Editing Rotary engine (section)

==History==

===Millet===
[[File:Felix Millet.jpg|right|thumb|An 1897 Félix Millet motorcycle]]
[[Félix Millet (inventor)|Félix Millet]] showed a 5-cylinder rotary engine built into a bicycle wheel at the [[Exposition Universelle (1889)|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 and Company London]] in 1900.<ref name="nahum20">{{cite book| last = Nahum| first = Andrew| title = The Rotary Aero Engine| year = 1999| publisher = NMSI Trading Ltd| isbn = 1-900747-12-X| pages = 20 }}</ref>

===Hargrave===
[[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.<ref>[http://www.adb.online.anu.edu.au/biogs/A090194b.htm Hargrave, Lawrence (1850 – 1915)] {{Webarchive|url=https://web.archive.org/web/20110524142500/http://www.adb.online.anu.edu.au/biogs/A090194b.htm |date=2011-05-24 }}. Australian Dictionary of Biography Online.</ref>

===Balzer===
[[Stephen M. Balzer]] of New York, a former watchmaker, constructed rotary engines in the 1890s.<ref>{{cite web|title=Balzer automobile patents|url=http://americanhistory.si.edu/onthemove/collection/object_1282.html|publisher=National Museum of American History|date=2016-11-02|access-date=2011-06-29|archive-date=2011-06-30|archive-url=https://web.archive.org/web/20110630214015/http://www.americanhistory.si.edu/onthemove/collection/object_1282.html|url-status=live}}</ref>  He was interested in the rotary layout for two main reasons:
* To generate {{convert|100|hp|abbr=on}} at the low [[Revolutions per minute|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 cooling|air-cooled]] engines.

Balzer produced a 3-cylinder, rotary engined car in 1894, then later became involved in [[Samuel Pierpont Langley|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===
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.<ref name=nahum20/>

===Adams-Farwell===
{{Main|Adams-Farwell}}

[[File:Adams-Farwell Gyro Motor Rotary 5.jpg|thumb|right|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.<ref name=nahum20/>

===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.

===World War I===
[[File:Siemens-Halske Sh.III 07.jpg|thumb|right|A [[Siemens-Halske Sh.III]] preserved at the ''[[Technisches Museum Wien]]'' (Vienna Museum of Technology). This engine powered a number of German fighter aircraft types towards the end of World War I]]
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]].<ref>{{cite book| author = Arthur Gould Lee| title = Open Cockpit: A Pilot of the Royal Flying Corps| year = 2012| publisher = Grub Street| isbn = 978-1-908117-25-0 }}</ref> 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, but 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.<ref name="AEHS">{{cite web |url=http://www.enginehistory.org/Gnome%20Monosoupape.pdf |title=Gnome Monosoupape Type N Rotary |access-date=2008-05-01 |last=McCutcheon |first=Kimble D. |publisher=Aircraft Engine Historical Society |url-status=dead |archive-url=https://web.archive.org/web/20080706041104/http://www.enginehistory.org/Gnome%20Monosoupape.pdf |archive-date=2008-07-06 }}</ref>  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 {{convert|1000|ft|abbr=on}}.<ref>{{cite book |author2=E. Eugene Larrabee |last=Abzug |first=Malcolm J. | title = Airplane Stability and Control|url=https://archive.org/details/airplanestabilit00abzu |url-access=limited | year = 2002| publisher = Cambridge University Press| isbn = 0-521-80992-4| pages = [https://archive.org/details/airplanestabilit00abzu/page/n30 9] }}</ref> 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&nbsp;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.12]]b and [[Vickers F.B.16|F.B.16]] aircraft,<ref>{{cite book| last = Fairney| first = William| title = The Knife and Fork Man - The Life and Works of Charles Benjamin Redrup| year = 2007| publisher = Diesel Publishing| isbn = 978-0-9554455-0-7 }}</ref> 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&nbsp;rpm to 2,000 rpm. 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&nbsp;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.
[[File:Gegenläufer Umlaufmotor.gif|thumb|right|Animation of the Siemens-Halske Sh.III's internal operation]]

====Siemens-Halske bi-rotary designs====
One clever attempt to rescue the design, in a similar manner to Redrup's British "reactionless" engine concept, was made by [[Siemens]]. The crankcase (with the propeller still fastened directly to the front of it) and cylinders spun counterclockwise at 900&nbsp;rpm, as seen externally from a "nose on" viewpoint, while the crankshaft (which unlike other designs, never "emerged" from the crankcase) and other internal parts spun clockwise at the same speed, so the set was effectively running at 1800&nbsp;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.<ref name="Gray_Profile">{{cite book |last=Gray |first=Peter L. |title=Aircraft in Profile No.86 — The Siemens Schuckert D.III & IV |year=1966 |publisher=Profile Publications |location=Leatherhead, Surrey, England }}</ref>{{rp|4–5}} 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.<ref name="Gray_Profile" />{{rp|12}}

One new rotary powered aircraft, Fokker's own [[Fokker D.VIII|D.VIII]], was designed at least in part to provide some use for the Oberursel factory's backlog of otherwise redundant {{convert|110|hp|abbr=on}} [[Oberursel Ur.II|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 the castor oil necessary to properly lubricate their rotary engines. Substitutes were never entirely satisfactory - causing increased running temperatures and reduced engine life.<ref>{{cite book| last = Guilmartin| first = John F. Jr.| title = Two Historians in Technology and War| year = 1994| publisher = [[United States Army War College]], [[Strategic Studies Institute]]| isbn = 1428915222| page = 10| chapter = Technology and Strategy: What Are the Limits? }}</ref><ref>{{cite book| last = Fisher| first = Suzanne Hayes| title = The European Powers in the First World War: An Encyclopedia| year = 1999| publisher = [[Taylor & Francis]]| isbn = 081533351X| page = 10| chapter = Aircraft, production during the war| editor = Spencer C. Tucker |editor2=Laura Matysek Wood |editor3=Justin D. Murphy }}</ref><ref>{{cite book |title=Tariff Information Surveys on the Articles in Paragraphs 44 and 45 of the Tariff Act of 1913 |year=1921 |author=[[United States International Trade Commission]]|page=40 |publisher=[[United States Government Publishing Office]]|location=Washington, D.C. }}</ref>

===Postwar===

By the time the war ended, the rotary engine had become obsolete, and it disappeared from use quite quickly. The British [[Royal Air Force]] 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 {{convert|230|hp|abbr=on}}) 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 504]]K, had a universal mounting to allow the use of several different types of low powered rotary, of which there was a large surplus supply. Similarly, the Swedish [[FVM Ö1 Tummelisa]] advanced training aircraft, fitted with a Le-Rhone-Thulin {{convert|90|hp|abbr=on}} rotary engine, served until the mid thirties.

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, and 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]].

Experiments with the concept of the rotary engine continued.

The first version of the 1921 [[Michel engine]], an unusual opposed-piston [[cam engine]], used the principle of a rotary engine, in that its "cylinder block" rotated. This was soon replaced by a version with the same cylinders and cam, but with stationary cylinders and the cam track rotating in lieu of a crankshaft. A later version abandoned the cam altogether and used three coupled crankshafts.

By 1930 the Soviet helicopter pioneers, Boris N. Yuriev and Alexei M. Cheremukhin, both employed by ''[[TsAGI|Tsentralniy Aerogidrodinamicheskiy Institut]]'' (TsAGI, the Central Aerohydrodynamic Institute), constructed one of the first practical single-lift rotor machines with their TsAGI 1-EA single rotor helicopter, powered by two Soviet-designed and built M-2 rotary engines, themselves up-rated copies of the [[Gnome Monosoupape]] rotary engine of World War I. The TsAGI 1-EA set an unofficial altitude record of 605 meters (1,985&nbsp;ft) with Cheremukhin piloting it on 14 August 1932 on the power of its twinned M-2 rotary engines.<ref>Savine, Alexandre. [http://www.ctrl-c.liu.se/misc/ram/1-ea.html "TsAGI 1-EA."] {{Webarchive|url=https://web.archive.org/web/20090126202112/http://www.ctrl-c.liu.se/misc/ram/1-ea.html |date=2009-01-26 }} ''ctrl-c.liu.se,'' 24 March 1997. Retrieved 12 December 2010.</ref>