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aviation Aviation includes the activities surrounding mechanical flight and the aircraft industry. ''Aircraft'' includes airplane, fixed-wing and helicopter, rotary-wing types, morphable wings, wing-less lifting bodies, as well as aerostat, lighter- ...
, an inline engine is a
reciprocating engine A reciprocating engine, also often known as a piston engine, is typically a heat engine that uses one or more reciprocating pistons to convert high temperature and high pressure into a rotating motion. This article describes the common fe ...
with
bank A bank is a financial institution that accepts Deposit account, deposits from the public and creates a demand deposit while simultaneously making loans. Lending activities can be directly performed by the bank or indirectly through capital m ...
s of cylinders, one behind another, rather than rows of cylinders, with each bank having any number of cylinders, although more than six is uncommon. The major reciprocating-engine alternative configuration is the
radial engine The radial engine is a reciprocating type internal combustion engine configuration in which the cylinders "radiate" outward from a central crankcase like the spokes of a wheel. It resembles a stylized star when viewed from the front, and is ...
, where the cylinders are placed in a circular or "star" arrangement. The term "inline" is used somewhat differently for aircraft engines than automotive engines. For automotive engines, the term ‘inline’ refers only to straight engines (those with a single bank of cylinders). But for aircraft, ‘inline’ can also refer to engines which are not of the straight configuration, such as V, H, or horizontally opposed.


Inline engine configurations

; Straight: Engines with a single bank of cylinders which can be arranged at any angle but typically upright or inverted, (e.g. upright ADC Cirrus, inverted de Havilland Gipsy Major). ; V:Engines with two banks of cylinders with less than 180° between them driving a common crankshaft, typically arranged upright or inverted (e.g. upright
Liberty L-12 The Liberty L-12 is an American water-cooled 45° V-12 aircraft engine displacing and making designed for a high power-to-weight ratio and ease of mass production. It saw wide use in aero applications, and, once marinized, in marine use both ...
, inverted Argus As 410). ; O or Horizontally Opposed: Engines with two banks of cylinders arranged at 180° to each other driving a common crankshaft, almost universally mounted with banks horizontal for aircraft use, or with crankshaft vertical for helicopter use, (e.g. horizontally mounted Continental O-190, vertically mounted
Franklin 6ACV-245 The Franklin O-425 (company designation 6AG/6V6) was an American air-cooled aircraft engine that first ran in the mid-1940s. The engine was of six-cylinder, horizontally-opposed layout and displaced . The power output was between and depen ...
). ; W:Engines with three banks driving a common crankshaft, arranged so that first and last banks are 180°or less apart, (e.g. upright Lorraine 12Eb, inverted Napier Lioness). ; X: Multiple bank engines with four banks arranged around a common crankshaft, usually spaced evenly, (e.g. evenly spaced
Rolls-Royce Vulture The Rolls-Royce Vulture was a British aero engine developed shortly before World War II that was designed and built by Rolls-Royce Limited. The Vulture used the unusual " X-24" configuration, whereby four cylinder blocks derived from the R ...
, unevenly spaced Napier Cub). ;Fan: Engines with more than three banks with 180° or less between first and last bank, akin to W engines. ''Note:'' Fan engines with single cylinder banks, typically from Anzani, are usually regarded as variants of the
Radial engine The radial engine is a reciprocating type internal combustion engine configuration in which the cylinders "radiate" outward from a central crankcase like the spokes of a wheel. It resembles a stylized star when viewed from the front, and is ...
. ; U:Engines with two banks of cylinders side by side driving separate crankshafts geared to a single output, (e.g.
Bugatti U-16 The Bugatti U-16 was a 16-cylinder water-cooled double-8 vertical in-line "U engine", designed by Ettore Bugatti in 1915-1916 and built in France in small numbers. The US Bolling Commission bought a license to build the engine in the US, and s ...
). ; H:Engines with four banks of cylinders driving two crankshafts geared to a single output, in effect, two Opposed engines coupled together and mounted either horizontally or vertically, (e.g. horizontally
Napier Sabre The Napier Sabre is a British H-24-cylinder, liquid-cooled, sleeve valve, piston aero engine, designed by Major Frank Halford and built by D. Napier & Son during World War II. The engine evolved to become one of the most powerful inline p ...
, vertically Napier Dagger). ; Opposed piston:Two-stroke engines, typically compression ignition/Diesel, with a single bank of cylinders driving two crankshafts where the pistons travel towards each other forming single combustion chambers, (e.g. Jumo 207). :Deltic: Engines with three banks of opposed piston cylinders arranged in a triangle with three crankshafts geared to drive a single output,(e.g. Napier Deltic) :Rhomboidal: Engines with four or more banks of opposed piston cylinders arranged in a square with four crankshafts geared to drive a single output,(e.g. Jumo 223) ''Note:'' There is no theoretical limit to the number banks in an opposed piston engine, limitations include cost, complexity and reliability. ;Multiple bank:Engines with more than two banks, arranged around a common axis and/or crankshaft with more than 180° between first and last banks. :Star: Multiple bank engines with an even number of banks (more than four) arranged around a common axis and/or driving a common crankshaft with more than 180° between first and last banks, (e.g. Jumo 222, Dobrynin VD-4K). : Inline Radial: Multiple bank engines, usually liquid-cooled, with an odd number of banks (three or more) arranged around a common axis and/or driving a common crankshaft with more than 180° between first and last banks, (e.g. air-cooled Armstrong Siddeley Deerhound, liquid-cooled BMW 803). ''Note'' The BMW 803 is not only an inline radial engine but is also a coupled engine with two engines arranged back to back on a common axis driving separate co-axial propellers through a common gearbox.


Inverted engine

An upright engine has the cylinder heads directly above the crankshaft. By contrast an inverted engine has the cylinder heads directly beneath it. In the inverted V layout, the cylinders angle downwards instead of upwards. For an aero engine, advantages of the inverted layout include improved access to cylinder heads and manifolds for the ground crew, having the centre of mass of a multi-bank engine lower in the engine and, for engines mounted in the nose, improved visibility for the pilot and placing the widest part of a multi-bank engine closer to the midline of the fuselage, which is typically its widest point. The
Hirth HM 60 The Hirth HM 60 was a four-cylinder inverted air-cooled inline aircraft engine designed in 1923 and first sold in 1924. The engine was of very high quality, and its sales success contributed to Hirth's rapid pre-war expansion. It was a popular ...
four-cylinder inverted inline engine was introduced in 1924, and inverted designs saw increasing popularity through the late 1920s and 30s. Widespread examples included the inline de Havilland Gipsy Major used in the
de Havilland Tiger Moth The de Havilland DH.82 Tiger Moth is a 1930s British biplane designed by Geoffrey de Havilland and built by the de Havilland Aircraft Company. It was operated by the Royal Air Force (RAF) and other operators as a primary trainer aircraf ...
, and the inverted-V Daimler-Benz DB 601 used in the
Messerschmitt Bf 109 The Messerschmitt Bf 109 is a German World War II fighter aircraft that was, along with the Focke-Wulf Fw 190, the backbone of the Luftwaffe's fighter force. The Bf 109 first saw operational service in 1937 during the Spanish Civil War an ...
.


References

Citations Bibliography * * {{refend Piston engine configurations Aircraft piston engines