Definition
A small, heavy cylindrical mass of metal used as a calibration weight or as a moving element inside certain mechanical and hydraulic devices. In aircraft engine and accessory contexts, a slug is a precisely weighted metal piece used during propeller balancing or as a sliding component within a valve or actuator.
Plain English
A short, dense chunk of metal used either as a known weight for balancing things or as a piece that slides back and forth inside a device.
Context Anchor
Seen in aviation maintenance and powerplant discussions when formulas use English units for force, mass, and acceleration.
Derivation
From Middle English 'slugge,' meaning a lump or heavy lazy mass. The aviation use keeps the 'lump of metal' sense — a compact, weighty piece serving a mechanical purpose.
Why Pilots Care
Accurate use prevents errors when converting between weight and mass in engine performance and balance computations.
Intuition Check
Do not read “slug” here as a metal piece, a bullet, or something found in fuel or oil. In this glossary context, a slug is a unit of mass.
Example Sentence 1
The technician added a calibration slug to the propeller hub to correct the imbalance found during dynamic balancing.
Example Sentence 2
Engine thrust calculations require mass in slugs rather than pounds to satisfy the force equals mass times acceleration equation.