Definition
The outer pivoting ring inside an attitude indicator that rotates about the aircraft's longitudinal (roll) axis, allowing the gyroscope's spin axis to remain vertical while the airplane banks left or right.
Plain English
A ring inside the attitude indicator that lets the spinning gyro stay upright while the airplane rolls. As the airplane banks, this ring tilts with it, but the gyro inside stays level so the instrument can show how far the wings are tilted.
Context Anchor
Seen in attitude indicator diagrams and explanations of how the gyro inside the instrument can show pitch and bank.
Derivation
Gimbal' comes from the Old French 'gemel,' meaning 'twin' or 'paired ring.' Gimbals are pivoting rings used in pairs (or sets) so that an object mounted inside can stay steady while the outer frame moves. The 'roll' part simply names which axis this particular gimbal handles.
Why Pilots Care
A functioning roll gimbal ensures the attitude indicator accurately shows bank angle, which is essential for maintaining control and orientation during instrument flight.
Analogy
Think of a drink holder mounted on gimbals in a boat: the boat rocks side to side, but the holder pivots so the cup stays upright. The roll gimbal does the same job for the gyro when the airplane banks.
Intuition Check
Do not read roll here as the airplane moving along the ground like a wheel. In this context, roll means the airplane tilting left or right around its nose-to-tail line.
Example Sentence 1
The roll gimbal allows the gyroscope inside the attitude indicator to remain level while the aircraft banks into a turn.
Example Sentence 2
During preflight, the instructor explained how a damaged roll gimbal would prevent the attitude indicator from showing changes in bank angle.