Aircraft Piston Engines and Their Types

The piston engine, also referred to as a reciprocating engine, is an engine that utilizes pistons to transform pressure into rotational motion. As an internal combustion engine, the piston engine performs similar to those that are present within cars, though they have certain modifications that make them more viable for use in aerospace applications. There are various piston aircraft engine types, and these include those such as inline, rotary, and radial engines. In this blog, we will discuss how piston engines function, as well as some common types.

Across all types of reciprocating aircraft engine types, there are some common functionalities and features. In all types, there are one or more pistons that contain cylinders. Within cylinders, pressurized gas expands through various processes to push the pistons in a stroke and the resulting linear motion is harnessed to produce a rotating motion. While this basic method of producing rotational motion is common across all types, the way in which they compress gas, utilize pistons, and perform other mechanical functions may differ.

The in-line engine, or straight engine, served as some aircraft raw material. Cylinders were placed in a line such as in an automobile, and this allowed for aircraft bodies to be constructed with more narrow shapes. Due to their assembly, in-line engines provided for increased pilot visibility, shorter landing gear, and were well adapted to streamlining. In-line engines do require cooling with the use of liquids or air, and thus mostly serve older light aircraft that have medium to low horsepower capabilities.

The rotary engine is a type of piston engine that was developed during World War I and was installed on military aircraft. At the time, rotary engines were beneficial as they were much lighter than previously used aircraft engine types, such as the straight or in-line piston engine. On a rotary engine, cylinders are placed around the crankcase in a circle and rotate around it. The rotary engine has various advantages, such as smooth running and improved cooling due to the rotating mass acting as a flywheel and fast moving airflow even while the engine is in standby. Despite this, rotary engines have disadvantages as well such as fuel waste, heavy power use for the spinning cylinders to overcome air resistance, and an inefficient total loss oiling system. By the 1920’s, the rotary engine was superseded by other piston engines.

Radial engines are a piston engine type that feature one or more rows of cylinders kits that encircle a crankcase that is placed within the center. Radial engines are considered to be reliable and rugged, and they are still in use for some cargo planes, crop spray planes, and warbirds. Radial engines also run efficiently and smoothly due to their placement of the cylinders with exposure to air. As compared to some other piston aircraft engine types, the radial engine also has a higher power to weight ratio.

While many lighter aircraft with propellers have switched over to other engine types, such as turboprops, there are still many aircraft that utilize the piston engine. As with any hardware piece, piston engines can continue to reliably serve aircraft with proper care and maintenance.