Definition
A component of a stabilized platform inertial navigation system that processes signals from the platform's gyros and drives the gimbal motors to keep the platform level and aligned with a fixed reference in space, regardless of aircraft attitude.
Plain English
It is the part of an inertial navigation system that keeps a small internal platform steady and level no matter how the aircraft pitches, rolls, or yaws. It listens to the gyros and tells the motors how to move the rings holding the platform so the platform itself stays still in space.
Context Anchor
Seen in discussions of gyro instruments, flight directors, autopilots, and maintenance troubleshooting for attitude-related systems.
Derivation
A gimbal is a pivoted ring that allows an object mounted inside it to remain level while its surroundings tilt -- the word comes from the Old French gemel, meaning 'twin' or 'paired,' because gimbals were originally made in pairs of nested rings. So a gimbal control unit is the electronics that control those pivoting rings.
Why Pilots Care
Inertial navigation accuracy depends on the platform staying perfectly aligned. If the gimbal control unit drifts or fails, the navigation solution degrades quickly, and position errors grow with time.
Intuition Check
Do not read “control unit” as meaning it directly controls the airplane. In this term, it controls or senses the gyro’s pivoting mount so other systems can use that information.
Example Sentence 1
The gimbal control unit kept the inertial platform level throughout the steep turn, so the navigation system continued to track position accurately.
Example Sentence 2
During preflight, the pilot verified that the gimbal control unit was receiving power before engaging the inertial navigation system.