Definition
A form of thrust augmentation used on turbofan engines in which extra fuel is injected into the fan discharge duct and burned, increasing the velocity of the fan airflow and producing additional thrust without using the engine's main combustion section.
Plain English
A duct heater is an afterburner-style system fitted in the fan air duct of a turbofan. Extra fuel is sprayed into the fan air and ignited, heating that air so it leaves faster and gives the engine a thrust boost.
Context Anchor
Seen in aircraft heating, defrosting, and engine air-intake heating discussions, especially during system inspection or troubleshooting.
Derivation
Duct' comes from the Latin ductus, meaning 'a leading' or 'channel,' and in jet engines refers to the fan air passage that carries bypass air around the core. 'Heater' simply means a device that adds heat. So a duct heater is literally a device that adds heat to the air flowing through the fan duct, which is exactly what it does.
Why Pilots Care
Maintains cabin temperature and prevents moisture or ice buildup in ducts during flight in cold conditions.
Intuition Check
A duct heater is not mainly heating the duct for its own sake. The important result is that the air moving through the duct gets warmer.
Example Sentence 1
When the pilot selected maximum power for takeoff, the duct heater ignited and added significant thrust to the fan airflow.
Example Sentence 2
Failure of the duct heater can result in cold cabin air during high-altitude cruise.