;
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, inverted
Argus As 410).
Napier Lion engine ;
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).
Napier Dagger engine on display at the
Royal Air Force Museum Hendon. ;
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, unevenly spaced
Napier Cub). 2-stroke opposed piston diesel engine ;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. engine ;
U:Engines with two banks of cylinders side by side driving separate crankshafts geared to a single output, (e.g.
Bugatti U-16). ;
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, 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). multibank aviation engine, four cylinders per bank. :
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==