Definition
A flared, rounded inlet shape used at the front of a turbine engine compressor (or air intake duct) that allows air to enter smoothly and uniformly with minimal turbulence and pressure loss. The curved profile guides incoming air gradually from a wide opening down into the narrower compressor inlet.
Plain English
A funnel-shaped opening at the front of an engine intake. Its smooth, curved lip helps air flow in cleanly instead of swirling or breaking up at the edges.
Context Anchor
Seen in aircraft engine maintenance when discussing air intakes, engine air passages, and parts that guide air into the engine.
Derivation
Named for its resemblance to the flared end of a bell (the musical instrument). The shape gradually widens outward, just like the mouth of a bell, which is why the same term is used for similar flared openings in plumbing, ducting, and acoustics.
Why Pilots Care
Reduces intake drag and turbulence, helping the engine breathe efficiently and lowering the risk of compressor stalls or uneven fuel mixture.
Intuition Check
A bell mouth is not related to sound or speaking. In this context, it means a bell-shaped opening that helps control airflow.
Example Sentence 1
Before the test cell run, the technician installed a bell mouth on the front of the engine to ensure smooth airflow into the compressor.
Example Sentence 2
During preflight the pilot noticed debris lodged inside the engine bell mouth and removed it before starting.