Aircraft engines are almost always either lightweight piston engines or gas turbines. Piston engines, also known as reciprocating engines and they are classified according to cylinder arrangement.
1. In-line engine:
In in-line engines, cylinders are lined up in a one row. Typically they have even number of cylinders, but there are some with three- and five- cylinders. If the engine crankshaft is located above the cylinders, it is called an inverted in-line engine. In-line engines are either air-cooled or Liquid-cooled.
2. V-type engine:
In V-Type engines cylinders are in two in-line banks, typically at an angle of 60-90 degrees apart from each other and driving a common crankshaft. The vast majority of V-type engines are water-cooled and provide higher power-to-weight ratio than an in-line engine, while having a small frontal area.
3. Horizontally opposed engine:
In horizontally opposed engines, cylinders are arranged in two flat rows opposing each other with centrally located crankshaft. The engines are predominantly air-cooled. Layout of the cylinders cancels the forces of reciprocating action, resulting in a smooth running engine.
4. H- configuration engine:
An H configuration engine is essentially a pair of horizontally opposed engines placed together, with the two crankshafts geared together
5. Radial engine:
In radial engines, cylinders are arranged radially around the centrally located crankshaft.