Definition
A small electrical device coupled to a rotating shaft that produces a voltage proportional to the shaft's rotational speed, used to measure and display engine RPM on a tachometer.
Plain English
A small generator attached to the engine that turns the engine's spinning into an electrical signal, which the cockpit gauge then reads as RPM.
Context Anchor
Seen in discussions of engine instruments, maintenance, and training devices that need to sense or display rotational speed.
Derivation
Tach' is short for tachometer, from the Greek 'tachos' meaning speed. A tach generator, then, is literally a 'speed generator' — a device that generates an electrical signal representing speed of rotation.
Why Pilots Care
Accurate RPM readings from a working tach generator let pilots maintain proper engine power settings and avoid overstress or underperformance.
Intuition Check
Do not read tach generator as the cockpit gauge itself. The tach generator is the sensing device that creates the signal the gauge or system uses.
Example Sentence 1
The mechanic traced the erratic RPM indication to a worn tach generator and replaced it during the next inspection.
Example Sentence 2
A loose connection at the tach generator caused fluctuating readings on the engine gauge throughout the flight.