Definition
A drum-brake design in which only one of the two brake shoes uses the rotation of the wheel to wedge itself harder against the drum, providing braking assist in one direction of wheel rotation only. The other shoe relies solely on the force applied by the brake actuator.
Plain English
A type of drum brake where the spinning wheel helps press one shoe harder against the drum to boost stopping power, but only when the wheel is turning in the forward direction. The other shoe gets no help from the wheel and just pushes against the drum on its own.
Context Anchor
Seen in aircraft brake system descriptions, especially when studying older drum brake designs during maintenance training.
Derivation
Servo comes from the Latin servus, meaning servant. In braking, a servo action is one where the wheel's own motion 'serves' the brake by helping it apply itself more firmly. 'Single' indicates that only one shoe receives this assist, distinguishing it from dual-servo brakes where both shoes benefit.
Why Pilots Care
Affects the amount of pedal pressure required and the braking behavior during landing rollout and taxi operations.
Analogy
It is like a door wedge: once the door starts pressing on the wedge, the wedge is forced in tighter. In a single-servo brake, the turning drum helps force one shoe into a tighter grip.
Intuition Check
Do not assume “servo” means an electric motor here. In this brake term, “servo” means the brake uses the wheel’s own turning motion to help increase braking force.
Example Sentence 1
The mechanic identified the unit as a single-servo brake because only the forward shoe showed the wear pattern of self-energizing action.
Example Sentence 2
Single-servo brakes on the trainer provided adequate stopping force during the short-field landing rollout.