Definition
An instrument that measures the speed of a moving fluid (such as air) by passing an electric current through a fine wire exposed to the flow. The moving air cools the wire, and the resulting change in the wire's electrical resistance is measured and converted into a reading of fluid velocity.
Plain English
A device that measures how fast air is moving by sensing how quickly a heated wire cools down when air flows past it. The faster the air, the more the wire cools, and that cooling is read as a speed.
Context Anchor
Seen in discussions of airflow measurement, wind-tunnel testing, and some aircraft sensor systems, rather than as a normal cockpit airspeed instrument.
Derivation
From 'hot-wire,' literally a heated wire, plus 'anemometer,' from the Greek 'anemos' meaning 'wind' and '-meter' meaning 'measuring device.' So the name describes exactly what the instrument is: a wind-measuring device that uses a hot wire as its sensor.
Why Pilots Care
Hot-wire anemometers are used in some airflow and mass-flow sensing systems, including certain fuel control and engine inlet measurement applications. Knowing the principle helps a pilot understand why such sensors are sensitive to contamination or damage to the wire element.
Analogy
Like holding a wet finger up to feel the wind: the faster the air moves, the faster your finger cools. The instrument does the same thing electronically with a tiny heated wire.
Grounding Statement
Moving air carries heat away from the heated wire, and stronger airflow carries heat away faster.
Intuition Check
“Hot-wire” does not mean the instrument measures hot air. It means the instrument uses a heated wire to measure how fast the air is moving.
Example Sentence 1
The technician used a hot-wire anemometer to verify airflow through the cooling duct during the ground test.
Example Sentence 2
Before reinstalling the cabin heater duct, the mechanic used a hot-wire anemometer to confirm the blower was delivering adequate air volume.