Editing U engine

{{Short description|Piston engine design}}
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A '''U engine''' is a [[piston engine]] made up of two separate [[straight engine]]s  (complete with separate crankshafts) placed side-by-side and coupled to a shared output shaft. When viewed from the front, the engine block resembles the letter "U".

Although much less common than the similar [[V engine]] design, several U engines were produced from 1915 to 1987 for use in airplanes, racing cars, [[Suzuki RG 500|racing]] and [[Suzuki RG500|road]] motorcycles, locomotives, and tanks.

== Design ==
{{unreferenced section|date=December 2023}}
The main benefit of a U engine layout is the ability to share common parts with a straight engine upon which is it based. Additionally, if the two crankshafts rotate in opposite directions, the [[gyroscopic effect]] of the rotating components in each cylinder bank cancel each other out.

A V engine is typically more compact and lighter than a U engine, in part due to the lack of a second [[crankshaft]], making V engines far more common than U engines. However, the V engine does not cancel the gyroscopic effect.

The [[H engine]] layout uses a similar concept to U engines, whereby two [[flat engine]]s are stacked vertically.

== History ==
=== Petrol engines ===
[[File:King-Bugatti U16 2.jpg |thumb |right |1915–1916 [[Bugatti U-16]] aircraft engine]]

The first U engine known to have been built was the 1915–1916 [[Bugatti U-16]] aircraft engine, which had 16 cylinders and a displacement of {{convert|24.3|L|cuin|0|abbr=on}}.<ref name="L’Ebe" >L’Ebé Bugatti, 1966, 'The Bugatti Story', Editions de la Table Ronde & L'Action Automobile, first British edition 1967, [[Len Ortzen]] (translator) and Souvenir Press Ltd, London, pps 70–72, p162</ref> Approximately 40 engines were built at the [[Duesenberg]] factory in the United States during World War I.<ref name="racer">{{cite web |url=http://museum.eaa.org/collection/aircraft/Bugatti%20Model%20100%20Racer.asp |title=Bugatti Model 100 Racer |publisher=Museum.eaa.org |date=1947-08-21 |access-date=2011-12-06 |url-status=dead |archive-url=https://web.archive.org/web/20111221082439/http://museum.eaa.org/collection/aircraft/Bugatti%20Model%20100%20Racer.asp |archive-date=2011-12-21 }}</ref> A small number of engines based on the Bugatti U engine were also produced after the war by [[Breguet Aviation]] in France.<ref>{{cite web|url=http://www.bugattirevue.com/revue3/rev3-3.htm#2breguet |title=Bugatti License Aircraft Engines |publisher=the Bugatti revue |access-date=2011-12-06}}</ref>

The ''Fiat 806'' was a 1927 Grand Prix racing car that was powered by a {{convert|1.5|L|cuin|0|abbr=on}} twelve-cylinder U engine.<ref name="Ludvigsen" >{{Cite book
 |title=The V12 Engine
 |last=Ludvigsen |first=Karl
 |author-link=Karl Ludvigsen
 |publisher=Haynes Publishing
 |location=Sparkford, Yeovil
 |year=2005
 |isbn=978-1-84425-004-2
 |ref=Ludvigsen, V12 Engine
  |pages=70–73
}}</ref> This engine, designated the 'Type 406', used a supercharger and had a single centrally-mounted intake camshaft which operated the intake valves located on the inside of each cylinder bank.<ref name="Fornaca, 1929" >{{Cite patent
  |country=US
  |number=1711882
  |title=Internal-Combustion Engine
  |fdate=26 November 1927
  |pubdate=7 May 1929
  |inventor=Guido Fornaca
  |assign1=
}}</ref> Two separate camshafts operated the exhaust valves (one per bank). On test the unit delivered 187&nbsp;bhp at 8,500&nbsp;rpm at maximum boost.<ref name="Ludvigsen"/> The Fiat 806 car competed in only one race, the {{convert|50|km|mi|0|abbr=on}} Milan Grand Prix on 4 September 1927 (not to be confused with the 500&nbsp;km [[1927 Italian Grand Prix]] held on the same day). The race was won by the Fiat 806; however, Fiat then retired from Grand Prix racing and the Type 806 did not race again.<ref>{{cite web |title=Book Review: Fiat en Grand Prix, 1920–1930 |url=https://www.velocetoday.com/fiat-en-grand-prix-1920-1930/ |website=www.velocetoday.com |access-date=11 November 2019}}</ref><ref>{{cite web |title=Fiat 806 GP (1927) |url=https://motor-car.net/fiat/item/21645-fiat-806 |website=www.motor-car.net |access-date=11 November 2019 |language=en-gb}}</ref>

The 1931–1959 [[Ariel Square Four]] motorcycle used a four-cylinder engine (also called a 'square four' engine). The engine was compact and had as narrow a frontal area as a 500&nbsp;cc, parallel twin. The rear pair of cylinders on this air-cooled engine were prone to overheating.{{cn|date=December 2023}}

The 1985–1987 [[Suzuki RG500]] motorcycle, and several related racing motorcycles, used a water-cooled four-cylinder U engine. Although some racing success was achieved, the road bikes did not sell well and the design was phased out in favour of a conventional inline-four engine.{{cn|date=December 2023}}

===Diesel===
In the 1930s [[Sulzer Brothers Ltd.]] began production of an 'LD series' twelve-cylinder U engine for use in rail locomotives. The LD series was replaced by the LDA series, for a combined production period of over 50 years. The Sulzer 12LDA twin-bank engine formed the mainstay of British locomotives built in the 1960s, with over 700 used in the [[British Rail Class 45|''Peak'']] and [[British Rail Class 47|Class 47]] locomotives.<ref>{{cite web
  |title=The Sulzer engine in diesel traction: A potted and incomplete history, 1912 – 1990
  |url=http://www.derbysulzers.com/sulzerengine.html
}}</ref> The Sulzer LDA engine used a smaller gear for the central output shaft than the two gears attached to the crankshaft. This resulted in the output shaft rotating at approximately 1000&nbsp;rpm while the crankshafts rotated at approximately 750&nbsp;rpm. The purpose of this gearing was to allow the use of a smaller, and lighter, electrical generator when the engine was used in a [[diesel-electric locomotive]].

The [[Detroit Diesel Series 71#WWII General Motors 6004/6046 engine|General Motors 6046]] is a twin-engine setup that was used by [[Sherman tank]]s during World War II. The 6046 was built using two straight-six engines that were separately clutched to a single output shaft, which was itself clutched to the transmission unit. A total of 10,968 6046D-powered M4A2 Shermans were produced.<ref>Ware, P., 2012, 'Sherman Tank 1941 onwards (all M4 variants); Owner’s Workshop Manual', Haynes Publishing, Yeovil, Somerset, BA227JJ, {{ISBN|978-0-85733-101-4}}</ref> After World War II, the Soviet Union produced several tanks powered by 16-cylinder and 18-cylinder engines that were reverse-engineered from the General Motors 6046 engine. These Soviet engines were designated Russkiy Dizel (Diesel Energo) DPN23/2H30 and the DRPN23/2H30.<ref>http://www.propulsionplant.ru/content/50/dvigateli/dizelnye-dvigateli/proizvodstvennoe-obedinenie-russkii-dizel/dizeli-tipa-dpn232h30-i-drpn232h30.html {{Dead link|date=February 2022}}</ref><ref>{{cite web |title=Was the M4 Sherman really that bad? A Soviet perspective |url=http://knowledgeglue.com/was-the-m4-sherman-really-that-bad-a-soviet-perspective/ |website=www.knowledgeglue.com |access-date=11 November 2019 |date=21 August 2016}}</ref>

==Variations==
===Tandem twin engine===
[[File:1976 Kawasaki KR250 02.jpg|thumb|right|A tandem inline-twin]]

A tandem twin engine, occasionally used in motorcycles and go-karts, is a two-cylinder engine which uses a similar design to U engines.
The motor has two crankshafts,<ref>Cycle World, Volume 46. CBS Publications, 2007</ref><ref>[http://www.brceng.com/pdfs/BRC250FE_Tech_Data_Sept05.pdf BRC250FE Tech Data Sept 05]</ref> one for each cylinder<ref>Transactions of the International Engineering Congress, 1916</ref><ref>{{cite journal|last= Anderson|first= Steve|title= The Bikes of Japan|page= 30|journal= [[Cycle World]]|date= November 1984|volume= 23|issue= 11|issn= 0011-4286|editor-last= Dean|editor-first= Paul|publisher= CBS Magazines|location= Newport Beach, CA US|url= {{Google books|MvO5RoR1buMC|Cycle World November 1984|page=RA10-PA30|plainurl=yes}}|access-date= 15 May 2015|quote= Both have at their heart a twin-cylinder two-stroke engine that is, in effect, two 125cc Singles mounted one behind the other in a common crankcase, their cranks connected by large gears.}}</ref> which are joined and kept in co-ordination by load carrying, crank-phasing gears connecting the two cylinders.<ref>Top Dead Center 2: Racing and Wrenching With Cycle World's Kevin Cameron. Kevin Cameron, Erik Buell. MBI Publishing Company, 12 Nov 2009</ref>

The tandem twin layout is used only with [[two-stroke engine]]s since these must have a discrete crankcase chamber per cylinder. The prime advantage of a tandem-twin two-stroke is that the engine can be very narrow while allowing chain final drive without a power-wasting 90° turn.

Between 1975 and 1982, Kawasaki used the design to win four 250&nbsp;cc and four 350&nbsp;cc world championships before they retired from Grand Prix racing.<ref>{{cite book |last1= Walker|first1= Mick|author-link1= Mick Walker (motorcycling)|title=Mick Walker's Japanese Grand Prix Racing Motorcycles|date= Nov 1, 2002|publisher= Redline Books|isbn= 0-9531-3118-1|pages= 91–97, 100|chapter= 5: Kawasaki|chapter-url= https://books.google.com/books?id=fpoF0PMZEjEC&q=Marco+Lucchinelli&pg=PA78|quote= Sato, like Kaaden, realised that the convention twin-cylinder two-stroke, with its cylinders across the frame, coupled to the outward facing carburettors of a disc-valve twin had a major drawback, because of excessive width.}}</ref> The engine design was also used for a road legal production motorcycle inspired by the racer.{{Sfn|Anderson|1984|p=30}}<ref>{{cite book|last= Walker|first= Mick|author-link= Mick Walker (motorcycling)|title= Japanese Production Racing Motorcycles|isbn= 0954435702|publisher= Redline Books|location= Low Fell, Tyne & Wear, UK|year= 2003|page= 152|url={{Google books|TB2v4CR7K4kC|Japanese Production Racing Motorcycles|plainurl=yes}}|access-date= 15 May 2015}}</ref> The Kawasaki KR models were instrumental in establishing the company as a manufacturer of high-performance motorcycles.<!--Wasn't Kawasaki already established as a manufacturer of high-performance motorcycles with the Mach III and the Z1?-->{{Sfn|Walker|2003|p=130}}

[[Rotax]] developed a similar tandem twin design, the model 256, which it sold to independent constructors. The [[Armstrong-CCM Motorcycles|CCM Armstrong]] 250&nbsp;cc, Waddon, [[EMC Motorcycles|EMC]], Hejira, Decorite, and Cotton racers used this engine. CCM Armstrong developed a 350&nbsp;cc version of the engine.<ref>{{cite book |last1= Walker|first1= Mick|author-link1= Mick Walker (motorcycling)|title= Mick Walker's European Racing Motorcycles|date= May 29, 2000|publisher= Redline Books|isbn= 0-9531-3113-0|pages= 25–27, Rotax 256 inline twin|chapter= Austria|quote= These hopes were due to the introduction of the Model 256 inline twin...}}</ref> [[Aprilia]]'s 1985 GP racing bikes also used the Rotax model 256.<ref name="Walker">[https://books.google.com/books?id=CNsRN9L5BYsC&dq=%22inline-twin%22&pg=PA1978 Italian Racing Motorcycles]. Mick Walker. Redline Books, 1 Jan 2000</ref>
{{Clear}}

===Single crankshaft===
An unusual variation on the U engine is the use of a single crankshaft which is linked to the pistons in both cylinder banks by rocking beams. This system was used in an eight-cylinder petrol engine produced by the [[All-British]] Car Company between 1906 and 1908.{{Citation needed|date=April 2021}}

==See also==
*[[Split-single engine]]
*[[List of motorcycles by type of engine]]

==References==
{{Reflist|colwidth=30em}}
{{Commons category|U engines}}

{{Piston engine configurations}}

[[Category:Piston engine configurations]]
[[Category:U engines| ]]
[[Category:Engines by cylinder layout]]