Definition
Pivoted weights mounted on a rotating shaft inside a mechanical governor or control unit. As the shaft spins faster, centrifugal force throws the weights outward; as it slows, springs pull them back inward. This inward and outward movement is used to operate a valve, lever, or linkage that controls something else — most commonly the propeller pitch in a constant-speed propeller governor, or fuel metering in a fuel control unit.
Plain English
Small weights inside a spinning component that swing outward as the shaft spins faster and pull back in as it slows. That motion is used to automatically adjust something else, like propeller pitch.
Context Anchor
Seen in propeller governors, engine governors, and other aircraft systems that sense and control rotational speed.
Derivation
A combination of 'fly,' used in the mechanical sense of 'to spin or whirl,' and 'weight.' The same root appears in 'flywheel.' The name simply describes what the parts do — weights that fly outward when spun.
Why Pilots Care
They are essential to constant-speed propeller operation; failure can cause RPM fluctuations that reduce engine efficiency or lead to overspeed damage.
Intuition Check
Flyweights are not weights used to measure how heavy an aircraft is. They are small moving parts inside a spinning mechanism that help sense speed.
Example Sentence 1
When the engine RPM rises above the selected setting, the governor flyweights move outward and signal the propeller to take a coarser pitch.
Example Sentence 2
During the preflight, the instructor pointed out how the governor’s flyweights prevent propeller overspeed in a dive.