaplane flight, of [[Henri Fabre]]'s ''[[Fabre Hydravion|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 80&nbsp;hp [[Gnome Lambda]]  and the 160&nbsp;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.<ref>{{Citation |last=Genchi |first=Giuseppe |title=The Rotary Aero Engine from 1908 to 1918 |date=2012 |url=http://link.springer.com/10.1007/978-94-007-4132-4_24 |work=Explorations in the History of Machines and Mechanisms |volume=15 |pages=349–362 |editor-last=Koetsier |editor-first=Teun |place=Dordrecht |publisher=Springer Netherlands |doi=10.1007/978-94-007-4132-4_24 |isbn=978-94-007-4131-7 |access-date=2022-12-12 |last2=Sorge |first2=Francesco |editor2-last=Ceccarelli |editor2-first=Marco|url-access=subscription }}</ref>

In 1913 the Seguin brothers introduced the new [[Monosoupape engine|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&nbsp;hp Monosoupape was built with 9 cylinders, and developed its rated power at 1,200&nbsp;rpm.<ref>{{cite book| last = Vivian| first = E. Charles| title = A History of Aeronautics| year = 2004| publisher = Kessinger Publishing| isbn = 1-4191-0156-0| pages = 255 }}</ref>  The later 160&nbsp;hp nine-cylinder Gnome 9N rotary engine used the Monosoupape valve design while adding the safety factor of a [[dual ignition]] system, and was the last known rotary engine design to use such a cylinder head valving format. The 9N also featured an unusual ignition setup that allowed output values of one-half, one-quarter and one-eighth power levels to be achieved through use of the coupe-switch and a special five-position rotary switch that selected which of the trio of alternate power levels would be selected when the coupe-switch was depressed, allowing it to cut out all spark voltage to all nine cylinders, at evenly spaced intervals to achieve the multiple levels of power reduction.<ref>{{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 |quote=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. |archive-date=June 9, 2021 |archive-url=https://web.archive.org/web/20210609142716/http://www.kozaero.com/look-at-the-gnocircme-9n-rotary-engine.html |url-status=live }}</ref> 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 Takoff |medium=YouTube |language=English |url=https://www.youtube.com/watch?v=EzdjWP0-mnM |access-date=August 13, 2021 |url-status=live |archive-url=https://web.archive.org/web/20210813130952/https://www.youtube.com/watch?v=EzdjWP0-mnM |archive-date=2021-08-13 |format=YouTube |time=0:12 to 2:00  |location=Old Rhinebeck Aerodrome |publisher=Sholom |id= |isbn= |oclc= |quote= }}</ref> and in flight. 
[[File:Oberursel U.III.jpg|right|thumb|A German Oberursel U.III engine on museum display]]
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&nbsp;hp (60&nbsp;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&nbsp;hp Gnome Lambda copy was known as the Oberursel U.0. It was not at all uncommon for French Gnôme Lambdas, as used in the earliest examples of the [[Bristol Scout]] biplane, to meet German versions, powering [[Fokker E.I]] 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&nbsp;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&nbsp;km/h (126&nbsp;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.