An aircraft piston engine, often called a reciprocating engine or “recip,” is an internal combustion engine that uses one or more pistons moving back and forth to convert pressure into rotational motion. These engines operate on principles similar to those found in most cars. However, aviation engines have special features like dual ignition systems for added safety and air cooling to keep weight down. Some piston engines also use turbochargers or, less frequently, superchargers to boost performance. While most aircraft piston engines run on AVGAS, diesel engines are becoming increasingly popular, especially in light aircraft.
Over the past century, aircraft engine design has evolved significantly since the first powered flight. Today, many aircraft use horizontally opposed engines. Yet, you’ll still find various engine types in production, experimental, and vintage aircraft.
In-Line Engines: The earliest aircraft engines were in-line or “straight” engines, which have cylinders arranged in a line, much like many car engines. This design is narrow, allowing for a slim front fuselage. However, it struggles with airflow for cooling, requiring liquid cooling, which lowers the power-to-weight ratio.
Rotary Engines: Developed during World War I, rotary engines feature an entire engine that rotates with the propeller, improving airflow for cooling. This design was particularly favored in military aircraft of the time.
V-Type Engines: A V-type engine is essentially two in-line engines configured in a “V” shape, sharing a common crankshaft. A well-known example is the supercharged Rolls Royce Merlin, used in iconic aircraft like the Supermarine Spitfire and the Avro Lancaster.
Radial Engines: A radial piston engine consists of one or more rows of odd-numbered cylinders arranged in a circle around a central crankshaft. This configuration offers a favorable power-to-weight ratio and allows for efficient cooling and smooth operation.
Horizontally Opposed Engines: Often referred to as boxer or flat engines, horizontally opposed engines feature two banks of cylinders positioned on opposite sides of a central crankcase. This simple and reliable design is easy to maintain, making it popular among aircraft manufacturers.
