Definition
Bearings that support a rotating shaft through direct sliding contact between two surfaces, rather than through rolling elements such as balls or rollers. In gyroscopic instruments, friction bearings produce drag on the gyro rotor, which limits rotor speed and contributes to instrument errors over time.
Plain English
A friction bearing is a simple support that lets a shaft spin by sliding against a surface, instead of rolling on tiny balls. Because the surfaces rub, they create more resistance than rolling bearings.
Context Anchor
Seen in discussions of gyroscopic flight instruments, especially how a gyro rotor is mounted so it can spin freely.
Derivation
From Latin 'fricare,' meaning 'to rub.' The name describes exactly what happens — the shaft rubs against its support — and explains why these bearings produce drag compared with rolling-element bearings.
Why Pilots Care
Friction bearings inside a gyro slow the rotor and introduce small errors. Knowing this helps explain why vacuum-driven gyros need adequate suction and why instruments wear out and require periodic overhaul.
Analogy
A smooth door hinge lets a door swing easily. If the hinge gets sticky, the door no longer moves freely; friction bearings in a gyro have the same basic problem, but inside a flight instrument.
Intuition Check
Do not read this as bearings designed to create friction. In this context, the important idea is that any friction in the bearings should be very small.
Example Sentence 1
The older attitude indicator used friction bearings in its gyro, which gradually slowed the rotor and introduced precession errors.
Example Sentence 2
Excessive wear in the friction bearings of a heading indicator can cause the card to drift noticeably after a turn.