Definition
The reduction in airflow pressure and energy that occurs as air travels through the ducting of a turbine engine's induction or bleed air system, caused by friction along duct walls, bends, joints, and changes in cross-sectional area.
Plain English
When air flows through a pipe or duct on the engine, some of its pressure is lost along the way. The longer or more bent the path, the more pressure is lost. That lost pressure is called duct loss.
Context Anchor
Seen in powerplant discussions of engine inlet ducts, cooling-air ducts, induction systems, and other paths that carry air to or from an aircraft engine.
Derivation
Duct comes from the Latin ductus, meaning 'a leading or channel.' A duct leads air from one place to another. Loss here means the energy the air gives up to friction and turbulence as it travels through that channel.
Why Pilots Care
Unaccounted duct losses reduce engine thrust, raise fuel burn, and can limit high-altitude performance.
Analogy
Like water pressure dropping in a long, kinked garden hose. The water still comes out the end, but with less force than it had at the tap.
Intuition Check
Duct losses do not mean the air is simply disappearing. They mean some of the air’s useful push is being used up or wasted as it moves through the duct.
Example Sentence 1
Engineers minimize duct losses by keeping induction ducts as short and straight as possible.
Example Sentence 2
Designers minimized duct losses by smoothing the transitions between the intake and the compressor face.