In aircraft control systems, what term describes a device that receives a small input signal and exerts a large output force to move a control surface?

• A. Servo tab
• B. SIDS
• C. Servo
• D. Signal-to-noise ratio

Answer: (C)

A servo, short for servomechanism, is the device that takes a small control input and produces a much larger output to move a control surface. In aircraft systems, the pilot’s small stick or wheel movement is sent to a servo actuator, which uses hydraulic or electric power to move the surface precisely and with greater force. Feedback keeps the surface at the commanded position, providing accurate and responsive control.

The servo tab is a related idea—a small surface that helps move the main surface by aerodynamic force—but the component that amplifies the input signal into a bigger actuation force is the servo itself. The other terms listed don’t describe an actuation device for moving a control surface.