Definition
The magnetism that remains in a ferromagnetic material after the magnetizing force has been removed. In aviation, residual magnetism is most commonly associated with the soft iron cores of generators, magnetos, and relays, where a small amount of retained magnetism is necessary to begin field excitation when the unit is started.
Plain English
Magnetism that stays inside a piece of iron or steel after the original magnetic force is taken away. It's a leftover magnetic effect that hangs on in the metal.
Context Anchor
Seen in aircraft electrical-system discussions, especially with engine-driven generators and charging-system troubleshooting.
Derivation
From Latin 'residuus' meaning 'remaining' or 'left over.' It describes magnetism that is left behind in the metal after the magnetizing source is gone.
Why Pilots Care
Residual magnetism lets a magneto create the first spark for engine starting without needing external power.
Analogy
It is like a screwdriver that still picks up a small screw after it has been rubbed against a magnet. The strong magnet is gone, but a little magnetism remains in the metal.
Intuition Check
Residual magnetism is not leftover electricity. It is leftover magnetism in metal, and that small magnetic field can help an electrical generator start making voltage.
Example Sentence 1
The generator failed to come on line because it had lost its residual magnetism and needed to be flashed before it would produce voltage.
Example Sentence 2
After an overhaul, technicians restore residual magnetism in the magneto before reinstalling it on the engine.