Definition
A rotating drum or spool used to apply tension to a control cable in an aircraft control system. The cable wraps around the capstan, and as the capstan turns it pulls the cable, transmitting force to move a control surface or trim tab.
Plain English
A small turning drum that a cable wraps around. When the drum turns, it pulls the cable, which moves something — like a trim tab or control surface — at the other end.
Context Anchor
Seen in aircraft control-cable systems, trim systems, and some autopilot drive units.
Derivation
From the Old French 'cabestan,' originally a vertical drum used on ships to wind in heavy ropes by turning it with bars. The aviation use carries the same idea — a turning drum that pulls a line — just much smaller and used for control cables instead of ship's rigging.
Why Pilots Care
Capstans are common in trim systems and autopilot servos. If a capstan slips, jams, or the cable wrap is incorrect, the associated control may bind, run away, or fail to respond. Recognising the part by name helps when reading maintenance notes or troubleshooting a stuck trim wheel.
Analogy
Think of a garden hose wound around a reel. When the reel turns, it takes up or lets out the hose; a capstan does a similar job with a cable.
Intuition Check
A capstan is not just any pulley. A pulley mainly redirects a cable; a capstan turns and uses the wrapped cable to move or drive something.
Example Sentence 1
The trim cable wraps several turns around the capstan so it grips firmly without slipping when the trim wheel is turned.
Example Sentence 2
Proper use of the capstan prevents over-tensioning that could lead to cable failure.