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A flat engine is an Internal Combustion Engine with pistons that are all relatively horizontal. A Straight Engine canted 90 degrees from straight up is a flat engine, as is one in which the Cylinder s are arranged in two banks on either side of a single Crankshaft . In both configurations, the motion of all the pistons is in the horizontal plane. German engineer Karl Benz Patent ed his design for the first internal combustion engine with horizontally opposed Piston s in 1896 . There are two main types of these engines:
In German , the term for flat engine is ''boxermotor'', which includes both types, not just those known as ''boxer engines'' in English . CONFIGURATION Flat engines are more compact than in-line engines, and have a lower Center Of Gravity than any other common configuration. Automobile s and Motorcycle s powered by a flat engine generally have a lower center of gravity, giving better stability and control. These engines, however, are also wider than more traditional configurations and are more expensive to build. The extra width may cause problems fitting the engine into the engine bay of a front-engined car owing to the interference with the steering wheels, and create cornering problems for a motorcycle. The flat configuration also fits very well with Air Cooling and Aircraft Engine s. Air-cooled designs such as in the VW Beetle used a Flat-4 , as did the Porsche 356 and 912 . The Chevrolet Corvair used An Air-cooled Flat-6 , a rarity in American designs. Both the older and newer models of the 911 use a Flat-6 , at first air cooled but later models are water-cooled. These automobiles situate the engine in the rear rather than the front, where its width does not interfere with the steering of the front wheels; the use of air-cooling obviates the need for connecting the engine to a Radiator , and also reduces the weight even more. Front-mounted air-cooled Flat-twin engines were used by Citroën in their model 2CV and its derivatives, while the Citroën GS used a Flat-4 , and a Flat-6 was proposed for the Citroën DS , but rejected. BMW uses an air-cooled flat-twin in many of their Motorcycle s. BOXER ENGINES Boxer engines probably got their name because the pistons of the motor, when observed from the top, resemble the fists of a boxer pummeling his opponent. Boxer engines of up to eight cylinders have proved highly successful in both Automobiles and motorcycles, and continue to be popular for Light Aircraft engines. One benefit of using a boxer engine versus a V-engine is that the design provides good balance because each piston's momentum is counterbalanced by the corresponding piston movement of the opposite side. Boxers are one of only four layouts that have a natural dynamic balance; the others being the Straight-6 , the Flat-12 and the V12 . These engines can run very smoothly and free of vibrations with a Four-stroke Cycle and do not require a Balance Shaft or counterweights on the Crankshaft to balance the weight of the reciprocating parts, which are required in other engine configurations. (Note that this is true of all boxer engines regardless of the number of cylinders, but not true for all V and straight, or inline engines.) Boxer engines tend to produce more noise than inline and V-engines because valve clatter is not so well dampened due to lack of covering by air-filters and other components, and produce a larger torsional vibration than a V-engine, and so, tend to require a larger flywheel. They have a characteristic smoothness throughout the rev range and, combined with the mounting position immediately ahead of the rear axle, offer a low center of gravity and more neutral handling. NOTABLE BOXER ENGINES
180° V-ENGINES Flat V Engine s are used in performance and racing cars, normally a 180 degree V12. Ferrari used a 180° version of the '' Colombo '' V12 in the Testarossa and Berlinetta Boxer models. SEE ALSO Flat engine designs Other engine designs |
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