Definition
The aerodynamic drag produced when outside air is routed through the engine compartment to cool the engine. As air enters the cowling, slows down to absorb heat from the cylinders, and exits, it loses energy and creates a rearward force on the aircraft.
Plain English
The penalty in speed and efficiency that comes from letting air flow through the engine to keep it cool. Cooling the engine costs you a small amount of forward performance.
Context Anchor
Seen in discussions of engine cooling, cowling design, cowl flaps, and aircraft performance.
Derivation
Cooling refers to lowering engine temperature; drag is the rearward aerodynamic force that resists motion. Together the term names the specific drag caused by the cooling airflow itself, distinguishing it from drag produced by the airframe.
Why Pilots Care
Excessive cooling drag reduces cruise speed and increases fuel consumption while still being necessary to protect the engine.
Analogy
It is like opening a vent on a moving car. The air helps cool the inside, but it also disturbs the smooth flow and adds resistance.
Grounding Statement
When air is brought inside the cowling to carry heat away from the engine, that air no longer flows cleanly around the airplane, so some performance is lost.
Intuition Check
Cooling air is necessary, but it is not free. In this term, “drag” means the performance cost of using airflow for cooling.
Example Sentence 1
Closing the cowl flaps in cruise reduces cooling drag and gains a few knots of airspeed.
Example Sentence 2
Designers shaped the cowling inlets carefully so that cooling drag would not offset the benefit of better engine temperatures.