Definition
A type of cowl flap consisting of multiple small, hinged louver-like panels arranged side by side around the rear opening of an engine cowling. The pilot opens or closes these panels to vary the amount of cooling air flowing through the engine compartment, controlling engine temperature.
Plain English
A set of small adjustable flaps at the back of the engine cowling that the pilot can open or close to let more or less air pass through the engine for cooling.
Context Anchor
Seen in engine cooling discussions, aircraft systems descriptions, and cockpit procedures for aircraft with adjustable cowl flaps.
Derivation
Called 'gill-type' because the row of small hinged panels resembles the gills of a fish — multiple narrow openings arranged side by side that open and close to regulate flow.
Why Pilots Care
Correct operation keeps engine cylinder head temperatures within limits, especially on the ground and during climbs.
Intuition Check
A cowl flap is not a wing flap. It does not help the airplane fly slower; it controls cooling airflow around the engine.
Example Sentence 1
After takeoff, the pilot left the gill-type cowl flaps fully open during the climb to keep cylinder head temperatures within limits.
Example Sentence 2
During the climb the gill-type cowl flaps were adjusted to keep cylinder head temperatures in the green arc.