Definition
Hinged, movable doors on the engine cowling that the pilot opens or closes to control the amount of cooling air flowing around an air-cooled piston engine. Opening them increases airflow through the engine compartment to remove heat; closing them reduces airflow to keep the engine warm and reduce drag.
Plain English
Small adjustable flaps on the engine cover that the pilot can open or close to let more or less air pass over the engine, controlling how cool or warm the engine stays.
Context Anchor
Seen in aircraft engine cooling procedures, especially during climbs, descents, and high-power operations.
Derivation
Cowl' comes from the Latin cucullus, meaning 'hood' -- the same root as the hooded garment worn by monks. The engine 'cowling' is the hood that covers the engine, and the cowl flaps are the adjustable doors built into that hood.
Why Pilots Care
Correct operation prevents engine overheating during high-power phases and avoids overcooling in descent, protecting engine life and performance.
Analogy
They work like adjustable vents on a car dashboard, but for engine cooling instead of cabin comfort.
Intuition Check
Cowl flaps are not the wing flaps used for takeoff and landing. They are engine-cooling doors in the cowling.
Example Sentence 1
Before takeoff, the pilot opened the cowl flaps to provide maximum cooling for the climb.
Example Sentence 2
After landing in cold weather the pilot closed the cowl flaps to help the engine retain heat while taxiing.