Definition
A device that converts hydraulic, pneumatic, or electrical energy into rotational mechanical motion, producing torque to turn a shaft or component through a limited angle or continuous rotation. Rotary actuators are used on aircraft to drive flight control surfaces, flap and slat mechanisms, cargo doors, and other systems that require controlled angular movement rather than straight-line motion.
Plain English
A unit that takes power from fluid or electricity and turns a shaft to move a part in a circular motion.
Context Anchor
Seen in aircraft maintenance when describing powered systems that rotate doors, valves, flight-control parts, or other moving components.
Derivation
Rotary comes from the Latin rotare, meaning to turn. Actuator comes from the Latin actus, meaning a doing or driving. Together the term means a device that produces turning motion, which is exactly what it does on the aircraft.
Why Pilots Care
Many flight-critical surfaces and systems rely on rotary actuators. Knowing whether a system uses a rotary actuator helps technicians and pilots understand failure modes, inspection points, and how a control surface is driven during normal and emergency operation.
Intuition Check
A rotary actuator does not always spin continuously like a drill. In many aircraft uses, it turns only through a limited range to place a part in the correct position.
Example Sentence 1
The technician inspected the rotary actuator that drives the inboard flap for any signs of hydraulic leakage.
Example Sentence 2
Maintenance replaced the leaking rotary actuator on the cargo door system.