Definition
A bell-shaped gear used in certain aircraft mechanical systems, most commonly in helicopter rotor head and swashplate assemblies, where its flared, cup-like form allows it to mesh with other gears at an angle and transmit rotational motion between non-parallel shafts.
Plain English
A gear shaped like an upside-down bell. Its flared shape lets it connect with another gear that sits at an angle to it, so motion can turn a corner instead of running in a straight line.
Context Anchor
Seen in aircraft maintenance manuals, parts lists, and engine or accessory drive descriptions, rather than in normal cockpit procedures.
Derivation
Named for its physical shape. The gear flares outward like the open mouth of a bell, and that flared geometry is what allows it to mesh with a mating gear set at an angle.
Why Pilots Care
Pilots usually do not operate a bell gear directly, but the term may appear in maintenance records or mechanical system descriptions. If the gear is worn or damaged, the part it drives may not work correctly.
Intuition Check
Do not read “Bell” as the aircraft manufacturer or as a cockpit warning bell here. In this term, “bell” describes the shape of the gear.
Example Sentence 1
The mechanic inspected the bell gear in the rotor head for wear before signing off the 100-hour inspection.
Example Sentence 2
During gear retraction testing, a binding bell gear prevented the nosewheel from locking up.