Definition
Thin metal projections cast or machined onto the outside of an air-cooled engine's cylinders and cylinder heads. They greatly increase the surface area exposed to the airflow, allowing heat from combustion to transfer from the metal into the passing air.
Plain English
Ridges sticking out from the outside of the engine cylinders. They give the engine more surface for air to flow over, which carries heat away and keeps the engine from overheating.
Context Anchor
Seen during engine preflight inspections and in discussions of air-cooled aircraft engines.
Derivation
The word fin comes from the Old English finn, the same word used for a fish's fin — a thin, flat projection sticking out from a body. In an engine, the fins do the same thing visually: thin metal blades sticking out from the cylinder.
Why Pilots Care
They keep engine temperatures within safe limits; damaged or obstructed fins can lead to overheating and engine failure.
Grounding Statement
As air moves across the cooling fins, heat passes from the hot engine metal into the cooler air.
Intuition Check
Cooling fins do not make cold air or cool the engine by themselves. They work by giving engine heat more surface area to escape into the air flowing past them.
Example Sentence 1
During preflight, the pilot checked the cooling fins on each cylinder for cracks or debris that could block airflow.
Example Sentence 2
Oil and dirt lodged between the cooling fins reduced airflow and caused the engine to run hotter than normal.