Definition
A large, multi-bladed fan housed inside a shroud (duct) at the front of a turbofan engine, driven by the engine's turbine. It accelerates a large mass of air rearward, producing the majority of the engine's thrust, while a smaller portion of the air passes through the engine core for combustion.
Plain English
The big fan you see at the front of a jet engine, surrounded by a round cover. It pushes a lot of air backward to make most of the engine's thrust.
Context Anchor
Seen in turbofan engine descriptions, especially when comparing how a turbofan moves air compared with a turbojet.
Derivation
"Duct" comes from the Latin ductus, meaning a channel or pipe that guides flow. The shroud around the fan acts like a channel, guiding the airflow straight through and improving efficiency compared to an open fan.
Why Pilots Care
Ducted fans enable the high bypass ratios that give modern turbofan engines better fuel economy, lower noise, and greater thrust at subsonic speeds.
Intuition Check
Do not read duct fan as a small cabin cooling fan. In this context, it is part of the main engine and helps create thrust.
Example Sentence 1
During the walkaround, the pilot inspected the duct fan blades for nicks or damage before the flight.
Example Sentence 2
Mechanics inspect the duct fan blades during preflight to ensure no foreign object damage has occurred inside the inlet.