Automobiles engine (viewed from rear) The beginnings of the flat-twin engine were in 1896, when Karl Benz obtained a patent for the design. A year later, his company
Benz & Cie unveiled the first flat-twin engine, a boxer design called the "contra engine". In 1900, The
Lanchester Engine Company began production of the
Lanchester 8 hp Phaeton, which used a flat-twin engine. This engine had an unusual design of two counter-rotating crankshafts, with each piston attached to its crankshaft by a thick connecting rod. and several
Jowett Cars models from 1910 to 1937. The
Citroën 2CV, produced from 1948 to 1990, was one of the first front-wheel drive cars to use a flat engine. The 2CV was powered by an air-cooled boxer-twin engine. Also in 1948, the
Panhard Dyna X was released with front-wheel drive and an air-cooled boxer-twin engine. Other cars following World War II using boxer-twin engines were the 1945-1954
Jowett Bradford van, and that a belt-drive or chain-drive system can be used to transmit drive to the rear wheel. However, the downsides are uneven heat distribution (the front cylinder is more heavily cooled than the rear cylinder) it was designed as a "bicycle engine system" which transmitted power to a pulley on the rear wheel via a chain. Manufacture of the Fairy was taken over by the
Douglas Engineering Company, one of Light Motors' suppliers, when the Light Motors Company folded in 1907. Later in 1907, Douglas changed the drivetrain from the chain and pulley design to a belt-drive system driven directly from the engine. Later developments of the Douglas motorcycle were made with the cylinders in line with the frame until the Second World War. which posed a design problem for motorcycles with transversely-mounted flat-twin engines. This gearbox could be relatively easily located behind a single-cylinder or V-twin engine, however this arrangement would result in an excessively long wheelbase for flat-twin engines. Solutions to this problem included using a countershaft below the engine (as used by the Douglas Fairy), or a gearbox located above the engine, although in some cases the cylinders were short enough to use the gearbox in the traditional location behind the engine. In 1916, most flat-twin motorcycles still used a transversely-mounted engine. The European models at this time included the
Bradbury , the
Brough HB, the
Douglas and models, the
Humber 3.5 hp and models, the
Matchless 6 hp, the
Montgomery 6 hp,
Williamson Flat Twin , and the Bayerische Flugzeugwerke Helios (the predecessor to BMW's first motorcycle). Models produced in the United States included the
Indian Model O and the
Harley-Davidson Model W.
Longitudinal mounting The main benefit of mounting a flat-twin engine with the crankshaft in line with the frame (therefore the cylinders sitting sideways in the frame) is that an air-cooled engine receives the same amount of cooling for each cylinder. A side benefit is that the cylinders provide protection to the rider in the event of a collision or fall, and keeps their feet warm in cold weather. and that it exposes the cylinders and valve covers to the danger of collision damage. One of the first motorcycles with a longitudinally-mounted flat-twin engine was the 1916
ABC, which was built in the United Kingdom. as do
Ural (Russia) and
Dnepr (Ukraine).
Aviation II installed in aircraft In 1902, the
Pearse monoplane (which would later become one of the first aircraft to achieve flight) was powered by a flat-twin engine built on a farm by a hobbyist inventor. This engine used the unusual design of a single shared
crank pin and double acting pistons. In 1908, the French company Dutheil-Chalmers began production of flat-twin aircraft engines, which used two counter-rotating crankshafts. The Dutheil-Chlamers engine was used by the 1907
Santos-Dumont Demoiselle No. 20 experimental airplane, with later versions of this airplane being produced with flat-twin engines from
Darracq and
Clément-Bayard. Most piston-engined aircraft used more than two cylinders, however other flat-twin aircraft engines from the 1920s and 1930s include the American
Aeronca E-107 and
Aeronca E-113, the British
Bristol Cherub, and the Czechoslovak
Praga B2. The
HKS 700E is an oil-cooled flat twin for ultralight aircraft that is currently in production. In larger aircraft, flat-twin engines have been used in
auxiliary power units (APUs). A notable example was made by
ABC Motors in the 1920s and 1930s. During World War II, the
Riedel firm in Germany designed and manufactured a two-stroke flat-twin engine as
jet engine starter motors for the Junkers Jumo 004, BMW 003 and Heinkel HeS 011 jet engines
Other uses The
Maytag 'Model 72' flat-twin engines— produced from 1937 until some time between 1952 and 1960— were used in various applications including clothes washing machines. Electrical generators using flat-twin engines were built by Norman Engineering Company from 1932 to 1968 and by Douglas during World War II.
Enfield Industrial Engines (part of
Royal Enfield) produced flat-twin two-stroke petrol engines during World War II which were used for generators and other military uses. After 1945, Enfield produced flat-twin diesel engines, with applications including farm and marine use.
Coventry Victor introduced a diesel version of its existing 688 cc petrol flat-twin in 1932, and went on to produce flat-twin diesel and petrol engines for a variety of industrial and marine uses into the 1950s. Two-stroke flat-twins were often used as
outboard motors for boats, as they were smoother than single-cylinder engines. In the 1940s, they were largely replaced by straight-twin two-stroke engines, which were easier to start and no longer had excessive amounts of vibration. == References ==