A flat-six engine , also known as a horizontally opposed-six , is a six-cylinder piston engine with three cylinders on each side of a central crankshaft . The most common type of flat-six engine is the boxer-six engine, where each pair of opposed cylinders moves inwards and outwards at the same time. An alternative configuration for flat engines is a 180-degree V engine, where both cylinders move to the right then the left at the same time.
24-447: The Franklin O-335 (company designations variations on 6A and 6V ) was an American air-cooled aircraft engine of the 1940s. The engine was of six-cylinder, horizontally-opposed layout and displaced 335 cu in (5.5 L). The power output of later variants was 225 hp (168 kW). These engines were commonly vertically mounted and used to power many early helicopters in
48-403: A flat-six engine does not have a rocking couple . The symmetry of the arrangement, in which one bank of three cylinders is mirrored by the other bank, means that there is no net force from any given mirrored cylinder pair along the axis of movement of the pistons. So not only is there no net primary or secondary reciprocating effect, there is no net turning force - moment - that would try to rotate
72-510: A flat-six engine was the 1904–1907 Wilson-Pilcher 18/24 HP , which used an engine based on a flat-four engine with two cylinders added. The Wilson-Pilcher was a front-engined car with the crankshaft in-line with the chassis and the cylinders between the chassis rails. Reports on this car quote it as being "remarkably silent and smooth running" and "almost total absence of vibration". Two American manufacturers briefly produced cars with flat-six engines—the 1948 Tucker 48 (water-cooled, based on
96-727: A large width (which can limit the maximum steering angle when used in a front-engined car), a large intake manifold being required when a central carburetor is used, and duplication of the inlet and outlet connections for water-cooled engines. The first production flat-six engine was in the 1904 Wilson-Pilcher 18/24 HP car. The most notable use of flat-six engines is the Porsche 911 sports car, which has used flat-six engines continuously since 1963. Several other car manufacturers, including Subaru, have produced flat-six engines at times. Flat-six engines have also occasionally been used in motorcycles, and commonly in general aviation aircraft, along with
120-677: A short period, the PFM was found on a variety of aircraft as the primary powerplant, or as one-off modifications. These included the Extra 330 , Mooney M20L , Socata TB-16 , Robin DR400 , Ruschmeyer MF-85 and others. Only the M20L went into production, with 40 produced in 1988, and one more in 1989. In a letter dated September 17, 2007, Porsche informed the Federal Aviation Administration (FAA) that it
144-647: The 1948 Tucker Sedan . Tucker liked the engine so much that he purchased the Aircooled Motors/ Franklin Engine Company , and it remained under the ownership of the Tucker family until 1961. Data from Wilkinson Comparable engines Related lists Flat-six engine The advantages of the flat-six layout are good engine balance (for reduced vibration), a low center of gravity, short length (compared with an inline-six engine ) and being well suited to air-cooling. The disadvantages are
168-528: The Pietenpol Air Camper homebuilt monoplane aircraft have used the air-cooled engine from the Chevrolet Corvair compact car. Compared with the engines used in cars, flat-six engines used by helicopters have large displacements and are low revving, producing more torque and less power. A notable recent flat-six aero-engine is the 4-litre side-valve Belgian D-Motor LF39 , a modular variant of
192-464: The Porsche 678 series. These relatively small engines displaced about 1.6 litres (97 cubic inches ) and produced between 41 and 52 kW (55 and 70 hp), depending on the version. Porsche decided to re-enter the aviation market with much larger engines derived from the engine used in the Porsche 911, starting development in 1981. As the engines ran at higher speed than most aircraft engine designs,
216-418: The Porsche 911 , a rear-engined sports car which has used flat-six engines exclusively since 1963. The engines were air-cooled until 1999, when Porsche started using water-cooled engines . Other Porsche models that use flat-six engines are the 1970–1972 Porsche 914/6 ( mid-engine ), the 1986–1993 Porsche 959 ( rear-engine ), and the 1996–2021 Porsche Boxster/Cayman (mid-engine). The first car to use
240-790: The Subaru ER27 , was added to the model range of the Subaru XT coupe. In 1991, the Subaru EG33 engine was used in the Subaru Alcyone SVX , the replacement for the Subaru XT. Following a hiatus of flat-6 engine production for four years, the Subaru EZ30 engine was introduced in the 2000 Subaru Legacy/Outback . The Subaru EZ36 engine was introduced in 2007 and was produced until 2019. All engines were used in front-engine cars with all-wheel drive, plus
264-411: The flat-four engine . A boxer-style flat-six engine is able to have perfect primary and secondary balance . As in other six-cylinder engines, the overlapping of the power strokes of the different cylinders (with a firing interval of 120 degrees in a four-stroke engine) reduces the pulsating of the power delivery relative to that of similar engines with fewer cylinders. In a boxer configuration,
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#1733084941115288-445: The propeller drive used a 0.442:1 reduction gearing so it could drive common propellers. The high operating speed meant the engine ran more smoothly than older designs, and the use of a muffler meant it was quieter as well. With about 3.2 litres (195 cubic inches) displacement, the normally aspirated N-series models produced about 160 kW (210 hp), while the turbocharged T-series produced about 180 kW (240 hp). This
312-423: The 2.7-litre flat-four D-Motor LF26 . Although the side-valve format has long been abandoned for most automotive applications because its combustion chamber is a bar to high engine rpm , the massively over-square (1.295:1) D-Motor is a very simple, low-revving, compact, reliable lightweight aero-engine (without the heavy (and bulky) complication of ohv valve-gear). The flat-six engine is often associated with
336-482: The Franklin O-335) and the 1960–1969 Chevrolet Corvair (air-cooled). Both are rear-engined cars with rear-wheel drive. Chevrolet produced over 1.8 million Corvairs of various types and utilized a turbocharger on some models; one of the first uses of a turbocharger on a mass-produced automobile. Japanese manufacturer Subaru produced water-cooled flat-6 engines from 1988–1996 and 2000–2019. Their first flat-6 engine,
360-570: The United States. They were closely related to the 2A4 and 4A4 2- and 4-cylinder engines. In various subtypes, the 6A4 remained in continuous production from 1945 to the time Franklin's United States operations ceased in 1975, with versions continuing in Polish production into the 1990s. In 1947 this engine was modified into a water-cooled version by the Tucker Car Corporation for use in
384-516: The XT and Alcyone SVX were also available with front-wheel drive. Most motorcycles use engines with four or fewer cylinders, however the Honda Gold Wing touring motorcycle has used a water-cooled flat-six engine since 1988. Initially, the engine had a displacement of 1.5 L (92 cu in), until it was enlarged to 1.8 L (110 cu in) in 2001. The Honda Valkyrie F6C (1997–2003)
408-472: The engine back and forth about its engine mountings. (The moment is not quite zero in practice because each cylinder pair is offset slightly from the other, or else they would clash at the crankshaft.) In this regard, the six cylinder boxer engine is the same as a flat-four boxer engine, which also does not experience any rocking couple. These characteristics result in low vibration for flat-six engines (as in straight-six engines ), especially when compared with
432-407: The engines, Porsche-Flugmotoren ("Porsche Flight Engines"). In the 1950s, European light aircraft builders began adapting the air-cooled automobile engines from the Porsche 356 and Volkswagen Beetle into aircraft engines with a series of limited modifications. Porsche cooperated with some of these builders and produced a series of factory-built engines for about six years between 1957 and 1963,
456-426: The fan system used for cooling. After being introduced in late 1985 and starting to generate increasing interest in the general aviation (GA) market, Porsche exited the field during the massive downturn in the market in the late 1980s, closing the lines in 1991. It is suggested that the program cost it US$ 75 million to develop and produce the small number of engines delivered (about 80). Although marketed for only
480-424: The historically more popular radial engines in small aircraft after World War II because they were less expensive to manufacture. The smaller frontal area compared with a radial engine also results in less drag. Some aircraft have used flat-six engines originally designed for cars. The Porsche PFM 3200 engine, produced from 1985 to 1991, was based on the engine used in the Porsche 911 sports car. Several examples of
504-654: The imbalances that are present in V6 engines with a 90-degree bank angle. Early flat-six engines include the Franklin O-265 which began production in 1940, and the Lycoming O-435 which began production in 1942. Several manufacturers use the letter O in their model codes for flat-layout engines as a designation for “opposed” cylinder layouts. The Franklin O-335 was used in the Bell 47 light helicopter. Flat engines largely replaced
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#1733084941115528-531: Was a cruiser based on the GL1500 Gold Wing. The limited edition 2004 Valkyrie Rune was based on the GL1800. Porsche PFM 3200 The Porsche PFM 3200 was a six-cylinder horizontally opposed air-cooled aircraft engine developed by Porsche from its air-cooled line of automobile engines from the famous Porsche 911 sports car. The PFM designation was derived from the name of the division that designed
552-519: Was roughly twice the power of a conventional lower- rpm design of the same displacement. With single-lever operation, fully aerobatic fuel and oil supplies, fuel injection with automatic altitude compensation and optional turbocharging, the PFM 3200 series were some of the most advanced engines on the market. However, when fully accessorized, they were heavier and larger than competitive engines, especially in cross-section (important for aerodynamics). Also they generated more aerodynamic cooling drag due to
576-457: Was surrendering the type certificate for the PFM 3200 engine and that it would no longer support the engine. In March 2009, the FAA issued a special airworthiness information bulletin stating that type certificates for existing aircraft with the PFM 3200 engine were still valid and would remain so as long as the aircraft meet Federal Aviation Regulations maintenance and operation requirements. However,
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