The speed brake is extended and retracted by a single actuator which is operated by

• A. Electric motors
• B. Pneumatic pressure
• C. Hydraulic pressure
• D. Tie rods

Answer: (C)

The idea being tested is what power source drives the mechanism that moves the speed brake. A single hydraulic actuator is used because hydraulic pressure can produce a large, smooth, and controllable force in a compact unit, which is ideal for moving a sizable speed brake surface against aerodynamic loads. Using hydraulic power allows precise control of extension and retraction and can hold the brake in place with minimal energy once positioned, thanks to hydraulic locking and valve control.

While electric motors can actuate systems, they tend to add complexity and may not deliver the same high, rapid force in a compact package, especially under varying aerodynamic loads. Pneumatic systems are lighter, but the air’s compressibility leads to less precise position control and lower force for large surfaces. Tie rods are a mechanical linkage, not an actuation method by themselves, so they require another power source to move the brake.