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Straight engine
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{{Short description|Cylinder layout for a piston engine}} {{multiple image | align = right | direction = vertical | width = 250 | image1 = Straight engine.svg | caption1 = Schematic drawing of a straight-four engine | image2 = AEG G.IV, Canada Aviation Museum, Ottawa.jpg | caption2 = [[Mercedes D.III]]s on a WW1 [[AEG G.IV]] | image3 = DHGipsyMajorengineDrover.JPG | caption3 = Inverted [[de Havilland Gipsy Major|Gipsy Major]] in a [[de Havilland Australia DHA-3 Drover|DHA-3 Drover]] | image4 = Indian 4 engine manifold side.jpg | caption4 = Straight-4 engine in an [[Indian Four]] motorcycle }} The '''straight engine''' (also called '''inline engine''') is a configuration of multi-cylinder [[piston engine]] where all of the [[cylinder (engine)|cylinders]] are arranged in a single row, rather than radially or in two or more cylinder banks. == Design == A straight engine is easier to build than an equivalent [[flat engine]] or [[V engine]], as it uses one [[cylinder head]] rather than two. Inline engines are also narrower than flat engines or V engines; however, they are longer and can be taller. The [[engine balance]] characteristics of a straight engine depend on the number of cylinders and the [[Firing_order#Firing_interval|firing interval]]. === Slant engines and horizontally-mounted engines === When a straight engine is mounted at an angle from the vertical it is called a ''slant engine''.<ref>Today's Technician: Automotive Engine Performance. Douglas Vidler. Cengage Learning, 1 Jul 2003</ref> Notable slant engines include the 1959-2000 [[Chrysler Slant-6 engine]], 1961-63 [[Pontiac Trophy 4 engine]] and the 1968-1981 [[Triumph Slant-4 engine]]. Some buses and [[diesel multiple unit]] trains take this concept further by mounting the engines horizontally (i.e. with a slant angle of 90 degrees). This is used to reduce the height of the engine, so that it can be located under the floor of the train or bus. === Number of cylinders === {{Div col|colwidth=30em}} * [[Straight-twin engine|I-twin]] (also known as "I2") * [[Straight-three engine|I3]] * [[Straight-four engine|I4]] * [[Straight-five engine|I5]] * [[Straight-six engine|I6]] * [[Straight-seven engine|I7]] * [[Straight-eight engine|I8]] * [[Straight-nine engine|I9]] * [[Straight-twelve engine|I12]] * [[Straight-fourteen engine|I14]] {{div col end}} == Usage in automobiles == The straight-three and straight-four configurations are the most common layouts for three- and four-cylinder engines respectively. Straight-five engines are occasionally used, most recently by Audi and Volvo. Straight-six engines were common prior to the 1990s, however most six-cylinder engines now use a [[V6 engine|V6]] layout. Similarly, straight-eight engines were popular in the 1920s to 1940s, however they were replaced by the more compact [[V8 engine|V8]] layout. ==Aviation use== {{refimprove|section|date=December 2022}} Many straight engines have been produced for aircraft, particularly from the early years of aviation and through the interwar period leading up to the Second World War. Straight engines were simpler and had low frontal area, reducing drag, and provided better cockpit visibility. Straight sixes were especially popular in the First World War, and most German and Italian and some British aircraft used descendants of [[Daimler Motoren Gesellschaft|Daimler's]] pre-war inline six. Prominent examples include the German [[Mercedes D.III]] and [[BMW IIIa]], Italian [[Isotta Fraschini V.4]] and British [[Siddeley Puma]]. The British [[de Havilland Gipsy]] family of engines and their descendants included straight-four and straight-six upright and inverted air-cooled engines which were used on a wide range of smaller aircraft around the world, including on the [[de Havilland Tiger Moth|Tiger Moth]] biplane, and helped made the configuration popular for light aircraft. [[Menasco Motors Company|Menasco]] and [[Ranger Engines|Fairchild-Ranger]] in the United States, [[List of Renault engines|Renault]] in France, [[Walter Aircraft Engines|Walter]] in Czechoslovakia, and [[Hirth]] in Germany all built a similar range of engines which were popular in their respective markets. The aviation use of term "[[Inline engine (aeronautics)|inline engine]]" is used more broadly than for straight engines, since it also applies to other configurations where the cylinders are located in rows (e.g. [[V engine]]s, [[W engine]]s, [[H engine]]s and [[horizontally opposed engine]]s).<ref name="USNA1919_41Glossary">{{cite book|last=Johnson|first= E. R.|title=United States Naval Aviation, 1919-1941: Aircraft, Airships and Ships Between the Wars|edition=illustrated |date=2011-04-20|publisher=McFarland|isbn=978-0786445509|page=326|quote=INLINE ENGINE–A type of reciprocating piston engine in which an even (4-6-8-12) number of cylinders are arranged either in a straight line or in a V-type configuration directly above (or below) the crankcase.}}</ref> === Inverted engines === {{unreferenced|section|date=December 2022}} Some straight aircraft engines have used an ''inverted engine'' configuration, whereby the crankshaft is at the top of the engine and the pistons hang downwards from it. Advantages of the inverted arrangement include a raised thrust line for improved clearance for the propeller, which either allows for the use of a larger, more efficient propeller, or for shorter undercarriage. Since the thrust line is higher, the engine can be mounted lower in the airframe, improving visibility forward, which is no longer blocked by the cylinder heads. It also allows for a simpler exhaust to keep gasses clear from the cockpit. ==Motorcycle use== {{See also|Motorcycle engine}} In motorcycling, the term "in-line" is sometimes used narrowly, for a straight engine mounted in line with the frame.<ref name="EncycloMotoGlossary">{{cite book|last=Wilson|first=Hugo|title=The Encyclopedia of the Motorcycle|url=https://archive.org/details/encyclopediaofmo00wils_1/page/309 |url-access=registration|year=1995|publisher=Dorling Kindersley|location=London|isbn=0-7513-0206-6|pages= 309-310|chapter=Glossary|quote='''in-line''' Engine layout in which the cylinders are arranged in a row, and in-line with the wheels of the machine.}}</ref><ref>{{Cite book |last=Henshaw |first=Peter |title=The BSA Bantam Bible |date=June 15, 2008 |publisher=Veloce Publishing |isbn=978-1-84584-159-1 |pages=42}}</ref> straight, and inline as equivalent, and use them interchangeably.<ref name=Duckworth2012>{{Citation |url= https://books.google.com/books?id=cQ6-B-tbcqMC&pg=PA126 |title= Motorcycle: The Definitive Visual History |editor-last=Duckworth |editor-first=Mick |first1= Phil |last1= Hunt |first2= Malcolm |last2= McKay |first3= Hugo |last3= Wilson |first4= James |last4= Robinson |publisher= [[DK Publishing]], [[Penguin Group]] |year= 2012 |isbn = 9781465400888 |pages=126, 210 }}</ref><ref name=Tuttle2005>{{citation |last= Tuttle |first= Mark Jr. |title= BMW F800S |magazine= Rider |date= December 2005 |page= 15}}</ref> {{clear right}} == References == {{Reflist|30em}} {{Piston engine configurations}} [[Category:Engines by cylinder layout|Straight]] [[Category:Straight engines| ]]
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