Definition
Flight instruments that use a physically spinning rotor or wheel to sense aircraft motion. The spinning mass resists changes in its orientation (a property called rigidity in space) and reacts predictably when force is applied to it (precession). These two behaviors are used to drive the attitude indicator, heading indicator, and turn indicator in older or analog cockpits. The rotor is spun either by engine-driven vacuum/pressure systems or by an electric motor.
Plain English
Older flight instruments that work by spinning a small wheel really fast inside them. The spinning wheel wants to keep pointing the same way, and the instrument uses that to show pitch, bank, heading, or turn rate.
Context Anchor
Seen in instrument-system discussions, especially when learning how attitude indicators, heading indicators, and turn indicators get their information.
Derivation
Gyro' comes from the Greek gyros, meaning 'circle' or 'turn.' 'Mechanical' here distinguishes these instruments from modern solid-state digital sensors. So 'mechanical gyros' literally means 'turning devices that work through moving parts' — which is exactly what they are: real wheels spinning inside the instrument case.
Why Pilots Care
They provide essential attitude and heading information in traditional instrument panels when outside visual references are lost.
Analogy
Like a spinning top — once it's going, it resists being tipped over and stays pointing the same way. A mechanical gyro instrument uses that same stubbornness to keep a steady reference while the aircraft moves around it.
Intuition Check
Do not read mechanical gyros as simply “old instruments” or “instruments with gears.” Here it means gyros that depend on a real spinning rotor, whether that rotor is driven by air suction or by electricity.
Example Sentence 1
Before takeoff, the pilot allowed a minute for the mechanical gyros to spin up to full speed after starting the engine.
Example Sentence 2
Many training aircraft still use mechanical gyros that require a working vacuum system to spin at operating speed.