Definition
A mechanical instrument that measures the rotational speed of an engine or shaft by using spring-loaded flyweights driven by the rotating component. As shaft speed increases, the flyweights swing outward against a calibrated spring, and this movement is converted into a needle indication on a dial calibrated in revolutions per minute (RPM).
Plain English
An RPM gauge that works by spinning small weights. The faster the engine turns, the further the weights fly outward, and that movement is what moves the needle on the dial.
Context Anchor
Seen in aircraft instrument and engine-system discussions, especially older or mechanically driven engine speed indicators.
Derivation
Centrifugal comes from Latin centrum (center) and fugere (to flee) — literally 'fleeing the center,' which describes how the spinning weights swing outward. Tachometer comes from Greek tachos (speed) and metron (measure). Together: an instrument that measures speed using the outward motion of spinning parts.
Why Pilots Care
It gives a dependable RPM reading on aircraft that lack electrical power to the instrument, allowing the pilot to set and monitor proper engine operating speeds.
Analogy
Picture a spinning amusement-park ride: as it spins faster, people feel pushed outward more strongly. A centrifugal tachometer uses that same outward effect on small weights to move its indicator.
Intuition Check
Do not think “centrifugal” means the tachometer is measuring outward force for its own sake. The outward movement is only the method the instrument uses to show rotational speed.
Example Sentence 1
The aircraft's centrifugal tachometer showed 2,300 RPM during the cruise climb.
Example Sentence 2
During the magneto check the centrifugal tachometer showed a smooth drop when each ignition system was selected.